SR12

GEOTECHNOLOGIEN Science Report

Mineral Surfaces – From Atomic Processes to Industrial Application Kick-Off-Meeting 13–14 October 2008 Ludwig-Maximilians-Universität München

Programme & Abstracts Number 1

No. 12

Impressum

Schriftleitung / Editorship Dr. Ludwig Stroink © Koordinierungsbüro GEOTECHNOLOGIEN, Potsdam 2008 ISSN 1619-7399 The Editors and the Publisher can not be held responsible for the opinions expressed and the statements made in the articles published, such responsibility resting with the author.

Die Deutsche Bibliothek – CIP Einheitsaufnahme GEOTECHNOLOGIEN Mineral Surfaces – From Atomic Processes to Industrial Application Kick-Off-Meeting 13–14 October 2008 Ludwig-Maximilians-Universität München Programme & Abstracts – Potsdam: Koordinierungsbüro GEOTECHNOLOGIEN, 2008 (GEOTECHNOLOGIEN Science Report No. 12) ISSN 1619-7399 Bezug / Distribution Koordinierungsbüro GEOTECHNOLOGIEN Heinrich-Mann-Allee 18/19 14473 Potsdam, Germany Fon +49 (0)331-288 10 71 Fax +49 (0)331-288 10 77 www.geotechnologien.de geotech@gfz-potsdam.de Bildnachweis Titel / Copyright Cover Picture: Gebrüder Dorfner

Preface Micro and nano scale reactions on mineral surfaces regulate a multitude of natural and technological processes. Accordingly they are of great significance for everyday life and industrial practice. Physical-chemical processes on mineral surfaces have a decisive effect on the manufacturing process for and the quality of paper, on production processes in the cement and ceramics industries and for the development and utilization of natural-bone-replacement substances as well as for the treatment of drinking and process water, e.g. by the fixing of pollutants to mineral surfaces.

In the frame of the R&D-Programme GEOTECHNOLOGIEN 13 joint projects between academia and industry have been launched in 2008. The overall target of the funded projects is to gain a better understanding of physical and chemical reactions on mineral surfaces and how to apply their technological relevant properties in more sophisticated production processes. The joint projects are funded by the Federal Ministry of Education and Research (BMBF) with about € 8 Million for the next three years.

Currently supported activities focus on the following key topics: 1. Quantitative investigations on the structure and properties of mineral surfaces.

2. Mineral surfaces in geogenic systems and interactions between organic materials and mineral surfaces (geo-bio interfaces).

3. Chemical/Mechanical modification of mineral surfaces in order to create new properties to improve production processes.

The main objective of the Kick-Off-Meeting is to bring together the scientists and investigators of the funded projects to present their ideas and proposed work plans to each other; several projects are interlinked and could therefore benefit from synergies. All who are interested in the forthcoming activities of the projects – from Germany, Europe or overseas – are welcome to share their ideas and results.

Ludwig Stroink Hartmut Fueß

Table of Contents Scientific Programme Kick-Off-Meeting »Mineral Surfaces«

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Understanding processes at the hot smectite-water interface for tailoring industrial bentonite applications (HYDRASMEC) Stanjek H., Schmahl W., Jordan G., Diedel R., Grefhorst C., Schellhorn M., Wolff H. . . . . . . . . . . . . . . . . . . . . . .

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Control mechanisms of clays and their specific surface area in growing media – assessment of clay properties and their parametrization for the optimization of plant quality Schellhorn M., Dultz S., Schmilewski G., Schenk M.K.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Optimization of Water Treatment Technology for As and Sb Scavenging

by Microbiologically Activated Fe Minerals (MicroActiv) Kersten M., Daus B., Driehaus W., Haderlein S., Kappler A., Stanjek H., Wennrich R. . . . . . . . . . . . . . . . . . . . . . . 25 Development and Optimisation of a Process to Biosynthesize Reactive Iron Mineral Surfaces for Water Treatment Purposes (SURFTRAP) Peiffer S., Burghardt D., Janneck E., Pinka J., Schlömann M., Wiacek C., Seifert J., Schmahl W., Pentcheva R., Meyer J., Rolland W.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Interfacial Processes between Mineral and Tool Surfaces – Causes, Problems and Solutions in Mechanical Tunnel Driving Fernandez-Steeger T. M.; Post C.; Feinendegen M.; Bäppler K., Zwick O.; Azzam R.; Ziegler M.; Stanjek H.; Peschard A.; Pralle N.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Nano-structure and Wetting Properties of Sedimentary Grains and Pore-Space Surfaces (NanoPorO) Altermann W., Heckl W.M., Stark R.W., Strobel J., Wolkersdorfer Ch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 The impact of mineral and rock surface topography on colloid retention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Fischer C., Lüttge A. & Schäfer T.

Microstructural Controls on Monosulfide Weathering and Heavy Metal Release (MIMOS) Pollok K., Langenhorst F., Hopf J., Kothe E., Geisler T., Putnis C.V., Putnis A. . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Simulation-supported development of process-stable raw material components and suspensions for the production of ceramic sanitary ware on the basis of modified mineral surfaces (SIMSAN) Agné T., Engels M., Rezende J. L. L., Latief O., Vuin A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Using Hydrophobins to Prevent Microbial Biofilm Growth on Mineral Surfaces Fischer R., Schwartz T., Obst U. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Functionalized mineral surfaces: Sorption mechanisms of growth-stimulating proteins on surfaces of bone substitutes based on calcium phosphates (BioMin) Fischer H., Seifert G., Gemming S., Jennissen H., Müller-Mai C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Identification and modification of the surface properties of calcite fillers as a basis for new, highly filled adhesives Diedel R., Geiß P.L., Wittwer W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Reactivity of Calcite/Water-Interfaces (RECAWA): Molecular level process understanding for technical applications Neumann T., Bosbach D., Winkler B., Herold G., Vucak M., Fischer U., Plöhn J. . . . . . . . . . . . . . . . . . . . . . . . . 122 Authors’s Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 GEOTECHNOLOGIEN Science Reports – Already published/Editions . . . . . . . . . . . . . . 133

Scientific Program Kick-Off-Meeting »Mineral Surfaces« 13–14 October 2008, LMU München Monday, 13. October 2008 13.30 – 14.00 14.00 – 14.40 14.40 – 15.20

15.20 – 16.00

Welcome Understanding processes at the hot smectite-water interface for tailoring industrial bentonite applications (HydraSmec) Control mechanisms of clays and their specific surface area in growing media – assessment of clay properties and their parametrization for the optimization of plant quality Optimization of Water Treatment Technology for As and Sb Scavenging by Microbiologically Activated Fe Minerals (MicroActiv)

16.00 – 16.30 16.30 – 17.10 17.10 – 17.50 17.50 – 18.30 18.30 – 19.10

Coffee Break and Poster Session Development and Optimisation of a Process to Biosynthesize Reactive Iron Mineral Surfaces for Water Treatment Purposes (SURFTRAP) Interfacial Processes Between Mineral and Tool Surfaces – Causes, Problems and Solutions in Mechanical Tunnel Driving – Nano-Structure and Wetting Properties of Sedimentary Grains and PoreSpace Surfaces (NanoPorO) The impact of mineral and rock surface topography on colloid retention

starting from 19.30

Dinner

Tuesday, 14. October 2008 08.30 – 09.10 09.10 – 09.50

09.50 – 10.30 10.30 – 10.50 10.50 – 11.30

11.30 – 12.10 12.10 – 12.50 12.50 – 13.30

Microstructural Controls on Monosulfide Weathering and Heavy Metal Release (MIMOS) Simulation-supported development of process-stable raw material components and suspensions for the production of ceramic sanitary ware on the basis of modified mineral surfaces (SIMSAN) Using Hydrophobins to Prevent Microbial Biofilm Growth on Mineral Surfaces

Coffee Break and Poster Session Functionalized mineral surfaces: Sorption mechanisms of growth-stimulating proteins on surfaces of bone substitutes based on calcium phosphates (BioMin) Identification and modification of the surfaces properties of calcite fillers as a basis for new, highly filled adhesives Reactivity of Calcite/Water-Interfaces: Molecular level process understanding for technical applications (RECAWA) Final discussion

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Understanding processes at the hot smectite-water interface for tailoring industrial bentonite applications (HydraSmec) Stanjek H. (1)*, Schmahl W. (2), Jordan G. (2), Diedel R. (3), Grefhorst C. (4), Schellhorn M. (5), Wolff H. (6) (1) Ton- und Grenzflächenmineralogie, RWTH Aachen, (CIM) e-mail: stanjek@iml.rwth-aachen.de (2) Department für Geo- und Umweltwissenschaften, Sektion Kristallographie, LMU München, (LMU) e-mail: wolfgang.schmahl@lrz.uni-muenchen.de, jordan@lmu.de (3) Forschungsinstitut für Anorganische Werkstoffe – Glas/Keramik– GmbH, (FGK) e-mail: Diedel@fgk-keramik.de (4) S & B Industrial Minerals GmbH, (SBM) e-mail: c.grefhorst@ikominerals.com (5) Stephan Schmidt KG, (SSKG) e-mail: matthias.schellhorn@schmidt-tone.de (6) Institut für Giessereitechnik gGmbH, (IFG) e-mail: wolff@ifg-net.de *Coordinator of the project: Prof. Dr. Helge Stanjek, RWTH Aachen

Abstract Smectites, the dominant minerals in bentonites, are used in quantities of millions of tons per year in very diverse industrial applications, e.g., as an addition to moulding sands in the foundry industry. The automotive industry, for instance, demands cast parts (cylinder blocks, crank shafts, brake discs, etc.) with increasing complexity but less weight. This requires tailoring of the moulding sand mixtures beyond their current performance.

However, it is not understood in detail why changes observed during the casting process are partly reversible in the laboratory, but not within the recycling time of moulding sands.

Another important market for bentonites is their application as adsorbing materials. However, industrially dried bentonites have significantly lower water uptake capacities and retarded uptake rates than the same materials, which have been dried in the laboratory to the

same water contents as the industrially dried ones. Properties such as swelling volume, water uptake and high liquid limits, which define the commercial value of smectites, are therefore considerably diminished.

Evidently, the complex kinetics of de- and rehydration of smectites with their concomitant impacts on the mechanical and physical behaviour have to be understood, before any improvements of performance can be made.

The rationale for this project is, therefore, to elucidate the underlying mechanisms by investigations embracing the atomic to the industrial scale. This will enable our industry partners to improve the efficient geotechnical usage of bentonites beyond the current trial and error approach.

1. Introduction The application of smectite minerals in industrial processes is, apart from other properties

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such as adsorption, closely related to their adhesive properties. In foundry moulding sands the smectite particles effect the required mechanical strength properties. These binding properties are closely related to the ability of smectites to swell and shrink the interlayer region with varying water activity. For Nasmectites, the basal spacings of the smectite layers increase in a step-wise fashion with increasing relative humidity and relates to the presence of zero, one, two, or three sheets of H2O molecules around the interlayer cation (e.g., McEwan and Wilson, 1980). Intermediate hydration steps (e.g., Collins et al., 1992; Devineau et al., 2006) can be explained by interstratification, which occurs either in a regular way or in a random fashion (e.g., Moore and Hower, 1986; Ferrage et al., 2005).

Hydration and rehydration of interlayer cations are in principle reversible processes, which have been studied in many quasi-equilibrium experiments performed at temperatures <300 °C (e.g., Kraehenbuehl et al., 1987; Prost et al., 1998; Komadel et al., 2002) and modelled by molecular dynamics (Young and Smith, 2000; Tambach et al., 2004). The dynamics of the hydration processes are less well investigated. It is known that apart from hydration energies of the cations size and charge determine whether heated smectites stay collapsed or rehydrate to their original volume (e.g., Chorom and Rengasamy, 1996).

The distribution of interlayer water relative to water in micro- and mesopores was studied by Cases et al. (1992) who observed pronounced hysteresis effects in the ad/desorption branches of water sorption isotherms. Wilson et al.

(2004) pointed out that parameters such as the water/smectite ratio and the attainment of complete smectite dispersion (among others) influence the dynamics of dehydration and very likely that of rehydration, too.

Detailed investigations of the hydration dynamics of smectites in moulding sands are lacking although improvements are required, because the degree of processing of moulding sands rarely exceeds 70–80% (Tilch, 2004).

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Own investigations showed that post-processing a moulding sand mixture by elevating its moisture content, then milling in a pan grinder, followed by re-drying to the previous moisture content, improved the plasticity, the compactibility, the green compression strength and the plastic limit (personal communication H. Wolff, 2007). Obviously, the kinetics of distributing water in the moulding sand, the hydration of smectite, and the reorientation of particles play an important role. Quantitative relationships, however, are lacking.

A further aspect of the interaction of water with smectites is the observation that hot steam reduces the swelling capacity significantly (Couture, 1985; Madsen, 1998; Oscarson and Dixon, 1989). Smectites heated in steam do not dehydrate in contrast to dryheated ones, but other paramaters such as cation exchange capacity (an indicator for partial interlayer contraction) or X-ray diffraction patterns with 00l reflections did not reveal significant changes. 27 Al-NMR spectra indicated that Al3+, which substitutes for Si4+ in the tetrahedral sheet, might have in parts a different coordination than before (Bish et al., 1999), but this interpretation could not be verified (personal communication D. Bish, 2007).

Measurements of contact angles showed – in the sense of van Oss’ theory of interface energy components (van Oss, 2002) – that a steam treatment increases also the degree of hydrophobicity. This would imply a reduced wettability of the smectite surface in agreement with a decreased rate of water uptake.

The latter effect, however, could also be due to a physical change in aggregation, thereby changing the pore volume (Oscarson and Dixon, 1989). Own investigations showed that fast drying at higher temperatures but elevated water vapour pressure invoked larger changes than slow drying at lower temperatures, although the final water contents were the same. The reduced uptake rates persisted for several months. This suggests that the kinetics and their elementary reactions need to be understood, before improvements can be made.

Figure 1: Simplified comparison of transport processes in the casting (a) and the drying process (b). Note that the directions of mass flux and heat flux are opposite for the drying process.

2. Project description It has been outlined above that the interaction of water with smectite has deteriorating effects in various industrial applications. We focus here on two aspects: 1. The hydration dynamics of smectites in moulding sands.

2. The change of surface properties of industrially dried smectites.

Both aspects have in common that the smectites experience elevated temperatures and partial pressures of water. However, the dynamics of both systems with respect to temperature gradients and water pressure gradients are different (see Fig. 1). The liquid melt in the casting process induces a heat flux towards the cool wall with a concomitant flux of water, whereas the drying process yields an anti-parallel movement of heat and mass (water). The very simplified situation of Fig. 1 does not reflect the highly dynamic progress of these systems with their position- and time-dependent temperature and concentration gradients.

It is clear that common heating experiments in the laboratory with static temperatures and fixed partial water pressures will not sim-

ulate the real situations of the casting and drying processes. Most important, spatial information is not available yet due to bulk sampling of both systems: The moulding sands are almost fully recycled and then refreshed for compensating inevitable losses during the casting process. On the long term, the whole material reaches a steady state.

Spatial information from the dried smectites is lost due to milling and homogenization processes, which follow the oven drying. Our knowledge about degrading effects therefore stems from material, which experienced significantly diverse conditions but has been averaged within the industrial processes. This disables the assignment of specific temperature-pressure-time conditions to certain processes and their kinetics.

In this project, we consider it as essential to start with two key experiments (KE) performed by our industry partners. The combination of de-facto real-life conditions with an elaborate sampling and measuring scheme will then allow us to margin the boundary conditions for subsequent experiments in the laboratory in which single parameters have to be isolated by appropriate variations of experimental conditions.

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The major goals of this project, therefore, are the answers to the following questions: – What happens on the interfaces of smectites when they experience highly varying partial pressures of water and highly dynamic temperature variations?

– How do these processes provoke suboptimal material properties?

– How can these processes be tailored to improve the material properties?

– Do the costs for improvements relative to the benefits effect an economy?

3. Work packages 3.1 Key experiment: Casting in a foundry The combination of in-situ measurements of T and modelled pH2O conditions of the key experiment with the full laboratory characterization will allow us to confine the conditions for subsequent laboratory experiments, in which certain parameters are varied for quantifying process rates.

WP 1 Casting experiment (IFG) A cast experiment will be designed with a cylindrical interface between the melt and the moulding sand. The temperature and moisture evolution in the moulding sand will be monitored by appropriate sensors and samples. The total volume of the moulding sand has to be sampled as soon as possible after the casting to minimize possible back reactions (redistribution of water and rehydration reactions). The sampling scheme will be on a three-dimensional grid with allocating sample positions to the project partners. Depending on the time need of the sample analyses, up to ten samples per cast are then investigated in detail. As a start for this key experiment, two bentonites commonly used in foundries will be used with three ratios of melt to mass of the mould, respectively. The latter ratios should be chosen to mimic the geometry of usual castings and its influence on the time-temperature profiles within the casting mould. For select analyses with the AFM special samples will be embedded within the moulding sand (see WP 2).

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WP 2 Texture, structure and AFM analyses (LMU) The thermal exposure and the significant fluxes of water either in the gaseous or in the liquid state may affect the orientation of mineral particles in the moulding sand. This in turn influences the mechanical strength and the pore size distribution. The orientational effects can be quantified in bulk samples together with data on the structural state of the smectites by neutron diffraction (ND) by comparing juvenile samples with samples from the foundry experiments. Vanadium tubes 10 mm in diameter and 50 mm in height will be used to take samples at defined positions in the mould for the ND experiments. The incoherent scattering of H will be used to determine the total H2O content. Fractured surfaces of the same samples are then investigated in an environmental scanning electron microscope (ESEM, available at the FGK).

A direct comparison of fresh smectite particles with those subjected to a casting cycle are investigated by HAFM on smectite samples, which have been placed in the mould across a temperature profile. For these investigations, smectite particles are affixed onto an appropriate substratum. They are analysed in the fresh state, then subjected to the pT conditions of the cast process and reanalysed again with respect to their hydration dynamics. One important aspect here is the fact that smectite particles are significantly smaller than the upto-date investigated minerals. A preparation technique, which is based on the PEI method (Bickmore et al., 1999), has been successfully tested by our group at temperatures up to 100 °C (see Fig. 2).

WP 3 Interface properties, hydration states, and rehydration kinetics (CIM, FGK) Cation exchange capacities are measured by the Cu-Trien method. Contact angle measurements on purified samples with polar and non-polar fluids will yield the Lifshitz-van der Waals and the polar surface energies. The smectite particles can be separated easily from the quartz matrix by ultrasonic treatment of

Figure 2: In-situ AFM image (5 × 5 µm) of PEI-fixed K-smectite at 100 °C in 0.1M KCl. Thick contaminating particles (left image, dashed arrow) could be removed by the tip in contact mode, but not smectite particles (arrows), which persisted even after 20 minutes of scanning.

ethanol- or aceton-based suspensions with subsequent size fractionation. The swelling behaviour of smectites prohibits measurements with liquids rising in a powder specimen. Instead, contact angles have to be measured by placing the liquids on films of smectite deposited on silver membrane filters. The contact angles are measured by an optical microscope at the FGK. Changes in the hydration state and configuration of interlayer cations affects the Brønstedt and Lewis acidity. Intercalation with metachromatic probe molecules such as acridin orange and congo red yield changes in the absorption spectra, which are measured on suspensions by visible spectrometry. The amounts of pore and intra-crystalline water are determined by thermogravimetric measurements at the FGK, in which both kinds of water molecules escape the sample at different temperatures. These data are scaled with the neutron data.

On select samples the rehydration kinetics of smectites are measured by X-ray diffraction in an environmental chamber, where temperature and humidity can be controlled. The smectite contents of the moulding sands are high enough to measure the 001 reflection

without an enrichment of the smectite component even in powder specimen. The lower intensities relative to textured samples are partly compensated by using a position sensitive detector. The various hydration states making a mixed-layer phase will be characterized by comparing the measured 00l reflections with NewMod simulations.

WP 4 Mechanical properties (SBM) In the industry fast and cost-effective methods have been developed for testing the mechanical properties of moulding sand mixtures.

These methods standardized according to DIN comprise the measurement of compactibility, tensile and shear strengths.

3.2 Key experiment: Industrial drying In the beginning, we need information about the gradients within the clay aggregates induced by the contact with the hot oven atmosphere. This information is best obtained from industrially dried material.

WP 5 Sampling and physical properties (SSKG) A drying experiment will be done with bentonite aggregates having a narrow range in aggregate size (preferably ≈50 mm) and hav-

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Figure 3: The industrial bentonite drier at Stephan Schmidt KG.

ing a homogeneous total water content. The bentonite aggregates are sampled before and immediately after the oven passage (Fig. 3).

After the oven passage, the clay aggregates have to be investigated immediately. Due to the initial mineralogical heterogeneity of the material und due to the necessity of getting sufficient amounts per sample, we estimate that 20â&#x20AC;&#x201C;30 aggregates have to be sampled.

With an Auger tube â&#x2030;&#x2C6;10 mm in diameter cores will be drilled through the aggregates.

The then sliced cores provide spatially resolved samples for determining the moisture contents gravimetrically. On cut aggregates the temperature gradients will be measured. After pooling sample regions from a sufficient number of clay aggregates into larger amounts of samples, rheological properties will be measured, because these properties are very sensitive towards processing. Water uptake rates according to Enslin-Neff are measured.

WP 6 Interface properties, hydration states, and rehydration kinetics (CIM, FGK) The same parameters as described above in WP 3 are measured on the samples: Hydration state by XRD and NewMod simulations, con-

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tact angles, Lewis and Brønsted acidity, cation exchange capacities and on select samples the rehydration kinetics by XRD in the environmental chamber.

3.3 Industrial experiment: Optimizing the rehydration dynamics The major aim here is to investigate the influence of relaxation effects on the rehydration of recycled smectites. It is known that both increased resting times and surplus water addition improve the mechanical properties of the moulding sands. A possible reason might be the slow intra-crystalline swelling, which, of course, proceeds according to the volumetric water content. Apart from these two parameters for the first time we test the influence of MgO upon the rehydration dynamics. In other bentonite systems, the addition of MgO had positive effects on the hydration properties.

The number of bentonites is enlarged to four commonly used ones, the materials are provided by the industry partner S & B Minerals.

These periodic cast experiments provide also fresh samples for rehydration experiments in the laboratory (WP 10 and 11 on the next page). The sampling scheme will be identical to that of WP 1.

WP 7 Resting times and addition of water and MgO (IFG) The number of possible experiments will be split into three series in which resting times, addition of (surplus) water and addition of MgO are varied within technically reasonable limits.

WP 8 Mechanical properties (SBM, FGK) The recycling processes have to be monitored by measuring the mechanical properties as outlined in WP 4. For this WP it is important to synchronize the measurements with the series of casting experiments for avoiding relaxation effects. Additionally, the water uptake according to Enslin-Neff is measured, because the Enslin-Neff values are common proxies in the industry from which other properties (usually less easy to measure) can be derived.

WP 9 Texture and structure changes (LMU) On select samples neutron diffraction experiments should give evidence, on how the above mentioned parameters affect the distribution of water in the interlayer and in the inter-particle space, respectively. The methods have been described in WP 2.

3.4 Laboratory experiment: Rehydation kinetics The influence of individual parameters on the rehydration process can only be isolated in laboratory experiments by varying single parameters at a time. By a comparison of samples, in which the hydration states have reached equilibrium with samples coming freshly from casting experiment (see WP 7), hysteresis effects in the porous system and within the interlayer space can be discerned. For understanding the mechanisms of processes, it is essential to monitor processes on a scale as small as possible. Investigations with a hydrothermal atomic force microscope (HAFM) will therefore complement bulk methods such as X-ray and neutron diffraction.

WP 10 Rehydration kinetics of bulk samples (CIM) The rehydration rates of smectites, which have been dehydrated to defined states with

defined rates, will be studied and compared to the rates of smectites, which have been locked out of casting experiments. The rehydration process will be monitored gravimetrically as a function of temperature and of the partial pressure of water in closed sample chambers.

The partial pressures are adjusted by appropriate salt solutions. Additional measurements with liquid water â&#x20AC;&#x201C; according to Enslin-Neff â&#x20AC;&#x201C; provide the linkage to technical parameters such as swelling capacity. Select samples will be studied by X-ray diffraction employing the above-mentioned techniques and evaluations.

WP 11 Rehydration kinetics on the particle scale (LMU) The hydrothermal AFM is able to provide timespace information about the advancing or receding hydration fronts within smectite crystals. The rate of hydration is strongly influenced by the charge and size of the interlayer cations. It is therefore likely that small fractions of divalent cations (Ca2+ or Mg2+) relative to the major interlayer cation Na+ may have nonlinear effects, because the aforementioned cations my prevent the whole interlayer from expansion by acting like local adhesives. The dynamics of such a pinning process can be followed in the HAFM by measuring first the hydration dynamics with a homo-ionic Na+ interlayer. Then a small fraction of Na+ is exchanged by Ca2+, the interlayer space is dehydrated and rehydrated again. Swellingdrying cycles are known to produce nonexpanding interlayers in smectites. The influence of the rates of de- and rehydration upon the expandability is measured by controlled heating and wetting in the HAFM, which will provide direct kinetic data of this process.

3.5 Laboratory experiment: Surface properties of steam-treated smectites For identifying the relevant processes, not only p, T and time have to varied, but also single properties of the smectites. Hence, a broad range of smectites is necessary in which, e.g., the position of the interlayer charge (montmorillonitic versus beidellitic), the particle size or the chemical composition vary.

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WP 12 Sample preparations (CIM) The identification of the mechanisms requires experiments on smectitic samples as pure as possible. The bentonite samples have therefore to be processed by sedimentation techniques, chemical removal of admixed iron oxides and exchanged with select interlayer cations. Relevant cations will be Na+, Ca2+, Mg2+, and K+. The bentonites are provided by S&B Minerals and by Stephan Schmidt KG. With the purified and ionexchanged smectites, kinetic experiments will be run in autoclaves at defined partial water pressures, temperatures, and reaction times.

A starting point for the experimental conditions will be derived from the KE Industrial drying (WP 5).

WP 13 Interface properties and hydration kinetics (CIM, FGK) The same methods for characterizing the interface properties (outlined in WP 6) will be applied here, too. The dynamics of water uptake is measured by the techniques mentioned in WP 10 on the preceding page.

WP 14 Rehydration kinetics on the particle scale (LMU) On select samples, HAFM experiments will be performed in order to show how the steam treatment affects the rehydration on the particle scale (the experiments are described in WP 11). This WP will only be conducted if WP 11 and 13 indicate that these experiments will very likely be performed successfully.

3.6 Validating experiment: Tuning the recycling process of a moulding sand Provided that the dynamics of the hydration processes are now sufficiently understood, the cycling of the moulding sands can be tailored accordingly.

WP 15 Casting cycles at optimized conditions (IFG) In the foundry, casting cycles are run with tuned conditions. In contrast to the experiments of section 3.3, where only single para-

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meters have been varied, the experiments in this work package extend now to a multiple parameter situation. Technical measures such as pre-moistening of the moulding sand mixture, resting time in the bunker and time of mixing are now combined with other parameters such as addition of MgO. These combinations have to be tested with sufficient cycles to warrant a recommendation for industrial application.

WP 16 Mechanical properties (SBM) Improved hydration processes result in improved mechanical properties. These will be monitored by the methods outlined in WP 4.

WP 17 Adaption of model relationships: bulk samples (CIM) In this stage, it will be impossible to measure the whole set of parameters as it was done in the previous experiments. Nevertheless, a mineralogical monitoring of select parameters will be required for validating relationships derived either from the laboratory and industrial experiments, respectively, and their adaption to a multiple situation.

WP 18 Test of mechanisms on the particle scale (LMU) The cast experiments provide also samples for testing our knowledge about the mechanisms of hydration on the particle scale. Select samples will be investigated by HAFM. 3.7 Validating experiment: Tuning the drying process The results of section 3.5 will provide insight into the mechanisms of steam-smectite interactions. Relationships between parameters such as initial water content of the aggregates, oven atmosphere, temperature, and residence time, respectively, and the resulting bentonite properties enter into a validating series of drying experiments with appropriate variations of those parameters. These experiments are also necessary to check the potential for up-scaling laboratory results to an industrial scale.

WP 19 Sampling and physical properties (SSKG) The process conditions are adjusted to new conditions, for which the relationships obtained by the laboratory experiments predict optimum material properties. The experimental set-up and the sampling scheme are equal to those described in WP 5 on page 6. The water uptake rate and capacity are measured

by Enslin-Neff.

WP 20 Adaption of models (CIM) Any success of the tuned drying process will show up in the improved water uptake kinetics and capacity as measured in WP 6. A prediction should be possible with the mechanisms and relationships obtained in WP 13, but the relationships have to be validated (and eventually corrected) for the recommended drying processes. Hence on select samples, measurements of pertinent parameters have to be done.

References Bickmore, B., Hochella, M., Bosbach, D. and Charlet, L. (1999) Methods for performing atomic force microscopy imaging of clay minerals in aqueous solutions. Clays and Clay Minerals, 47, 573–581.

Bish, D., Wu, W., Carey, J., Costanzo, P., Giese, R. J., Earl, W. and van Oss, C. (1999) Effects of steam on the surface properties of Nasmectite. In: Clays for our Future (H. Kodama, A. Mermut and J. Torrance, editors), Proceedings of the 11th International Clay Conference, 569–579. ICC97 Organizing Committee, Ottawa.

Cases, J. M., Bérend, I., Besson, G., Francois, M., Uriot, J.-P., Thomas, F. and Poirier, J. (1992) Mechanism of adsorption and desorption of water vapor by homoinonic montmorillonite.

1. The sodium-exchanged form. Langmuir, 8, 2730–2739.

Chorom, M. and Rengasamy, P. (1996) Effect of heating on swelling and dispersion of different cationic forms of a smectite. Clays and Clay Minerals, 44, 783–790.

Collins, D., Fitch, A. and Catlow, C. (1992) Dehydration of Vermiculites and Montmorillonites: A Time-resolved Powder Neutron Diffraction Study. Journal of Materials and Chemistry, 2, 865–873.

Couture, R. (1985) Steam rapidly reduces the swelling capacity of bentonite. Nature, 318, 50–52.

Devineau, K., Bihannic, I., Michot, L., Villieras, F., Masrouri, F., Cuisinier, O., Fragneto, G. and Michau, N. (2006) In situ neutron diffraction analysis of the influence of geometric confinement on crystalline swelling of montmorillonite. Applied Clay Science, 31, 76–84.

Ferrage, E., Lanson, B., Malikova, N., Plançon, A., Sakharov, B. A. and Drits, V. A. (2005) New insights on the distribution of interlayer water in bi-hydrated smectite from X-ray diffraction profile modeling of 00l reflections. Chemistry of Materials, 17, 3499–3512.

Komadel, P., Hrobarikova, J., Smrcok, L. and Koppelhuber-Bitschnau, B. (2002) Hydration of reduced-charge montmorillonite. Clay Minerals, 37, 543–550.

Kraehenbuehl, F., Stoeckli, H., Brunner, F., Kahr, G. and Mueller-VonMoos, M. (1987) Study of the water-bentonite system by vapour adsorption, immersion calorimetry and X-ray techniques: I. Micropore volumes and internal surface areas, following Dubinin’s theory. Clay Minerals, 22, 1–9.

Madsen, F. T. (1998) Clay mineralogical investigations related to nuclear waste disposal.

Clay Minerals, 33, 109–129.

McEwan, D. and Wilson, M. J. (1980) Interlayer and intercalation complexes of clay minerals. In: X-ray Identification and Crystal Structures of Clay (G. Brindley and G. Brown, editors), Mineralogical Society Monograph No. 5, 197–248. Mineralogical Society, London.

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Moore, D. M. and Hower, J. (1986) Ordered interstratification of dehydrated and hydrated smectite. Clays and Clay Minerals, 34, 379–384.

Oscarson, D. and Dixon, D. (1989) The effect of steam on montmorillonite. Applied Clay Science, 4, 279–292.

Prost, R., Koutit, T., Benchara, A. and Huard, E. (1998) State and location of water adsorbed on clay minerals: consequences of the hydration and swelling-shrinkage phenomena. Clays and Clay Minerals, 46, 117–131.

Tambach, T. J., Hensen, E. J. and Smit, B. (2004) Molecular simulations of swelling clay minerals. Journal of Physical Chemistry, B 108, 7586–7596.

Tilch, W. (2004) Ermittlung des Aufbereitungsverhaltens bentonitgebundener Formstoffe (Betriebssande). Giesserei-Praxis, 1, 12–18. van Oss, C. (2002) Use of the combined Lifshitz-van der Waals and Lewis acid-base approaches in determining the apolar and polar contributions to surface and interfacial tensions and free energies. Journal of Adhesion Science and Technology, 16, 669–677.

Wilson, J., Cuadros, J. and Cressey, G. (2004) An in situ time-resolved XRD-PSD investigation into Na-montmorillonite interlayer and particle rearrangement during dehydration. Clays and Clay Minerals, 52, 180–191.

Young, D. A. and Smith, D. E. (2000) Simulations of clay mineral swelling and hydration: Dependence upon interlayer ion size and charge. Journal of Physical Chemistry B, 104, 9163–9170.

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Control mechanisms of clays and their specific surface area in growing media – assessment of clay properties and their parametrization for the optimization of plant quality Schellhorn M. (1), Dultz S. (2)*, Schmilewski G. (3), Schenk M. K. (4) (1) Stephan Schmidt KG, e-mail: Matthias.Schellhorn@schmidt-tone.de (2) Institute of Soil Science, Leibniz University Hannover, e-mail: dultz@ifbk.uni-hannover.de (3) Klasmann-Deilmann GmbH, e-mail: schmilewski@klasmann-deilmann.de (4) Institute of Plant Nutrition, Leibniz University Hannover, e-mail: schenk@pflern.uni-hannover.de *Coordinator of the project: PD Dr. Stefan Dultz, Leibniz University Hannover

1. Introduction Growing media are operating resources in horticultural industry which have to fulfil highest demands with regard to automated fertigation and »just in time production«. A suitable media is essential for the production of healthy, optimal grown and non-perishable plants. During transplant production with ornamental as well as vegetable crops pricking robots are used to transfer plantlets from smallest growing units and plant them. A prerequisite for this procedure is a stable root ball to prevent losses. An important substrate component is clay which makes up to 30% (v/v). Chemical as well as physical characteristics of growing media strongly depend on the clay amendment. The addition of clay to growing media aims at constant supply of potassium, phosphorus and micro nutrients, pH-buffering, improvement of wettability, and coherence of substrate.

Currently no proven standards are available for evaluation of clay for use in growing media and to design substrates perfectly for specific crops and production methods. Up to now,

selection, modification and amendment of clay in peat is handled empirically based on simple data of mineralogical and chemical composition. The classification of natural or modified clays based on routine methods or by means of methods to be developed is a prerequisite for product and cultivation safety as well as market transparency.

2. State of the art Peat and peat/clay mixtures were introduced as growing media into horticultural industry around 1950. The first universal growing media, the »Einheitserde« according to Prof. Frustorfer, contained 40% (v/v) clay. Nowadays mostly 10–30% (v/v) clay is contained. In 2005 about 200.000 tons of clay were used in Europe for growing media. In Germany, the world leading country in substrate manufacturing, 130.000 to a–1 were processed. Although introduced already more than 50 years ago, the sale of substrate clay is still increasing in Germany. In The Netherlands, where clay has been used in growing media for ca. 10 years, about 20.000 to a–1 are used nowadays.

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Clays are added to growing media in order to optimize the chemical and physical properties and to produce more or less risk-free growing media; they can buffer mistakes made during horticultural production such as erroneous fertigation. It is generally accepted that clay in growing media buffers – due to its cation exchange capacity (CEC) – the potassium concentration in pore solution and thus ensures continuous K supply of plants. Also the P concentration in substrate solution is buffered, because the anion phosphate is bound by variable charged sites. The regulation of the P-availability by clay could be used to form compact plants. Charged surface sites support the wettability of substrates and, due to their microstructures, improve the amount of water available to plants. Therefore a common recommendation is to use finegrained hydrous phyllosilicates like smectites with a high specific surface area. Despite the clarification of some effects of clays in growing media, defined parameters for the selection of substrate clays for specific areas of application (buffering of nutrients and toxic compounds, clays as binding agents of the root ball in trays, improvement of the wettability, optimization of the water holding capacity, etc.) are missing in the growing media industry.

The amelioration of agricultural soils by clay amendments was scientifically investigated in the past (Ismail and Ozawa, 2007; Miller and Miller, 2000; Reuter, 1994; Straaten, 2007; Suzuki et al., 2007). However, literature dealing with the influence of clay on characteristics of growing media is scarce and on a very empirically level, although it is widely used in horticultural industry.

3. Open questions In horticulture growing media are needed, which are tailor-made to suit any specific crop and production technique. At present, reliable criteria for selection of original and modified clays for growing media are missing. There is a need for a classification system for substrate clays by use of routine methods or

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methods which have to be developed. This is the prerequisite for improved product safety and risk-free plant cultivation as well as market transparency.

Instead of the empirical practice for selecting substrate clays, suitable criteria will be defined and parameterized (e.g. specific surface area, contact angle, Fe(II)-content, oxalate soluble Fe, amount of Fe released from the silicate layer by oxidation), which allow a reliable evaluation of the raw material, products of different modification techniques and blends for the successful use in growing media. Open questions exist for manufacturing of growing media as well as for basic research. The Dutch Foundation for Growing Media (RHP) (Regeling Handelspotgronden) set critical levels for manganese and boron in substrate clays whereas in Germany plant damage due to toxic concentrations in clay is not known. Thus vegetation trials are necessary for investigating the relevance of the catalogue of requirements of RHP. Related to these applied aspects are questions related to basic research such as the effect of the oxidation of Fe(II) in the structure of smectites on surface properties (Stucki et al., 2002).

This reaction, which may occur if clays originating from a reducing environment are used in growing media, is not fully understood. In the Mesozoic-tertiary weathering layer of the Rheinisches Schiefergebirge are huge reduction horizons occurring at depths of 40–70 m (Felix-Hennigsen, 1990). Little is known about the behaviour of clay rich saprolites contained in this layer.

4. Objectives In the project the selection of clays for growing media will be based on the one hand by clay research and on the other hand by horticultural practice. Suitable mineralogical, chemical and physical parameters for the selection, quantification, blending and modification of substrate clays will be developed. Specified and well characterized substrate clays for defined horticulture shall be deliverable in the same high quality in long-term.

The knowledge of surface properties and reactions of substrate clays, which will be determined in the project is essential for their use in growing media. Clay amendments to growing media have combined chemical and physical effects. Chemical properties include the sorption and desorption of K and the trivalent anion PO4, protolysis kinetics, release and precipitation of structural cations on mineral surfaces after their oxidation, while important physical properties include wettability, binding capacity, surface charge at different conditions (pH, ion concentrations) and surface roughness. By different pretreatments, which could be realized with relatively simple technical methods, clays will be modified (functionalized) and tested on their optimization for use in growing media.

4.1 Scientific and technical objectives The main benefit for the technical application is the identification of suitable substrate clays, which help control, specific for each horticultural crop, the chemical and physical properties of the growing media. The existing practise for the selection of substrate clays will be renewed and based on a knowledgeable scientific and horticultural basis. The proposed modification (functionalization) of clays is directly related with the technical application, as the objective of modification is the optimization of clay properties for their use in growing media.

The benefit for science is the detection of sorption parameters, changes by oxidation of structural cations of clay minerals, surface charge properties, wettability, binding capacity and other properties and processes of clays, which are mainly from the deeply weathered mesozoic-tertiary saprolites of the Rheinisches Schiefergebirge. The improved knowledge of the mechanisms and processes in these clays is also of technical benefit, once the prognosis of clay properties becomes more reliable.

5. Description of the working plan 5.1 Overall plan The focus of research is on the quality of substrate clays regarding buffering of the nutrients K and P and the stabilization of the pHvalue. Besides other physical parameters the wettability of the growing media is of great importance, being decisive for the design of the irrigation system. The binding capacity of the substrate is a prerequisite for the use of pricking-robots in commercial horticulture.

Due to the ban of some growth regulators in ornamental crops, ferigation with phosphate has gained attention. However, usage of substrate clays can result in P-fixation.

The project is divided into four different subprojects and combines expertise of two different groups each, from research and industry: – Subproject 1: Selection of suitable clays, modification, blending and pelletizing – definition of performance characteristics, Stephan Schmidt KG – Subproject 2: Chemical and physical effects of clay amendment in growing media, Institute of Soil Science, Leibniz University Hannover – Subproject 3: Selection and characterization of suitable peats and other growing medium constituents and additives for the production of tailor-made growing media for plant trials – Optimization of buffering capacity and binding ability, Klasmann-Deilmann GmbH – Subproject 4: Effect of clay amendment on nutrient fluxes – investigations on crop level, Institute of Plant Nutrition, Leibniz University Hannover In the proposed research the interactions between the surfaces of clays and other compounds of growing media together with the effects on the crop will be determined and evaluated for the selection of clays in growing media industry.

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The company Stephan Schmidt KG has clays with different mineralogical compositions of various petrographic origins and total Fe-contents from less than 1 up to approximately 20%. The content of Fe(II) and Fe(III) and the binding forms of Fe can also vary. Different modes of preparation (partly saturated, granulated, ground, tempered, etc.) will be included in the study. For the detection of suitable raw materials and methods of modification the Institute of Soil Science will determine surface charge properties of the substrate clays and their dynamics during the cropping period, which affect nutrient availability (focus K and P) and the capability of water uptake.

Decisive clay parameters (chemical and mineralogical composition, kinetics of element release during oxidation of structural cations, specific surface area, surface charge and wettability of surfaces at different pH-values and ion concentrations, release of different elements in sequential extraction procedures) will be rated and used for the definition of quality parameters for substrate clays, which can be clearly operated.

As a manufacturer of growing media the company Klasmann Deilmann GmbH provides all growing media samples for growth trials at the Institute of Plant Nutrition, characterized on the basis of their nutrient buffering ability and other substrate properties. The company has practiceoriented relations to horticulture. The Institute of Plant Nutrition focuses on nutrient balances for K and P in pot cultures, the dynamics of pH and the feasibility of defining threshold values for B and Mn in substrate clays.

5.2 Descriptions of the subprojects â&#x20AC;&#x201C; Subproject 1: Selection of suitable clays, modification, blending and pelletizing â&#x20AC;&#x201C; definition of performance characteristics, Dr. Matthias Schellhorn, Stephan Schmidt KG Objectives The overall objective of this subproject is the evaluation of decisive parameters of substrate clays in order to get scientifically based knowledge about the concepts of ideal clays for

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growing media. This knowledge is the basis for quality controlled production. The scientific knowledge gained in the project will be used to define new quality parameters for substrate clays. It is expected that the resulting new and newly defined substrate clays will improve the conditions for horticulture by easing the production of high quality crops and sustainable plant production.

The development of new clay blends for growing media can only be conducted by simultaneous evaluation of clay parameters and results of horticultural growth trials. Upon intensive exchange with the cooperation partners, a step by step optimization will be conducted. The above mentioned parameters of the clays together with their specific characteristics will be considered.

Description Substrate clays with different mineralogical compositions and pretreatments (modifications) will be provided to the cooperation partners. The production is planned in different cycles and will be adapted to the results from the determination of chemical and mineralogical parameters as well as to the results of the pot experiments. The chemical composition of the bulk sample and of different particle size fractions (clay-, silt- and sand fractions) will be determined by X-ray fluorescence. After the first growth trial, optimizations will be performed in three cycles, each six months. A pilot study will be performed on the water uptake capability according to Enslin/Neff in dependence of aggregate size and other parameters.

WP. 1: Selection and procurement of the required raw materials The substrate clays for growing media which are available at present on the market are more or less empirically developed products, strongly related to the specific wishes of the customers and guidelines of the market. In the past the focus of attention was in particular on technical aspects of marketing as well as the economy of the final product. Up to now scientific results on the effects of clay

products in growing media are from subordinate importance. The requirements, which are set at present for clays in this economic sector rely exclusively on parameters which were developed more or less empirically in the past.

Untill now the validity of these parameters is not proven.

As demands on quality will increase in future there is need for a sophisticated study on different clays regarding their effects in growing media. The Stephan Schmidt KG has large tonnage clay deposits with different parameters such as: – primary and secondary types of deposits – strong variations in mineralogical composition (content of smectite, kaolinite, illite, chlorite, corrensite) – variations in chemical composition, e.g. total Fe expressed as Fe2O3 from 0,5 to 20% In close coordination with the cooperation partners already marketed substrate clays as well as newly defined clays will be mined in sufficient amounts and representative quality and characterized according to well established parameters.

WP. 2: Laboratory preparation methods and industrial implementation Depending on the purpose of utilization different preparation methods have to be considered. Economic aspects also must be taken into account. The intended use of prepared clay granules (moist and dried) is primarily for potting media, whereas for blocking media and seedling substrates more cost-intensive pretreatments like extensive drying and grinding have distinct advantages. From the viewpoint of optimized product development the different preparation methods have to be compared in general. The following variations are planned: – production of partly saturated granules – production of partly saturated granules containing small amounts of peat – production of dry granules

– production of ground clay products, considering different process parameters such as product fineness and temperature WP. 3: Development of new quality parameters for production control and concurrent quality assurance Based on the results obtained in the project new parameters which can be applied on a laboratory scale will be defined. With the help of these parameters, industrial processes can be controlled and optimized. The efficiency of new production procedures has to be extensively studied and judged from an economic point of view. New process parameters have to be implemented into the internal quality management system according to DIN ISO 9001 and the environmental management systems EMAS. Subproject 2: Chemical and physical effects of clay amendments in growing media, PD Dr. S. Dultz, Institute of Soil Science, Leibniz University Hannover Objectives / Substantiations The clay amended to growing media has a decisive role for the nutrient and water regime. For automatized pricking the binding capacity of the growing media, depending on the cohesion between clay particles and the peat is very important. For the detection of suitable raw materials/methods of modification and definition of decisive quality parameters of substrate clays, chemical and physical surface properties of the clays and their dynamics during the growth period, buffering for K and P and the capability of water uptake will be determined. Different clay parameters will be rated including the results from the growth trials and used for the definition of decisive quality parameters for substrate clays.

The clays from the mesozoic-tertiary saprolites of the Rheinisches Schiefergebirge belong to the most important clay deposits in Germany.

In more than 100 million years deeply weathered layers formed, which have a considerable variability in the mineralogical composition of their vertical profile. In addition variability is

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given by the change from oxidizing to reducing conditions at ~40 m depth. The Westerwald area contains huge clay deposits with long-term clay availability. Untill now an extensive study of these clays and their modified forms regarding their beneficial effects and problems in growing media is lacking, even though this knowledge is essential for the production of growing media.

For the original and modified clays under investigation various parameters will be determined: – sequential extractions on different binding forms of Fe, Mn and Al – pH-values (H2O, CaCl2), soluble salts, exchangeable cations, effective and potential cation exchange capacity – specific surface area – particle size distribution and separation of the fractions <0.2, 0.2–0.6, 0.6–2, 2–6, 6–20, 20–63, 63–200, 200–630 and 630–2000 µm.

– chemical and mineralogical composition of the clay, silt and sand fractions, C, N and S-content of the bulk sample These data are the basis for the selection of clays for the extensive investigations. Different parameters of the substrate clays will be rated regarding their significance in the growing media.

WP. 1: Buffering of K, P and pH Optimum buffer capacities of substrate clays for K and P are given if these macro nutrients are adsorbed with high capacity by reversible binding and a suitable concentration of K and P in the soil solution is present for longer periods. Missing interactions of K and P with the clay as well as fixation by the clay are undesired effects. The K- and P-state of original and modified clays as well as fertilized growing media will be determined with the help of sorption isotherms. Due to the opposite charge of K and P their sorption mechanisms are completely different. Four different sets of data will be derived from these analyses, the desorbed amount, the slope of the isotherm

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after linearization as a measure of buffering, the concentration in the equilibrium solution where no sorption or desorption occurs (AR0value), and the sorption capacity.

Desorption properties will be determined in time series. In order to get more insights into the prevailing sorption mechanisms of P, analyses on different Fe- and Al-fractions of the clays, strongly P-sorbing phases by element mapping with an electron microscope, and competitive effects of dissolved organic matter on the sorption of P will be carried out. With the experiments recommendations can be given for the optimum K- and P-content in the growing media at the beginning of the growth trial.

Due to the respiration of roots, uptake of cations by roots and decomposition of organic matter protons are released. In addition acidification can be intensified by oxidation reactions (see WP 3). With the exception of some special plant species the buffering of the pH-value by the substrate clay is a desired effect. After the dissolution of carbonates protons will be buffered by exchangeable Na, K, Mg and Ca and by protolysis reactions with the silicates, until the Al-buffer is reached. The buffering by silicates is mainly due to the structure and chemical composition of the minerals and their specific surface area. The weathering rate of minerals might increase with their porosity as the specific surface area is enlarged (Fig. 1). Grinding which supports the formation of fresh mineral surfaces might increase protolysis and element release, as fresh surfaces have a higher reactivity than those which are affected by chemical long-term weathering. The progression of protolytic reactions of the clays will be determined by stationary pH-titrations including the quantification of released elements.

Acid extractions will be performed in order to characterize the contribution of different particle size fractions to the buffering of protons. The capacity of the exchange buffer will be quantified by the sum of exchangeable Na, K, Mg and Ca.

curve is obtained. The shear strength parameters soil cohesion and the angle of internal friction will be determined in tests at varying confining stresses.

Figure 1: Backscattered electron image of a feldspar (vein perthite) from a saprolite developed on granite.

Exsolution lamellae increase the specific surface area and have greatest impact on proton consumption.

WP. 2: Surface charge properties, binding capacity and wettability Surface charge has a decisive role for the aggregation, sorption properties, wettability and mineral stability. Surface charge depends on the pH and ion concentrations in solution.

Sorption of dissolved organic matter can lead to a further decrease of surface charge which in turn increases the amount of Ca needed for stable aggregation. Decisive factors for the cohesion of the clays and growing media will be determined by surface charge properties at different pH levels and ion concentrations and related to the aggregation behaviour and wettability of the samples. Surface charge determinations will be carried out by applying polyelectrolyte titration in the cell of a particle charge detector. Results from experiments on aggregation and sorption will be discussed from the viewpoint of surface charge. By doing this sorption properties and the conditions for a stable aggregation, prerequisite for the binding capacity of the growing media, can be derived.

The binding capacity will be determined in simple experiments on the plasticity. In a shear box a confining stress is applied vertically to the specimen, and also laterally until the sample fails. From the load applied and the strain induced at frequent intervals a stress-strain

The wettability of the growing media is of high importance for the design of the irrigation system. The wetting of dry organic matter is commonly restricted, whereas charged surfaces of 2:1 layer silicates show hydrophilic properties. Surface roughness increases the wettability. In this way the presence of clay minerals on coarse structured organic matter is of high importance. The contact angle determined with a microtensiometer at different pH values and ion concentrations will be used for the characterization of the wettability of different substrate clays and growing media.

WP. 3: Forms of charge compensation during oxidation of structural Fe(II) In clay deposits, especially in layers with reducing conditions trioctahedral 2:1 layer silicates and primary chlorites can contain in their structure distinct amounts of divalent Fe and to a lower extent also Mn(II). For the oxidation of Fe(II) on octahedral positions, three forms of charge compensation are known: deprotonation (Fe(II)-OH-Silicat = Fe(III)-O-Silicat + H+ + eâ&#x20AC;&#x201C;), release of structural cations and a decrease in layer charge. Therefore the oxidation of Fe(II) in growing media can induce a decrease in the pH-value combined with increased protolysis, precipitation of Feoxides (â&#x2020;&#x2019;decrease of P-availability) and a decrease in cation exchange capacity. A decrease in the pH-value and the formation of Fe-oxides can also be due to the oxidation of exchangeable Fe(II), Fe-sulphides and siderite. The clays will be analyzed for their content and binding forms of Fe(II) and Mn(II). Forms of charge compensation will be determined in oxidation experiments with O2 and H2O2 respectively by stationary pH-titrations, quantification of released structural cations and the determination of the cation exchange capacity.

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WP. 4: Functionalization of clays for their use in growing media Clays can be modified easily by grinding, tempering, heating and the addition of surfactants. These modified clays might have a better functionality than the original clay. By grinding the specific surface area can be increased and fresh surfaces of the minerals are obtained which have an increased buffer reactivity for protons. This is of special importance for the minerals of the sand- and silt fractions, as those are most affected by the decrease of particle size. Tempering (e.g. at 70 °C) supports the crystallisation of Fe-oxides which in turn decreases the fixation of P. Heating induces the oxidation of structural Fe(II).

As a consequence of this pretreatment, a decrease of pH and the release of structural Fe due to oxidation reactions during the vegetation trial can be avoided. By addition of certain tensides the wettability of the growing media can be improved. The different methods of modification will be determined based on their effects on the function of the substrate clays and used for the optimization of the clay amendment.

Subproject 3: Selection and characterization of suitable peats and other growing medium constituents and additives for the production of tailor-made growing media for growth trials â&#x20AC;&#x201C; Optimization of buffering capacity and binding ability, Dipl.-Ing. G. Schmilewski, Klasmann-Deilmann GmbH. Objectives Production of growing media and assessment of the impact of clays on plant growth based on horticultural quality criteria, i.e. compact growth and shelf-life. Optimization of root ball firmness of young plants by supplementation of clay to blocking and tray media. Still today clays are added empirically and as such can show beneficial effects. Plant trials will be conducted together with the Institute for Plant Nutrition in Hannover.

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Arguments The importance of the relatively small growing media industry and the products they produce becomes evident, when one acknowledges that growing media are just as essential operating resources as water, fertilizers or pesticides.

Without these modern horticulture would not be sustainable. Clays are used for fine-tuning the characteristics of growing media and thus have a considerable economic impact. In Germany alone some 120.000 m3 of clays are blended into growing media each year.

The lack of knowledge on clay properties and media-clay interactions limits the selection and proper dosage of clays for their purposeful application for specific growing media and crops. Currently dosage rates are set empirically. Defined parameters for clays suitable as growing medium constituents, based on standardized methods or standards accepted throughout the industry are non-existent.

In particular science and industry are lacking clay-specific parameters for certain applications, i.e. rewettability of the medium, influence of different growing medium constituents (especially peats) on the effect of clays, effect of various clay processing methods on the bulk density of growing media and thus on transport costs of the final products and, the effect of clays as binding agents in media for seeding and cuttings. The application of well-dosed amounts of clays would improve plant quality and optimize plant cultivation.

In particular when growing young vegetable and ornamental crops, pricking-robots are used. Via computer scanning the robots select rooted young plantlets from multi-trays. Module-size dependent, the size of the root ball may be as small as 2 mm. The robot transplants the plantlets into larger vessels for growing-on (Fig. 2). If the firmness of the root ball is not sufficient, high losses of tansplants may be the consequence. This occurs mainly during periods with insufficient solar radiation and in the main production periods. Clay can act as a binding agent and improve the stabil-

growth. Compact growth and improved selflife are priority objectives. Some main floricultural crops, increasingly important pot herbs and important vegetable crops will be considered. In this context clay will also be assessed in its function as a long-term wetting agent (plant shelf-life).

WP. 1: Selection of peat raw materials, other growing medium constituents and media additives After agreement with all partners on the composition of the media appropriate mixes, growing media will be produced for growth trials at the Institute for Plant Nutrition. These mixtures will be provided as needed and in principle during the full length of the project.

For the purpose of the experiments these growing media will be blended on a laboratory scale but mainly in greenhouse relevant quantities in order to obtain homogeneous trial samples consistent in quality.

Figure 2: Pricking robots transplant young plantlets from multi-trays into larger vessels. Clay is a binding agent in growing media. Insufficient firmness of the root ball would result in losses of transplants.

ity of the root ball. Klasmann-Deilmann GmbH has already conducted numerous trials without finding a satisfactory solution to this problem.

A tool to determine the binding capacity of clays is needed.

Description of the work plan Production of trial media for subproject 4.

According to the work schedule KlasmannDeilmann GmbH is responsible for the production of well-characterized growing media based on the selection of suitable constituents and additives. These media will be provided according to the work schedule for chemical and physical analyses as well as for plant growth trials in the different segments of application. Most growth trials will be carried out in cooperation with Prof. Schenk at the Institute of Plant Nutrition, but also using facilities of Klasmann-Deilmann GmbH. The focus of the experiments will be on the positive and market-oriented effect of clays on plant

Growing media will be provided according to the requirements of the trial crops using selected and specifically prepared clays from our partner Stephan Schmidt KG. When selecting peat raw materials it must be assured already at the outset of the project that trials can be carried out with the same materials during the complete duration of the project.

This is essential in order to avoid botanical, chemical and physical influences or changes of any unknown or unsuitable peats. To ensure this it is necessary to cool-store the various peats (e.g. weakly and moderately humified peats, milled and sod peats), mixtures for growth trials and specimen samples under controlled conditions at + 4 째C. Initial analyses of peats and growth trial media will be carried out. If available, European methods (EN methods) will be used for analysis. References to EN standards are preferable for publication and presentation of the results and will enhance the use of these methods.

Chemical properties of selected clays will be analyzed according to the RHP-Product Certification Scheme.

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WP. 2: Binding capacity of clays In addition to the laboratory tests and analyses conducted by our partners at the Institute of Soil Science, the binding capacity of clays will also be tested in plant growth trials. It is intended to produce and identify clay powders that show good binding capacity by giving more firmness to the root ball during cultivation of young plants. Growers and KlasmannDeilmann GmbH seek a clay or combination of clay materials that can stabilize the structure of the growing medium without reducing its air capacity or having an adverse effect on other physical properties, i.e. water permeability. The binding/stabilizing effect must not occur before the medium is wetted in the growth module. On the basis of the analyses results of our project partners Stephan Schmidt KG and the Institute for Soil Science a number of selected clays will be powderized and trialed in appropriate growth trials with seedlings or plant cuttings.

Subproject 4: Effect of clay amendments on nutrient fluxes â&#x20AC;&#x201C; investigations on crop level, Prof. Dr. M.K. Schenk, Institute of Plant Nutrition, Leibniz University Hannover

Objectives Potential chemical and physical parameters, which will be determined in the subproject 2 of PD Dr. S. Dultz, are investigated in growth trials with regard to their suitability to describe clays for substrate application. Besides the effect of clay characteristics on nutrient dynamics in the growing medium, plant growth will be assessed. Nutrient flux will be described by a mechanistic simulation model to evaluate cation exchange capacity (potassium) and binding forms of Fe in the clay as well as other factors (P) with regard to supply of plants. The results will be used to define quality standards of substrate clays.

Rationale Growing media are generally based on peat because of the suitable physical and chemical characteristics, which can be improved by the

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amendment of clay. Thus the addition of clay increases the buffering of the nutrients potassium and phosphorus as well as of pH. This affects nutrient dynamics in the substrate and cultivation security. Buffered substrates shall ensure that optimum conditions adjusted at start of the crop remain constant during cultivation and level the effect of factors such as water quality, concentration and composition of the fertigation solution and radiation. With crops grown in the open field, precipitation is especially significant, since torrential rain may lead to nutrient leaching from the substrate in the container. This holds true for potassium as well as phosphorus.

Plant availability of nutrients in substrates is characterized by extraction methods.

However, it is not known which extractable P- and K-content is necessary for adequate supply of plants in dependence of nutrient buffering of the substrate. Likewise it is not known how buffering affects nutrient dynamics in the substrate.

Particularly important are P-dynamics in the medium, since continuous restricted P-supply may hinder extension growth of plants, as it is necessary for the production of marketable pot plant quality. It was shown that this effect may be achieved by the addition of a strongly P-binding mineral to the substrate.

Restricted P supply also may be necessary for other reasons. Blue colouring of hydrangea, for instance, is promoted because aluminium availability in the substrate is increased. With citrus zinc nutrition is supported so that typical chlorosis of this crop is prevented. Also with other pot plants a restricted P supply may prevent typical leaf damage appearing due to excess phosphorous.

To colour hydrangea blue, not only a restricted P supply but especially a pH-value of 4,3 (CaCl2) is necessary to ensure a sufficiently high Al concentration in the substrate solution. Exceeding or shortfall of this value results

in quality reduction. A highly buffered substrate is not suitable for this purpose since adjustment of pH at the beginning of forcing would require a high rate of Al2(SO4)3. Generally highly buffered substrates ensure that in the long run the optimum pH for plant growth, especially for micro nutrient availability, is maintained. The effect of bicarbonate content of irrigation water, N-form in the fertigation solution and mineral nutrient metabolism of plants is buffered.

Due to genesis clay may contain elements such as Cl, Na, Mn or B which are harmful to plants. For Cl and Na threshold values are known which have to be kept to prevent nutritional disorders. Manganese can occur in clay in very different concentrations; it is speculated that high concentrations may induce plant damage. However, experimentally proven threshold values are not known. The same holds true for boron.

WP. 1: Potassium Peat/clay mixtures with varying contents of K will be supplied by project partner KlasmannDeilmann where upon supply of other nutrients and pH-value will be kept constant. The used clays differ in cation exchange capacity.

The substrates will be investigated in greenhouse and open field trials. The open field crops will be grown in a vegetation hall in order to control precipitation and to simulate defined torrential rains. K leaching will be determined by means of mini lysimeters. In treatments without K top dressing the availability of K bound in clay will be determined under horticultural growing conditions. The significance of K buffering for constant K nutrition will be investigated with varied K concentration of the fertigation solution.

Data will be used to describe K uptake by means of a mechanistic simulation model and to demonstrate K dynamics in the rhizosphere.

Based on the outcome conclusions will be drawn with regard to standards for clay. The mechanistic simulation model (NST 3.0) of N. Claassen considers transport of nutrients

to root surface by mass-flow and diffusion.

The uptake into the root follows MichaelisMenten-kinetics. For the calculation it is assumed that the distribution of roots within the substrate is homogenous. Competition between roots is considered. The model allows the inclusion of root hairs into the calculation of the nutrient flux.

WP. 2: Phosphorus Project partner Klasmann-Deilmann mixes clays with different P sorption capacity with peat and fertilizes the growing media with varying amounts of P. The dosage of other nutrients and pH are provided at a constant level. The mixtures will be stored for 8 weeks at room temperature (20 째C) in order to fasten sorption of fertilized P and to equilibrate P fractions. The prepared substrates will be investigated in greenhouse and open field cultivation. The open field crops will be grown in a vegetation hall for simulation of defined torrential rain. P leaching will be measured by means of mini lysimeters. It is of special interest to identify clay characteristics which ensure a continuously restricted P availability in the substrate as it is necessary to dwarf growth, to colour hydrangea blue, and to grow citrus, respectively. The effect of P buffering on stability of P availability in the substrate will be investigated with varying P concentrations in the fertigation solution.

The simulation model NST 3.0 will be used to demonstrate P dynamics in the rhizosphere.

The significance of parameters for P transport within the substrate to the plant root surface will be evaluated by means of sensitivity analysis to identify standards for clay.

WP. 3: pH-buffering Project partner Klasmann-Deilmann provides substrates with clay of different pH-buffering: pH and basic fertilization are kept constant.

The effect of pH-buffering on stability of pH during cultivation will be investigated with varying bicarbonate contents and N-forms in the irrigation water. The test plant is an ironinefficient species.

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WP. 4: Manganese and Boron Clays with different manganese and boron content, respectively, will be mixed with peat by project partner Klasmann-Deilmann: pH value as well as nutrient addition are kept constant. Crops having a low manganese and boron tolerance, respectively, will be grown in these substrates. For comparison, also treatments will be included where Mn- and B-excess, respectively, is induced by Mn- and B-fertilization. Results will be used to define critical levels for clays.

References Felix-Hennigsen, P. (1990): Die mesozoisch-tertiäre Verwitterungsdecke im Rheinischen Schiefergebirge – Aufbau, Genese und quartäre Überprägung. Relief Boden Paläoklima 6, 192 S., Bornträger.

Ismail, S. M., K. Ozawa (2007): Improvement of crop yield, soil moisture distribution and water use efficiency in sandy soils by clay application. Applied Clay Science 37, 81–89.

Miller, D. M., W. P. Miller (2000): Land application of wastes. In: Handbook of Soil Science, Ed.: M. E. Sumner, G-217-G245.

Reuter, G. (1994): Improvement of sandy soils by clay-substrate application. Applied Clay Science 9, 107–120.

Straaten, P. van (2007): Agrogeology – the use of rocks for crops. 440 p., Enviroquest Ltd., Ontario.

Stucki, J. W., K. Lee, L. Zhang, R. A. Larson (2002): Effects of iron oxidation state on the surface and structural properties of smectites.

Pure Appl. Chem. 74, 2145–2158.

Suzuki, S., A. D. Noble, S. Ruaysoongnern, N. Chinabut (2007): Improvement in water-holding capacity and structural stability of a sandy soil in Northeast Thailand. Arid Land Research and Management 21, 37–49.

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Optimization of Water Treatment Technology for As and Sb Scavenging by Microbiologically Activated Fe Minerals (MicroActiv) Kersten M. (1)*, Daus B. (2), Driehaus W. (3), Haderlein S. (4), Kappler A. (4), Stanjek H. (5), Wennrich R. (2) (1) Johannes Gutenberg-Universität Mainz, e-mail: kersten@uni-mainz.de (2) Departments Analytik und Grundwassersanierung, UFZ-Helmholtz-Zentrum für Umweltforschung, e-mail: birgit.daus@ufz.de (3) GEH Wasserchemie GmbH & Co. KG, e-mail: info@geh-wasserchemie.de (4) Zentrum für Angewandte Geowissenschaften (ZAG), e-mail: andreas.kappler@uni-tuebingen.de (5) Ton- und Grenzflächenmineralogie, RWTH Aachen, e-mail: stanjek@iml.rwth-aachen.de *Coordinator of the project: Prof. Dr.-Ing. Michael Kersten, Johannes Gutenberg-Universität Mainz

Abstract The main research activity of this collaborative research effort is the optimization of water treatment technology on basis of granulated Fe hydroxides (= GFH, or in German GEH).

GFH is applied by the SME-Partner, the GEH Wasserchemie GmbH & Co. KG established in 1997 and now one of the leading providers of iron-based high-capacity adsorbents for use in fixed bed filter process. Over 2000 plants have yet been delivered into more than 20 countries worldwide. Main purpose is treatment of Asand Sb-tainted waters, providing e.g. in India more than half million people with treated tap water. GEH® is based on pure synthetic iron hydroxide (β-FeOOH, akaganeite) with a large surface area (>220 m2/g) and an adsorption capacity of up to 55 g/kg As. This enables a simple, low maintenance removal procedure with capacities of up to 300,000 bed volumes over years without producing hazardous Asloaded sludges to be costly deposited. The main practical problem is the yet less well understood efficiency variation between dif-

ferent ground water regimes. Our hypothesis is that these effects are not only due to dissolved inorganic (mainly Si species) but also due to organic compounds interfering with the metalloid oxyanion sorbates. Natural organic matter (NOM) compounds may in particular lead to varying microbial activation of and subsequent more or less intense redox reactions on the surfaces involving redox-sensitive metalloids and trace (chloro-)organic pollutants. An open question to be solved for the SME partner is whether a specific functionalization of the surface may help in optimizing these effects towards a more versatile filter technology, pending a detailed elucidation of the basic mechanisms.

Introduction Fe(III)-bearing mineral surfaces are an important affiliate of the As species arsenate and arsenite which represent currently the most serious environmental problem with (anoxic) groundwater pollution in many countries all over the world. The environmental relevance

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of antimonate is currently being increasingly considered. There exist much literature on the As but less on Sb sorption efficiency in pure laboratory batch systems. Not much is known, however, about the molecular mechanisms and kinetics of competing compounds in natural waters such as Si- and NOM bearing species. During a long-lasting practice with natural groundwater, the SME partner has observed complex competition relationships, such as even an antagonistic effect by Ca which may significantly mitigate the Si oxyanion competing effect (Smith and Edwards, 2005; Driehaus 2006). Understanding these effects to a degree enabling their quantitative prediction by adsorption models, however, is a key to optimize appropriate mitigation technologies by applying GEH速 based filter materials (Meenakshi & Maheshwari, 2006).

Humified natural organic matter (humic substances) is present in most aquatic and terrestrial environments; it is redox-active, can be reduced chemically and microbially and interacts with inorganic contaminants by adsorption, complexation, and redox reactions. However, redox properties of humic substances and its interactions with microorganisms and Fe(III)minerals are not well described on a quantitative and mechanistic basis. About the consequences of humic substance reduction for their interactions with toxic, redox-active onyanions almost nothing is know at all. In this project, we focus not only on the role of inorganic competitors, but in particular also on humic substances in microbial and chemical electron transfer processes on the Fe-bearing sorbent surface. We hypothesize that humic substances can function as electron acceptor in microbial redox processes and, because humic substances are able to transfer the accepted electrons further to insoluble electron acceptors such as Fe(III)-minerals, represent therefore a main pathway for the electron flow on the sorbent surface.

Redox reactions of humic substances with microorganisms and iron minerals may also play an important role in the surface reactivity

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towards organic pollutants. One important property of iron is the potential of providing Fe(II) cations adsorbed on mineral surfaces to reduce organic pollutants. Dissimilatory metal reducing bacteria like Shewanella oneidensis are wide-spread in the environment, and are able to form these surface reactive Fe(II) species. The bacteria mobilize and/or produce proteins that specifically interact with the Fe hydroxide surface as terminal electron acceptor for the oxidation of various carbon substrates, potentially coupled to microbiological alkylation and hence volatilization known as the primary natural attenuation mechanism at least for Sb. The latter reaction, albeit adding to the overall water purification efficiency, may cause serious hazard for plant workers. Not much is known about surface structurereactivity relationships on a molecular scale triggered by such biogenic surface processes, e.g., in the context of natural organic matter or (co-metabolized) organic disinfection byproduct (e.g. chloramines) degradation on mineral surfaces.

The SME partner expects a major breakthrough by the scientific deliverables of this collaborative project with potential for optimizing his water treatment technology. This is of particular importance with respect to thirdworld applications like in Bangladesh with a well known arsenic problem, or for ground water remediation in the framework of superfund sites in the USA. The project is aimed at resolving these open questions and hypotheses by a collaborative activity according to the complementary methodology and expertise of the participants. These activities are namely concentrating on experiments with water purification units based on Fe oxide phases in laboratory columns and on a field scale with different ground water regimes (WP 1, GEH Wasserchemie GmbH), spectroscopy of the species involved in the surface reactions of the oxoanions sorbates on a molecular scale (WP 2, Geoscience Institute of Univ. Mainz), characterization of redox reactions on microbiologically activated iron mineral surfaces (WP 3, ZAG at Univ. T端bingen), characteriza-

Bioprocesses (ZAG)

Sorbate Speciation (UFZ)

Sorbent Targets (GEH)

Surface Structure (RWTH)

Sorbate Structure (Univ. Mainz) Figure 1: Collaboration scheme of the five partners within this joint research effort

tion of the sorbent surface structures on a nanoscale by applying X-ray techniques (WP 4, RWTH Aachen), and batch experiments and analytical characterization of potentially formed intermediate organic metalloid species (WP 5, UFZ-Helmholtz Leipzig). A sketch of the structure of this collaborative effort is given in Fig. 1 below.

Work package 1 (GEH Wasserchemie GmbH) The SME partner GEH Wasserchemie (GmbH & Co. KG) is one of the leading manufacturers of iron-based adsorbents which can refer to approx. 2,200 GEH速 plants worldwide treating an estimated amount of 450,000 m3 of tap water for daily use. In the badly affected areas of India (Meenakshi & Maheshwari, 2006), half a million people are supplied with arsenic-free tap water, thanks to the use of GEH速. Scientific work focuses since 2001 on the development of reliable prediction and calculation methods for the adsorption and removal of arsenic from natural (anaerobic) waters. A more recent but prominent site is the Olympic Park athletics residence area in Beijing equipped with our filter plants to clean the water reservoir within the framework of a Chinese-German BMBF research project (Figure 2).

Natural groundwater has a complex composition, affecting and reducing the performance

of treatment plants with granular ferric hydroxides as adsorbents for arsenic removal (Sperlich & Werner, 2005). This is especially true for ground water in the tropical regions with its high organic matter content, and in arid regions with its enhanced salt content.

Performance monitoring of treatment plants showed competitive adsorption of silica (H4SiO4) and also competition from natural organic matter. Competitive interference can decrease the treatment capacity of such adsorptive treatment by as much as 80%. Current adsorption modelling uses surface complexation models (SCM) fine-tuning the model parameters to get best fit of experimental data (Smith & Edwards, 2005). This is done without a deeper mechanistic understanding of surface structural interactions of the target contaminants, competitors, and the sorbents surface. A better understanding of the mechanism of competitive adsorption is highly required for reliable projections of capacities and improvements of our adsorbents to make them less sensitive for competition, and more selective for the target contaminants arsenic and antimony.

For the investigations by ourselves and by the project partners we will prepare samples of granular ferric hydroxide from the production (GEH速) and exhausted sorbent material from

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Figure 2: Water treatment plant with GFH used in four parallel filter containers, designed to treat 4,000 m2 of water daily like that from the reservoir lake in the Olympic Park in Beijing

long-term applications in water works. So far used materials loaded with arsenic and other contaminants are concerned, a life cycle analysis and description will be done including operating conditions and water profiles. It is also necessary to produce adsorbent samples loaded with arsenic and antimony under strictly controlled conditions using small column adsorption trials in our own laboratory with known but still raw groundwater composition.

Contact time will be varied between the trials, and different water qualities with regard to As(V) and As(III) concentration, pH, silica, PO4, humic acids, and other water quality parameters will be varied in these trial scenarios. The received samples and laboratory samples need to be characterized for grain size distribution, equilibrium pH, pHPZC, surface area, mineral composition, and chemical composition. The data are needed to interpret results and understand differences from spectroscopic investigations performed by the other WPs. Results of the investigations and the trials will help to develop an advanced SCM for adsorption capacity predictions with regard to water quality parameters. We will also manufacture and supply modified sorbents for investigations to identify versatile improvements of sorbent properties for extreme water treatment.

Work package 2 (Mainz University) Any attempt to understand solid-water interaction in aqueous environments necessitates

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studies of the inherent processes on a molecular scale. X-ray absorption spectroscopy (XAS) and attenuated total-reflection infrared spectroscopy (ATR-FTIR) are currently the most productive techniques to study on a molecular level oxyanion sorption phenomena including formation of complexes, heterogeneous nucleation and co-precipitation on oxide surfaces (e.g., Marcus et al. 2004). ATR-FTIR spectra can be collected in situ during the surface reactions, by which molecular information can be gained on the kinetics of these processes.

FTIR spectroscopy is a fast, sensitive, and noninvasive benchtop method that provides structural information on tetrahedral coordinated oxyanions. A major problem with environmental surface analysis is, however, that H2O is a strong IR adsorber. The penetration depth dp, at which the light intensity decays to 1/e is in the order of only one µm at 1100 cm-–1. A relatively new technique that conveniently provides the equivalent of such short path lengths is »Attenuated Total Reflection»(ATR-)FTIR (Figure 3). The spectroscopic signature of infrared interrogation of wet oxide slurry on an ATR crystal can provide insight into the nature of the bonding networks of oxyanions.

An IR-translucent crystal prism (e.g., Germanium) is covered by a fluid cell, while the IR beam is passing from below the prism and is reflected by the wet particle layer sediment at the bottom of the cell. After recording a background spectrum with layer and solvent, spectral changes are monitored in situ during titra-

Figure 3: Scheme of the ATR cell. Upon each reflection on passing through the ATR crystal, the evanescent light interacts with the sorbent particle layer sediment in the aqueous suspension cell

tion of a sorbate and/or adding (natural or pollutant) organics and/or microbes to the solution. The resulting sets of IR spectra measured as a function of time and solution monitoring parameters (concentrations, pH, redox, cell density, etc.) allow a direct link between spectral information and theoretical models. ATR-FTIR is also used as a screening tool to collect the most promising samples for the XAS experiments, which are commonly hampered by the scarce synchrotron beamtime allotted to the measurement campaigns.

XAS spectra are obtained by measuring the X-ray absorption as a function of energy in eVresolution at synchrotron facilities. XAS data have provided important insight into chemical processes on a molecular scale at the solidwater interface between the oxide surface and oxoanion species (e.g., As on goethite: Marcus et al. 2004, As on akaganeite: Guo et al. 2007). However, experiments with laboratory and field samples cannot be readily compared, because other oxyanions common in nature like silicate could compete with arsenate for the same inner-sphere surface sites. We will therefore perform As, Fe, and Si K-edge EXAFS analyses with samples from the collaborative partners.

Based on the possibility to gain atomistic models, recent advances in steady-state surface complexation modeling (SCM) will be employed, where it is now possible to include

spectroscopic information (Kersten and Kulik, 2005). For this, a series of classical pH-dependent titration experiments with oxyanionic species of As and Sb in akaganeite particle suspensions with and without addition of competing ions will be performed. The new SCM approach can be used to model the sorption continuum applying the nanostructure information available from the spectroscopic measurements on fits to titration data from the batch sorption experiments. This new development will be extended to competing multi-component systems such as those identified by the SME partner, and with experimental data from other partners within this collaborative effort (e.g., for silicate by WP 4, or for organic As and Sb species by WP 5).

Work package 3 (T端bingen University): Motivated by the ubiquity of microbe-mineral interactions and by the lack of detailed understanding of these complex processes, we propose to investigate the mechanisms of microbially catalyzed redox processes involving iron mineral surfaces, and the consequences of these redox processes for the fate of (in)organic pollutants. The overall goal of the proposed research is to identify the effects of biogenic iron surface coatings at minerals (oxides, clays, carbonates) representative of those present in bank filtration systems and water purification filters on surface mediated reactions with i) organic micropollutants, and ii) arsenic(V).

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Members of our research team have experience in studying the precipitation and dissolution of Fe minerals by Fe(II)-oxidizing and Fe(III)-reducing microorganisms, and the role of reactive minerals and humic compounds on the fate of (in)organic pollutants in the environment (Kappler and Straub, 2005). In this project we will focus on how the properties of minerals produced either by microbial reduction of Fe(III) minerals by the iron-reducing microorganism Shewanella oneidensis strain MR-1 or by oxidation of Fe(II) by the iron-oxidizing microorganism Acidovorax sp. Strain BoFeN1 compare with non-biogenic minerals in terms of redox reactions with organic compounds and arsenate (Chen et al., 2008). One key question here is to what extent cultivation conditions commonly used in geomicrobiological lab experiments (Kappler et al., 2005) affect the properties of biogenic minerals, especially with regard to the presence of phosphate. Further, we propose to clarify to what extent redox active natural organic matter (humic substances) that serves as electron acceptor for bacteria and as electron shuttle to Fe(III) minerals, influences the identity and reactivity of the Fe minerals. We will determine to what extent the reactive mineral species produced during these microbial redox processes react with redox sensitive pollutants (metalloids, disinfection byproducts). First, we will chose a set of iron(II)-containing iron minerals (produced either by microbial Fe(III) reduction of common natural iron(III) oxides like ferrihydrite, goethite, and hematite or by Fe(II) oxidation), clay minerals like nontronite, as well as poorly crystalline akaganeite phases from natural settings delivered by the SME partner. We will then follow their redox reactions with As(V) and organic compounds that occur as byproducts during drinking water treatment. More specifically, we will focus in our research on the following objectives: – Determination of the effect of adsorbed phosphate and DOM on the formation and properties of biogenic minerals (during microbial reduction of Fe(III) by Shewanella oneidensis strain MR-1 and oxidation of Fe(II)

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by Acidovorax sp. strain BoFeN1) as compared to abiotic systems. From these experiments we expect to gain also insights to what extent results from model systems can be transferred to complex natural conditions.

– Investigations on pure iron minerals as compared to mixtures of different minerals to determine the effects of mineral templates on mineral formation and activation during microbial reduction of Fe(III) and oxidation of Fe(II).

– Quantification of the reactivity of microbially activated mineral surfaces with respect to the oxidation of chloramines and reduction of As(V) and halomethanes in the presence and absence of phosphate and humic substances and comparison to abiotic systems.

We propose to address these goals by studying oxidation and reduction reactions of the organic and inorganic target compounds in well defined laboratory model systems (mineral suspensions) of different degrees of complexity (combinations of setups with and without microorganisms, pure and mixed mineral systems, absence and presence of phosphate and humic substances). We shall therefore investigate our own relatively simple model systems, as well as samples delivered by the SME partner. For each subtopic we will evaluate on a mechanistic level how environmental factors including pH and ionic strength affect the surface mediated reactions of the target compounds. The studies with phosphate and NOM will be complemented by the sorption modeling studies done in WP 1 and 2. In order to understand these complex systems and to follow and identify the processes we will use a set of modern analytical tools such as µ-X-ray diffraction, Mössbauer spectroscopy, scanning and transmission electron microscopy, HPLC, GC-MS, GC-isotope-ratioMS, electron microscopy techniques (STXM) and X-ray techniques (XANES).

The major goal of this WP is also to investigate the rates of heterogeneous redox reactions in

pure and poised (NOM, phosphate) systems as a function of environmental conditions and mode of formation of the mineral coatings involved. The proposed work includes (i) reactivity studies in aqueous suspensions of biogenic and abiogenic iron-(hydr)oxides (both from WP 2 and SME partner), (ii) comparison of the rates with control experiments in suspensions of non-redox active minerals (quartz, alumina) and in homogenous solution (O2 as oxidant), and (iii) establishment of structurereactivity relationships on pollutant transformation rates by studying model compounds.

The organic analyses will be performed in our laboratories and the As redox state will be determined by wet-chemical analysis (collaboration with WP 5) and synchrotron-based XAS spectroscopy (in collaboration with WP 2).

Work package 4 (RWTH Aachen) As has already been outlined in the introduction, oxyanions such as phosphate, silicate, and sulfate may compete with both As species for sorption sites. The most relevant oxyanion in many groundwaters, especially those with alkaline pH, is silicate. In water plants operated by our industry partner, concentrations up to 50 mg/L were observed and decreased the sorption capacity of the akaganeite filter material significantly. Furthermore, the specific adsorption of silicate will shift the point of zero charge and subsequently the sorption behaviour. Adsorption isotherms for silicate on akaganeite are to the best of our knowledge not known. For tuning the sorption behaviour in water plants using akaganeite, equilibrium models based on isotherms will not be sufficient, because kinetic aspects are also to be considered.

For the sorption and kinetic experiments larger amounts of homogeneous samples of akaganeite have to be synthesized. Crystal shape and size distribution can be tuned by various recipes (e.g., Sugimoto et al., 1993). Since the biologically controlled mineralization of iron oxides by bacteria (see WP 2) produces iron phases in amounts being too small for largescale sorption experiments, a further emphasis will be on syntheses as close to the biological

conditions as possible. The known uptake of carbonate into iron oxides requires all works to be performed in a controlled atmosphere within a glove box.

Sorption and kinetic experiments require markedly pure phases. Especially impurities with high specific surface area (notably ferrihydrite) need to be removed or at least quantified. X-ray diffraction on spiked samples and Rietveld analysis will quantify even minor contributions of impurities, and may then prompt selective dissolution treatments for removing such impurity phases. Since sorption is a surface area-dependent property, specific surface areas by N2 and Kr sorption have to be determined. Apart from measuring BET surfaces, the contributions of micro- and mesoporosity need to be quantified, because these pores exert major influence on the dynamics of sorption.

For phosphate sorption, the importance of the multidomainic character of many synthetic iron oxides with its concomitant microporosity has long been known (e.g., Strauss et al., 1997).

The crystal morphology will be determined by SEM (WP 3) and by TEM (this WP).

With the suite of akaganeite samples (including the industrially used product from WP 1), ad- and desorption isotherms within the relevant pH range will be measured in stirred batch experiments. From the material balance between silicate remaining in solution and initial silicate amounts the isotherms can be constructed and modeled. Select samples will be investigated within WP 2 by FTIR-ATR and XAS spectroscopy.

In a mixed-flow reactor (MFR), solutions with select inlet concentrations of arsenate are pumped through the reactor by a HPLC pump.

Such a pump ensures precise flow rates. Output concentrations are then a measure of the reaction progress and provide a data base for a kinetic evaluation of the sorption process.

The possibility to vary single parameters and to test the reversibility of reactions will enable us to identify rate-determining steps and parameters in the sorption process. The solution con-

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centrations are measured by ICP-OES. For calibrating and cross-checking the analytical procedures, a set of 50 samples will be measured by speciation techniques available from WP 5. The kinetic experiments will also be extended to the silicate sorbate.

Work package 5 (UFZ Leipzig): This WP will investigate the sorption processes of selected species of arsenic and antimony from waters onto iron bearing phases using species analysis techniques (Daus et al 2002).

The main hypothesis to follow is that there are species-specific factors disturbing the overall sorption efficiency. The following questions have to be answered in this context: – Are there differences between the different species in their sorption behaviour onto the relevant Fe-bearing mineral phases?

– Is there a potential change in the aqueous speciation pattern which has a direct influence on the sorption process, and what triggers such a change?

– Which possible biogenic reactions (oxidation, reduction, alkylation) influence the species transformation processes? Can these processes result in a remobilisation of metalloids subsequent to sorption?

First, adsorption isotherms of the most important alkylated species of As and Sb onto the relevant sorbent phases will be determined, with and without interfering ions. The adsorption equilibrium constants of alkylated species (monomethylarsonic acid, dimethylarsinic acid, trimethylantimony) will be determined by surface complexation models fits (FITEQL 4.0 code) from batch experiment data in cooperation with WP 2. Sorbent samples for the experiments will be selected in cooperation with WP 1 (abiogenic formed akaganeite of GEH Wasserchemie GmbH) and WP 3 (microbially formed akaganeite) in order to trace any differences in the sorbent preparation route.

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A new method (»rotation coiled columns«, RCC) using centrifugal forces will allow the fast and detailed investigation of the interaction of the metalloid species and the Fe-bearing sorbent materials (Fedotov et al., 2002).

The technique is based on the retention of the solid phase in RCC under the action of centrifugal forces while the other liquid (mobile) phase is being continuously pumped through.

A very strong interaction between the stantionary phase (sorption material) and the liquid phase (model groundwater) is forced by the planetary centrifuge system. There are two aims in appying this novel technique, (i) forced kinetic investigations by the intensive contact of the solid and the liquid phase, and (ii) the possiblity to investigate (re-)mobilisation or disturbing processes on a small scale (creating reducing conditions, variation of pH, etc…), in short experiment time and under well defined (pH, eH, geochemical) conditions. A novel experimental setup using a micro-sampling system will allow a high spatial resolution for, e.g., sampling along a steep redox potential gradient. Such micro-sampling enables us to take samples near the sorbent surface to analyse and quantify possible transformation products of the added species (arsenite, arsenate, antimonite, antimonite) near the surface electrical double layer. The analysis of all species will be done by chromatographic hyphenation systems coupled with an element-specific and highly sensitive ICP-MS detector.

References Chen X.P., Zhu Y.G., Hong M.N., Kappler A., Xu Y.X., (2008): Effects of different forms of nitrogen fertilizers on arsenic uptake by rice plants. Environ. Toxicol. Chem. 27, 881–887.

Daus, B., Mattusch, J., Wennrich, R., Weiß, H. (2002): Investigation on stability and preservation of arsenic species in iron rich water samples. Talanta 58, 57–65.

Driehaus Granular for the Water. J.

W., Jekel M., Hildebrandt U. (1998): Ferric Hydroxide-A New Adsorbent Removal of Arsenic from Natural Water SRT – Aqua 47, 30–35.

Driehaus, W. (2006): Understanding silica Interference in arsenic adsorption – The role of cations. AWWA, Water Quality and Technology Conference, Denver, 11.-14. Nov. 2006.

Fedotov P.S., Zavarzina A.G., Spivakov B.Ya., Wennrich R., Mattusch J., de P.C. Titze K., Demin V.V. (2002): Fractionation of heavy metals in contaminated soils and sediments using rotating coiled columns. J. Environ. Monit. 4, 318–324.

Guo X., Du Y., Chen F., Park H.-S., Xie Y. (2007): Mechanism of removal of arsenic by bead cellulose loaded with iron oxyhydroxides (β-FeOOH): EXAFS study. J. Colloid Interf. Sci. 314, 427–433.

Kappler, A., Schink, B., Newman, D.K. (2005): Fe(III)-mineral formation and cell encrustation by the nitrate-dependent Fe(II)-oxidizer strain BoFeN1. Geobiology 3, 235–245.

Sperlich A., Werner A. (2005): Breakthrough behaviour of granular ferric hydroxide (GFH) fixed–bed adsorption filters: Modeling and experimental approaches. Water Res. 39, 1190–1198.

Solozhenkin P.M., Deliyanni E.A., Bakoyannakis V.N., Zouboulis A.I., Matis K.A. (2003): Removal of As(V) ions from solution by akaganeite β-FeO(OH) nanocrystals. J. Mining Sci. 39, 287–296.

Strauss R., Brümmer G., Barrow N. (1997): Effects of crystallinity of goethite: I. Preparation and properties of goethites of differing crystallinity. Europ. J. Soil Sci. 48, 87–99.

Sugimoto T., Khan M., Muramatsu A., Itoh H. (1993): Formation mechanism of monodisperse peanut-type β-Fe2O3 particles from condensed ferric hydroxide gel. Colloids Surf. 79, 233–247.

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Development and Optimisation of a Process to Biosynthesize Reactive Iron Mineral Surfaces for Water Treatment Purposes (SURFTRAP) Peiffer S.*, Burghardt D. (1), Janneck E., Pinka J. (2), Schlรถmann M., Wiacek C., Seifert J. (3), Schmahl W., Pentcheva R. (4), Meyer J. (5), Rolland W. (6) (1) Department of Hydrology, University of Bayreuth, e-mail: s.peiffer@uni-bayreuth.de (2) GEOS Freiberg Ingenieurgesellschaft mbH, e-mail: e.janneck@geosfreiberg.de (3) Department of Environmental Microbiology, Technical University of Freiberg, e-mail: Claudia.Wiacek@ioez.tu-freiberg.de (4) Department of Earth and Environmental Science, Section Crystallography, University of Munich, e-mail: pentcheva@lrz.uni-muenchen.de (5) Wismut GmbH, Chemnitz (6) Vattenfall Europe Mining AG, Cottbus *Coordinator of the project: Prof. Dr. Stefan Peiffer, University of Bayreuth

1. Introduction Water pollution with metals, metalloids and nutrients severely affects both, the supply of clean drinking water and the stability of ecosystems in large areas of the world. Unfortunately, most techniques used for water treatment today produce high maintenance costs and are therefore not suitable for remote application, e.g. in rural areas of developing countries or as passive systems to treat effluents of abandoned contaminated sites such as mines. Therefore, inexpensive removal of arsenic is certainly one of the major challenges these days in environmental geochemistry, since many remote areas in the developing countries (especially in southeast Asia) with access to water treatment plants are affected by arsenic contamination in drinking water.

2. Objectives and Concept In this project we aim to develop a low-cost technology to remove ionic constituents from raw waters such as arsenic species.

The proposed technology is based on the reactivity of schwertmannite, an oxyhydroxo sul-

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fate of the mean stochiometry Fe8O8(OH)6SO4.

This mineral typically forms in acidic and sulfate rich mine waters as a secondary mineral upon oxidation of Fe(II) in a biologically mediated process. Schwertmannite can be generated in a biotechnological process after aeration of mining process waters. It forms surface-rich aggregates of needle-like nanocrystals. It rapidly transforms into ferric hydroxides of high specific surface area once exposed to water containing at least some alkalinity. Our rationale follows the concept to make use of this transformation reaction by adding biosynthesized schwertmannite to contaminated raw waters where it generates a large sorption capacity to remove the pollutants. The proposed process to generate reactive surface sites (Fig. 1) is advantageous both, in economical and ecological regard compared to existing techniques. It requires per mol iron oxide formed only 8% of the amount of alkalinity compared to the use of Fe(III) containing salts (Eqation 1), and releases only 4% of the amount of salts.

Eq. (1)

Figure 1: Scheme of the proposed research concept SURFTRAP

Schwertmannite can be therefore be used in active water treatment plants instead of FeCl3, e.g. as pellets. This research concept was developed based on previous studies of the Research Team. It has, to the best of our knowledge, not been the subject of previous research and is entirely innovative. It implies several research questions from which our scientific objectives are derived: – Optimisation of the schwertmannite synthesis process with special emphasis on the understanding of the role of biomineralization (subproject SP 1).

– Optimisation of the biotechnological process to generate schwertmannite (SP 2).

– Understanding of the long-term stability of contaminants bound to the surfaces of precipitated ferric (hydr)oxides with regard to binding stability and redox state in order to evaluate the potential for disposal of the sequestered substances (SP 3).

– Understanding the kinetic aspects of the interaction between contaminated raw water and the surface of schwertmannite and its transformation products (SP 4).

– Test of a pilot plant to compare the novel technique with conventional treatment technologies with regard to efficiency and costs emphasizing on arsenic containing effluents from mine sites (SP 5).

Our proposed research will yield specific results with respect to the applicability of iron mineral surfaces in water treatment:

– A mechanistic model and a technical solution to biosynthesize iron minerals from mine waste water, – a quantitative model for the separation kinetics and efficiency of ions by the proposed treatment technology in dependence of the raw water composition, – a conceptual framework for the understanding of redox transformations mediated by iron (hydr)oxide surfaces emphasizing the oxidation of arsenite, – an assessment of the long-term stability of the chemical bonding of adsorbed ions (particularly arsenic species) upon ageing of precipitated iron minerals based on a combination of state-of-the-art theoretical and surface science techniques, – a feasibility study of the purification technique on a pilot plan scale, – expected cost and energy demand for a novel water purification technique replacing Fe(III)Cl3 with a waste product of lignite mine water treatment.

3. State of the Art 3.1 International Involvement of the Proposed Research Concept The demand for reliable and cost-efficient techniques for treatment of polluted raw waters is steadily increasing. Worldwide about 21 countries are affected by ground water arsenic (As) contamination with high risk of chronic As poisoning (Rahman et al., 2002).

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Similarly, the water quality of surface waters is affected by mining world-wide mainly through a large number of sources that are abandoned with no company being in charge (Nordstrom & Alpers, 1999). It is estimated that in the US approximately 8000 km of rivers are contaminated with inorganic constituents from abandoned hard-rock mine (Pelley, 2007). Approximately 1100 soil and ground water sites contaminated with chromium are on the national cleanup priority in the US according to the US Agency for Toxic Substances and Disease Registry (Everts, 2007). The situation in Germany is similar. For example an average As load of 3â&#x20AC;&#x201C;5 kg/d from old mining effluents seeps into the river Mulde since many years (Kauk, 2006).

Retention of the pollutants at the surfaces of Fe(III) minerals is regarded to be a key process of which can be made use technologically.

Unfortunately, most techniques used to remove contaminants produce high maintenance costs, require technically trained staff and are therefore not suitable for remote application, particularly in rural areas of developing countries.

Our proposed research will contribute to this effort by developing, studying and evaluating an innovative technology of which technological use can be made in passive or on-site treatment systems. The technology combines the recycling of lignite mine water constituents with the treatment of polluted waters. As an outcome, this study will deliver definite results with respect to i) the biosynthesis of a ferric iron pool that provides reactive iron (hydr)oxide surfaces for water treatment, ii) a theoretical framework for the assessment of the long-term stability of the iron mineral surface-adsorbent interaction, iii) the scientific, technological, legal and logistic feasibility of the proposed treatment process, and iv) the expected costs. Overall, our study will contribute to the European Water Framework Directive that demands the good chemical state of ground and surface waters.

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Mineral surfaces have been used since decades to remove certain water constituents.

For example, removal of As from groundwater is based mainly on precipitation and adsorption of arsenate with ferric iron-, aluminum-, manganese or calcium hydroxides (Robbins, 1981; Fuller et al., 1993; Gao & Mucci, 2001; Anderson et al., 1976; Thanabalasingam & Pickering, 1986; Takamatsu et al., 1984). Several studies have been performed, which examined the use of natural and common adsorbing materials for low-cost removal of As, such as Fe(III) and Si-rich red mud (GencFuhrmann et al., 2004), zerovalent iron (Leupin et al., 2005), iron-oxide coated cement (Kundu et al., 2005), ferrihydrite containing sand (Jessen et al., 2005) or coagulation with aluminum (Gregor, 2001). Hitherto, no significant progress has been made to develop a cheap and easy-to-handle technique.

3.2 Adsorption at Ferric (hydr)oxide Surfaces The adsorption properties of an iron oxide surface have been widely investigated in the last decades (e.g. Stumm & Morgan, 1996, Cornell & Schwertmann, 2003). Oxide surfaces in contact with water are hydroxylated, and show distinct acid-base properties that result in a net surface charge. The adsorption of heavy metals onto oxide surfaces is rationalized in terms of surface complexation, in which the surface hydroxyl groups act as ligands to bind cations.

Surface complexation models (SCM), frequently used to describe the biogeochemical cycling of trace elements (Pointhieu et al. 2006 and references therein), rely on a set of parameters, e.g. the binding characteristics (energetics, sites) of trace elements to the mineral surface, which are, however, not easily accessible from experiments and often unknown.

An important aspect is the long time behaviour of adsorbates. For example in the current project the schwertmannite nanoparticles interacting with raw water of higher alkalinity are expected to ultimately transform to goethite. This requires a microscopic understanding of the As- (and heavy metal) sorption on iron oxide and oxyhydroxide surfaces with

respect to both structural aspects and energetics. Assuming that the akaganeite-like structure model for schwertmannite is correct, arsenate-sorption, notably in exchange for sulfate groups, must be considered both at inner surfaces (structural channels) and at outer surfaces of the needle-like nanocrystals.

Further, upon transformation to goethite, the contaminants may either be surface-adsorbed or incorporated into the bulk, which will make a signifycant difference with respect to long-term disposal of the contaminated product. Quantum mechanical calculations based on density functional theory (DFT) can provide accurate information on adsorption geometries and the corresponding binding and activation energies that can be used in the fitting of parameters for SCM (Stachowitz et al.

2006). Their necessity is starting to be recognized and first studies of AsO43â&#x20AC;&#x201C; on iron oxy(hydr)oxide surfaces have been reported (Sherman & Randall, 2003, Stachowitz et al.

2006), where different corner and edge sharing adsorbate geometries were studied. However, it is questionable whether the small clusters used in these studies containing only two Fe-ions are adequate to model the complexity of the mineral surface. To this end the periodic DFT codes, planned to be used in this project, allow to consider explicitly the specific structure and chemical composition of an extended mineral surface interacting with the adsorbate. As a full-potential allelectron code, WIEN2k is particularly suitable for the treatment of transition metal oxides.

Due to recent code developments and the increase of computational capacities it has only now become possible to address these questions from first principles. A prerequisite for studying ad- and absorption processes on mineral surfaces is a detailed understanding of the bulk materials. To this end systematic DFT-calculations on the stability, structural, electronic and magnetic properties of the different FeOOH polymorphs (goethite, akageneite, lepidocrocite, hp-phase) have recently been completed by the working group material science of the LMU (Otte, 2007, Otte et al., 2008).

The theoretical results require experimental verification. Experimentally the sorption on iron oxy(hydr)oxides has been studied extensively with EXAFS/ XAS (x-ray adsorption spectroscopy) and XPS (x-ray photoelectron spectroscopy). (e.g. Waychunas et al. 1995, Sherman & Randall, 2003, Dinge et al., 2000). A detailed structural determination of the adsorbate systems is important and can be provided by surface sensitive diffraction techniques such as Scanning Tunneling Microscopy (STM) and Spectroscopy (STS) measurements in combination with DFT calculations (preliminary work of LMU: Pentcheva et al., 2005, Pentcheva et al., 2008, Tanwar et al., 2007). A first SXRD study of As adsorption on a wet hematite surface has been recently reported (Waychunas, 2005), but the surface structure of goethite has not been determined so far.

Scanning Tunnelling Microscopy (STM) as an atomically resolving real space technique is capable of identifying adsorption sites without the need for long range ordered adsorbate superstructures. Comparing measured and simulated STM images can be used to identify the surface structure (Fonin et al., 2005). Scanning tunnelling spectroscopy (STS) (Feenstra 1994) is the only technique which provides information on the local density of both occupied and unoccupied electronic states in a single measurement and that can be directly related to the electronic structure obtained from DFT. This approach can be used to determine but also manipulate e.g. the oxidation state of the adsorbate (Repp et al., 2004).

3.3 Schwertmannite Transformation and Sequestration of Anions Schwertmannite has an affinity to anions and is an efficient sink for As(V) in mine waters (e.g. Schroth & Parnell, 2005; Acero et al., 2006). The adsorption of As(V) has been demonstrated to be an exchange reaction with non-structural sulphate (Fukushi et al., 2003).

In previous experiments of the working group Hydrology at the UBT, we have tested a novel method to remove arsenate from groundwater based on schwertmannite dissolution and subsequent formation of a new iron hydroxide

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Figure 2: As(V) concentration as a function of time

Figure 3: Schwertmannite generating pilot plant Nochten

phase that provides fresh adsorption sites. Dissolved arsenate (c = 0.027 mmol L–1) was readily removed by the suspended materials formed and decreased below the detection limit within 2 h. We were able to purify 65 L of water within 2 h. As(V) had been adsorbed to the surface of the freshly formed materials which had been sedimented after additional 14 h (Fig. 2).

the proposed use of schwertmannite as a reactant. In particular the short-time behaviour (< 24 h) of SHM upon reaction with alkalinitycontaining water has not been addressed previously and needs to be understood from a mechanistic point of view.

The concept was developed based on the metastability of schwertmannite. Once suspended in water, it ultimately transforms into goethite, thereby lowering the pH (Schwertmann & Carlson, 2005; Regenspurg et al., 2004, Jönsson et al., 2005). The transformation rate is slow under acidic conditions (pH ~3) and increases signifycantly at higher pH (Regenspurg et al., 2004, Schwertmann & Carlson, 2005) being driven by a supply of alkalinity (Peine et al., 2000). It appears that under these conditions sulfate is coordinated in an outer sphere mode to the schwertmannite surface, whereas a stronger, possibly inner-sphere complex dominates at low pH (Jönsson et al., 2005). The feedback of the coordination chemistry on its exchange properties with other oxoanions has not been studied yet.

Contrary to the previous observations, goethite could not be detected at very low solid/ solution ratios (2 g/L, Knorr & Blodau, 2006).

An explanation for this observation is still lacking although it may be of high relevance for

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All ferric hydroxides are known to have a high capacity and a strong affinity to adsorb both anions and cations (Cornell & Schwertmann, 2003), the extent of which de-pends strongly on the pH. A laboratory study on the effect of ageing on As sequestered by schwertmannite from an effluent of an abandoned mine site revealed that > 99% of the As remained in the solid phase that had formed after a 1 year ageing process and which consisted of mainly goethite and to a lower extent of jarosite (Acero et al., 2006).

Elucidation of these complex interplay between transformation kinetics, chemical composition of the treated water and the specific interactions between the pollutants and the surface of the new mineral phases will be one principal objective in this project.

3.4 Generation of Schwertmannite in a Technical Scale As pointed out above, schwertmannite has a large potential as a reactant suitable for water treatment purposes. It can be generated in a biotechnological process in a pilot plant designed and constructed by a collaboration partner (GEOS mbH) of the SURFTRAP research

team (Glombitza et al., 2007) in order to treat mine water in the Lusatia lignite mining area.

The pilot plant consists of an inflow and aeration chamber (1.88 m3), an oxidation pond (8.14 m3) with growth carriers and sludge treatment facilities, a precipitation chamber (0.5 m3) with stirrer (to adjust the pH), a sludge container for temporary storage of schwertmannite and diverse pumps for the inand outflow and reflow of sludge plus devices to measure flow rate, pH, dissolved O2 and Eh. The maximum hydraulic load is 5.0 m3/h. To date a maximum load of 2.5 m3/h was achieved at oxidation rates of 70 g Fe(II)/(m3/h).

The plant was run at pH 2.9–3.0. Under these conditions, at a residence time of 5 to 8 h, 50 to 70% of the Fe(II) are being oxidized and 50 to 80% of the oxidised iron is precipitated as schwertmannite.

3.5 The Role of Fe(II) Oxidizing Bacteria for Schwertmannite Mineralization Schwertmannite is the characteristic seconddary iron mineral forming in aquatic mining environments (Bigham et al., 1990). It seems to be at equilibrium with Fe(II) (Regenspurg et al., 2004) which suggests a relationship between its formation and the oxidation of Fe(II) being typically catalysed by aerobic, usually chemolithotrophic bacteria.

The first and most intensively studied representative of the acidophilic iron oxidizing bacteria is Acidithiobacillus ferrooxidans. The genus Acidithiobacillus (Kelly & Wood, 2000) shows a high diversity, even within species, and most of the species are easy to cultivate. Because of this, in the past Acidithiobacillus spp. were considered to be the dominant, acidophilic iron-oxidizing bacteria in the environment and were used in biotechnological applications for the leaching of metallic sulphide ores (Hackl et al., 1992). The formation of iron hydroxysulfates like jarosite and SHM in the presence of A. ferrooxidans was studied by (Eneroth & Bender Koch, 2004). They discuss the precipitation process as an indirect result of bacterial oxidation, with no influence of the bacterial cell.

(Ferris et al., 2004) showed the direct contact between the bacterial cells and the crystal formation. The coherence between temperature and mineral formation in the presence of psychrotolerant A. ferrooxidans cultures were shown by (Kupka et al., 2007).

In recent years, a number of other acidophilic, iron oxidizing bacteria were described and investigated. Leptospirillum ferrooxidans, Sulfobacillus acidophilus, Sulfobacillus thermosulfidooxidans, Acidimicrobium ferrooxidans and the incompletely described ‘Ferrimicrobium acidophilum’ are thermophilic and acidophilic bacteria, respectively, which oxidize Fe(II). Iron oxidizing archaeal species are Sulfolobus metallicus, Metallosphera sedula, Acidianus brierleyi, Sulfurococcus yellowstonensis and Ferroplasma acidiphilum. The current knowledge about the distribution and biodiversity of these extremophiles is reviewed by (Johnson, 2007).

Analyzing the bacterial communities of acidic, iron- and sulfate-rich mine waters with molecular and cultivation methods, strains were found belonging to the class of Betaproteobacteria as the dominating group. They were closely related to the neutrophilic iron oxidizing Gallionella ferruginea (Hallberg et al., 2006). The dominance of this bacterial group in acidic mine waters could be confirmed by previous experience of the working group of environmental microbiology at the TUF as well (Hedrich et al., 2007; Heinzel et al., submitted). It therefore appears that our view on the role of microorganisms for the formation of schwertmannite is rather incomplete. In particular, the influence of novel â-proteobacterial species needs to be considered. We therefore hypothesize that schwertmannite can be produced in large quantities as a biomineralisation product and its formation rate is linked to the physiology and growth kinetics of Fe(II) oxidizing bacteria. To our knowledge, no systematic study has been performed in this regard until now. Understanding of the formation kinetics is, however, a clue for successful technical generation of schwertmannite.

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Figure 4: Cooperation scheme

4. Description of Work Schedules 4.1 Cooperation Scheme Based on our scientific objectives we have formed a research team that combines expertise in hydrogeochemistry, microbiology, process engineering as well as theoretical and experimental surface mineralogy. As shown in Fig. 4, we have splitted our project into five subprojects with differing responsibility of the project partners, however with mutual interdisciplinary collaboration.

4.2 Work Packages of SP 1: Understanding the Biomineralisation Process of Schwertmannite The syntheses of schwertmannite (SHM) and the resulting crystal structure, crystal morphology of schwertmannite and the biomineralistion texture will be studied based on biotic and abiotic experiments.

The biosyntheses will be performed using both, mixed cultures directly from mine water, and pure cultures of Fe(II) oxidizing bacteria obtained from isolation experiments.

The variation of the formed crystal structure depending on the previous described tests will be visualised and investigated in more detail using structural techniques like diffraction and

40

electron microscopy. The active involvement of microorganisms to control the crystal formation by the production of Fe(III) is still unknown. Thus, cell membranes will be isolated from pure cultures and the location of the crystal formation at the cell membrane will be analysed by isotopic labelling and secondary neutral mass spectrometry. Further, growth conditions for the Fe(II) oxidizing bacteria will be optimized in order to increase the yield of schwertmannite.

WP 1.1 Synthesis of SHM in the presence/ absence of an acidophilic Fe(II)-Oxidising bacterial consortium.

WP 1.2 Investigating the relationship between microbial growth kinetics and the morphology of schwertmannite.

WP 1.3 Characterisation of schwertmannite crystal growth by isotopic labelling and SNMS or microautoradiography.

WP 1.4 Isolation of outer cell membranes from pure cultures and investigation about their influence at the schwertmannite formation.

4.3 Work Packages of SP 2: Optimization of the Biotechnological Schwertmannite Synthesis as a Reactant for the Arsenic Elimination from Ore Mining Waters Results about the optimum growth conditions of Fe(II) oxidizing bacteria obtained from SP 1 will be directly adopted to an existing mine-

water treatment plant in the Lusatian lignite mining area in order to increase its efficiency and stability. In these experiments the effect of acidity, pH and biomass concentration on the oxidation rate and a technical option to increase the fraction of fixed biomass will be studied. The properties of schwertmannite precipitating in this plant (in particular the specific surface area) will be investigated as a function of process parameters such as pH and flow velocity.

Different application forms for the utilisation of schwertmannite as a reactant in active or passive water treatment plants will be developed (pellets, powder, suspensions, components of porous materials), some of which will be tested in the SP 5 in comparison with the conventional dosage of FeCl3.

WP 2.1 Optimisation of growth conditions for newly isolated bacteria. Test of various carrier materials with mixed and pure cultures.

WP 2.2 Investigating the influence of various process parameters on the efficiency and the schwertmannite yield of the existing mine water treatment plant.

WP 2.3 Development and design of different application forms of schwertmannite with special emphasis on specific surface area and handling in different water treatment processes.

4.4 Work Packages of SP 3: Structure and Energetics of Interaction between As and Cr Species and the Surfaces of Schwertmannite, Ferrihydrite and Goethite The goal of this SP is to investigate experimentally and theoretically using density-functional theory (DFT) calculations the adsorption and incorporation of As(V) and As(III) species in and on the surfaces of Schwertmannite (Fe8O8(OH)x(SO4)y with x = 8 â&#x20AC;&#x201C; y, 1 < y < 1.75) and iron-oxy-hydroxide phases. It is expected that the long-term product in disposal sites of contaminated schwertmannite will be contaminant-doped goethite. This study shall serve as a basis for an atomistic understanding of the binding of toxic metal and metalloid contaminants and the reaction mechanisms during the transformation of schwertmannite to goethite.

The binding form is decisive for the long-term retention of the contaminants; DFT-calculations shall explore the relative stability for adsorption on reactive surfaces compared to incorporation into the bulk structure. Experimentally, the crystallographic state of the phases and orientation of their reactive surfaces shall be determined with electron microscopy and x-ray diffraction. Atomic-scale imaging of surface-structure in the presence of the contaminants will be made with scanning tunnelling microscopy and -spectroscopy (STM and STS) at least on available model systems such as hydroxylated hematite. On one hand the experiments reduce the parameter space for the DFT calculations. On the other hand the ad-/absorption geometries and bond lengths from the DFT calculations shall assist the interpretation of diffraction patterns and XAS spectra for which model assumptions are always needed. An additional aspect to be investigated is the mechanism of biomineralisation of schwertmannite (SHM).

WP 3.1 Particle morphologies and reactive surfaces WP 3.2 SHM crystal structure and its variations WP 3.3 Structural aspects of SHM to goethite transformation WP 3.4 XAS measurements on the Ad-/ Absorbed contaminants WP 3.5 Atomic resolution microscopy and spectroscopy WP 3.6 DFT calculations on As Ad-/Absorption on goethite WP 3.7 Density-Functional Theory calculations on As adsorption on SHM 4.5 Work Packages of SP 4: Interactions between Contaminated Waters and Schwertmannite and its Transformation Products Schwertmannite biosynthesized in SP 1 will be reacted with raw waters of different composition in order to study the transformation kinetics as a function of pH, sulfate, alkalinity and the extent of adsorption of various ions. Our main focus will be directed to the negatively charged or uncharged arsenic species with minor attention also to the positively charged

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Table 1: extraxtion of the actual quality of the flooding water Schlema/ Alberoda (Wismut, 06/2007)

Cr3+ ion (cf. SP 3). The ferric (hydr)oxides that have formed upon the transformation reaction will be characterised with respect to their mineralogical composition and the binding strength of the adsorbed ions. Long-term stability will be estimated experimentally and in consideration of the theoretical framework created in SP 3. Special attention will be given to the influence of the morphology of schwertmannite on its dissolution behaviour.

These results can be directly used for the design of specific schwertmannite specimen to be applied in different water treatment systems (e.g. on-site or in-situ) and provide the framework for the pilot scale experiments planned in an active water treatment system (cf. SP 5): WP 4.1 The transformation kinetics of Schwertmannite will be studied as a function of pH, sulphate concentrations and synthesis pathway.

WP 4.2 The interaction between Fe(II) and schwertmannite is studied with respect to the adsorption of Fe(II) and schwertmannite transformation rates and product formation.

WP 4.3 Behaviour of As species during transformation of schwertmannite WP 4.4 Testing the long-term stability and the requirements for the deposition of arsenic contaminated transformation products WP 4.5 Optimising the water treatment process for the pilot test planned in SP 5 WP 4.6 Testing different application forms of schwertmannite for an On-Site treatment of punctual discharging ore mining waters 4.6 Work Packages of SP 5: Testing the Developed Process Technology in a Pilot Scale Test SP 3 and 4 will establish the scientific platform for the design of a pilot scale test

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that allows the comparison between a conventional treatment using FeCl3 and schwertmannite as the Fe(III) source. In order to identify the technical an economic parameters for the proposed process, a pilot plant will be constructed that is connected to an active water treatment plant that treats arsenic-rich waters from a former mine site.

The plant was constructed for the daily treatment of about 27.500 m3 flooding water from the old uranium mining facilities SchlemaAlberoda and is run by our collaboration partner WISMUT GmbH. The flooding water contains a high alkalinity and a large number of contaminants (table 1) which requires a complex and cost-intensive water treatment proess.

After a first CO2 stripping step (HCl dosage to decrease the pH to 3–3.5 in reactor 1), BaCl2 is added to precipitate 226Ra in reactor 2. In reactor 3, addition of a Ca(OH)2/FeCl3 mixture remove both, As and U after an increase of pH to 6.5–7.5). Reactor 4 implements a KMnO4 dosage for manganese elimination. In reactor 6, a flocculant is added for the sedimentation of contaminant-loaded sludge.

WP 5.1 Realization of a pilot scale test with schwertmannite application in an active water treatment plant of the Wismut GmbH WP 5.2 Determination of costs and energy demand for the developed water treatment technology.

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Interfacial Processes between Mineral and Tool Surfaces – Causes, Problems and Solutions in Mechanical Tunnel Driving Fernandez-Steeger T. M. (1)*, Post C. (1), Feinendegen M. (2), Bäppler K. (5), Zwick O. (4), Azzam R. (1), Ziegler M. (2), Stanjek H. (3), Peschard A. (6), Pralle N. (4) (1) Chair of Engineering Geology and Hydrogeology (LIH), RWTH Aachen University, e-mail: azzam@lih.rwth-aachen.de, Fernandez-steeger@lih.rwth-aachen.de, post@lih.rwth-aachen.de (2) Chair of Geotechnical Engineering and Institute of Foundation Engineering, Soil Mechanics, Rock Mechanics and Waterways Construction (GIB), RWTH Aachen University, e-mail: feinendegen@geotechnik.rwth-aachen.de, ziegler@geotechnik.rwth-aachen.de (3) Clay and Interface Mineralogy (CIM), RWTH Aachen University, e-mail: stanjek@iml.rwth-aachen.de (4) Herrenknecht AG (HK), Schwanau, e-mail: baeppler.karin@herrenknecht.de (5) Ed. Züblin AG (ZÜB), Stuttgart, e-mail: zwick.otto@zueblin.de, norbert.pralle@zueblin.de (6) Condat Lubrifiants (CL), Chasse-sur-Rhône / F, e-mail: arnaud.peschard@condat.fr *Coordinator of the project: Dr. rer. nat. Fernandez-Steeger, RWTH Aachen

Abstract During mechanical headings with tunnel boring machines (TBM) in soft rocks (clay stones, silt rocks, etc.), the excavated material often sticks to the cutting tools, cutting wheel or conveying system. This may cause great difficulties in its excavation, transport and reuse or dumping, as well in the course of the construction progress. Responsible are mainly adhesion processes that occur at the interfaces and at the surfaces of the clay minerals and tools. In the frame of the joint project methods for the prediction and quantification, as well as appropriate countermeasures to face the problem of stickiness of the geomaterials and subsequent clogging will be investigated. Therefore, the geoscientific knowledge of interfacial processes and manipulation techniques on a micro- and nanoscale will be linked to the engineering sciences knowledge of macroscale processes and technical requirements.

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1. Introduction Mechanical tunnel driving is a world-wide popular method within tunnelling, whereby the limits of its application (diameter, length, overburden, water pressure, subsoil, etc.) are being constantly pushed ahead ([1]). Rock units with changing strength properties have frequently to be crossed. During the excavation and transport of the material, the mechanical wear may cause a loss of strength which may even lead to a complete disintegration of the composite structure.

This may be a desired effect, for example, if one considers the slurrification of the excavated material within an EPB shield, which allows its advance and transport in the first place ([2]). In many cases, however, and particularly in combination with water inflow, the excavated material sticks to the cutting tool (Fig.s 1 and 2) or conveying system. This leads

Figure 1: Cutting disk blocked due to adhesion

Figure 2: Adhesion in the working chamber of an EPB TBM

Figure 3 and 4: Closed cutting wheel with extensive clogging

to far-reaching obstructions in the course of the construction progress ([3]). The problem is also described in [4], where we read: »Eventual clogging of the cutting wheel in case of slurry-support considerably influences the rate of advance. Countermeasures are: […]. In the case of EPB-shields, eventual clogging is countered by the conditioning of the slurry (adding foam and / or bentonite)«. Often this can be observed in fine- and finest-grained soils and soft rocks, where the excavated material sticks to the cutting tools or conveying system causing clogging (Figs. 3 and 4). Responsible for these difficulties are mainly processes that occur at the interfaces/surfaces of the clay minerals of the excavated material.

Interactions at the interfaces between geomaterials and/or tools or construction materials are often a desired effect in civil engineering.

Typical examples are sorption and linkage of contaminants on clay minerals, suspensions for slurry walls or borehole stabilization.

Anyhow in mechanical tunnel driving these interfacial processes may cause the above described problems usually called »adhesion« or »stickiness«. They cause significant troubles such as high energy demand during the advance of Earth Pressure Balanced (EPB) shields, blocking or breakdown of excavation tools (e.g. roller bit), clogging of screws or belt conveyors, problems in reuse caused by lower shear resistance of the conditioned excavation

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material. This leads to a reduced advance, time consuming cleaning works at the cutting wheel and standstill of tunnel driving.

Besides these technical effects, the impact on the economic efficiency and success of a tunnelling project may be substantially endangered. The resulting delays in the progress of construction work, costly additional measures and often protracted disputes between the (mostly public) awarding authorities and executing companies represent an almost incalculable risk for both parties and cause great economic damage.

Although the negative effects of stickiness in tunnelling are quite high and countermeasures on an empirical base are for some situations available, a systematic investigation of the processes is missing to this day. Systematic research to classify rock types or mineral compositions regarding their potential to cause stickiness has not been done yet.

2. Objectives and Conception Since the choice of suitable construction methods (face support, rock/soil cutting, material transport, supporting and lining, etc.) depends strongly on the geological framework and its requirements to the construction processes, the detailed knowledge of the expected geological and geotechnical conditions and processes is an important factor for the successful completion of a tunnel construction project. In particular the problem of adhesion of excavated material to the surface of cutting and transportation equipment is of great importance.

Besides technical optimisation of tunnelling operations, the well directed manipulation of interfacial processes can reduce, if not even completely eliminate unfavourable effects of adhesion on the construction process.

The aims of this research project are: – investigation of changing geotechnical properties and the resulting adhesion behaviour of a soil or rock during tunnelling operations,

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– a better understanding of the processes that occur at the mineral surfaces and interfaces, – development of a standard laboratory test for quantification of adhesion propensity, – development of a classification scheme for the adhesion potential, – development of suitable methods for surface manipulation in tunnelling, – determination and quantification of processes resulting in adhesion, – scale-up of findings and verification by largescale tests.

The project consortium and the project structure are derived from the core competences of the project partners and consider the problem of adhesion on all scales and along the entire functional chain in mechanical tunnel driving. Figure 5 shows the project’s structure schematically. The arrows between the project partners illustrate the exchange of information and/or samples for further tests and express the main assignments which are not complemented, but indicate the most important cooperational work between the clusters.

Cluster 1 (Clay Mineralogy, Engineering Geology) focuses on the scientific fundamentals on the small-scale effects (nm to mm) in a mineralogical and geological context and investigates the manipulation of mineral surfaces on that scale, as well as possible environmental impacts of the manipulation methods.

Cluster 2 (Geotechnical, Civil and Mechanical Engineering) concentrates on the engineering implementation and scale-up of the findings to the large-scale (mm to m) in a geotechnical and construction method context. Especially geotechnical properties before and after manipulation, classification for construction purposes, implementation and the dissemination to practical applications in tunnelling are main tasks.

Figure 5: Project structure and clustering of working groups

The project will mainly consider possible adhesion-caused impacts on the various construction sequences in connection with EPB shield driven tunnels. The overall aim is to provide knowledge and methods to identify possible adhesion problems in the preliminary phase of a tunnelling project and to provide a selection of suitable methods to cope with this problem with a minimum of negative side effects. This will have an overall positive effect on the efficiency, sustainability and profitability of projects.

3. State of Science and Technology 3.1 Clay Interfaces and Manipulation Interfaces The mechanical properties of clay and clay suspensions are primarily determined by surface geochemistry and charge distribution at the interfaces ([5]), which in turn affect the arrangement of the clay minerals (structure) ([6]). The clay leaflets are either arranged in a loose house-of-cards structure or a more sta-

ble stair-step structure depending on the edge charge. The surface charge and thus the charge distribution can be externally manipulated by chemical or physical methods. This has a corresponding effect on the structure and thus also the geotechnical properties of clay such as adhesion behaviour, porosity, shearing strength, consolidation, viscosity or water absorption capacity ([7], [8]).

According to the DLVO theory, far-reaching repulsive forces at the mineral surfaces occur with highly charged surfaces in diluted electrolytes that prevent dispersed particles from approaching the so-called Âťprimary minimumÂŤ. Densely coagulated particles, on the other hand, cannot disperse since they cannot leave the attractive maximum. An increase in the electrolyte content depresses this energy barrier and thus changes the dispersion behaviour (see Fig. 6).

The degree of disintegration and the loss of strength depend on the mineralogical compo-

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Figure 6: Interactions of attraction and repulsive forces of charged colloids or colloids to a surface according to the DLVO theory. Increases of the energy barrier improve the stability of the suspension and reduce coagulation

sition and primary strength properties of the penetrated material, subsequently leading to a reactivation of phyllosilicates ([2]). Highly viscous pastes may form, which stick to the tool surfaces depending on the dispersibility of the rock (both mechanical and chemical). The rheological properties of these pastes depend on both, the solid and fluid properties ([8]).

Concerning the solids, permanent and variable particle surface charge, such as in smectites ([9]), is just as important as the species composition and their ion concentration in pore water.

The interaction energies in such suspensions cannot be directly observed; however they do correlate with the easily detectable zeta potential ([10]), which describes the surface potential as the charge of the particle. Interaction between the different particle surfaces or edges can be selectively adjusted by changing the solvent chemistry (salt concentration, valency of the cations and anions, pH-value) ([6], [10]). The surface geochemistry can be modified in this way by ion substitution. This affects the mechanical properties as well as the permeability (K-value) or porosity of the material ([7]). Only this scale-graduated approach, which considers the specific attributes of phyllosilicates, is able to perform and optimize the geotechnical constitution of the soiltool system. Alternatively, electrokinetic mani-

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pulation, e.g. by applying an electric potential between the tool and clay suspension can affect the adhesive forces ([11]).

3.2 Geotechnical effects of interfacial processes and countermeasures The success of mechanical headings with tunnel boring machines (TBM) in fine- and finestgrained soils and soft rocks depends very much on the adhesion potential of the actual geological formations encountered. The frequently resulting clogging has a massive influence on the performance especially with earth pressure balanced (EPB-) shields in clayey soil.

Therefore, reliable information about adhesive soil conditions to be expected as well as the determination and quantification of possible adhesion related problems are of major importance for a tunnelling project.

The adhesion of clayey soft rocks in mechanical tunnel driving with slurry shields has already been investigated in several research projects ([12]). Nevertheless, up to now there has been no attempt to determine its causes and effects through a specific consideration of interfacial processes on the mineral surface level.

The properties of soft rock and soils with high content of finest grain that may be produced during disintegration have already been inves-

tigated in numerous studies. The adhesion of soils to steel surfaces like excavation tools for various purposes has also been examined in different tests ([14], [15]). In connection with EPB shields only the behaviour of conditioned uncohesive soils in the screw conveyer has been studied so far ([16]).

However, no generally accepted (standardized) tests currently exist to quantify the variable strength properties and to determine the adhesion from a practical (tunnel) construction point of view.

ing agitation in areas prone to material settlement can help to reduce adhesion to the TBM and subsequent clogging. Furthermore, continuous controlling and optimisation of driving parameters can help to reduce adhesion to the cutting tool and cohesion in the chamber. So, optimised shield pressure, penetration and rotation rate can help to generate large soil chips in order to reduce the adhesion-prone surface of the excavated clay in relation to its volume.

– dispersion: distribution of the clay in inflowing ground water.

If clogging occurs in shield drives also with EPB Shields, chemicals and additives (e.g. polymers or tensides) are used to reduce adhesion (Figs. 7 and 8). Technically this aims to disperse the clay particles by a reduction of surface energy. Some practically tested techniques for conditioning the excavated material are described in [17]. The application of additives often affects the mechanical properties of the material in a desirable way, but it causes problems concerning environmental aspects in land filling as well as in the reuse of the excavated material due to the prevention/reduction of the colloid formation.

Some aspects can be considered in the technical design of the TBM and in the logistics for material transport. For example, an optimized cutting tool design, the avoidance of narrow passages and other obstructions for the transport, an open cutting wheel center or increas-

The colloid formation is an important process with major influence on the later structure and stability of the material. The project aims at reduction of adhesion and/or repulsion between the mineral and the tool surface, whilst retaining the ability of clay particles to

With regard to the risk of stickiness and subsequent clogging the following three principal mechanisms have to be considered: – adhesion: sticking of soil particles at component surfaces such as steel, – cohesion: adherence of clay particles between each other,

Figure 7 and 8: Cohesion of a coarse grained material without (left) and with foam additives. Similar products are available for fine-grained materials like clays

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coagulate. A well-controlled (temporary) dispersion of the excavated material in the shield and subsequent manipulation for coagulation is also possible. This may favourably affect the long-term geotechnical properties with respect to the reuse of materials.

4. Work Plan As described the project works on all scales to investigate the problem and to develop suitable solutions. As the tasks on the small scale differ from the ones on large-scale, the partners are arranged in two clusters in a matrix to ensure an efficient workflow and cooperation. The focal point of the first cluster is the manipulation in the crystal structure of clays through an active modification of the mineral surfaces that allows a temporary or permanent influence on the geotechnical properties. The second cluster centres on large-scale effects (mm to m) in a geotechnical and construction method context which includes geotechnical properties before and after manipulation and their practical applications in tunnelling. An important point is the transfer of findings from small to large scale and vice versa, as well as the evaluation of outcomes on all scales.

First of all, a review of available data regarding tunnel projects with serious adhesion problems and construction processes that have a direct influence on the adhesion will be done to identify exemplary sample sites and main problem fields. Simultaneously, relevant methods to manipulate clay surfaces will be studied and evaluated regarding their potential to change surface charge and subsequently their geotechnical properties under tunnelling conditions. Supplementary preliminary tests on manipulation, like changes in fluid chemistry or electrokinetic manipulation are conducted with samples from tunnelling projects. X-ray diffraction and fluorescence spectroscopy help identifying and quantifying minerals with contents >0.01 g ¡ gâ&#x20AC;&#x201C;1.

The next step is the creation of a web-based SQL database with relevant data from various completed and current EPB driving projects:

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basic geological conditions, clay mineralogy, natural and admitted water content, type and amount of conditioning agents, etc. Analyzing these data will give an impression of an optimum consistency of the excavated material in tunnel driving to maintain appropriate earth pressure slurry. In laboratory and field tests the geotechnical properties like shear strength, consistency, durability, etc. are determined to classify applicable standards, rules or recommendations. Parallel studies at nanoscale comprise the determination of cation exchange capacity, the estimation of exchange isotherms, zeta potential and the specific surface of the clay minerals (BET).

Beside the mineral manipulation another important aim of the project is the development of a standardised adhesion test that identifies the adhesion forces realistically. The above described clay mineralogical investigations will be used to calibrate and evaluate the standard test. This test will be used to benchmark the success of chemical and electrokinetic manipulation methods to prove the desired effects of surface charge manipulation or concerted ion change. Outcome of these investigations is the development of a classification scheme that characterizes the adhesion propensity and clogging potential of excavated material. The transfer of the results and their assessment are then tested in laboratory scale in cooperation with the industrial partners. The advanced step is the transfer into large scale, which means into geotechnical scale. Definition of the construction operations and machine technology requirements and choice of methods that are appropriate under mechanical tunnelling conditions will be made. Those methods found to be effective will be evaluated with respect to their environmental impact and suitability for construction operations and the transportation process. Above all, long-term effects are to be assessed and clarified by supplementary investigations (long-term stability, thermal stability). Last but not least a practical pilot plant is planned to analyse the effects of reducing adhesion.

5. Preparatory Work and First Results In the relevant literature different experimental set-ups for adhesion tests are described. Many of the tests are quite similar to tests from the 1930ies which were common at that time to determine the tensile strength of soils. This indicates that most of these tests address the influence of the tensile strength to the problem of adhesion. In the case of cohesion and adhesion the strength determined by these experiments is a mixture of both vectors. In the case one of them is considerably higher than the other, the results will show the strength of the weaker one.

Nevertheless a typical experiment, comparable to other tests, was set up to evaluate the results from the so called pull or separation tests (Figs. 9 to 11). The tests were carried out with samples from a tunnelling project where clogging was observed. Yet, the results are not totally satisfying in terms of repeatability and interpretability. Especially the prediction of potential adhesion problems and clogging from the measured values is very difficult and not satisfying.

Since the above described test layouts may not represent all processes taking place at the head of a TBM, additional concepts are recently under investigation. Besides the tension forces also shear forces may influence adhesion as well as cohesion of the material. One aspect in this context is the quantification of the sticking soil mass instead of or additionally to the adhesion forces. Therefore, some new experimental set-ups are tested, considering as well tensions as torsion and shear

Figure 9: Separation (pull) test

stress (Fig. 12). From the first test results, of course, the adhesion potential of the tested soils cannot be evaluated reliably so far. However these first tests provided substantial information for the optimization of existing and conceptual design of new adhesion tests.

An extensive literature research ([27]) has been carried out regarding the problem of adhesion in mechanical tunnel driving with earth pressure balanced (EPB) shields. It shows that measurable adhesion forces in experiments depend on numerous influences including soil/soil physical properties as well as varying test parameters. Findings from most studies stress the importance of the type and ratio of swellable clay minerals as key parameters for the adhesion potential. Subsequently the plasticity and consistency of the excavated material in the chamber has been seen as an important indicator for a possible adhesion process. With respect to the test parameters, contact pressure and contact time, wetting of the surfaces as well as surface roughness and separation velocity seem to be additional determining factors. Table 1 gives a short review of the different parameters and effects that were investigated by the different authors.

The investigated parameters and the findings indicate that as well cohesion processes of the excavated material as adhesion to the tool surfaces play an important role. Parameters like water content, consistency and plasticity interdepend and are controlled by particle size distribution and reactive mineral content. The extent of swelling potential, water absorption capacity and cation exchange capacity are also

Figure 10: Test set-up

Figure 11: Evaluation of the test

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Figure 12: Preliminary test to investigate adhesion of clayey soil on a test blade, considering also torsion and shear stress to the sample

Table 1: Effects on adhesion as investigated by different authors (see list of literature)

linked to the mineral composition emphasising the above mentioned nano-processes. The used methods show the tendency to apply standard geotechnical laboratory tests to determine the mineral composition and inter-

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facial processes indirectly. To consider the impact of machine operations and tool surfaces some studies investigate also the influence of tool surface roughness, surface wettability and contact pressure. Regarding inter-

Figure 13: Mountain water inflow and clogging at the TBM cutter head

face processes, one problem might be that different processes may interact or cause the same effect. As the water content of the material in the chamber seems to be an important factor, the chemistry of mountain water may also influence the material behaviour. Changes in pH-values or mineralisation have a large impact on the energy barrier according to the DLVO theory and subsequently the cohesion of the material.

To get an impression of the impact of mountain water, some data from a tunnel project were available for a first analysis. The data show a close relation between the inflow of water during standstill periods and extensive clogging at the cutter head as shown in Fig. 13. The most likely reason for the adhesion in this case is the wetting of the surfaces in connection with the change of consistency of the material in the EPB-TBMs working chamber.

However the extent of clogging and water inflow does not correlate always in the same way and magnitude. One reason might be differing operation parameters for the TBM. Another factor might be water chemistry and mineral composition of the excavated material. This example shows very well that simple solutions are not expectable and that a keen analysis of findings is necessary.

6. Conclusion The project provides an important contribution to improve the efficiency in tunnel construc-

tion projects. First, the interactions at the interfaces between tool and the past-like excavated material and interface processes between colloids in the paste are to be understood. Previous research shows that interfacial processes influence and even change the geotechnical behaviour of clays or clay rich soils. A change in the structure of these minerals through an active modification of the mineral surfaces allows a temporary or permanent influence on the geotechnical properties of the clay. This can be achieved through a selective modification of the particle surface charge distribution of the clay lamina. The modification of the mineral surfaces can be achieved either chemically, e.g. by using additives, changes of the fluid chemistry, or alternatively physically, e.g. by applying electric voltage fields (electrokinetics). The results shall help to improve the prediction of problems that can be expected with reactive phyllosilicates on the basis of preliminary investigations for tunnel projects. Subsequently, these results may be used to adapt the active manipulation of the clay minerals to the relevant site conditions and industrial requirements. The interdisciplinary aspect of the project will ensure research on all scales.

The geoscientific knowledge of interfacial processes on a micro- and nanoscale will be linked to the engineering sciences knowledge of macroscopic pro-cesses, such as adhesion phenomena during mechanical tunnel driving.

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[11] Virkutyte, J.; Sillanpää, M.; Latostenmaa, P. (2002): Electrokinetic soil remediation – critical overview. – Sci. Total Environ.

298: 97–121.

[12] Thewes, M.: Adhäsion von Tonböden beim Tunnelvortrieb mit Flüssigkeitsschilden.

In: geotechnik 26 (2003), Heft 4, S. 253–261.

[13] Thewes, M.; Burger, W.: Verklebungen beim Schildvortrieb in Tonformationen – Erkennen und Begrenzen technischer und vertraglicher Risiken. In: Forschung + Praxis 40, Vorträge der STUVA-Tagung 2003 in Dortmund. Gütersloh: Bertelsmann Fachzeitschriften GmbH, 2003.

[14] Segler, G.; Riek, H. G.: Entwicklung eines Gerätes zum Messen der Bodenadhäsion. In: Landtechnische Forschung 14 (1964), Heft 5, S. 150–152.

[15] Littleton, I.: An experimental study of the adhesion between clay and steel. Journal of Terramechanics, Vol. 13 (1976), No. 3, S. 141–152.

[16] Pella, D. et al.: Screw Conveyor Device for Laboratory Tests on Conditioned Soil for EPB Tunneling Operations. In: Journal of Geotechnical and Geoenvironmental Engineering 133 (2007), No. 12, S. 1622–1625.

[17] Langmaack, L.: Advanced Technology of Soil Conditioning in EPB Shield Tunnelling. In: Proceedings of the North American Tunnelling Congress 2000 in Boston. Ozdemir, L. (ed.).

Rotterdam: Balkema, 2000, S. 525–542.

[18] Beretitsch, Stefan: Kräftespiel im System Schneidwerkzeug-Boden; Karlsruhe Institut für Maschinenwesen im Baubetrieb, 1992.

[19] Burbaum, Ulrich; Sass, Ingo: »Verfahren zur Bestimmung der Adhäsionseigenschaften bindiger Böden als Grundlage zur Einschätzung des Verklebungsrisikos bei maschinellen Tunnelvortrieben«; Darmstädter GeotechnikKolloquium 13. März 2008.

[27] Lonzen, Judith: Das Problem der Adhäsion beim maschinellen Tunnelvortrieb mit Erddruckschilden. Diplomarbeit am Lehrstuhl für Geotechnik im Bauwesen der RWTH Aachen, 2008. (unveröffentlicht).

[20] Hammoud, F.; Boumekik, A.: Experimental Study of the Behaviour of Interfacial Shearing between Cohesive Soils and Solid Materials at Large Displacements, Asian Journal of Civil Engineering (Building ans Housing) Vol. 7, No. 1 (2006), Pages 63–80, Department of Civil Engineering, University of Batna, 05000 Batna, Algeria, Department of Civil Engineering, Mentouri University, Constantine, Algeria.

[21] Hollmann, F.: Kurzfassung: Verklebungsproblematik im Bereich des […] und darauf aufbauendes Konzept einer möglichen Dissertation; 2007 (unveröffentlicht) [22] Kooistra et al.: Appraisal of stickiness of natural clays from laboratory tests; Proceedings of the 25 Years National Symposium of Engineering Geology in the Netherlands 1999.

[23] Schlick, Gunter: Adhäsion im BodenWerkzeug-System; Institut für Maschinenwesen im Bauwesen, Karlsruhe 1989.

[24] Subba Rao et al.: An Apparatus for Evaluating Adhesion Between Soils and Solid Surfaces; Journal of Testing and Evaluation, JTEVA, Vol. 30, No.1, 2002.

[25] Thewes, Markus: »Adhäsion von Tonböden beim Tunnelvortrieb mit Flüssigkeitsschilden«; Wuppertal 1999.

[26] Zimnik, A.R. et al.: The adherence of clay to steel surfaces. In: Proc. GeoEng 2000 an International Conference on Geotechnical & Geological Engineering (CD-Rom), Melbourne 2000, p. 1–6.

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Nano-structure and Wetting Porperties of Sedimentary Grains and Pore-Space Surface (NanoPorO) Altermann W. (1)*, Heckl W. M. (2), Stark R. W. (3), Strobel J. (4), Wolkersdorfer Ch. (5) (1) Ludwig-Maximilians-Universität München (LMU), Geology, Sedimentology; e-mail: Wlady.Altermann@iaag.geo.uni-muenchen.de (2) Deutsches Museum München – DM and LMU, Crystallography, CeNS; e-mail: w.heckl@deutsches-museum.de (3) Ludwig-Maximilians-Universität München, Research Group NanoBioMat, e-mail: stark@lrz.uni-muenchen.de (4) RWE Dea, Hamburg, Petropysik & Formation Evaluation; e-mail: Joachim.Strobel@rwe.com (5) Ludwig-Maximilians-Universität München, Hydrogeologie und Geothermie; Cape Breton University, Sydney, N.S., Canada; e-mail: christian@wolkersdorfer.info * Coordinator of the project: Prof. Dr. Wladyslaw Altermann, Ludwig-Maximilians-Universität München

Introduction The interaction between mineral surfaces and fluids depends on the mineral surface structure and its wetting properties and surface tension on the nanoscale. One of the best known nano-properties of surfaces is the »lotus effect« used by nano-technology to prevent dirt adhesion on surfaces of e.g. glass or ceramics.

The project presented herein, on such interaction between mineral surfaces and fluids, is a national venture between Ludwig-Maximilians-University, Deutsches Museum München and the largest German oil and gas company, the RWE Dea AG. In this project, the morphology of mineral grain surfaces and the sedimentary-diagenetic cement surfaces, facing the pore space in clastic sedimentary rocks and the interaction of these surfaces with different fluid phases (including gases), will be investigated on the nano-scale. Relevant fluids include e.g. water and water salt

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mixtures, oil or super critical CO2 (scCO2) within the Enhanced Oil Recovery (EOR) methods. The final goal is to enhance tertiary exploitation methods in oil and gas exploitation and to improve the storage potential of hydrocarbons in reservoirs. To achieve this goal, the interaction of fluids and mineral surfaces on the molecular scale in rocks must be better understood. Such reactions are of prime importance in oil and gas exploitation but also in general sedimentary and diagenetic processes and have a crucial input on the possible exploitation degree and storage capacity of hydrocarbon deposits. Thus, a better knowledge of these nano-scale processes in the pore-space of sediments and sedimentary rocks will help to explain the migration processes and the permeability for fluids, gas and scCO2 within sedimentary rocks. This in turn, will allow for better modelling of the deposits and for optimization of their exploitation.

Methods Surfaces of varying mineral grains (e.g. quartz, feldspar, micas, carbonates) and surfaces of cement minerals facing the pore space will be investigated. The investigations on the nanoscale will be performed mainly by atomic force microscopy (AFM) on dry and naturally wetted samples. The nanomorphology of the pore space as a function of mineralogy and the adhesion properties of the fluids will be described quantitatively. The newly gained experience and data will build a base for latter modelling of hydrocarbon deposits in order to enhance their exploitation. The nanomorphology has a significant impact on the behaviour of the water-gas contact depth (WGC).

Thus, it is expected, that some intriguing problems such as gas exploitation, like the stability of the water-gas contact depth in some deposits might be solved with the help of the planned research. The gained data will be used in petrophysics and petrochemistry for designing new technologies in tertiary exploitation measures (EOR, enhanced oil recovery) and CO2-storage (Carbon Capture and Storage: CCS).

The dispersion, migration, adhesion and reactivity of fluids in geological bodies depends on pressure and temperature conditions but also on the nanomorphology of the mineral surfaces, their wetting ability and surface tension.

This behaviour influences the absorption of ground water and pollutants on mineral surfaces and the migration and adsorption of oil and gas in the pore space. In the oil industry, EOR measures allow only for the recovery of a maximum of about 33% of the oil in a deposit. Fluids weakening the adhesion of hydrocarbons to pore walls are injected to the deposits in order to enhance recovery. To allow for modelling of the reactions between such fluids and the minerals, experimental data are crucial and detailed knowledge of the nanomorphology of the mineral surfaces is indispensable. Initial experiments demonstrate that certain molecules hydrated in a specific fluid develop strong adsorptive forces to the underlying mineral surface and organize

themselves into a molecular monolayer. Such processes of self-assembly can be observed in situ with the AFM and STM. They can be manipulated to create stronger adsorptive forces between the added molecules and the mineral surface than that of other fluids and to supersede other fluids (e.g. hydrocarbons) from the mineral surface (Kampschulte et al.

2006). Selected samples will be treated with scCO2 in high pressure flow-through-cells in order to observe possible alteration and potential mineral changes in the rock. On the nano-scale and at molecular resolution it can be expected that even relatively resistant minerals will be affected by alteration which could be used for optimization of enhanced oil recovery (EOR and carbon capture and storage (CCS).

The data recovered in this project can be utilized for the modelling of fluid migration in rocks and for engineering of EOR-fluid additives, to influence the adhesion of oil and gas on mineral surfaces. This know-how will ensure the competitive advantage for the German oil and gas industry, but also in groundwater and geothermal technology, and it will help to increase the reserves in these commodities. It will also positively affect the technology transfer between universities and industry in Germany.

Previous experience Although Tietz (2007) has claimed that the classical distinction between aquatic and aeolian sand grains based on SEM images of grain surfaces is incorrect and the interpretation of erosive and etching marks on sedimentary grain surfaces is wrong, because not chemical erosion but rather incomplete diagenetic overgrowth processes are responsible for the triangular pit marks, many others have demonstrated that aquatic and aeolian grain surfaces differ significantly. The typical triangular pit marks on quartz were reproduced experimentally in aquatic environments, in the 60-ies to 70-ies of the last century (for an overview comp. Krinsley & Doornkamp 1973).

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Figure 1: Optical microscopy and SEM micrographs of sand grains from aeolian environment (left) and marine shore facies (right). Differences in surface marks, grain roundness and surface roughness are striking. Contrary to light and SEM the AFM offers the advantage of quantitative measurement of such differences in 3-D (comp. sub-project proposal »Nanotechnology«

1µm

1µm

Figure 2: Measurements of the surface roughness of a sand grain along a linear profile. Left side an aeolian grain from the Kalahari desert and middle picture an aquatic grain from Sri Lanka. The profiles in the right figure show three different statistical roughness parameters calculated along the three profile lines in the small surface picture (sand from Jutland shore facies)

In a Dissertation at the LMU (Kempe 2003) and several Diploma theses, various sand grain surfaces were measured (e.g. quartz, feldspar, monazite, lithic fragments). These initial investigations have demonstrated that our aim can be achieved successfully (e.g. Bantzhaff 2003; Frei 2003). The research was initiated by the desire to characterize surfaces of sand grain minerals in order to identify aquatic, aeolian, and glacial transport mechanisms with the AFM in parallel to classical optical and SEM investigations. It was planned to use an AFM device on a Mars rover for the identification of paleo-aquatic environments (e.g. Kempe et al.

2004). A miniaturized scanning probe microscope was constructed and tested in a parabolic flight under zero gravity conditions by ESA and DLR (Drobek et al. 2004). Further dis-

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sertations in dealt intensively with the phenomenon of molecular self assembly and AFM, SEM, and TEM methods on early diagenetically silicified Precambrian microfossils, their fossilization processes, and nanomorphology (Kazmierczak & Altermann 2002, Kempe et al. 2002, Kempe et al. 2005). The experience gained in the above research can directly be applied to the studies of the herein described project.

Sediment petrography and scCO2 In sediments, during their diagenesis, a rearrangement of mineral grains and mineralogical alteration take place, which can lead to cementation often occurring in several phases (resumed in Füchtbauer and Müller 1988). Diagenetic processes are economically

very important as they can radically alter porosity and permeability, and thus storage and migration properties of the bedrock for fluids like hydrocarbons, groundwater or scCO2. They are routinely investigated by classic approaches like thin-section petrography, scanning electron microscope and the related analysis methods (e.g. EDX, cathodoluminescence). The detection of transport mechanisms from the surface of sediment grains, particularly at quartz grains, also belongs to the classic approaches of sedimentology. (e.g. Krinsley & Doornkamp 1973; Altermann 1986). In the first years of the new century new approaches to understand the transport mechanisms of sand sediments from the morphology of the grain surface by AFM techniques emerged.

Despite the technical progress, the gain of data and digitalized respectively automated options for interpretation, the studies showed that classic sediment petrographic methods, especially in the development of new nanoscopic methodology, can not be discarded.

These methods are in the focus of the subproject present here.

The morphology of the pore space determines the size of the contact area between the rock and the pore content, even on a scale of nanometres. Thus, it also determines adhesion and friction forces between gases or fluids and the pore wall. The physical and chemical properties of the mineral surface, and thus the character of interactions depend on the molecular arrangement. To understand and influence reactions between minerals and fluids, mineral surfaces have to be magnified about 1 × 103 fold closer than in classic light- and scanning electron microscopy. For this purpose, the surface of quartz grains is approached by optical, scanning-, and atomic force microscopy. Systematic, quantitative investigations on the nano-scale of pore space and its interaction with fluids has never been performed before. The AFM offers an advantage over the SEM in enabling three dimensional quantitative characterizations down to the pico-scale. Imaging of nano-morphology, three-dimensional measurements of the sur-

face and their physical properties like adhesion under various fluids, as well as the measurement of surface tension of fluid droplets or their adhesion on different mineral surfaces is possible. In the project described herein, optical microscopy and SEM with cathodoluminescence will support the investigations in order to control pore volume morphology and cement stratigraphy. The characterization will be carried out at all scales, to display the pore volume archetype. From this knowledge, new strategies and techniques to amend the tertiary petroleum and natural gas production, e.g. injection of supercritical CO2, will emerge.

So far, in Germany, tertiary extraction procedures with CO2 (Enhanced Oil Recovery: EOR) for petroleum and natural gas play a minor role, whereas they are of great importance in Canada and the USA. Only in the natural gas reservoir of Altmark, operated by the Erdgas Erdöl GmbH, an experimental production with the aid of CO2 injection is being carried out in the framework of the Geotechnologien project CSEGR (TU Clausthal). According to the relatively small German oil deposits, the potential to store CO2 is small, compared to natural gas deposits (Busch et al. 2006). Petroleum has a storage capacity of about 81 Mt, whereas natural gas has a capacity of 1800 to 2600 Mt CO2 storage capacity. It is assumed that globally about 80% of all oil deposits are appropriate for CO2 storage (GEO-SEQ Project Team 2004) and can produce oil or natural gas, by use of EOR measures. A further future application of scCO2 emerges in the use of geothermal energy (Börner et al. 2006). Supercritical CO2 can be used in Hot-Dry-Rock projects (HDR) instead of water, to be able to gain electricity also at low reservoir temperatures (at least 120 °C). So far, there is no research or experience available concerning the interactions of scCO2 with the rock on the nano-scale.

Interaction of sediments respectively of bedrock with fluids play a major role in EOR, CCS and HDR. For EOR and CSS numerous investigations exist on the macro scale (e.g.

GEO-SEQ Project Team 2004 [and many refer-

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ences therein]; Kovscek & Wang 2005; Vosteen & May 2007; GEOTECHNOLOGIEN-Projects at TU Clausthal and RWTH Aachen), whereas the relation between EOR or CCS on the nano-scale has not been investigated yet according to our knowledge. Based on earlier investigations on EOR and CCS, on the megaand macro-scale and the investigations by the LMU working team on sediments, on the nano-scale, studies are planned to examine the interaction of the oil-gas-CO2 phase and the grain surface. Therefore, selected samples will be injected by different mixtures of fluids subsequently to their detailed macroscopic, microscopic, and nanoscopic characterization. Thereafter, the macroscopic, microscopic, and nanoscopic properties as well as permeability will be measured again. The aim of the research is to understand the relationship between the different mixtures of fluids and to develop scCO2 methods for optimization of EOR, CSS and the use of geothermal energy.

A first approach to the problem could be the studies by Fouillac et al. (2004) and the calculations by Pruess & Azaroual (2006). Consistent with these authors, interactions between CO2 and the rock matrix result in mineral neomorphism, leading to increase of the pore volume of up to 12%. This, in turn, would result in an increase of the porosity and under ideal conditions also in an increase of the permeability, whereby the fluids can better migrate through the rock. The product of the reaction of the gaseous CO2 with the mineral Wairakit (Ca(Al2Si4O12) · 2 H2O), belonging to the group of zeolites, is carbonate.

Moreover, it is well known that scCO2 is a very good solvent for organic matter (e.g.

Silva & Macedo 1998). In how far the above reactions are relevant to the problem of scCO2 in oil, natural gas, or HDR reservoirs and which processes are active on the nano-scale, is not known yet. This will be quantitatively and qualitatively examined for practical application in EOR, CSS and scCO2-HDR, within the NanoPorO project.

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Drill core selection, sample provision and sedimentological and petrophysical investigations; Application in the exploitation process The recovery of the relatively small German oil deposits is complicated because of the considerable depth of the reservoir. The first drill holes in the North See oilfield of »Mittelplate«, in 1980/81 have uncovered considerable oil deposits. Since 1987 over 15 million tons were recovered and a further 35 to 45 million tons are estimated to be recoverable.

Nevertheless, the world wide oil recovery rate of the oil deposits is very low, despite of costintensive and advanced as well as complicated methods applied. Independently from the world markets, development and the investment of 485 million Euro not more than 20–30% of the Mittelplate oil deposit is recoverable. Thus a big part of the oil remains in the deep rock. By secondary and tertiary oil recovery measures, like pressure and permeability enhancement via fluid or gas injection, or measures decreasing the oil viscosity through additives, the total recovery rarely exceeds 33%. Thus, about 70% of the oil of any oilfield remains inaccessible by the enhanced oil recovery (EOR) measures known.

Natural gas deposits are recoverable of approximately 50 to 80% of the total content of a deposit, but up to 50% remains inaccessible by classical recovery methods. Thus, the development of new methods to increase the recoverable part of oil and gas will automatically increase the German and worldwide reserves. Therefore, a high political pressure exists, to enforce collaboration of the national and international oil industry, research institutions, ministries, and political agencies to develop new and improved tertiary hydrocarbon recovery methods. RWE Dea AG is active in this field and participating in recovery technology, methods increasing pore saturation and volumetry and other technological EOR processes.

Reserve estimations for hydrocarbons are based on the area and depth of the hydrocarbon to water contact. This depth is given by the deep free water level and mineral specific

Figure 3: (Kempe et al., 2004): Comparison of aeolian and aquatic sand: a) three dimensional AFM image of a sand grain (Pegnitz River, close to Nuremberg), displaying a well developed aquatic texture. Arrows indicate typical v-shaped aquatic corrosion marks. b) distribution diagram of the orientation of linear elements on the surface of this quartz grain. c) the same area of the quartz grain as in a) after an automated image editing to emphasize the edges of the surface structures. d, e and f) the same illustration of a quartz grain as in a), b) and c), from Pegnitz, with corrosion marks as well as fresh fracture marks (erosion). g) h) and i): Typical sand grain from the Kalahari desert with aeolian erosion marks of equal spatial distribution. Illustration as in a), b) and c) or d), e) and f)

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capillary forces acting on this interface. Surface roughness and hence contact angels are of prime importance for these calculations.

The amount of available worldwide hydrocarbon reserves rest to great portion on precise knowledge of these governing parameters.

Mineral and roughness dependent surface angels are so far not available. Parameters eventually available from this study will fill this gap and hence help in better reserve estimations and forecast planning.

Contribution of the RWE Dea AG RWE Dea AG will conduct the sample recovery and selection for the project. It will participate in the sedimentological investigations of the samples and will provide petrophysical data on the samples. Furthermore, RWE Dea will support the technical application of the research and lead the subsequent implementation of the results into their production processes. The sedimentological laboratories of RWE Dea in Wietze will be open for the research in this project and commercial laboratories servicing the needs of the research will be involved through RWE Dea. RWE Dea is operating the only offshore oil rig in Germany, the »Mittelplate«. Because of its environmentally critical location in the centre of the North See Nature Reserve »Wattenmeer«, this oil rig is unique as to the technological, environmental, and economic conditions. Drill samples from this oilfield will be made available for this project, including samples of fluviatile and marginal marine reservoir sandstones. Furthermore drill core and plugs from various onshore boreholes in northern Germany and cores from the aeolian sandstones of the borehole Völkersen will be investigated. The available petrophysical and sedimentological data on these samples will be provided and new necessary investigations will be performed at RWE laboratories.

The depositional facies, cement mineralogy, and cement stratigraphy influence the porosity. For example, aeolian sands are generally well sorted and well rounded and thus have

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high primary porosity and reservoir properties.

On the other hand it seems plausible and probably that diagenetic cements display other surface roughness within the pore space than abraded aquatic or aeolian sand grains. Thus the adhesion and wetting property of pores between cement overgrowth will be different than that of directly pore spacing clastic mineral grains. The characterization of the pore space in rocks is routinely performed in RWE Dea drill holes and will be provided within this project. This includes capillary pressure measurements (Hg/air and air/H2O), measurement of the inner surface of the samples (BET, fluid nitrogen method), NMR measurements (Nuclear Magnetic Resonance) for deep pore space characterization. If necessary, X-ray CTmethods (Computer Tomography) in 3-D can be performed on samples at service laboratories (e.g. TU Clausthal; 225 kV X-ray tomograph). The TU Clausthal X-ray CT can scan large samples in axial and transversal direction with a resolution of 50 µm and thus visualize the distribution of the pore space in the sample. Saturation and fluid migration (flow) can be measured on small core samples.

The preparatory work for this project is comprehensive and requires a detailed characterization of the sedimentary rocks under investigations. For this purpose all available and necessary stratigraphic, petrographic and geophysical routinely acquired data are of importance. Such data will be made available to the project by RWE Dea. The research team of RWE Dea and of its laboratories in Wietze will take an active part in the project and closely cooperate with the other sub-projects of NanoPorO. The interaction of sediment grains, pore fluids, cements and their influence on tertiary recovery methods, like scCO2 injection are of foremost importance to the oil industry. However, these processes were never investigated on the nano-scale before. Mineral and grain oriented physical processes as the attraction in a sediment grain lattice or reaction with fluids below the resolution of optical microscopy, for

example, are poorly understood. The spontaneous attraction between quartz grains at distances below 1µm, and cavity effects in a rigid frame, where grains can not move, are probably not simply explained by mass attraction effects (Scientific American, November, 2006).

Together with the wetting ability and orientation of the grains this could have a strong influence on the fluid-mineral interaction and lead to new important insights.

Other experiments within this sub-project originate, from a core of Rotliegend Sandstone (2 × 18 m) from the drill hole Völkersen Z6 (depth of ca. 5500 m, locality Verden/Aller, aeolian dunes and sabkha sediments). Some samples have been modelled with an experimental software (E-Core from Numeriacl Rocks) replicating the pore structure, coordination number, wetting characteristics and capillatriy forces. This model can be improved with surface roughness estimation, changing the wetting angel and thus giving an improved fit to the real data. Furthermore, plugs will be taken and the magnetic susceptibility vectors will be measured in a laboratory in UK. These investigations will be conducted with a magnetic fluid in order to measure the vector of the maximum permeability in the rock on an oriented sample (oriented cores were taken).

From these measurements it should be deducible whether the magnetic susceptibility vector depends on the orientation of the quartz grains in the sedimentary rock. These investigations will be performed as preparatory work for the NanoPorO project, to ensure best possible sample selection.

Within this project, a large array of samples from various drill holes with differing mineralogy will be selected. The selection criteria will be driven by factors of technical feasibility, interaction of different fluid–mineral surfaces and wetting properties, in combinations that are common in natural reservoir rocks. Possible reactions between rock minerals, fluids and scCO2 will be observed. Up to date, there is no experience available in this regard, but it can be envisaged that the scCO2, which is

generally inert in a dry environment, will react with the minerals on the nano-scale. In rocks, such reactions seem doubtful outside of geological time spans, but on molecular dimensions reactions are possible even on technical time scale. Modifications of the mineral surfaces would automatically alter the size of the reactive surface between mineral and fluid and thus affect the adhesion and wetting properties and the migration behaviour of the fluid in the rock (for possible reactions compare sub-project 3).

Nanotechnology Nanotechnology focuses on the three-dimensional micro- and nano-scale characterization and mathematical classification of sediment grain surface topography, and wetting or adhesion properties. These data will provide a solid base for the development of new methods to enhance the hydraulic conductivity in sediments. To this end, different aspects of the sediment grain and pore surface (Fig. 4) shall be investigated by optical methods and atomic force microscopy. The topographic data shall be stored in a database to allow for a statistical analysis based on modern methods. This will allow for characterization of the variability of topography, adhesion, and wetting properties by statistical means. Based on these statistically representative data, the variation of chemical and morphological properties of rough mineral surfaces will be analyzed. As an important factor for the hydraulic conductivity, the local adhesion properties of wetted and unwetted sediment grain as well as pore surfaces shall be characterized with high spatial resolution. Special emphasis will be put on the local interaction of supercritical CO2 (scCO2) with mineral surfaces in order to achieve an enhanced oil recovery.

State of the art Wetting of three dimensional pore networks by different fluids was investigated under the aspect of oil recovery and contaminant management. Numerical simulations of the three phase (oil, gas, water) wetting problem show that variations of the contact angle between

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Figure 4: Surface properties on the micro to nano-scale influence the wetting properties of mineral grains and cements in sedimentary rocks

the different phases can lead to a large variability of the hydraulic conductance of porous networks. (Al-Futaisi & Patzek 2002). Further investigations of the two phase problem revealed that sediment wetting varies with the contamination of the surfaces and depends on surface roughness, surface charges, and the chemical composition of the liquid phase. Taking into account the large local variability of these properties, it is clear that sediment wetting has to be treated as a spatial heterogeneous random variable – on the macroscopic scale as well as on the scale of an individual pore (Al-Futaisi & Patzek 2004). Thus, we expect that nano-scale topography and wetting properties are highly important for the three-phase problem and thus co-determine the hydraulic conductivity.

This relation implies that the surface roughness (ρW > 1) enhances wetting properties such as hydrophilic or hydrophobic. Kamusewitz & Possart (2003) showed that the geometric roughness factor ρ = Ar /Ap, as measured by AFM, very well agrees with Wenzel’s correction factor rW as obtained by contact angle goniometry. The relation ρW ≈ r holds in good approximation for a surface roughness with Gaussian distribution. Nanoscopic methods for a are ideal tools to measure local roughens and adhesion properties with high resolution in order to go beyond the classical Wenzel-theory (see for example Kunzler et al. 2006, Spori et al. 2008).

Statistical methods are required in order handle the variability and to link this data with hydraulic conductivities.

The influence of micro- and nano-scale roughness can be seen at the relation between the macroscopic contact angle θ, surface energies of liquid γ l and solid γs, and the interfacial energy γsl, which are connected through Young’s equation

Previous work In earlier works we investigated the surface structure of sand grains by atomic force microscopy and classified the topographic data by means of a multi-dimensional statistic approach. The statistical analysis allowed for the discrimination of erosion due to different paleoenvironments such as environments dominated by aeolian or aquatic transport (Kempe et al. 2004) or due to bioerosion (Kempe et al.

2005). For example, various sediment grains (quartz, feldspar, olivine, monazite) from well characterized environments which yielded detailed three dimensional maps of the surface structure were imaged by atomic force microscopy. Briefly, an automatic analysis of the distribution pattern of characteristic surface marks such as grain-grain collision marks, etch-

γsl = γs – γ l cos (θ) The surface roughness modifies the macroscopic contact angle θW. Wenzel (1936) thus introduced a correction factor rW into Young’s equation which accounts fort he ratio between true and projected surface area.

According to Wenzel macroscopic contact angle of a rough surface is given by: cos (θW) = rW cos (θ0) .

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ing, or cement growth marks showed that linear elements tend to be longer and are oriented with respect to the crystal symmetry. In contrast, the mineral surface of grains which were subject to aeolian transport shows short linear elements with a random distribution.

The respective pattern distribution is diagnostic for aeolian and aquatic transport since in an aqueous environment the mineral grains are etched correspondingly to their symmetry (or »heal« due to precipitation and overgrowth) whereas grain-grain random collisions during aeolian transport leave statistically distributed marks. The different processes are also reflected by the statistics of roughness parameters as they were obtained by atomic force microscopic measurements. The planned activities within this project part will thus be based on this successful approach.

Methodology The experimental approach directly continues and extends the methodology of our previous work. The measurement of the surface topography with nanometer resolution shall be carried out by atomic force microscopy in order to achieve a very high resolution in all spatial directions. Pulsed force mode measurements with chemically modified tips shall be used in order to determine adhesion and wetting properties with high resolution. Thus, also local modification of the mineral surface due to chemical processes or scCO2 will be monitored. For a meaningful statistical analysis a large number of data sets are essential. In order to overcome speed limitations of the atomic force microscope we foresee an optical characterization of the surface by white light interferometry (z-resolution 10 nm). The topographic data shall be included into the existing data base system (Kempe et al. 2004) for a subsequent statistical analysis. Additionally, the adsorption of molecules at liquid solid interface shall be investigated

by STM (DM).

This integrative approach is designed to contribute to the understanding of the role of

nanotopography and local adhesion for the hydraulic conductivity of multiphase fluids in sediments. Research and development towards methods to enhance oil recovery will surely benefit from this knowledge.

References Al-Futaisi, A. Patzek T.W. (2002): ThreePhase Hydraulic Conductances in Angular Capillaries. – SPE Journal 8 (3): 252–261, Proceedings 2002 SPE/DOE Improved Oil Recovery Symposium.

Al-Futaisi, A., Patzek, T.W. (2004): Secondary imbibition in NAPL-invaded mixed-wet sediments. Journal of Contaminant Hydrology 74 (1–4): 61–81.

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The impact of mineral and rock surface topography on colloid retention Fischer C. (1)*, Lüttge A. (2) & Schäfer T. (3) (1) Georg-August-Universität Göttingen, Abt. Sedimentologie/Umweltgeologie, e-mail: cornelius.fischer@geo.uni-goettingen.de (2) Rice University, Dept. of Earth Science & Dept. of Chemistry, Houston, Texas U.S.A., e-mail: aluttge@rice.edu (3) Institut für Nukleare Entsorgung, Forschungszentrum Karlsruhe, e-mail: schaefer@ine.fzk.de *Coordinator of the project: Cornelius Fischer, Georg-August-Universität Göttingen

Abstract Goal of this project is a systematic approach to determine the interaction between the mineral surface topography and colloidal particles.

We will focus on artificial surfaces with welldefined topography in the submicron range.

First experiments will focus on plastic surfaces and colloids to avoid chemical and surface charge heterogeneities. As a second part, experiments are planned with mineral precipitates of well-known topography and with several mineral colloids. It is expected to improve the understanding of colloidal retention in the environment as a function of macroporous surface topography of minerals and rocks.

Because colloids are ubiquitous in natural fluids, a broad field of engineering applications exists for the expected results of this study.

Implications for contaminant transport and waste management are important examples.

1. Introduction McCarthy & Zachara (1989) discussed key questions about the importance of colloids (particles: 1 nm < d < 1 µm) in the environment. They asked about occurrence, properties, and mobility of colloids in the groundwater zone. Furthermore, they asked about implications for contaminant transport and waste management. During the last years a lot of research was done about occurrence and

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mobility of colloids in the groundwater zone.

Experimental, modeling and field study approaches were performed (Lead et al. 2005).

Sen & Khilar (2006) give a review about recent results. Inorganic material (mineral precipitations, fragments), organic matter, and biological matter (viruses, bacteria) cause the occurrence of colloids in the groundwater zone.

Release of colloids is caused by changes in solution chemistry, surface chemistry and fluid flow. The retention of particles is much greater in presence of divalent ions with respect to monovalent ions. Theoretical approaches to calculate the interaction energy of colloids and surfaces, using the Derjaguin-Landau-VerweyOverbeek (DLVO) theory (e.g., Bhattacharjee et al. 1998; Hoek and Agarwal 2006), show a reduction of repulsive interaction energy caused by surface roughness. Experiments confirmed these findings (e.g., Cooper et al. 2000). Furthermore, it was demonstrated that the particle size can modify particle adsorption processes (Katainen et al. 2006). However, Sen & Khilar (2006) highlighted limitations of all of the previous predictions about interaction between surfaces and colloids in nature due to chemical and physical complexity.

Lead & Wilkinson (2006) concluded that analytical in-situ methods are necessary to clarify reaction processes between colloids and inter-

Figure 1: Roughness of rock surfaces is a result of the occurrence of half pores.

The investigations proposed here will elucidate the role of rough macroporous (IUPAC 1994) surfaces on surface reactivity for colloidal reactions

faces in nature. The here proposed research is designated to this aspect. We want to apply a systematic approach to analyze the impact of micron- to submicron-sized surface topography structures on colloid retention. For this purpose, we will apply a three-dimensional microscopically method, providing a large field of view and sufficient spatial resolution. This enables simultaneous measurements of reacted different-sized surface topographies. With this approach it is intended to provide a connection between (i) the theoretical background about the impact of surface morphology on colloidal interaction processes (Bhattacharjee et al. 1998) and (ii) previous observations about the potential interaction between mineral surfaces and natural colloids (Lead and Wilkinson 2007). Therefore we have chosen the approach to verify the impact of variations of surface topography features on colloidal retention (Katainen et al. 2006) as a first step of our investigations. We will use well-defined artificial micron- to submicron surface topography structures, similar to the half pores which are found at natural mineral and rock surfaces (Fig. 1).

2. Surface topography characterization and quantification A concept about fluid-rock interface quantification over multiple length scales was developed to combine and evaluate surface roughness data (Fischer and Gaupp 2004). As an example, the application of this concept offered the opportunity to quantify rock interface alteration caused by weathering of a rock component. From the quantitative data it was possible to substantiate the isotropic dissolution of highly mature organic matter in black

shales during oxidative weathering (Fischer and Gaupp 2005).

2.1 The concept of converged surface roughness parameters Until now, statistical topography parameters were not used quantitatively to explain processes of mineral and rock surface reactions.

The main reason is the sensitivity of such parameters on spatial resolution and field of view of the method used for measurements (Dong et al. 1992; Dong et al. 1993). Recently a conceptual model was proposed to quantify surface roughness parameters caused by different surface building blocks. Such data are able to provide statistical information about surface area alterations. As an example, rock surface topography alterations at the micron and submicron scale were quantified.

The new concept is capable to provide information about surface reactivity alterations, e.g., caused by rock weathering (Fischer et al.

2007; Fischer and L端ttge 2007).

2.2 Surface topography and reactivity The micron and submicron surface topography of iron oxide encrustations, formed during oxidative weathering of rocks, was quantified (Fischer et al. 2008). For some encrustations the new results show a linear correlation between surface roughness Rq (root mean square roughness) (e.g., Thomas 1999) and the uranium concentration of the encrustation (Fig. 2). However, the process responsible for this correlation remained unknown. A reasonable hypothesis is a possible interrelation between surface topography and retention and subsequent incorporation of uranium bearing colloids. With the experiments pro-

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Figure 2: Linear correlation between root mean square roughness Rq of an iron oxide encrustation precipitated on a weathered rock and the iron normalized uranium concentration of the encrustation (Fischer et al. 2008)

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Figure 3: Surface topography measurements by regular vertical scanning interferometry (VSI) [left side] and super-resolution (SR) VSI [right side]. The sample consists of periodical arranged bumps, length is 300 nm and height is 250 nm.

The surface shape and topography of the sample was not detected by regular VSI measurements (left). The here shown topography is an example similar to that what is intended to use for the experiments described here. Adsorption of colloids can be quantified by height and shape alterations of the original surface

posed here it will be possible to verify if surface topography parameters of natural iron oxides could control the intensity of colloid retention processes. From the preliminary work the range of natural surface topography variations is known and can therefore be used as a constraint to the here proposed experiments.

ca. 0.5–1 µm to ca. 50–100 nm (Fischer et al. subm.). An example which demonstrates the increase of lateral resolution is shown in Figure 3. SR-VSI provides the opportunity to obtain new information about the impact of different-sized macropores on mineral and rock surface reactivity.

2.3 Enhancement of lateral resolution of Vertical Scanning Interferometry (VSI): »Superresolution« (SR) Recently a technique was developed to enhance the lateral resolution of VSI. With this technique the lateral resolution was increased from

Benefits of the non-contact VSI technique (e.g., Lüttge et al. 1999) are the large field of view (ca. 1 mm2) and the fast data acquisition.

The large field of view enables simultaneous measurements of surface alterations over multiple length scales and on representtative

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Figure 4: Colloid probe technique (Veeramasuneni et al. 1996): A SEM image shows a carboxylated latex colloid attached to AFM cantilever. This technique is used to quantify point of zero charge functions.

(PhD project of Andre Filby, FZK-INE)

sample areas. Therefore, for the application of the here proposed investigations, statistical data will be available to quantify the retention of colloids.

2.4 Surface charge heterogeneities: Currently a PhD project at Forschungszentrum Karlsruhe, Institut fĂźr Nukleare Entsorgung (FZK-INE) is performed to quantify the influence of surface charge heterogeneities on colloidal retention. For this purpose, atomic force microscopy (AFM) measurements are used to quantify interaction forces between colloids and surfaces. Results of current research show the opportunity to map the point of zero charge (pHpzc) of adsorbent surfaces (Fig. 4).

3. Interaction between surface topography and colloids The project includes the following research parts: (i) Interaction between macroporous plastic (latex) surfaces and plastic colloids (ii) Interaction between mineral-coated macroporous plastic surfaces and plastic colloids (iii) Interaction between the substrates of (i, ii) and synthetic mineral colloids (iv) Application of the synthesis of (iii) to column experiments and to experiments with natural material (e.g. eodiagenetically formed sand grain coatings) (v) Methods and concepts; conclusions and suggestions for technical applications

Figure 5 illustrates the research concept and the connections between the several parts of the proposed research. Part (i) will apply a simple model system of plastic (latex) surfaces and colloids. Parts (ii) and (iii) will apply synthetic minerals for surface coatings and colloids.

Within the fourth part of this research (iv) we expand the investigations to more complex systems, including column experiments with eodiagenetically altered sand grains. The synthesis part (v) is the interface between the several research parts. For example, the results of (i) will modify several experimental parameters such as surface topography features to be applied for the investigations of (ii) â&#x20AC;&#x201C; (iv). (i) Interaction between plastic macroporous surfaces and plastic colloids We will use artificial plastic surfaces with homogeneous surface charge (e.g., carboxylated latex) to study the influence of surface roughness on colloidal retention (e.g., Adamczyk et al. 2003; Cooper et al. 2000). Substrata will show several lattice widths and heights to represent different-sized macropores. An example of such a surface which consists of a lattice with several lattice widths and heights is shown in Figure 5. Initial experiments will be performed using inexpensive lithography standard lattices. After interpretation of the first results about the impact of the lattice widths and heights we will apply custom-built lattices.

Here we will focus on the more reactive lattice widths and height ranges which were identified by the first experiments.

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Figure 5: Research concept and research components. The research program includes collaboration with Rice University, Houston (application of super-resolution vertical scanning interferometry) and Forschungszentrum Karlsruhe (INE)

Figure 6: Lattices with several lattice widths and different heights. Such lattices will be used for experiments to elucidate the interaction between macroporous surfaces and colloids

The large field of view of VSI enables investigations of areas of ca. 1 mm2. This will help to identify lateral inhomogeneities of the surface reactions. Additionally to AFM investigations (e.g., Bowen and Doneva 2000), the new investigations will show simultaneously the influence of a wide range of surface topography variations. It will enable to of apply just one sample substratum for a broad topography variation during just one experiment. This approach will provide a realistic analogue model of natural surface topogra-

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phy variations and therefore it will be used for the other parts of the investigations as well.

Lattice width variations will represent several sizes of macroporous half pores. Plastic colloids of several sizes (and potentially of several shape properties) will be used to study surface reactions. We will apply vertical scanning interferometry (VSI) to quantify what size range of macropores is important for surface reactions. Moreover, with this technique we

will attain very precise data about the height modifications of half-pores due to colloidal retention.

The experiments about colloid adsorption in aquatic systems will be performed using several flow rates in column experiments. The resulting data will define hydrodynamic constraints to column experiments (connection to research part iv).

Additionally, experiments will be conducted using different colloidal material to evaluate the influence of surface charge on colloid adsorption. Calculations showed for some colloidal material a modification of electrostatic interactions between colloids in aquatic solutions and by particle size and surface roughness (Eichenlaub et al. 2006).

The results showed that in contrast to, e.g., alumina colloids, the adsorption of other materials like polystyrene latex particles is not controlled by electrostatic interactions.

Based on experimental and theoretical results a well-defined example of a mineral or rock surface (well defined in terms of surface charge and topography) will be selected. With this surface we will repeat the adsorption experiments to evaluate the first experimental results. This will provide a connection to the questions raised in research part (iv) as well. (ii) Interaction between mineral-coated macroporous plastic surfaces and plastic colloids For the here proposed experiments, structured plastic surfaces will be coated by mineral layers (e.g., iron oxides or alumia). In contrast to part (i), in this research part (ii) the impact of structured mineral layers on colloid adsorption is the focus of the investigations. We will use again plastic colloids (carboxylated latex) to analyze the impact of particle size and shape.

Interfaces in natural systems are formed very often by iron oxides. Their possible importance as a reactive surface for colloidal retention is

caused by the occurrence of iron oxide encrustations at high permeability zones at bounding surfaces in rocks. Therefore, iron oxide films on well-defined surface structures will emulate the occurrence of different-sized macroporous half pores. Macroporous half pores were often found on natural iron oxide encrustations (Fischer et al. 2008).

The results of this project part will also define constraints to the investigations planned for part (iv). The column experiments of (iv) will be performed using plastic grains with welldefined surface roughness according to the results of (ii). (iii) Interaction between the substrates used for (i) and (ii) and synthetic mineral colloids In contrast to (i) and (ii), this part of the project will study the reaction behavior of several mineral colloids, e.g., phosphate, hematite, goethite, and bentonite. With respect to the results about more or less surface reactivity as a function of topography [results of (i) and (ii)], the experimental setting of (iii) will be defined and modified. With this strategy we want to avoid the application of a multitude of nonreactive surface topographies, identified by experiments of research part (i) and (ii). Furthermore we expect experimental constraints regarding the size, shape, or surface roughness of colloids.

Additional experiments will provide information about fractionation of colloidal grain spectra of the mineral colloids during reactions. Such fractionation is well-known from investigations of natural material (Ranville et al. 2005). An additional focus of the experiments in part (iii) is the detection of differences of the model system parameters used in (i) & (ii) vs. the more realistic approach of (iii). (iv) Application of the synthesis of (iii) to column experiments and to experiments with natural material (e.g., eodiagenetic coated sand grains) The new experimental constraints will be used to perform column experiments (Hu et al.

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2004). First experiments will use plastic spheres to provide well-defined grain substrata. As a next step we will apply coated plastic grains (coated by, e.g., iron oxide). Such a coated grain experiment provides a realistic model of the common situation of natural sediment grains (e.g. quartz grains) in the environment.

Iron oxide encrustations are ubiquitous in the environment. Such encrustations are formed often during early diagenesis.

The experiments provide information about hydrodynamic constraints to colloid adsorption in sediments. From these experiments we expect information about the conditions providing high vs. low colloidal retention in sediments.

As a more realistic approach we plan to expand these experiments using natural material. We will use natural quartz grains with goethite or hematite encrustations. Such material will be available from crushed sandstone of the diagenetic hematite type (Gaupp 1996).

For the purpose of column experiments we will investigate the size distribution of macropores of the encrustations. Other potential rock types for such experiments are fine-grained carbonate rocks (micrite) or mudstones.

Other interesting material for surface-colloid interaction reactions are fault planes. In the end of our investigation we probably will be able to expand the experiments to investigate the surface reactivity of such surfaces. (v) Methods and concepts; conclusions and suggestions for technical applications Central part of the first investigations is the adaptation of surface topography quantification and characterization by roughness parameters. The adaptation will lead to statistically derived quantitative data about the surface topography alterations during the experiments. These data will also be a new basis for surface-colloid interaction model calculations (e.g., Monte Carlo simulations).

This part (v) of the project also will evaluate the importance of the experimental results for nat-

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ural processes in the environment. The potential importance of surface topography on colloid adsorption must be tested in natural systems. An important example is the case of clastic sediments of the saturated zone (iv). Final investigations and interpretations are necessary to show if the results of parts (i – iv) are similar to the results of column experiments with natural grains (Puls et al. 1993; Roy and Dzombak 1996). Experiments will apply quartz grains with several natural iron oxide encrustations to show the reactivity range.

This part of the project will define applications of the new results as well. An important application could be, e.g., the field of nuclear waste disposal. We will evaluate this application in our close collaboration with the Institut für Nukleare Entsorgung, Forschungszentrum Karlsruhe. Some of the experimental settings are defined by this application. E.g., experiments will be performed wuth iron oxide and phosphate colloids because they are important for this application. Iron oxides are very common natural colloids. Natural phosphates are important due to their often very high trace element content. Therefore phosphate colloids could act as an important carrier for trace metal transport in the environment. As an example, phosphates can show very high U contents (e.g., Wang et al. 2006).

We expect information about the importance of iron oxide encrustations for the retention of trace elements (e.g., Fischer et al. 2008).

Another important application of the expected results will be in the field of drinking water quality.

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Microstructural Controls on Monosulfide Weathering and Heavy Metal Release (MIMOS) Pollok K. (1)*, Langenhorst F. (1), Hopf J. (1, 2), Kothe E. (2), Geisler T. (3), Putnis C. V. (3), Putnis A. (3) (1) Universität Bayreuth, Bayerisches Geoinstitut, e-mail: {kilian.pollok | falko.langenhorst | juliane.hopf}@uni-bayreuth.de (2) Friedrich-Schiller-Universität Jena, Institut für Mikrobiologie, e-mail: erika.kothe@rz.uni-jena.de (3) Westfälische Wilhelms-Universität Münster, Institut für Mineralogie, e-mail: {tgeisler | putnisc | putnis}@nwz.uni-muenster.de *Coordinator of the project: Dr. Kilian Pollok, Universität Bayreuth

Introduction and objectives Weathering processes strongly involve interactions with the hydrosphere, atmosphere, and biosphere and are basically controlled by reactions at mineral surfaces. The kinetics of mineral weathering and the precipitation of secondary phases play a fundamental role for the local and global geochemical cycles.

The MIMOS project aims at understanding the effect of microstructure, mineral chemistry, and crystallography of natural metal monosulfides on their dissolution and weathering behavior. Monosulfides are a geologically important mineral group with a considerable structural and chemical variability and represent a substantial portion of most ore deposits. The oxidative alteration of sulfured ore due to natural events and mining activities leads to the production of acid rock drainage (ARD) and acid mine drainage (AMD), respectively, releasing acidity (low pH) and high concentration of metals (like Zn, Pb, Ni, Co, Ag, Cd, Cu, Cr) and semi-metals (especially As) as well as sulfate to the environment. ARD and AMD are an environmental concern for the water quality of ground and surface waters worldwide. A vast number of reviews and book chapters have been published on this issue (e.g. Albers & Blowers,

1994; Jambor & Blowers, 1994; Jambor et al., 2000; Jambor, 2003; Lottermoser, 2003). The oxidation of pyrite and the associated reactions are the main focus of most studies (e.g. Evangelou & Zhang, 1995; Rimstidt & Vaughan, 2003), while the oxidation of monosulfides is still less extensively studied.

Hazardous element release is controlled by the reactivity of the primary sulfides and the subsequent formation of a secondary mineral assemblage. Many of the newly formed phases (oxides, hydroxides, sulfates) exhibit very small grain sizes (nanoparticles, colloids), which affects their stability, adsorption capacity, mobility and, thus, also their bioavailability.

The topic of monosulfide degradation is also of fundamental importance for industrial metal extraction and the treatment of low-grade ores or concentrates e.g. by the catalytic interaction with microorganisms (»bioleaching«). In addition, for the remediation of iron- and sulfaterich groundwater and lakes, the process of sulfide dissolution can be reversed. Sulfate-reducing microorganisms facilitate the formation of monosulfides, resulting in a reduction of the iron and sulfur concentration as well as a neutralization of natural waters. The stability of these freshly precipitated iron sulfides is not

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well known because studies on structure, chemistry and grain size are still incomplete.

The basic approach of the project is to combine experiments in simple systems with studies on naturally weathered assemblages to address the kinetics and textural controls of monosulfide weathering and to study phase stabilities in weathered systems. MIMOS will focus on monosulfides in the system FeS-ZnSPbS using a multi-analytical approach offering high spatial resolution for the determination of structure and chemistry of primary and secondary phases. Transmission electron microscopy (TEM) is the central analytical tool for this study. It offers high resolution imaging, electron diffraction and spectroscopy and thus provides structural (crystalline/amorphous, structural defects, polymorphism) and chemical information (up to the point of the distribution of valences from transition metals) at the nanometer scale. Complementary analytical techniques (AFM, Raman, IR, Mössbauer, XRD, ICP analytics) will be used to generate a complete picture of the reactions.

The determination of rates and mechanisms of reactions, including the secondary mineral formation and the microbial influences, will provide a reliable estimate of natural weathering rates and elemental release. The results will be integrated in a geochemical model of sulfide weathering, which considers processes and parameters affecting the stability of phases at different spatial-temporal scales.

the hexagonal NiAs structure type with a hexagonal closest packed array of sulfur atoms and iron occupying all of the tetrahedral sites.

The deviation from stoichiometry allows ordering of vacancies in the iron sublattice resulting in a large number of superstructures (stacking sequences with different order) with possibly varying composition (from Fe7S8 to Fe11S12).

A detailed description on structure types, lattice parameters, composition, thermal stability, and phase relations of minerals in the Fe-S system have been compiled by Fleet (in: Vaughan, 2006), a description of possible structural units and superstructures in pyrrhotite observed using TEM are given by Pósfai & Buseck (1997).

Oxidative dissolution of pyrrhotite can be facilitated by oxygen or, at pH-values less than 4, by Fe3+ with the formation of sulfuric acid:

Under acidic conditions pyrrhotite can be dissolved directly producing hydrogen sulfide (H2S). Furthermore, partial oxidation of sulfur can result in the precipitation of elemental sulfur:

Monosulfides: state of knowledge FeS – Pyrrhotite, Mackinawite After pyrite, pyrrhotite is the most common iron sulfide in nature. Investigations on pyrrhotite oxidation are less frequent, although the oxidation rates are on the order of 20 to 100 times higher compared with pyrite (Nicholson & Scharer, 1994).

Pyrrhotite (Fe1–xS) has a nonstoichiometric composition with x ranging from 0 (FeS) to 0.125 (Fe7S8). The crystal structure is based on

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Fe2+ can oxidise to Fe3+ resulting in the formation of iron hydroxide:

Possible end products of iron oxidation are goethite and jarosite:

The aforementioned reactions are based on observations of secondary phases (e.g. Gunsinger et al., 2006) but without identifying intermediate reaction steps chemically and structurally with high spatial resolution. Thus the rate limiting factors are often unclear. The local coupling of reactions (e.g. pyrrhotite dissolution and sulfur and/or goethite precipitation) limits the use of dissolution rates measured under conditions suppressing the precipitation of secondary phases. Moreover, reactions can be significantly catalysed by sulfide oxidising microorganisms like the group of Acidithiobacillus (Nordstrom & Southam, 1997; Bhatti et al., 1993).

A large number of secondary phases, mainly sulfates, hydroxides, oxides, and carbonates, have been found resulting from sulfide weathering (Jambor et al., 2000; Hammarstrom et al., 2005). The thermodynamic and kinetic stability of such phases as well as their adsorption properties and grain size are critical for the mobility of metals in surface waters. In this respect, Hochella et al. (1999, 2005a,b) showed that phases with a high content of heavy metals are commonly nanocrystalline or poorly crystalline and can not be identified by conventional X-ray diffraction methods.

A review by Belzile et al. (2004) reports on the experimental oxidation rates of pyrrhotite in the range of 10–8–10–9 mol m–2 s–1. Variable results are interpreted by the structural complexity although the role of structure on the rate is not yet established. Fe3+ concentration, pH value, and the influence of microorganisms are linked to each other and lead to quite variable results (e.g. in the potential to produce acid), which make an extrapolation to normal environmental conditions difficult. The reliable

knowledge of rates is however crucial for the practical assessment of the priority and remediation strategy for mine tailings (Schippers et al., 2006).

For the remediation of iron- and sulfate-rich groundwater and lakes the process of sulfide dissolution can be reversed. Sulfate-reducing microorganisms facilitate the formation of monosulfides, which results in a reduction of the iron and sulfur concentration as well as in the neutralisation of natural waters. The phase formed by this process is mackinawite Fe1+xS, a tetrahedral iron monosulfide with a low excess in iron. It is metastable and is the first phase to be precipitated from aqueous solutions (Rosso & Vaughan, in Vaughan, 2006).

The kinetics of formation and the solubility of this phase have been studied by Rickard (1995). Mackinawite is commonly nanocrystalline and can adsorb other metals. It plays a significant role in the global iron cycle as well as for the immobilisation of metals for remediation.

ZnS – Sphalerite Sphalerite, the prevalent ore mineral of zinc, is extremely common and can be found worldwide. It is commonly associated with galena (Zn–Pb ore deposits), but also with other sulfides (pyrite, pyrrhotite, chalcopyrite). Sphalerite is cubic with a cubic closest packed array of sulfur. In contrast the polymorph wurtzite (metastable at low temperature) has a hexagonal closest packing. A number of different hexagonal and cubic closest packed stacking sequences (so-called polytypes) are common for sphalerite. Iron can be substituted up to considerable amounts (up to 50 mol% FeS).

Furthermore, deviation from the stoichiometry is possible which particularly affects the electrical conductivity (Fleet, in: Vaughan, 2006).

Temperature, Fe3+ concentration, pH value, and grain size are relevant factors for the oxidative weathering (Acero et al, 2007). The mechanisms of the specific processes (oxidation by O2 and Fe3+; formation of elemental sulfur) are not fully understood. Most studies

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refer to the dissolution within the first hours of the experiments and not to »steady state« dissolution. De Giudici et al. (2002) reported a decrease in surface reactivity and aqueous concentrations with time. In natural samples the formation of elemental sulfur and goethite at the reaction front has been described (Jeong & Lee, 2003).

The catalytic interaction of microorganisms to the monosulfide weathering is used to extract metals from low-grade ores or concentrates (Rawlings, 2002; Rawlings et al., 2003). Such »bioleaching« enables a more environmentally friendly processing and does not require high amounts of energy (e.g. for smelting). In this procedure, the insoluble monosulfide (where M stands for divalent metals like Fe, Zn, Pb) are microbially (e.g. with the group Acidithiobazillus or others) transferred into soluble sulfates by the polysulfide mechanism (Schippers & Sand, 1999):

It has been tested for sphalerite (Pina et al., 2005; Mousavi et al., 2006) as well as for pyrrhotite which is processed for Ni (Ke et al., 2006). The reaction mechanism of the microbe-mineral interaction essentially controls the Fe3+ activity via the microorganisms.

Zinc sulfide precipitation can be mediated by sulfate-reducing bacteria. As with iron sulfide, a simultaneous reduction of the metal and sulfate concentration can be achieved. In laboratory this reaction produces sphalerite with a grain size of about 10 µm (Esposito et al., 2006), whereas the same reaction in natural biofilms leads to nanocrystalline ZnS (Labrenz et al, 2000). Stability and reactivity are again the main issues which are mainly related to structural parameters and control the bioavailability of the fixed metals.

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PbS –Galena Galena possesses the NaCl structure and is cubic. It was subject for a number of spectroscopic studies and computer simulations (Vaughan, 2006) due to its simple structure and chemistry (no extensive substitutions). The mechanisms of the oxidative mineral dissolution are reviewed by De Guidici et al. (2005).

Although both galena and sphalerite have simple structures, they show significantly different dissolution rates as well as different reaction mechanisms in presence of Fe3+ (Rimstidt et al., in: Alpers & Blowes, 1994). Investigations using XPS show microscopic secondary phases like sulfates, lead hydroxides, lead oxides as well as layers with non-stoichiometry forming during oxidation (e.g. De Guidici et al., 2007, and references therein). Some phases are thermodynamically unstable but kinetically favoured and have a short durability. Dissolution rates are commonly measured in flow-through cells because anglesite (lead sulfate) has a low solubility and can precipitate at the surface of galena and thus change the reactive surface. The benefit of such rates for weathering processes in mine tailings is difficult to assess. Naturally weathered galena usually shows a replacement texture of anglesite together with the formation of plumbojarosite (Jeong & Lee, 2003). The stability of plumbojarosite depends strongly on pH and is important for the release of lead into the solution.

Mineral weathering: dissolution and precipitation The formation of secondary minerals in weathering reactions is commonly closely related with mineral dissolution and is interpreted as a mineral replacement reaction. In this process a reaction front is formed between the primary and the secondary mineral which generally moves from the outside into the mineral during the reaction (Putnis, 2002; Putnis & Putnis, 2007). Volume changes associated with such coupled dissolution-precipitation reactions can be texturally observed e.g. as porosity and are a critical parameter for the kinetics of the reaction. Similar reaction textures have been observed in replacement experiments, e.g. on

Figure1: Backscattered electron image of partially weathered pyrrhotite (po) and secondary pyrite (py).

At least 4 different secondary phases can be identified in the reaction zones

apatite (Pollok et al., 2004), pyrochlore (Geisler et al., 2004, 2005) and a KBr窶適Cl model system (Pollok et al., 2002; Putnis & Mezger, 2004; Pollok, 2005).

Mineral dissolution rates are either measured in laboratory experiments or in field studies and should be transferable to similar geological settings. Applying measured rates to another system requires knowledge of the mechanisms of dissolution and the reactive surface area. However, reactivity is considerably influenced by the microstructure (exsolution, grain sizes and) and the defects (vacancies, dislocations, twin planes, stacking sequences) present. In addition, the formation of secondary phases at the reacting interface influences the dissolution kinetics in natural systems.

Observations on partly weathered natural pyrrhotites (Figure 1) typically show a preferential conversion in certain crystallographic directions and the formation of secondary phases with significant porosity. The reaction zones consist of at least 4 different mineral phases and are chemically heterogeneous.

Mineral stability as function of grain size, chemistry and microstructure The stability of minerals at a given temperature and pressure is determined by the Gibbs free energy as a macroscopic thermodynamic parameter. Calorimetric techniques and heat capacity measurements can be used to directly determine the enthalpy of formation and

the standard entropy, respectively. For natural minerals, phase equilibrium studies are the major source of internally consistent thermodynamic data sets. Furthermore, different computational modeling approaches exist to determine thermodynamic parameters of solid solutions.

The equilibrium condition for a mineral (assemblage) in an aqueous solution is generally expressed in terms of its solubility and can be modeled using two different approaches: 1. a law-of-mass action algorithm and solubility constants (as in PHREEQC), or 2. a direct Gibbs energy minimization routine (e.g.

GEMS). A chemical thermodynamic database provides the relevant information to calculate phase stability. However, the energy contribution of small grain size, solid solution chemistry (on both major and trace element level) and microstructure of relevant phases is generally not included.

Solubility as function of grain size The solubility of a particle is enhanced at very fine grain sizes. This phenomenon can be described relative to the solubility of large grains (bulk) in a modified Kelvin equation which relates the solubility of a material to its surface free energy ﾎｳ and grain size d:

Figure 2 shows that this effect becomes significant at grain sizes of less than 100 nm

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Figure 2: Grain size dependent solubility related to bulk solubility

Figure 3: Excess Gibbs energy of mixing for a substitution of Fe2+ in sphalerite at 25 °C (parameters from Balabin & Sack, 2000)

(10â&#x20AC;&#x201C;7 m) on the example of different iron oxides/hydroxides based on the surface enthalpies for hydrated surfaces given by Navrotsky et al. (2008). It certainly influences the stability of iron oxides and other secondary phases relevant for monosulfide weathering.

The excess Gibbs free energy for the substitution of Fe2+ for Zn in sphalerite can be expressed by an expansion series:

Thermodynamic mixing properties of solid solution Non-ideal thermodynamic mixing behaviour is common for sulfides, oxides and sulfates.

Microscopically, the mixing of atoms in a structure (e.g. Fe in ZnS) results in strain and chemical interactions. Macroscopically, it is reflected in changes of the enthalpy and entropy, which are reported as so-called excess functions.

In nature, substitutions of up to 50 mol% of FeS in ZnS are possible. The excess energy provided by cation substition is shown in figure 3. The thermodynamic excess properties have direct consequences for the solubility of a mineral, i.e. for instance a sphalerite containing a considerable amount of Fe2+ will be less stable during dissolution than a Fe-free sphalerite.

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Figure 4: Project structure and goals

Energetics of extended defects Reliable calculations of the defect energies for dislocations and planar defects (so called »extended« defects) are largely missing for minerals. Liu et al. (1995) measured the energy difference of undeformed (dislocation density <106 cm–2) and deformed quartz (~1011 cm–2). The differences were found to be rather small (0.6 ± 0.6 kJ/mol). For sulfides, the contribution of the microstructure to the overall energy might be neglected. However, the strain field caused by a dislocation is highly localized. The energy E of a dislocation based on elasticity theory is:

where G is the shear modulus and b is the Burgers vector of the dislocation. The energy of a dislocation is in the order of a few eV and decays with 1/r from the dislocation core. It is generally accepted that dislocations are the primary location for dissolution and mineral reactions and thereby affect the kinetics and textural evolution of minerals (e.g. Poirier, 1985; Veblen, 1992).

Project outline and scientific goals The project is divided into three sub-projects (Figure 4): Project 1 »Microstructural controls on sulfide weathering« provides an extensive chemical and (micro-)structural characterization of monosulfides. Sample assortment will account for natural chemical endmembers (pyrrhotite, spha-

lerite, galena) as well as for solid solution compositions with various superstructures. These will be used to experimentally determine the dissolution/weathering rates as a function of crystal structure, chemistry, and microstructure while taking further parameters (pH, redox potential, temperature and oxygen fugacity) and the formation of secondary minerals into account. The motion of the reacting front and the textural relationships will be studied to identify reaction mechanisms and effective rates.

Furthermore, the influences of crystallographic orientation and structural defects (like dislocations, twin planes, stacking sequences) on the reactivity of a surface will be studied. For this purpose a new experimental approach using thin films (prepared by ultramicrotomy, focused ion beam thinning [FIB]) will be developed. It allows a direct comparison of the same unreacted and reacted sample without the need of further preparation.

Project 2 »Microbially mediated weathering reactions on sulfide mineral surfaces« aims for a deeper insight into the mineral-microbe interaction. The main emphasis is on the effect of microorganisms on the dissolution and the progressive movement of the reaction front into the altered mineral and, thus, on the reaction rate.

Primary prokaryotic microbes specialized for iron and/or sulfide oxidation (e.g. Acidithiobacillus, Leptospiririllum) will be chosen for the biologi-

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cally mediated experiments. Secondary the influence of microorganisms isolated from low pH soils (e.g. Streptomyces) on the dissolution of monosulfides will be assessed. Furthermore, the effect of microbial eukaryotes, especially fungi, to the surfaces of the mineral will be tested.

Monosulfides which have been characterized in project 1 will be used to allow a direct comparison of the abiotic and biotic results.

In addition, the microstructure and stability of freshly precipitated monosulfides (mackinawite) will be studied with special emphasis on their stability. Such monosulfides can be formed by microbially catalysed sulfate reduction (e.g. by Desulfovibrio) and are used in the course of remediation actions on acidic mining lakes.

Project 3 »Monosulfide weathering and heavy metal release – mechanisms, processes, modeling« studies naturally weathered monosulfides with different genesis and degree of alteration with regard to environmental parameters (temperature, pH, redox potential, microbial activity). It will focus on secondary minerals and the distribution of heavy metals in the mineral assemblage. The natural alteration pattern is intended to be reproduced by laboratory experiments using realistic environmental parameters. To generate a reliable dataset for a complex system the measured rate will be compared to the approaches used in project 1 and 2. The results will be incorporated into a geochemical model of monosulfide weathering which is based on thermodynamics (Gibbs free energy) but also considers morphological, structural and chemical parameters as well as kinetics. An understanding of processes at different spatial and temporal scales is proposed.

The presented approach analyses mineral surfaces and alteration processes in full complexity down to the nanometer scale and in terms of the interaction with microorganisms. By this means, MIMOS makes a contribution to evaluate the short and long-term effects of mine wastes on the environment and for remediation actions needed worldwide.

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Simulation-supported development of process-stable raw material components and suspensions for the production of ceramic sanitary ware on the basis of modified mineral surfaces (SIMSAN) Agné T. (1), Engels M. (2)*, Rezende J. L. L. (3), Latief O. (4), Vuin A. (5) (1) Villeroy & Boch AG, e-mail: agne.thomas@villeroy-boch.com (2) Forschungsinstitut für Anorganische Werkstoffe – Glas/Keramik-GmbH (FGK), e-mail: engels@fgk-keramik.de (3) Center of Computational Engineering Science of RWTH Aachen, e-mail: rezende@ghi.rwth-aachen.de (4) Stephan Schmidt KG, e-mail: othmar.latief@schmidt-tone.de (5) Zschimmer & Schwarz GmbH & Co. KG, e-mail: a.vuin@zschimmer-schwarz.de * Coordinator of the project: Marcel Engels, Forschungsinstitut für Anorganische Werkstoffe-Glas/Keramik-GmbH

Abstract 1. Introduction In modern sanitary ware production as performed by Villeroy & Boch AG (hereafter referred to as V & B), the speed of the technical process for the production of geometrically complex articles has been significantly increased by pressure casting, without the corresponding adaptation of the raw material mixture concepts and the process control to the associated new demands. Deviations in the mineralogical composition, but also the particle size distribution and the morphology of the used natural raw materials like clays, kaolin and feldspars lead to instable processes in the following processing steps of forming, decoration and firing, and to increased reject rates for the intermediate and end products.

This is accompanied by an environmental impact through additional emissions and energy consumption. A fundamental influencing factor of the raw materials mixtures is derived from the mineral surfaces. The term »mineral

surface« is synonym to numerous parameters, which can be allocated to the surfaces of the different two- and three-layer clay minerals (kaolinite, halloysite, illite, smectite) and of non-clay materials (feldspar, quartz): specific surface, charge densities and their influence on the interaction with the surrounding medium in a water based slip (adhered water molecule layers, defining zeta potential, flow potential), cation exchange capacity, morphology and topography. The character of the mineral surface is the basis for the rheological behaviour of a suspension for casting and the structure of the formed filter cake, the crack sensibility of the formed product during drying, the deformation behaviour of the green product and the green strength, and the speed of body formation during slip casing. It is the origin of the colloidal behaviour of the ceramic raw material.

Within the scope of this project therefore the chemical and physical characteristics, which apply to the surfaces of the mineral raw mate-

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Figure 1: The functional properties of the material influenced by the mineral and the mineral surfaces

rials, and the intensity and the significance if their impact on the process will be exemplary clarified for the ceramic casting processes with highly automated sanitary ceramic pressurecasting systems. Within the framework of the above parameters of the mineral surfaces it is important to establish to what extent, and in which combination they influence the rheology of the pressure-cast slurry and the filtration properties on the surface of the pressure-casting moulds. The findings will be used in the extracting and processing technology of the raw material companies, in this project represented by Stephan Schmidt KG (hereafter referred to as SSKG), and in the production of the casting compound and process control during pressure-casting in the ceramic production. This will be supported by a numeric model that is to be developed within the framework of this project by the Center of Computational Engineering Science of RWTH Aachen (hereafter referred to as CME). This model will describe in a reliable manner the body formation rate and the microstructure of the body during pressure casting of sanitary ware. To be able to influence specific characteristics of the clay raw materials in a controlled way, chemical additives have to be developed, which can provide the required performance characteristics. For this reason a supplier of additives for the ceramic industry, Zschimmer & Schwarz GmbH & Co. KG (hereafter referred to as Z&S) was included in the

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consortium. The mineral surfaces will be influenced systematically to address required processing characteristics. In this way the processing stability will be adjusted and assured, as well as occurring raw material variations subsequently compensated.

2. Objectives The primary goal of this project is to enable the raw material suppliers and the ceramics industry to develop stable raw material mixtures and casting slurries that are adapted to the modern pressure casting technology and thereby establish robust processes in the interest of consistent economic management, by way of quantitative predictions from simulation calculations regarding the effectiveness of additives and process-defining parameters.

By concentrating on the mineral surfaces, new insights are to be gained in the field of clay mineralogy and the technical application of clay minerals which can also be transferred to areas outside the ceramics industry. The results will make a major contribution towards securing modern workplaces for the German ceramics industry and its suppliers. By the mentioned increase of processing capability, leading to a reduction of reject rates for intermediate and end products, a reduction of the environmental pollution by reduction of emissions and energy consumption will be reached.

In terms of research the industrial enterprises are supported by three expert bodies. The Forschungsinstitut für Anorganische Werkstoffe – Glas/Keramik-GmbH (hereafter referred to as FGK) functions as the ceramic competence institute and contributes its expertise in the field of colloid chemistry and the identification of mineralogical/ material influencing magnitudes on the ceramic process technologies, supported by the department of Applied Mineralogy from the Soil Moisture Group of the University of Karlsruhe, in cooperation with the Working Group »layer silicates« of the Nano-mineralogy department of the ICT-WGT (hereafter referred to as SMG). In the development of a specific algorithm and with regard to the over-all concept, the Center of Computational Engineering Science of RWTH Aachen (hereafter referred to as CME) contributes its competence in the simulation of microstructure formations.

3. Technology The composition of the associated partners is a major advantage and precondition for the positive conclusion of the research project.

With raw material suppliers operating throughout Europe (SSKG, extraction and processing), one of the largest European producers of ceramic process additives (Z & S) and Germany’s leading ceramics producer (V & B), all the principal partners of the industrial process chain are integrated in the project so that the correlation of the raw material prop-

erties with the process parameters of ceramics production is assured.

3.1. Ceramic casting technology To describe ceramic casting processes (conventional or pressure casting) a precise knowledge of the flow characteristics (rheology) and the filtration characteristics (body formation rate) of the employed clay/water/additive-systems is essential. The rheological characteristics can be controlled by the mineralogy (given the presence of known dependencies) and by chemical additions. The first academic publications on this subject have been around for more than 50 years, e.g. by Norton et al. [1].

However, in spite of the special interest in this subject and diverse scientific publications, opinions are often still contradictory. Until today many still consider the card house model suggested by U. Hofmann [2] to be a generally valid description of the geometric arrangement of clays caused by particle/particle interaction in an aqueous environment (fig. 2). The papers of Weiss and Frank [3] as well as Rand and Melton [4] discuss further possibilities for the geometric arrangement of the particles such as edge/edge and surface/ surface aggregation. These interactions and the possible arrangements are the key to an understanding of the rheological behaviour of clays. Until now there have been speculations on the kind of structures by way of indirect reasoning resulting from the interpretation of so-called flow curves. The formation of aggre-

Figure 2: A simplified representation of the formation of the filter cake body. If the medium is extracted from the slip, the clay particles, which at first were apart (A) are drawn together (B), whereupon they agglomerate, the structure being dependent on particle size distribution, mineralogical characteristics of the material as well as the chemical environment (additives). The formed filter cake may have a dense, close packed structure with high filtration resistance (C) or a more open, card house like structure in a flocculated situation (D)

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gate structures within suspensions not only influences the flow properties but also the filtration body forming characteristics within the ceramic casting process [5, 6]. Haas et al. [7] discuss requirements and advantages on additive systems for the pressure casting process.

3.2. Mineralogical characteristics An important cause for the natural diversity of the clays group and the differences and compositions of the natural deposits are the specific mineralogical characteristics regarding layer and surface characteristics, particle size, specific surface and morphology. The chemical environment of the particle influences to a large content the real behaviour of clay suspensions: the aggregation behaviour and subsequently the rheological and filtration behaviour. The pH value, the concentration of salts and processing additives influence the interaction of the particles and so the rheological properties [8]. A commonly known example is the deflocculating behaviour of the clays to increase the solids content in aqueous systems.

The observed, totally differing sensibility for the reaction with certain chemical molecules [9], depending on the origin and material stock, indicates a kind of key/lock relationship to be assumed for such reactions. Different possibilities of species-related adsorption are often discussed for the interpretation of such a behaviour but they have been rarely examined. For instance the deflocculation of clays by anions is generally attributed to adsorption at the edges of clay minerals [10], but proof by measuring the adsorption is still lacking.

The measurement of the surface charge determination is being developed, but proves to be very laborious and can up to now only be performed at single phases with high requirements regarding sample preparation [11].

Even in modern, fully automated pressure casting productions process variations in the form of textures, inclusions and segregation are known to occur, despite that no differences are detected in the raw materials control using the common techniques. This con-

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sequently supports the assumption that important intrinsic material characteristics as well as their influences on the rheology and the process ability are not known. In addition to the customary chemical analysis of the principal elements in the past, only the grain size distribution of >0.5 Âľm of the minerals was measured to characterise crude clays for ceramic production. Only individual potential influencing factors on the rheological and filtration properties were separately determined. These are the qualitative mineral-phase composition and the sum parameter of the flow behaviour of suspensions established by single-point viscosity measurements with flow cups (Ford, Lehmann) and rotation cylinders (Gallenkamp).

3.3. Characterization technology To characterize rheological behaviour of the ceramic casting slips and glazes sensibly detecting rotational viscosimetry methods according to the state of the art are proposed [12].

Modern microscopy techniques (transmission microscopy, ESEM (environmental scanning electron microscopy) could support the clarification of the interdependencies. The examination of the colloid vibration potential (zeta potential) and the particle or aggregate size for the determination of the particle charge is made possible by electro-acoustic spectroscopy.

By targeted fractioning and subsequent X-ray diffraction investigations mineral phases can be separately detected and their influence on the colloidal behaviour can be assessed.

The characterisation of the mineral surfaces based upon the assessment of colloidal properties is a complex issue, and therefore almost never taken into account to support the production control. To derive relevant conclusion from the measurement of the particle charge and the absorbed ionic layers through measurement of the flow potential, the zeta potential and the cation exchange capacity, a combination of X-ray diffraction analyses, particle size distribution measurements and fractioning in the lowest grain size range and specification of the ceramic properties is required, which

Figure 3: Kaolinite (left image) and illite/muscovite right image) clay particle structures as by scanning electron microscopy

cannot be achieved by the equipment as used in the regular production laboratory. The composition of the joint project group therefore offers a unique basis to perform the basic characterisation of the raw materials and the mixtures to define the critical parameters for the optimal slip processing.

The SMG has been subcontracted as relevant competence to address the special requirements regarding surface characterization on a atomic level, and to estimate the additional parameters regarding the local charge distribution and potential correlations of the colloidal particles, necessary for the numeric calculations.

The working mechanisms of the influencing factors of a raw material mixture, dependent on the consistency of the mineral surfaces of the different two- and three-layer clay minerals (kaolinite, halloysite, illite, smectite) and the non-clayish silicates (feldspar, quartz) are not known. The identification of these mechanisms and their assessment in regard to their correlation to the processing performance is an essential objective of this project proposal.

3.4. The hybrid model Concentrating on the chemical-physical characteristics of the mineral surfaces of natural raw materials is a completely new area of research to clarify the material influences on pressure-casting slurry with which correlations can be established for the process parameters of flowability and body forming rate. CME has

just recently presented a new hybrid multiscale approach with which the complex processes associated with glass corrosion can be described. It is a combination of the observation of the continuum and the atomic formulation [14]. The influence of convection on the liquid phase on structure development [15] is also an area of research to which the CME Group has dedicated itself and which is of special relevance for the current proposal. Other studies take into consideration the influence of convection on micro-structural formation, including the treatment of multi-phase systems with the so-called phase-field simulation [16]. To explain the mentioned mechanisms and correlations on a theoretical level a multiple scale approach is used for simulation modelling. The mentioned pressure casting process is a filtration process, of which the average flow rate to be applied for the computer modelling is well known.

The suggested model to calculate the microstructure consists of the following two starting points: (a) A constant model for the calculation of flow (b) A discrete model for the calculation of the movement of solid particles The entire model incorporates a hybrid algorithm that is two-dimensionally executed. Step (a) uses standardised algorithms for the flow of fluids under consideration of the individual

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Figure 4: The hydrodynamic interactions of the particles with the convection flow and the electrostatic particle-particle interaction defining the structure formation of the cast body

solid particles of the slurry. Step (b) is based on a »molecular modelling« approach that takes hydrodynamic and electrical forces into account. The distribution of the shapes and sizes of the solid particles that exist in the system within the differing mineralogical classifications are explicitly incorporated in the model concept. Moreover, the electrical potential emitted by the particle is influenced by the pH-value, the solid content in the casting slurry and by the ion charge and concentration in the mixture. These dependencies make it necessary to examine the influence of these factors on the microstructure of the green sample with the help of this simulation tool.

The question raised as a result of this application can only be adequately answered by the methods of the multiple scale approach. The subjects covered range from the macroscopic scale (formation of the body) and the mesoscopic scale (microstructural formation) right up to the atomic scale (Debye length, colloidal system, ion interaction). In the light of this aspect hybrid approaches, including the intended development of the description of the mineral surfaces of a raw materials mixture can be very helpful and promising.

4. Subprojects To reach the described goal of the project the following subprojects with their specific targets are highlighted:

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4.1. Subproject »meaningful characterization of mineralogical characteristics« Responsible: Forschungsinstitut für Anorganische Werkstoffe – Glas/Keramik-GmbH Subcontractor: Soil Moisture Group of the University of Karlsruhe (department of Applied Mineralogy, cooperation with the Working Group »layer silicates« of the Nano-mineralogy department of the ICT-WGT) The FGK is called upon to provide safe process management concepts for clay mineral suspensions in an automated ceramic casting process by applying the available analytical, colloid-chemical and rheological methods.

These concepts could be applied in the raw material sector for the formulation of optimal compositions for adapted mixtures, to provide additive suppliers with synthesis solutions for optimized or new additives or to supply manufacturers with tools and knowledge for safe process control.

Within the scope of the project, the scientific and technical principles of the characterization of the mineral surfaces and their modification are to be elaborated at the Forschungsinstitut für Anorganische Werkstoffe – Glas/KeramikGmbH (FGK). The implementation of the findings in a characterization method with reliable results is ensured by the involvement of industrial partners in the consortium. The subproject

focuses on the validation and development of the measurement methods for this specific application, in the end providing the mentioned characterization method. The requirements, procedures and algorithms for the interpretation of the complex interactions of the mineralogical effects with performance characteristics will be developed and defined using the competence of the FGK regarding materials science and ceramic analysis.

The given complexity of the interface, which combines the atomic description of the charge consistency and the physical characteristics of the clay minerals with the interactions in industrial raw material mixtures, measured by relevant and reliable measuring methods, defines the need to include the department of Applied Mineralogy from SMG, which supplies the necessary expertise in the area of applied mineralogy and layer silicates.

4.2. Subproject »Simulation based development of ceramic sanitary ware« Responsible: Center of Computational Engineering Science of RWTH Aachen The primary goal of this subproject is the development and implementation of a computer model which is able to reliably describe the cake formation rate and the corresponding cake microstructure for the pressure slip casting of a clay-water suspension. The model shall take into account the presence of plate

like particles contained in the clay and quartz – feldspar (non-clay globular silicates) in the mineral composition of the slip. The influence of the additives like sodium silicate (Na2SiO3) on the process will be also taken into consideration in the model conception. The model will then permit the realization of parameter studies, through numerical simulation, on the influence of additive content and mineral composition (including particle size distribution) on the product characteristics.

In this subproject there will be a strong interaction with V & B as ceramic manufacturer using the pressure casting technique for the development and the validation of the model, based upon the characterization of the casting slip as provided by the FGK. 4.3. Subproject »Pressure casting tests on new developed slips« Responsible: Villeroy & Boch AG From an industrial production perspective, shaping processes relying on die-casting as a key technology in the ceramics industry require demanding and constant properties in the slip to be processed throughout the storage period and in regard to recovered raw materials. The subsequent process chain at the same time requires adequate raw stability coupled with an optimal re-workability of the green ceramics.

Resource and energy savings in combination with increased productivity are furthermore

Figure 5: The laboratory pilot pressure casting unit (left) with laboratory scale moulds (right)

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indispensable in order to enhance competitiveness. The raw materials and slip formulations and not least of all the conventional measuring methods at the given state of the art only partly meet these higher requirements.

The contribution from (V & B) consists of the implementation of the findings from the activities of the partners regarding characterization, functionalisation and preparation of the raw materials in the production process. The experiences regarding ceramic body composition development, the forming process using modern pressure slip casting techniques and the available pilot plant facility enable the transfer of the basic developments in the industrial practice. In alignment with the overall working plan the work packages of the subproject contain laboratory development tests up to pilot plant tests in the sanitary ware production facilities.

4.4. Subproject »Sanitary clay blend« responsible: Stephan Schmidt KG Within the scope of the project, the characterization method for the pit clays with regard to the stability of the rheological properties is to be improved. Furthermore, the possibilities of preparation processes are to be optimised.

Current characterization methods for pit clays do not render a sufficient picture of the influ-

ence of mineralogy on rheological properties.

In particular, it is not possible to make any statement regarding the characteristics of the surface of the minerals. In some first examinations specific surfaces have been determined, however, the influence of surface charges has not yet been analysed. This will be the target of the examinations carried out at FGK’s laboratory within the scope of this project. The surfaces of the different clays shall be analysed with regard to their topographic structure.

These clays will be the basis material for the additive testing by Z & S and the processing trials by V & B. The expected gain in knowledge about the effects and intensity of influence of mineral surfaces will not only be used to develop and supply constant raw material blends for the sanitary ware industry, but the results of the project will be transferred to the development of casting clays for other fields of application (laboratory ceramics, special containers) and an optimal and thus considerate use of natural raw materials and use of suspensions by long-term stabilisation.

Subproject 4.5. »The development of novel additive systems for the production of processstable clay mineral suspen-sions for use in the manufacture of sanitary ceramics« Responsible: Zschimmer & Schwarz GmbH & Co KG

Figure 6: Clay mining in the pit

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Figure 7: Using slip casting additives in pressure casting

The objective of Zschimmer & Schwarz GmbH & Co KG is the modification of mineral surfaces by the use of novel chemical additives and the reaction products resulting from them in such a manner as to make it possible to guarantee the required processing properties.

Novel additive systems are intended to make it possible to employ the suspensions in both conventional casting and pressure casting without changing the composition. Here it is necessary to guarantee the constancy of the rheological properties of the slip over an extended period of time. The filtration behaviour and the handling properties during further processing of the demoulded components are to be improved.

basis of their influence on the mineral surface are targeted to enable the use of more economically priced ceramic raw materials.

The development of »basic additive systems« is envisaged, acting as »chemical buffers« to create a fundamental suspension behaviour, thus improving compensation for natural raw material variability. The net result is a positive effect on the processing stability and product quality.

5.1. Inventory of raw materials and processes; development of a hybrid model Next to the selection and provision of samples, the industrial partners determine already in this stage the targets for the raw material mixtures that are to be developed. An optimally designed concept for the raw materials to be processed, as well as sampling, storage, characterization and processing of the samples, form the basis for the comprehensive mineralogical and colloid-chemical characterization of the raw materials, as well as the characterization of the mineral surfaces, representing significant input date for the initial configuration of the simulation calculations. CME will develop and realize a hybrid model during this stage of the project. The marginal and initial conditions for simulation or the range within which they are present, will be supplied by the

The further application of small quantities of specific chemical additives can be used to influence specific characteristic properties such as filtration behaviour and strength of the cast piece.

Based on the knowledge to be gained from the mineralogical characterization new additive systems, which can modify specific properties such as the binding forces between individual particles or the surface activity on the

Ecological factors are likewise considered: the investigation of new raw material sources for chemical additives is intended to create products, that are less polluting of the environment and improve the working environment of those employed in production.

5. Methodology In the following the methodology is described, following the chronologically defined work packages in the project, to which the subprojects of the partners are aligned:

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co-operation partners at the end of this phase, using validated measurement methods with a defined reliability.

5.2. Producing laboratory batches; calibrating the model New raw material batches are developed on the basis of the previous inventory. The aim is to influence the colloid-chemical and rheological properties by a physical change (grinding raw material components, exchanging crude clays of differing mineralogy and particle distribution) and chemical change (functionalising with organic additives through adsorption at the mineral surfaces). During this phase CME will conduct preparatory examinations of the model system and use approximately estimated values for the charge potential and density. Furthermore, CME will develop an analytical model for the electrical potential and charge density which are to be determined in the real process on the basis of the associated value fields by FGK, for example by electro-acoustic methods.

5.3. Pilot plant tests; numerical studies After successful completion of the laboratory tests the mixtures are transferred to the pilot pressure-casting plant at V & B where test bodies and articles can be produced. In addition to the assessment of the flow and body formation behaviour under differing pressures and process times, the green products are also examined with regard to their packing density and texture which, among other things, can result in tension cracks while the articles are being dried and fired and therefore result in waste. Furthermore, these data are used for the calibration of the simulation calculations for the body formation rate and the microstructure of the green products. After the model has been calibrated CME will conduct systematic studies by parameter variation. FGK will focus on the specification of the settings for a relevant process control. Industrial processing tolerances regarding raw materials as well as performance indicators for the shaping process will be compared and specified.

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5.4. Transfer to industrial practice The project will be terminated by the implementation of the development results in the form of pilot tests and tests under production conditions at the site of the project partners, representing the raw material and additives suppliers and the ceramic producers. These examinations will be accompanied by detailed rheological, mineralogical and chemical analyses and then evaluated under the aspects of a process capability analysis. The aim of the concluding project phase is to formulate recommended actions for changing the clay mixtures at the raw material suppliers and raw material processing at the ceramics company. The numerical studies from work phase 5.3 will be taken further to specify for optimal production conditions which are not only of interest to the producers of the initial materials but also for the feasibility of ceramics production in general.

6. Outlook Besides the development of innovative raw material blends, including the use of new additive systems based on the functional knowledge acquired, the prominent tangible results of the joint project will be: â&#x20AC;&#x201C; A requirement specification for ceramic raw material and production process control, defining the relevant parameters and their characterization, as well as the adequate characterization technology, including sampling, sample preparation and measurement settings. â&#x20AC;&#x201C; A reliable multi-scale model for the simulation of the pressure casting process of clays, enabling the specification of processing settings by simulation, and so the development of new raw material concepts as well as processing settings.

It is expected that the clay-processing industry will increasingly come to rely on the knowledge which already exists and is still to be developed at the FGK by the developed fundamental understanding of the interaction of the additives with the clays and their influence on the rheological properties, also applicable

to future challenges in the handling, optimization and adjustment of aqueous nano-particle systems. With this knowledge and in connection with the existing, modern equipment, the FGK will in the future be able to provide interested partners in industry and research with competent services. The topic presented is as interesting for raw material operations as it is for processing operations, and this not only applies to the ceramics industry, but also to all sectors where clays are used in industrial applications. The findings will be published in established trade magazines (Clays Clay Minerals, Applied Clay Science, Keramische Zeitschrift, Ceramic Forum International) and via lectures at specialist conferences (annual conference of the Deutsche Keramische Gesellschaft, the European Ceramic Society EcerS, the Deutsche Ton- und Tonmineralgruppe e.V. DTTG, FGK seminars).

The CME will operate as service provider in following projects regarding simulation calculations in the ceramic industries as well as in similar production processes, based on the availability of a software application for the improvement of product-and process performance.

SSKG will be enabled to develop stable raw material mixtures for the sanitary ware industry, as well as casting clays for other applications (laboratory ceramics, special containers) by an optimal use of the raw materials. Shortterm, the results shall be used for the development of casting blends for other ceramic branches. Mid-term the results will influence the development of plastic bodies for the production of insulators and honeycombs to reduce energy consumption and textures during the extrusion process.

The results to be expected from the project will not only allow V & B to enhance core competences for high-quality, individual, but also low-cost products in relatively small lot sizes by a highly productive, extremely flexible production technology with Germany as the industrial location, but also to explore new business areas. The findings and experiences

gained in the project run can also be integrated in other sanitary production plants, as well as in table crockery production. At the same time the prospects regarding further increase in export and sales volume are expected.

The development of new additive systems will provide Z & S from the market-oriented point of view, as well as regarding economical and ecological aspects new potentials on the European and the world market. On short term basis new customers will be acquired and the sales with existing customers improved. New application areas will be developed for the pressure casting technology and in oxide and non-oxide industries.

Every associated partner is active in the European scientific units and economic associations and maintains bilateral, trans-national business contacts. The European Ceramic Society ECERS and the Clay Mineral Society are of special importance for scientific dissemination, while the Fédération Européene Céramique Sanitaire FECS, the European Clay Group Association ECGA and the Industrial Minerals Association IMA are important for transfer of the results to the companies. The CME belongs to the EU network SIMU. CME additionally takes part in the programme COST Action P13 MOLSIMU. This programme is devoted to the methods of integrated multi-scale simulation which links molecular simulation with other techniques for measurements in the order of micrometers and seconds. It coordinates the DFG priority program »Heterogeneous seed and microstructure formation« and is in direct exchange with a international group of evaluators.

Acknowledgement Based upon the described complexity of the thematic issue the combination of competence in the joint project group makes it possible to perform the necessary characterization of the mineral surfaces and the interactions with the processing characteristics. The multiple scale approach is a novel application which can only be performed by combination

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of the competence of the joint project partners.

Therefore the funding of the project »Simulation-supported development of process-stable raw material components and suspensions for the production of ceramic sanitary ware on the basis of modified mineral surfaces« (SIMSAN) (»Simulationsunterstützte Entwicklung prozessstabiler Rohstoffkomponenten und Suspensionen für die Produktion von Sanitärkeramik auf der Basis modifizierter Mineraloberflächen«) by the German Ministry of Education and Research (BMBF) by grant no. 03G0716A et al. within the framework of the of the geotechnologies initiative (http://www.geotechnologien.de) is gratefully acknowledged.

The responsibility of the contents of this publication is by the authors.

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[2] Hofmann U., Hausdorf A. (1945), Über das Sedimentvolumen und die Quellung von Bentonit, Kolloid Z. Z. Polymere 110: 1–17.

[3] Weis A., Frank R. (1961), Über den Bau der Gerüste in thixotropen Gelen, Z. Naturforsch. 16b: 141.

[4] Rand B., Melton I. E. (1977) Particle interactions in aqueous kaolinite suspensions, J. Colloid Interface Sci. 60 (2): 308–320.

[5] Klein G., Druckgießen in der Keramikindustrie, DKG Technische Keramische Werkstoffe, 40 Erg-Lfg (Juli 1997), Kap. 3.4.10.0, S.1–55.

[6] Nürnberger G., Entwicklung und Einführung des Schlicker-Druckgießverfahrens in der Sanitärkeramik, keramische Zeitschrift, Teil I – 40. Jahrgang Nr. 4 (1988), S. 227–232, Teil II – 40. Jahrgang Nr. 5 (1988), S. 304–307.

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[7] Haas S., Bohlmann C., Quirmbach P., Additive für die Optimierung des Druckgießverfahrens, Keramische Zeitschrift, 52. Jahrgang Nr. 5 (2000), S. 390–397.

[8] Duran, Ramos-tejeda, Arroyo, GonzalesCaballero, Rheological and Electrokinetic studies of sodium montmorillonite suspensions, J. Colloid Interface Science 229 (2000) 107–117.

[9] Penner D., Lagaly G., Influence of anions on the rheological properties of clay mineral dispersions, Appl. Clay. Sci. 19 (2001): 131–142.

[10] Swartzen-Allen L., Matijevic E., Surface and colloid chemistry of clays. Chemical Reviews 74 (3)(1974): 385–400.

[11] Kaufhold, S., Dohrmann, R., Kationenaustauschkapazität und Ladung von Tonmineralen, Vortrag zum 3. Höhr-Grenzhäuser Keramik-Symposium »Rohstoffe Pulver«, Additive, Analytik, 26/27 September 2007 Ceratechcenter Höhr-Grenzhausen.

[12] Becker C., Dohrmann R., Environmental scanning electron microscopy (ESEM)- A new method in clay science, Applied Mineralogy (2000), Rammlmair et al. (eds) Balkema, Rotterdam.

[13] Diedel R., Silicate Ceramic Raw Materials: »Nothing Left to Research?«, cfi/Ber. DKG 83 (2006) No. 2, E 34–E 38.

[14] Radke de Cuba M., Emmerich H., Gemming S., Zwei-Skalen-Modellierung von Adsorptionsprozessen an strukturierten Oberflächen, Z. Anorg. Allg. Chem. 12/13, (2006), p. 632.

[15] Müller-Krumbhaar H.,. Emmerich H., Brener E., Hartmant M., Dewetting Hydrodynamics in 1+1-Dimension, Phys. Rev. E 63, (2001), p. 026304.

[16] Emmerich H., Siquieri R., The influence of convection on peritectic growth in Numerical Heat Transfer, A. Nowack, R. A. Bialecki eds., ISBN 83-922381-2-5, (2005).

Using Hydrophobins to Prevent Microbial Biofilm Growth on Mineral Surfaces Fischer R. (1)*, Schwartz T., Obst U. (2) (1) Institut für Angewandte Biowissenschaften, Abteilung für Angewandte Mikrobiologie der Universität Karlsruhe, e-mail: reinhard.fischer@KIT.edu (2) Forschungszentrum Karlsruhe – in der Helmholtz Gemeinschaft Institut für Technische Chemie – Wasser- und Geotechnologie, Abteilung Mikrobiologie natürlicher und technischer Grenzflächen, e-mail: thomas.schwartz@itc-wgt.fzk.de *Coordinator of the project: Prof. Dr. Reinhard Fischer, Universität Karlsruhe

Summary Microbial biofilms consist of normally planctonic bacteria, which adhere to surfaces and form stable and resistant communities. They produce a matrix of organic molecules in which they are embedded and which offers new habitats to other organisms, such as other bacteria or fungi. If a biofilm covers medical equipment such as catheters, pathogenic bacteria, which may be living in the biofilms, are a continuous source of infection of the patients. In addition, the metabolism of the biofilm microorganisms may change the composition of the fluids or contaminate them with their products. Biofilms can also cause damage to mechanical devices and block moving pieces in e.g. pumps. Therefore, the understanding of the formation of biofilms and the prevention of their formation are or prime importance in microbiology and material sciences.

In this interdisciplinary project, structured surfaces coated with hydrophobin will be be produced, and their properties studied with respect to bacterial cell adhesion, cell differentiation and cellular growth. Approximately fifteen years ago, hydrophobins were detected as small proteins occurring naturally on the surface of fungi. These proteins assemble spontaneously on a number of synthetic sur-

faces into extremely stable films, whose thickness can be controlled, where they apply specific physico-chemical properties to the coated surface. This behavior makes hydrophobins attractive to a number of technological applications, for instance in coating surfaces, among other things also in medical applications. Because hydrophobins are proteins, they may be used as anchors for other molecules, such as enzymes or peptides. This opens the avenue for novel surface functionalization approaches.

Introduction Biofilms Microbial biofilms represent a special symbiotic form of life of bacteria and fungi (Spormann, 2008). It is now generally acknowledged that bacteria can establish a kind of permanent growth as a biofilm on a variety of natural and synthetic surfaces. Probably nearly all bacterial species are able to exhibit a type of growth firmly adhering to a substrate as a biofilm, in addition to the planktonic freely floating growth variety. A special characteristic of all biofilms, besides firm adhesion to one site, is their highly structured character (Costerton, 1995; Stewart & Costerton, 2001) (Fig. 1).

Some bacterial species express special adhesins on the cell surface, which mediate stable

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Figure 1: Scheme of the formation, structure and functioning of a bacterial biofilm. On the surface one or different bacterial species settle and form microcolonies. The bacteria are embedded into a matrix of polymers and the physiology of the bacteria changes within these colonies (indicated with the white color). Between the microcolonies water channels can be found, which enable the flux of nutrients and metabolites. Some bacteria can be released again and search for new surfaces for attachment

Figure 2: Primary adhesion of bacteria. left: Adhesion of bacteria through flagella (e.g. Pseudomonas aeruginosa); right: Adhesion through specific receptor proteins (e.g. Streptococcus mutans)

adhesion to the surface. Adhesins in most cases are proteins or polysaccharides, like the »polysaccharide intercellular adhesin/hemagglutinin« (PIA/HA) or the »biofilm-associated protein« (BAP) (Fig. 2). The adhesins of streptococcal species frequently are lectin-like proteins entering into simple, non-covalent, stereochemical interaction preferably with carbohydrate compounds, frequently with galactoside compounds, and generate a mechanical link by this receptor-ligand reaction. The establishment of bacterial biofilms on mineral surfaces begins with the deposition of the pellicle layer made up of different glycoproteins, mucins and enzymes (Rupp et al., 1999).

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In a direct comparison of the two types of organization, bacteria of an identical species in biofilms are found still to be resistant to concentrations of an antibiotic corresponding to 1000 times the minimum inhibition concentration for planktonic suspensions (Ceri et al., 1999). As a consequence of the pronounced tendency for manifestation on inorganic surfaces, biofilms initially were considered a major problem especially in environmental biology and water technology. After a few weeks, compartments exposed to water regularly exhibit persistent colonization with various bacterial species (Boe-Hansen et al., 2003). The characteristic high resistance of

bacteria in biofilms to antibacterial substances underlines the finding that, so far, no disinfection process has become available for effective and permanent removal of bacterial biofilms. Especially the extremely high resistance to nearly any type of antibacterial agents of bacteria in biofilms referred to above is now considered the main cause of a number of instances of consequential damage also to mineral surfaces (biocorrosion of metal and mineral substrates; odors developed by biofilms in air filter units; pathogens emanating from biofilms on medical treatment units).

While bacterial communities in biofilms are well characterized, reports about the relevance of fungi in biofilms are rare. Here, the yeast Saccharomyces cerevisiae is the most studied organism (Reynolds & Fink, 2001). Subsequent investigations demonstrated similar adhesion mechanisms in other fungi, such as human pathogenic fungi (Bauer & Wendland, 2007).

A number of different fungal species were also detected for example in drinking water biofilms (Doggett, 2000).

Fungal hydrophobins Hydrophobins are a unique family of small proteins (approx. 100 amino acids) secreted by filamentous fungi. They fulfill a number of functions in the growth and development of fungi. By reducing the surface tension of ambient water, hydrophobins allow the fine filaments of fungi (hyphae) to escape the substrate and grow into the air so as to form spore-producing structures, such as the pileus.

These airborne structures are covered with hydrophobins, which makes them water repellant (Wösten, 2001; Wösten et al., 1996; Wösten et al., 1999). Consequently, the fungus cannot grow back into the wet environment, the spores are distributed effectively by the wind and by insects, and gas exchange in the fruit bodies is possible even in a humid environment. Moreover, the hyphae use hydrophobins to stick to water repellant surfaces. Hydrophobins fulfill their function in nature by producing a 10 nm thin film at the interface between a hydrophilic and a hydrophobic surface. One prominent example for the occurrence of hydrophobins is the surface of spores of molds. The rodlets can be visualized by scanning electron or by atomic force microscopy (Fig. 3).

These interfaces occur, e.g., between water and air, and between the surface of a fungus and air, or between the surface of a fungus and a water repellant surface. This surface can be that of a host (like a plant) or a piece of teflon, like that of a coating in a frying pan serving to prevent sticking. While the film is being produced, in a stage called assemblage, the protein undergoes several conformational changes. The soluble protein, via an intermediate form called the α-helix form, is transformed into the stable final form, the socalled β-pleated sheet from. At the interface between water and teflon, the hydrophobin is kept in the α-helix form. Transition into the βpleated sheet form occurs only when the coated material is treated with a diluted soap solu-

Figure 3: Hydrophobins on the spore surface of molds. left: typical occurence of molds on food. middle: Scanning electron microcope picture of a conidiophore of Aspergillus nidulans, with hundrets of conidiospore. Each spore is about 3 µm in diameter. right: Atomic force microscope picture of the spore surface. The 10 nm rodlets are visible

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tion (e.g. 2% SDS) at high temperatures. Like soap, the hydrophobin film has a hydrophilic and a hydrophobic side. The film is sparingly soluble and adheres firmly to water repellant surfaces. The assemblage of hydrophobins to teflon makes the material capable of water resorption. The degree of water resorption capability depends on the hydrophobin used.

The surface modifying properties of hydrophobins are of special interest in a number of medi-cal and technical applications. The use of hydrophobins on a larger scale has been prevented so far by the fact that there was no expression system for these proteins, requiring them to be isolated, e.g., from Schizophyllum commune in a lengthy process (Scholtmeijer et al., 2001). Recently a breakthrough with the expression of the A. nidulans hydrophobin, DewA, in E. coli was achieved.

In this way, large quantities of the protein can be isolated in a simple way and are available for coating experiments.

Although the entire variability of this protein family is yet unknown, for some hydrophobins molecular structures are available (Hakanpää et al., 2004; Hakanpää et al., 2006; Torkkeli et al., 2002).

As the coating agent represents a protein, there is the possibility to modify this protein and, for instance, fuse it with other proteins. In this way, it ought to be possible to coat surfaces not only with hydrophobins, but also, for instance, with a specific enzymatic activity, with biocides or protease inhibitors. Biocides would support the growth-inhibiting hydrophobic property of the surface and inhibit bacterial growth. Protease inhibitors prevent degradation of the hydrophobin proteins by bacterially secreted protease, and would clearly increase the longevity of the surface structure.

Goals and working plan Coating of surfaces with hydrophobins Protein coating of mineral surfaces can help control their properties with a view to their changed biocompatibility with microorganisms

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at the interface with aqueous phases. As a function of an envisaged application in various areas employing mineral products (ceramics) it is necessary, however, to adapt the specific properties of the treated surface to the respective requirements. This makes it desirable to study the untreated surfaces by controlled coating with hydrophobins and, in this way, represent their altered biocompatibility as a result of the new surface properties.

In this interdisciplinary project, structured surfaces coated with hydrophobins are to be produced, and their properties are to be studied with respect to bacterial cell adhesion, cell differentiation and cellular growth.

In a parallel development, it has been possible in recent years to apply to large surface areas defined patterns of characteristic longitudinal scales from nano- to microscales (molecular editing, micro-contact printing, polymer blend lithography), which can serve as substrates for coating with biological macromolecules. In this way, the size of hydrophobins (10 nm) defines the maximum resolution on a nanoscale of the structures generated in this way, while the characteristic size of the adhering cells (micrometers) defines a meaningful minimum resolution of the structures. In this project, surfaces prepared in this way are to be modified by coating with different hydrophobins such that structural properties of the surfaces can be converted into functionality properties of the material with respect to cell adhesion and growth.

Effect of hydrophobins on the composition of the biofilm The mineral surfaces coated will be studied microbiologically and by molecular biology techniques with respect to their bacterial cell adhesion and growth properties. The commercially available ceramic filter material Siporax® will be applied in the first phase of the investigations. In aquaculture, Siporax® is widely used as a carrier for the cultivation of natural microorganisms. Natural hydrophobins will be used to coat the ceramic

materials with natural hydrophobins. Coating itself will be achieved by a »selfassembly« process, in which the proteins are supposed to form a nanoscale film on the surface. This coating process will be verified with the help of protein-specific marker substances. Variations of hydrophobicity of the treated ceramic material will be studied compared to untreated materials (e.g. contact angle measurements).

The growth behavior of various microorganisms will be studied on coated and uncoated ceramic surfaces. We will use representatives of gram-negative bacteria with a high biofilm formation potential. One of these bacteria will be Pseudomonas aeruginosa, a bacterium that may occur ubiquitously and is described as being pathogenic. Enterococci and staphylococci will be applied as representatives of gram-positive bacteria. They are often described to be pathogens causing nosocomial infections. All bacteria mentioned have already been identified to be biofilm formers on implants and catheter materials.

To simulate natural milieu conditions, coated and uncoated ceramic materials will be incubated with natural bacteria-contaminated waters (grey water, clear water) for three weeks up to three months.

The growth behavior of both reference bacteria and natural populations on the surfaces will be controlled mainly using molecular biology methods. Quantitative methods will allow for a determination of the population density of bacteria on the surfaces. Such methods include the already established fluorescence in-situ hybridization (FISH) and quantitative real-time PCR. Both methods are suited to calculate a cell number per cm2 without an existing biofilm having to be removed mechanically from the surface. Furthermore, these methods determine the total cell number and living cell number of non-defined bacteria populations. In this case, molecular biology fingerprint methods (PCR-DGGE) serve to characterize adherent bacteria. Ribosomal DNA sections are amplified

with eubacterial primers by a PCR process. The resulting PCR products are subjected to electrophoresis in a gradient polyacrylamide gel to determine the GC content. As the GC content in the amplified rDNA section of eubacteria is variable, a bacteria-specific separation takes place. Ideally, each band can be assigned to a bacterium. The separated DNA bands are eluted from the gel and sequenced. By comparing the sequence with ribosomal databases (NCBI, ARB) for procaryotes, the biofilm bacteria may be identified.

Parallel to the use of molecular biology methods, cultivation experiments will be performed. However, they are specific for the reference bacteria applied and reflect a fraction of the natural population only.

Molecular biology expression analyses for adhesion genes and their gene products exhibit a correlation between surface treatment and biofilm formation in »hydrophobinresistant« groups of microorganisms. These studies are to allow specific requirements for applications to be met, such as for products in the ceramic industry (filter systems, medical systems, etc.), by rational optimization of the composition and structuring of the underlying surfaces.

Besides the characterization of bacteria in biofilms, we are going to study the growth of fungi on ceramic surfaces. In a previous project, various fungi in biofilms were isolated from water pipelines (Doggett, 2000). Within the framework of the project proposed here, the occurrence of fungi in these biofilms shall be investigated in more detail. First, the existence of fungi shall be verified by rapidly determining the concentration of 1,3-beta-D-glucane in various biofilms from a natural milieu with grey or clear waters. Positively tested biofilms shall be characterized by Nadicom GmbH creating a clone library. In parallel, the fungi from the biofilms will be cultivated. Modern molecular techniques, e.g. in-situ hybridization, also allow for a spatially resolved determination of the distribution of microorganisms.

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Investigation of the adhesion properties of certain microorganisms Bacteria and fungi exhibiting biofilm growth in spite of the hydrophobin-mediated surface property shall be characterized taxonomically via the ribosomal DNA. By means of a transcriptome analysis on the mRNA level, we will determine, which genes of these »resistant bacteria« are activated when the surface is colonized by unmodified hydrophobins first.

Based on the results of the taxonomic characterization, gene expression analyses will be made with respect to the induction of already known adhesion mechanisms (see state of the art). For this purpose, RNA will be isolated from the biofilms. The total mRNA will be transcribed to a cDNA by reverse transcription and the presence of adhesion gene-specific cDNA will then be quantified by real-time PCR. By comparison with ribosomal gene activities as a so-called housekeeping gene product, gene activity will be determined.

Optimization of hydrophobins for biofilm prevention Whereas so far, we only considered coated surfaces with unmodified hydrophobins, in a further part of the project we are going to apply modified molecules. As a modification, protease inhibitors tested in previous studies may be used for coupling (see above). Coupling with biocides (antibiotics, quarternary ammonia compounds) would be another alternative to optimize the prevention of biofilms.

References Bauer, J. & Wendland, J. (2007). Candida albicans Sfl1 suppresses flocculation and filamentation. Eukaryot Cell 6, 1736–1744.

Boe-Hansen, R., Martiny, A., Arvin, E. & Albrechtsen, H. (2003). Monitoring biofilm formation and activity in drinking water distribution networks under oligotropic conditions.

Water Sci Technol 47, 91–97.

Ceri, H., Olson, M. E., Stremick, C., Read, R. R., Morck, D. & Buret, A. (1999). The calgary biofilm device: new technology for rapid deter-

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mination of antibiotic susceptibilities of bacterial biofilms. J Clin Microbiol 37, 1771–1776.

Costerton, J. W. (1995). Overview of microbial biofilms. J Ind Microbiol 15, 137–140.

Doggett, M. S. (2000). Characterization of fungal biofilms within a municipal water distribution system. Appl Environ Microbiol 66, 1249–1251.

Hakanpää, J., Paananen, A., Askolin, S., Nakari-Setala, T., Parkkinen, T., Penttila, M., Linder, M. B. & Rouvinen, J. (2004). Atomic resolution structure of the HFBII hydrophobin, a self-assembling amphiphile. J Biol Chem 279, 534–539.

Hakanpää, J., Linder, M., Popov, A., Schmidt, A. & Rouvinen, J. (2006). Hydrophobin HFBII in detail: ultrahigh-resolution structure at 0.75 A. Acta Crystallogr D Biol Crystallogr 62, 356–367.

Reynolds, T. B. & Fink, G. R. (2001). Bakers’ yeast, a model for fungal biofilm formation.

Science 291, 878–881.

Rupp, M. E., Ulphani, J. S., Fey, P. D., Bartscht, K. & Mack, D. (1999). Characterization of the importance of polysaccharide intercellular adhesin/hemagglutinin of Staphylococcus epidermidis in the pathogenesis of biomaterialbased infection in a mouse foreign body infection model. Infect Immun 67, 2627–2632.

Spormann, A. M. (2008). Physiology of microbes in biofilms. Curr Top Micorbiol Immunol 322, 17–36.

Stewart, P. S. & Costerton, J. W. (2001).

Antibiotic resistance of bacteria in biofilms.

Lancet 358, 135–138.

Torkkeli, M., Serimaa, R., Ikkala, O. & Linder, M. (2002). Aggregation and self-assembly of hydrophobins from Trichoderma reesei: lowresuolution structural models. Biophys J 83, 2240–2247.

Wösten, H. A. (2001). Hydrophobins: multipurpose proteins. Ann Rev Microbiol 55, 625–646.

Wösten, H. A. B., Bohlmann, R., Eckerskorn, C., Lottspeich, F., Bölker, M. & Kahmann, R. (1996). A novel class of small amphipathic peptides affect aerial hyphal growth and surface hydrophobicity in Ustilago maydis.

EMBO J 15, 4274–4281.

Wösten, H. A. B., van Wetter, M. A., Lugones, S. G., van der Meri, H. C., Busscher, H. J. & Wessels, J. G. H. (1999). How a fungus escapes the water to grow into the air. Curr Biol 9, 85–88.

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Functionalized mineral surfaces: Sorption mechanisms of growth-stimulating proteins on surfaces of bone substitutes based on calcium phosphates (BioMin) Fischer H. (1)*, Seifert G. (2), Gemming S. (3), Jennissen H. (4), M端ller-Mai C. (5) (1) Department of Ceramics and Refractory Materials, Institute of Mineral Engineering, RWTH Aachen University e-mail: h.fischer@rwth-aachen.de (2) Department of Chemistry, Theoretical Chemistry, TU Dresden e-mail: gotthard.seifert@chemie.tu-dresden.de (3) Institute of Ion Beam Physics and Materials Research, Research Center Dresden-Rossendorf e-mail: s.gemming@fzd.de (4) Institute of Physiological Chemistry, Biochemical Endocrinology, University of Duisburg-Essen e-mail: hp.jennissen@uni-duisburg-essen.de (5) Clinic for Surgery, Department of Trauma Surgery and Orthopaedics, Knappschaftskrankenhaus Bochum-Langendreer e-mail: ch.mueller-mai@kk-bochum.de * Coordinator of the project: Prof. Dr.-Ing. Horst Fischer, RWTH Aachen University

Abstract In the field of biomaterials, i.e. of materials that are used for medical prostheses and implants, recent research is focused on the interface between implant material and biological environment. This is true in particular for bone substitute implants. Focusing on bone substitutes, the calcium-phosphatebased minerals (CaP) are of special interest, because of their similar chemical composition compared to natural bone. Mineral materials based on CaP are bioactive and degradable in vivo. Therefore, the strategy using bone substitute implants made of calcium phosphates is, that these materials are slowly degraded inside the body and successively substituted by natural bone tissue. The natural bioactivity of calcium phosphates is limited. The bioactivity and subsequently the bone remodelling process weakens especially when greater bone defects are to be restored by this class of material. It is known that the growth of bone

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tissue can significantly be stimulated by so called Bone Morphogenetic Proteins (BMPs).

Such proteins are synthesized during build-up of bone tissue by the human body. Since a couple of years it has become possible to produce BMPs synthetically. Therefore, different research groups use the method of coupling BMPs to CaP surfaces in order to additionally bioactivate the interface. The mechanism of protein coupling and especially the desorption kinetics of BMP on mineral surfaces is not known in detail. However, this knowledge is important for the development and manufacturing of tailored CaP-based bone substitute implants, so that degradation of the substitute material and build-up of new bone tissue can go hand-in-hand in vivo. The respective knowledge will be acquired in the project BioMin. Introduction Biomineral calcium phosphates can be found in almost all eruptive rocks, in sedimentary,

and in metamophic rock formations. Moreover, CaP minerals can be of maritime (implantological alga products) or of animal source (in the field of biomaterials: bovine-based bone substitute implants). Those products are problematic from the clinical point of view because of impurities/undesired chemical phases which cannot be excluded although time- and costconsuming processing is performed. Another disadvantage are the varying CaP-phases (and thereby varying resorption kinetics in vivo) that can only hardly be controlled in such maritime or bovine products. Therefore, it was a break through in the field of bone substitute materials, when synthetically manufactured, highly pure calcium phosphates in the form of granulates and pastes were available on the medical-technical market in the end of the 1990 years. Small bone defects can be restored using these granulates without a medical risk.

However, the spongious-like structure of the bone cannot be remodelled using such granulates. With the help of the generative manufacturing techniques (rapid prototyping tools) it has become possible in the meantime, to build-up even large, three-dimensional structures that are adapted to the macro- (geometry) and microstructure (spongiosa) of the bone. As already mentioned, the process of bone remodelling – degradation of the bone substitute implant and successively build-up of new bone tissue – weakens after a defined duration intervall especially if large-sized scaffolds are used. Therefore, research activities worldwide focus on methods to stimulate the scaffold/bone remodelling process. In this context the methods of tissue engineering are used as well as techniques to couple growthstimulating factors to the surface of the scaffolds. Respective clinical studies have proved that especially Bone Morphogenetic Proteins (e.g. BMP-2) can stimulate the human body to accelerated build-up added bone tissue in the area of the bone defect. However, the desorption kinetics of the coupled proteins and thereby the kinetics of the resorption process of the mineral scaffold can only hardly be controlled. It is the objective of the research project BioMin to study these kinetics

in detail. With the help of the results of this project, strategies can be developed to specifically control the processes at the functionalized mineral surface.

Strategy To obtain the described objective, a detailed analysis of the chemical-physical processes between mineral surface and bone morphogenetic proteins on the one hand and of the biochemical interaction between BMP and native hard tissue on the other hand is required. Preliminary tests have shown that Bone Morphogenetic Proteins can be coupled especially via OH-groups onto the mineral surface. This finding requires the made-to-measure synthesis of a resorbable CaP-glass-composite to induce hydroxyl groups at the mineral materials surface.

Modern analytical methods on the sub-microand nanometer scale are required to analyze the mechanisms at the interface in detail.

Thus, especially Secondary Ion Mass Spectrometry (SIMS), and Transmission Electron Microscopy (TEM) will be performed. The experimental and analytical studies of the project will be accompanied by scale-bridging model calculations, which span from microscopic ‚first-principles’ calculations to simulations with approaches from macroscopic continuum theory. Especially the density functional theory will be a helpful numerical tool for the quantification of the reaction kinetics at the surface. With the help of density-functional theory basic quantities such as the binding strength at the protein-ceramic interface will be calculated on the basis of the quantum-mechanically derived electron density and serve as input to the classical modelling.

For BioMin a scale-bridging concept has been developed: learning from simulation results on the atomistic and mesoscopic scale for experiments on the microscopic and macroscopic scale. The project is spilt into four subprojects.

Thereby aspects within a wide area reaching from simulations on the nano scale to a clinical evaluation of the results will be investigat-

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ed. Accurately coordinated work packages in the field of material synthesis and analysis (RWTH Aachen), investigations concerning the protein coupling (University of DuisburgEssen), simulation of the sorption and desorption kinetics (TU Dresden, and Research Center Dresden-Rossendorf) and experimental resorption studies in vivo (Knappschaftskrankenhaus Bochum-Langendreer) are due to improve the understanding of processes proceeding on the interface of mineral surfaces and functionalizing proteins. On the basis of the expected results biologically modified bone grafts on a mineral base could be developed with an improved efficiency for individual patients and specific applications.

In the following chapters the objectives and workpackages of the four subprojects will be presented in detail.

Subproject 1: Bioceramic material development and analysis Department of Ceramics and Refractory Materials, Institute of Mineral Engineering, RWTH Aachen University Objective of subproject 1 The objective of the first subproject is the experimental development of tailored bioceramic composites based on calcium phosphates. This includes the synthesis of the materials and additionally the microstructural analysis. The different requirements, defined by the other subprojects must be considered for the development of the novel materials.

For the project partner from Essen, the surface of the materials must be functionalized in a way that the bone morphogenetic proteins can couple. This includes that active hydroxy groups are available on the surface of the bioceramic material. Hydroxy groups at the surface can be achieved by synthesizing a composite made of tricalcium phosphate and bioactive glass. It must be considered in this context that the partners from Dresden need accurate data of the materials. The more complex the developed composite is, the more dif-

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ficult and time-consuming is the numerical modeling process. Besides a composite made of tricalcium phosphate and bioactive glass, hydroxyapatite as well is a suitable material with respect to the requirement of hydroxy groups at the surface for protein coupling.

Hydroxyapatite, however, is not sufficiently biodegradable. The overall objective of the joint project is that the functionalized bioceramic material is controlled biodegradable in vivo. This final aim is represented by the clinical partner from Bochum as the ‚user’ of the developed product. This makes clear that a compromise will be made for the development of the materials within this project. On the one hand the fundamental mechanisms of the protein sorption/desorption process on the mineral surfaces must be investigated. On the other hand the clinical requirements for a subsequent application in vivo of a tailored composite material must be considered.

Work packages of subproject 1 Development of tailored bioactive CaP-bioglass composites In order to characterize the connection of the Bone Morphogenetic Proteins (BMP) on a surface, different types of substrates are necessary. The focus directs on the material class of calcium phosphates. Out of this material class there are to mention especially the tricalcium phosphates (TCP), in particular the beta modification of the TCP (β-TCP), and the hydroxyapatites (HA). From the phase pure synthesis up to any mixture ratio it can be reverted to the experience of the Institute of Mineral Engineering (GHI). Other calcium phosphates can also be synthesized at the GHI. However, these do not play an important role because of their lower importance in the clinical field. Furthermore, to examine the effect e.g. of other calcium phosphate ratios on the ceramic-BMP interface, there are also other calcium phosphates suitable (e.g. tetracalcium phosphate, calcium pyrophosphate, etc.).

A further material group are biocompatible glasses for the examination of the coupling

behavior between substrate surface and BMP. Such glasses are synthesized in the ternary system SiO2â&#x20AC;&#x201C;CaOâ&#x20AC;&#x201C;Na2O. The bioactive characteristics of the glass phase are depending on their composition. According to this, the properties of the glass can be varied from bioinert to bioresorbable. Furthermore the curvature of the surface (plane, convex, concave) could influence the chemical potential of the material with the possible result of different adsorption characteristics. A first glass fabrication specifically in this substance system was recently successfully manufactured at the GHI. It is another option to activate recrystallization of the glass by thermal treatment and to investigate its effect on the interface of substrate and BMP. Moreover, a composite material for a further substrate solid is offered by a combination of ceramic and glass material in a user-defined mixing ratio.

Manufacturing of samples Different samples especially pressed thin cylindrical specimens of the respective bioactive CaP-materials are manufactured for the coupling experiments with BMP. Besides the manufacturing of specimens the synthesis of different granulates and powders is planned for the coupling tests. The surfaces of the samples can be treated with different agents. The samples for the animal tests can be manufactured as cylindrical specimens in different sizes.

Variation/Optimization of the mineral materials On the basis of the experiments, coupling the spacer molecules to the mineral surface, the samples will be optimized with respect to the chemical composition and the different phases. Furthermore, the crystallinity and the surface morphology will be adapted. These steps of development should successively result in a material with the desired adsorption properties for the spacer molecule. Different adsorption properties of the monolithic materials and composites will result in different resorption kinetics. This will make it possible to adapt the resorption properties of the bone substitute to different applications.

Characterization of the materials and surface analytics The qualitative and quantitative amount of different phases in the substrate can be detected by the method of x-ray diffraction. The measurement itself guarantees a near-surface analysis. Dense materials like pressed pills have a detection area not deeper than 100 Âľm. In order to identify the phase content of a solid body, the solid first has to be pulverized. The components of the substrate are then statistically distributed and the phase contribution of the whole substrate can be measured with the same instrumentation. Furthermore this measuring technique can detect whether there are pure glassy phases or whether there are crystal fractions in the glass.

Scanning electron microscopy (SEM) can identify the surface morphology of the substrate.

The resolution reaches down to 300 nm. This measuring technique can characterize how rough and uneven the surface substrate is. A specifically manipulated surface, caused for example by polishing or sintering, can be qualitatively analyzed by this method. This way a reference can be established between coupling experiments and surface morphology. Moreover this measuring technique offers a determination of the chemical elements on the surface with the same given lateral solution.

The transmission electron microscope (TEM) at the GHI can detect structures down to atomic scales. In contrast to the SEM, limited by sample preparation, there is only a small area of the specimen presentable. However, with the TEM it is possible to detect crystal phases and to define their crystal structure. Thus, this measuring technique offers the advantage of a lateral resolution and the identification of individual crystal phases at the same time. Out of this, with the same lateral resolution, it is possible to determine if the examined solid is a crystal or a glass. Moreover the texture and surface morphologies can be detected in the STEM Modus.

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The secondary ion mass spectrometry (SIMS) is a measuring technique coming from the surface chemistry of solid states. This method is a highly sensitive analyzing tool with a detection limit down to ppm range. The ablation using ion etching can remove the edge layers of a sample. Therewith deeper located areas can gradually be analyzed as well. This is particularly interesting for degradation processes taking place at the surfaces of CaP materials at in vivo experiments, where also the first surface layers are ablated.

Subproject 2: Molecular dynamic simulations – Modelling the coverage of ceramic surfaces with growth proteins Department of Chemistry, Theoretical Chemistry, TU Dresden, and Institute of Ion Beam Physics and Materials Research, Research Center Dresden-Rossendorf Objective of subproject 2 The interactions within the contact area of the growth protein layer and the bone substitute ceramics determine how fast and over which

period of time the growth protein can deliver its bone morphogenetic effect. The aim of the present subproject is to quantify these interactions and thus at deriving the basic principles for a systematic optimization of the interface area and of the functionalized ceramic bone replacement system. As the relevant sorption processes span several length scales, the modelling will be performed with the help of the scale-bridging methods developed in the groups of the applicants. In this way, an overall description of the BMP sorption from the single protein up to the formation small protein agglomerates shall be achieved with the help of model systems, which are adapted to cover the relevant physical and bio-chemical processes at their own specific length and time scales.

Work packages of subproject 2 The project comprises three inter-related work packages (WP), which address the factors of influence on the sorption dynamics. The three topics and the corresponding modelling methodology are schematically depicted in Figure 1.

Figure 1: Sorption modi of the proteins on the mineral surface, relevant work packages (WP) und theoretical approaches. [Fig. 1 is cited on Page 5, line 43 in chapter ‚Work packages of subproject 2’]

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The key for an optimization of the sorption and desorption kinetics of the BMP molecules at the mineral surface is the protein-ceramic binding strength, mediated by an interfaceactive spacer molecule, which is bound to the surface. The BMP macromolecule can either be incorporated into the spacer layer as a physisorbed species that is weakly attached by non-bonding interaction (case A) or it is covalently linked to a suitable head group of the spacer molecule (case B); a direct interaction of the protein and the mineral surface is less favorable for a high coverage with BMP and a slow release of it. The type of the proteinspacer interaction determines the BMP release rate and the local BMP concentration. Therefore, the optimization of the spacer molecule itself and its interaction with the ceramic surface (WP 1) and with the reactive sites of the protein (WP 2) provides the basis for the understanding and optimization of the protein sorption kinetics (WP 3).

The theoretical study thus addresses the three important topics in corresponding WPs: WP 1: bonding of the Spacer at the mineral surface WP 2: spacer-protein interaction WP 3: time evolution of the protein concentration on the mineral surface Although the three WPs are inter-related they can be investigated in parallel, because the initial data for the model development can be taken from the experiments of the project partners. The experimentally determined structure of the mineral surfaces (WP 1), of the spacer and the protein molecule (WP 2) and especially data on the non-optimized sorption kinetics (WP 3) serve as starting values, which are refined by further calculations and transferred between the WPs and to the other subprojects. For WPs 1 and 2 mainly electronic structure and QM/MM hybrid methods will be employed to quantify the binding mechanism and bond strength within the spacer-protein layer on the ceramic surface. WP 3 comprises the modelling of the free and the spacercovered mineral surface with electronic struc-

ture methods and – together with the results from WP 1 and 2 – the parameter determination for the classical simulation of the protein sorption kinetics.

Subproject 3: Chemical and biological functionalisation Institute of Physiological Chemistry, Biochemical Endocrinology, University of Duisburg-Essen Objective of subproject 3 Present concepts are based on the hypothesis that the problems resulting from delayed healing and integration (i.e. resorption) of bone replacement materials can simply be solved by employing nanocrystalline minerals e.g. nanoapatites. Both bone and tooth dentin are mainly composed of highly ordered nanoscale carbonate/apatite (CAP) crystals on type I collagen fibrils. It is concluded that the preparation of nanoscale minerals alone will suffice in simulating a physiological biomineralization and with that creating an optimal bone replacement material. It is often overlooked that the involvement of cells is decisive for the mineralization process i.e. the synthesis of an organic matrix and the initiation of the mineralization process itself. It has been known for decades that in bone-generating tissues of mammals biomineralization is effected by highly specialized extracellular organell-like structures so-called »matrix vesicles«. These vesicles are formed by budding from chondrocytes or osteoblasts both during the primary and secondary mineralization phases. This physiological mechanism of cell-mediated biomineralization could also be shown in an osteogenic cell line of new-born mouse calvarial cells (MC3T3-E1 cells). This is of special interest here, since MC3T3-E1 cells have been employed by the proposer for many years. The exact mechanism of biomineralization in mammals via matrix vesicles is still largely unknown although it is clear that phospholipids, acid proteoglycans and acid proteins such as annexin II and annexin V play an important role. Most important, cell mediated mineral-

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ization requires the interaction of a number of different growth factors that either promote or inhibit this process. Among others are bone morphogenetic proteins (BMPs), a family of growth factors that stimulate proliferation of chondrocytes and osteoblasts and cause increased matrix production in each cell type.

From the text above it is clear that mineralization in mammalian bone occurs in an extracellular membrane-protected space (matrix vesicles) under the control of various growth factors. Although a true simulation of these processes in vitro is not possible at present, in groundwork we have succeeded in immobilizing recombinant human bone morphogenetic protein 2 (rhBMP-2) on the biogenic mineral surfaces. In this project it is therefore proposed to synthesize and employ biofunctionalized, bioactive minerals (e.g. coated with immobilized BMP) in order to attract bone precursor cells by chemotaxis followed by bone induction and simultaniously offering osteogenic minerals for inducing, guiding and accelerating bone growth.

Work packages of subproject 3 The major aim of the subproject is to acquire basic knowledge for understanding the process of ÂťfunctionalizingÂŤ geogenic and biogenic mineral surfaces and elucidating the causal relationship of biocoating in respect to the elicited biological effects. A major emphasis will be on the interaction of biologically active proteins with pure and chemically modified surfaces and on the underlying basic mechanisms of protein-immobilization. It is suggested to immobilize the bone growth factor rhBMP-2 on biogenic monophasic and biphasic hydroxy apatite (HA) and tricalcium phosphate (TCP) mineral surfaces such as Algipore and Algisorb (Algoss GmbH), highly polished glasses and glass ceramics. Work packages include: (i) preparation of recombinant human BMP-2 and genetic variants, (ii) functionalization and biocoating of mineral surfaces with rhBMP-2 and antibiotics, (iii) measurement of protein sorption and sorption kinetics on glass model surfaces by evanescent wave technology, (iv) in vitro testing of biocoated

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surfaces, and (v) preparation of sterile biocoated implant surfaces for in vivo experiments.

Subproject 4: Animal experiments on functionalized bioactive implants Clinic for Surgery, Department of Trauma Surgery and Orthopaedics, Knappschaftskrankenhaus BochumLangendreer Objective of subproject 4 After the production of novel biomaterials and their evaluation by biomaterials scientists, e.g. at RWTH Aachen University as well as evaluation of protein-attachment at the University of Duisburg-Essen and after simulation of sorption and desorption kinetics of the implants at TU Dresden and Research Center DresdenRossendorf, an in vivo evaluation of the produced biomaterials is demanding.

Only this procedure generates results, which are helpful to choose materials for clinical applications. Therefore produced biomaterials will be implanted for 7, 28, 84 and 168 days.

After sacrificing the animals (preferably chinchilla-rabbits) light microscopicalâ&#x20AC;&#x201C;analysis of regenerated bone as well of degradation mechanisms of the implants (material response, host-response) has to be performed.

Additionally, scanning- and transmission electron microscopy for further analysis of degradation mechanisms is demanding. A histomorphometrical evaluation is important to describe the bone regeneration as well as the kinetics of the implant degradation. These methods allow to draw valuable conclusions about the process of bone-generation and implant degradation.

Work packages of subproject 4 For evaluation of newly created biomaterials a well established animal model should be used.

Therefore, implantation behind the patella sliding plane in the distal femur of Chinchillarabbits will be performed. The advantage of this model is, that there are many former results about other implant materials available.

For implantation, cylindrical implants have to be produced. Explantation of the implants has to be performed at 7, 28, 84 and 168 days. These time intervals are important, since these days allow an exact description of bone regeneration as well as degradation kinetics of the implants.

References Aebli N, Stich H, Schawalder P, Theis JC, Krebs J (2005). Effects of bone morphogenetic protein-2 and hyaluronic acid on the osseointegration of hydroxyapatite-coated implants: An experimental study in sheep. J Biomed Mater Res 73A: 295–302.

Many other implant materials were evaluated by using this animal model and these time intervals. For the present experiment, functionalized implants have to be used, as well an non-functionalized implants as a negative control. We need to check at least 6 implants per material and time interval, meaning that 3 animals are necessary. Using 4 time intervals, 12 animals are necessary.

Blom JE, Klein-Nulend J, Klein CPAT, Kurashina K, van Waas MAJ, Burger EH (2000). Transforming growth factor-1 incorporated during setting in calcium phosphate cement stimulates bone cell differentiation in vitro. J Biomed Mater Res 50: 67–74.

Light microscopically evaluation This type of histological evaluation is the basis to describe the process of bone and tissue regeneration as well as the degradation of the produced implants. If there is tissue regeneration (e.g. bone) and accompanying biomaterial degradation this can be described according to light-microscopy. Special stainings have to be used (e.g. von Kossa/Fuchsin; ToluidinBlau, Giemsa etc.) According to the different time intervals, the incorporation of the implant materials can be described quantitatively.

Additionally, due to histomorphometrical analysis, the amount of newly formed bone can be quantified. The degree of implant degradation can be measured as well.

Ultrastructural Evaluation By using electron microscopy (scanning and transmission electron microscopy) structural changes of biomaterials in the range of some micrometers can be detected. These evaluations are important especially for characterizing mechanisms of implant degradation.

According to the aim of achieving bone regeneration during implant degradation this is of outermost importance. If necessary, single specimens can be used for secondary ion mass spectroscopy.

Deisinger U, Irlinger F, Pelzer R, Ziegler G (2005). 3D-Druck von HA-Scaffolds zur Verwendung als Knochenersatzmaterial. Fortschr Ber Dtsch Keram Ges – Verfahrenstechnik 19: 147–154.

Duarte HA, Heine T, Seifert G (2005). DFTxTB – a unified quantum-mechanical hybrid method. Theor Chem Acc 114: 68–75.

Fischer H, Niedhart C, Kaltenborn N, Prange A, Marx R, Niethard FU, Telle R (2005). Bioactivation of inert alumina ceramics by hydroxylation. Biomaterials 26: 6151–6157.

Fischer H, Wilkes J, Bergmann C, Kuhl I, Meiners W, Wissenbach K, Poprawe R, Telle R (2006). Bone substitute implants made of TCP/glass composites using selective laser melting technique. cfi/Ber DKG 83: 57–60.

Gemming S, Seifert G (2006). SrTiO3(001)| LaAlO3(001) multilayers: A density-functional investigation. Acta Mater 54: 4299–4306.

Gemming S, Seifert G (2007). Nanocrystals: Catalysts on the edge. Nat Nanotech 2: 21–22.

Gross UM., Müller-Mai CM, Voigt C (1990).

The interface of calcium phosphate and glassceramic in bone, a structural analysis. Biomaterials 11: 83–85.

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Jennissen HP (2002). Accelerated and improved osteointegration of implants biocoated with bone morphogenetic protein 2 (BMP-2).

Annals N Y Acad Sci 961: 139–142.

Jennissen HP, Zumbrink T (2004). A novel nanolayer biosensor principle. Biosens Bioelectron 19: 987–997.

Jennissen HP (2005). Boundary-layer exchange by bubble: A novel method for generating transient nanofluidic layers. Phys Fluids 17: 100616-1-100616-9.

Kaltenborn N, Sax M, Müller FA, Müller L, Dieker H, Kaiser A, Telle R, Fischer H (2007).

Coupling of phosphates on alumina surfaces for bioactivation. J Am Ceram Soc 90: 1644–1646.

Khalyfa A, Vogt S, Weisser J, Grimm G, Rechtenbach A, Meyer W, Schnabelrauch M (2007).

Development of a new calcium phosphate powder-binder system for the 3D printing of patient specific implants. J Mater Sci Mater Med 18: 909–916.

Laffargue P, Fialdes P, Frayssinet P, Rtaimate M, Hildebrand HF, Marchandise X (2000). Adsorption and release of insulin-like growth factor-I on porous tricalcium phosphate implant. J Biomed Mater Res 49: 415–421.

Loppacher C, Zerweck U, Eng LM, Gemming S, Seifert G, Olbrich C, Morawetz K, Schreiber M (2006). Adsorption of PTCDA on a partially KBr covered Ag(111) substrate., Nanotechnology 17: 1568–1573.

Müller-Mai C, Voigt C, Knarse W, Sela J, Gross UM (1991). The early host and material response of bone-bonding and non-bonding glass-ceramic implants as revealed by scanning electron microscopy and histochemistry. Biomaterials 12: 865–871.

Müller-Mai CM, Amir D, Schwartz Z, Sela J, Boyan BD, Wendland H, Gross UM (1991).

Ultrastuctural histomorphometry of extracellu-

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lar matrix vesicles in primary calcification around bone-bonding and non-bonding glassceramics. Cell Mater 1: 341–352.

Müller-Mai CM, Stubb SI, Voigt C, Gross U (1995). Nanoapatite and organo apatite implants in bone: Histology and ultrastructure of the interface. J Biomed Mater Res 29: 9–18.

Mundy GR (1996). Regulation of bone formation by bone morphogenetic proteins and other growth factors. Clin Orthop 234: 24–28.

Peters F, Reif D (2004). Functional materials for bone regeneration from beta-tricalcium phosphate. Materialwiss Werkst 35: 203–207.

Schwartz Z, Swain L, Sela J, Gross U, Amir D, Kohavi D, Müller-Mai C, Boyan B (1992). In vivo regulation of matrix vesicle concentration and enzyme activity during primary bone formation. Bone and Mineral 17: 134–138.

Seifert G (2007). Tight-Binding Density Functional Theory: An Approximate Kohn-Sham DFT Scheme. J Phys Chem A 111: 5609–5613.

Zurlinden K, Laub M, Jennissen HP (2005).

Chemical functionalization of a hydroxyapatite based bone replacement material for the immobilization of proteins. Materialwiss Werkstofftech 36: 820–827.

Identification and modification of the surface properties of calcite fillers as a basis for new, highly filled adhesives Diedel R. (1), Geiß P. L. (2)*, Wittwer W. (3) (1) Forschungsinstitut für Anorganische Werkstoffe – Glas/Keramik-GmbH (FGK); e-mail: Diedel@FGK-Keramik.de (2) University of Kaiserslautern, Department Mechanical and Process Engineering, Workgroup Materials and Surface Technologies (AWOK); e-mail: geiss@mv.uni-kl.de (3) Kömmerling Chemische Fabrik GmbH, e-mail: Wittwer@Koemmerling.De *Coordinator of the project: Prof. as Jun.-Prof. Paul Ludwig Geiß, University of Kaiserslautern

Abstract The flow behaviour of adhesives that is crucial for the processing and application can be significantly influenced by fillers, such as calcium carbonates due to the physical and chemical interaction between the filler particles and the polymer matrix. Furthermore the mechanical characteristics after curing can also be controlled to a certain extend by the use of filling compounds with predefined surface properties.

to feature intrinsic characteristics which have not yet been examined sufficiently and whose effect on the processing and product characteristics of highly filled reactive adhesive systems are still unknown.

In this project the influence of different types of natural calcites (chalks) as mineral filling compounds of adhesives is to be investigated regarding the processing and handling properties (before curing) as well the material properties (after curing).

Furthermore the influence of the surface condition (morphology and chemistry) of the fillers on the characteristics of the adhesive compounds is taken into account through the variation of the chemical surface modification of the particles. The interactions of the calcite particles (Figure 1) with the polymer matrix and the resulting effect on the flow behaviour during processing and application, as well as on the mechanical behaviour after the curing in adhesive compounds, are of particular interest.

Introduction Natural calcium carbonates, which are used as fillers in adhesive systems to improve processing and performance characteristics, show varying processing properties in routine outgoing goods inspections despite unvarying particle-specific measurements (e.g. density, chemical composition and particle size distribution). This means that the raw material has

It is the objective of this research project to examine the influence of different natural calcium carbonates on the processing behaviour of adhesives in a liquid-pasty state and the technical performance characteristics in the cured state and to correlate them with the particle-specific morphological and chemical characteristics of synthetically precipitated fillers. The project results shall provide a basis for

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Figure 1: Scanning Electron Microscope image of a milled calcite particle

developing compounds with improved processing characteristics (rheological stability in self-levelling substance systems and stability in non-sagging blends with reduced viscosity and higher thixotropy).

State of technology Fillers are fine aggregates to the adhesive, which are at most adhesively bonded with the polymer. In most cases they are inorganic. The importance of the fillers is often underestimated, and in many cases it is assumed that they are only used to decrease the amount of expensive polymers in the adhesive. However, fillers can achieve much more.

They can be used, among others purposes, to targetly influence the shrinking behaviour, the modulus of elasticity, the thermal conductivity or the thermal expansion coefficient of the adhesives. Fillers can decisively influence the viscosity and the flow characteristics of an uncured adhesive. Fillers with active surfaces are able to influence the curing kinetics of adhesives and the structure of the polymer matrix. This is one reason why fillers are also used to improve thermal stability of adhesives. In addition, filler-induced inhomogeneities in the polymer matrix are often advantageous to the fracture mechanics. For instance, they can work as tougheners and hence improve the impact resistance of adhesives and adhesively bonded joints. Thus, fillers are important components in the formulation of adhesives, according to the given examples of their efficiency.

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Despite the long-term, regular use of natural minerals as fillers problems occur at regular intervals regarding the process and product stability (rheological variations in the form of altered settling and flow behaviour, disturbances when being applied e.g. in the automotive assembly, window and industrial floor construction). There are numerous open questions about the chemical and physical formation of the mineral surfaces, be it geogenically as a result of different deposit conditions (diagenesis, degree of crystallinity) or the subsequent preparation (among others particle distribution, particle form, particle topography, specific surface, grinding additives adhered to the mineral surface).

Previous papers (Berghoff, Gysau, L端hr and Janowski) take up the basic characteristics and mode of action of fillers in polymer systems.

However, open questions remain about the formation of mineral surfaces, which represent the boundary and hence the immediate reactive surface towards the polymer components.

In addition, there are still no concrete papers about the correlation between the characteristics of uncoated carbonates and the processing characteristics of adhesive systems.

Methodology The project starts with the identification of the intrinsic, chemical-physical material characteristics of the filler particles. The focus of the test is on the mineral surfaces because in the subsequent industrial use they represent the

active interfacial surfaces towards the polymer networks. Tests by means of mercury pressure porosimetry and nitrogen adsorption play an important role in the assessment of influences of microporous particles unknown so far. In addition to the »natural« interfacial areas of the calcites, the influence of the organic grinding additives, which are applied in raw material preparation and partially still adhere to the surface on the processing characteristics, is to be examined. On the basis of the mineral surface examination, coating methods are applied using stearic acid and its derivatives, which are adjusted to the calcites’ surface and the chemical and physical interaction of the adhesive systems.

In order to achieve a process-capable adhesive modification for the realization of application-specific characteristics, we have to learn more about the filler-polymer-interactions in order to be able to stabilize them in the manufacturing process and to manipulate them deliberately. The objective is the development of compounds with improved characteristics (rheological stability in self-levelling substance systems and in non-sagging blends with decreased extrusion viscosity and higher thixotropy, Figure 2).

Apart from sagging during application, the storage stability (sedimentation) and the technical processability in conveying and blending systems, as well as the extrudability in cartridge processing, which is especially impor-

tant for the manual preparation in craft application, of the mineral filled adhesive systems, are influenced by the alteration of the timedependent rheological characteristics. At this point, improving the processing characteristics leads to an immediate and noticeable increase in efficiency and on the one hand adds to an increase of the net product both for the user and the adhesive manufacturer, and on the other hand makes a differentiation towards competition possible.

The influence on the curing reaction of adhesives is determined by means of thermal and thermomechanical analysis. The change of mechanical properties and of the adhesive behaviour is established by means of stressstrain analyses of substance samples, as well as by means of shear stress-strain measurements of adhesive-bonded compounds. The influence on brittleness by modification with calcitic additives is established by means of notched-bar impact tests.

In the research project, the main influencing parameters of the structure- or propertyeffect relationship for the system of unmodified and modified, ground and natural calcitic fillers for adhesive applications should be identified and characterized. Regarding the parameters, the test matrix contains the following factors: – geological source of raw materials – grinding process and grinding aids

Figure 2: Calcitic mineral fillers give industrial adhesives their special rheological properties

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– grinding degree (entire spectrum of particle size distribution) – modification state (uncoated, coated with stearates)

– viscosity change depending on storage time over a period of 6 months – thixotropy characteristic (adhesive bead adhesion and sagging)

The matrix of the filler parameters is then mirrored in and correlated with the physically and chemically measurable property profile. Here, the property profile is divided into factors of the »dry« filler systems and the measurable factors which interact with interfacial areas of liquids, particularly of the polymer basis component as exemplary polyether pre-polymer formulation. The resulting analytical effort is the following:

The characteristic material properties of adhesives after curing are quantified by means of the following methods:

»Dry fillers«: – porosity (Hg pressure porosimetry) – mineral surface (BET nitrogen adsorption) – surface topography (AFM) – chemical composition of the particle surface (Tof-SIMS, XPS) – mineral composition and crystallinity (X-ray diffractometry) Fillers and dispersion (dissolver, defined weight ratio filler-pre-polymer): – viscosity depending on shear rate (plateplate viscosimeter) – zeta potential in aqueous suspension (PCD measuring cell) In the next step, the objective property criteria are indicated with regard to their effect on the quality establishing factors of the »adhesive« system. Technical methods, which are specific to the use of adhesives, are applied here, in contrast to the analytical techniques for the objective property characterization.

These methods are divided into the fields of storage stability and processing properties (before curing), and »material properties« (after the curing process). The methods applied in the course of this test step are the following: – sedimentation and phase segregation during storage over a period of 6 months

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– curing kinetics (DSC measurements) – stress-strain behaviour (with polymer test specimens according to DIN EN 527-2) – adhesion (tensile shear specimens according to DIN EN 14869-2) – fracture toughness (notched-bar impact test) Thus, it is the aim of the research project to identify an objectively and physically measurable property corridor for fillers, which results in a safe process effect with regard to the technological target values of storage and process properties within a defined tolerance window, but without negatively influencing the cured material properties beyond the tolerance limits.

Summary The project is designed so as to take into consideration the whole process chain starting from the natural mineral raw materials up to the end product. Kömmerling Chemische Fabrik GmbH as an internationally recognized manufacturer of industrial adhesives is supported by two research facilities which cover the whole process chain. The Forschungsinstitut Glas/Keramik, a branch institute for natural mineral raw materials, covers the first part of the process chain, from the evaluation of the raw materials up to the process capability tests. The research group AWOK at the University of Kaiserslautern, is responsible for the evaluation of the internal polymer network structure and their curing reactions in interaction with the fillers, as well as for the evaluation of adhesive properties after curing by means of standardised mechanical test methods.

On account of the expected results, the risk of deviating batches due to fluctuations in the supply of raw materials is reduced. The knowledge of the technically relevant characteristics provides the basis of the selection of cost-optimized sources of raw materials. As a result the development cycles of new adhesive products with improved application characteristics are shortened and new adhesive products with improved characteristics will be available to e.g. the transportation or the building and construction industry.

References Berghoff, U. (2007): Calciumcarbonat – Neue Anforderungen an mineralische Modifier für Kunststoffe; SKZ-Seminar Peine, 4.12.2007.

Gysau, D. (2005): Füllstoffe; Vinzentz Network GmbH & Co.KG; 214 S. Lühr, J., Janowski, F. (1991); Zur Bestimmung des Modifikatorgehaltes von stearinsäureund titanat-modifizierten CaCO3-Füllstoffen; Angew. Makromol. Chem. 205 (1993), S. 1–17.

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Reactivity of Calcite/Water-Interfaces (RECAWA): Molecular level process understanding for technical applications Neumann T. (1)*, Bosbach D. (2), Winkler B. (3), Herold G. (4), Vucak M. (5), Fischer U. (6), Plöhn J. (7) (1) Universität Karlsruhe (TH), Institut für Mineralogie und Geochemie, e-mail: thomas.neumann@img.uni-karlsruhe.de (2) Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung, e-mail: bosbach@ine.fzk.de (3) Goethe Universität Frankfurt, Institut für Geowissenschaften, e-mail: b.winkler@kristall.uni-frankfurt.de (4) Universität Karlsruhe (TH), Institut für Massivbau und Baustofftechnologie, e-mail: gunther.herold@ifmb.uni-karlsruhe.de (5) Schaefer Kalk GmbH & Co. KG, e-mail: marijan.vucak@schaeferkalk.de (6) Rheinkalk Akdolit GmbH & Co. KG, e-mail. Uwe.Fischer@rheinkalk.de (7) Lafarge Zement Wössingen GmbH * Coordinator of the project: PD Dr. Thomas Neumann, Universität Karlsruhe (TH)

Abstract RECAWA intends to develop a fundamental understanding of the reactivity and dynamics of calcite surfaces during crystal growth in aquatic systems. Specifically, the mechanisms of crystal growth and the role of dissolved inorganic and organic species will be studied. The interactions between the aquatic system and the calcite surface are complex, and their control would provide opportunities to develop and improve a number of technical applications.

The planned investigations include studies of the effect of the adsorption and incorporation of foreign ions/molecules on the reactivity of calcite surfaces, and of the effect of organic and inorganic additives on the crystal growth of calcite. Experimental data will be generated in four sub-projects focussing on industrial applications such as water treatment technology, cement processing and PCC production. The experimental results will be complemented by molecular modelling studies, which will provide

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the basis for a conceptual model regarding the reactivity of calcite surfaces.

1. Introduction Carbonates cover approximately 20% of the earth’s surface. They are of high economic interest and represent an important resource for the chemical and pharmaceutical industry, the glass and paper industry, the construction material industry, for the production of fertilizers and for the quality of drinking water. Due to their abundance, carbonates are considered as mineral mass products.

The reactivity of calcite, the thermodynamically most stable and most abundant carbonate phase in nature plays a prominent role for numerous natural processes in our environment. Calcite affects in various ways and to a significant extend the global circulation of matter. Calcite regulates the pH and controls the chemical composition of various natural

Figure 1: Atomic force microscopic image of the calcites surface (1 × 1 µm)

aquatic systems. Calcite can structurally incorporate and immobilize biologically active elements such as phosphorus, calcium, magnesium, iron, arsenic, selenium and other toxic trace elements. The understanding of the immobilization of dissolved species must include thermodynamic considerations as well as kinetic aspects, which contribute to various sorption mechanisms on different time scales. Adsorption reactions are usually rather fast compared to co-precipitation reactions. In particular with respect to kinetic aspects of trace element sorption, the molecular level reactions at the mineral/water interface need to be understood.

Different aspects of technical applications can be derived from the fundamental knowledge about the reactivity of calcite/water interfaces (Fig. 1). Calcite crystal growth is affected by organic and inorganic additives. This can be used to produce specific crystal/particle morphologies and sizes and it is important e.g. for the production of technical precipitated calcium carbonate products (PCCs). Sorption (adsorption, co-precipitation) of toxic components takes place preferentially on certain reactive surface places. A »tuning« of the mineral surface may lead to an optimization of the pollutant uptake by the mineral. So far, various studies have focused on a limited number of analytical methods, which provide not necessarily a coherent picture of the reactivity of calcite surfaces.

2. Aim and concept of RECAWA RECAWA investigates the molecular level processes at calcite/water interfaces via an integrated approach using a suite of analytical (AFM, µXRF, µXRD, µXANES, µEXAFS, GIXAFS) as well as computational techniques (Fig. 2).

The complementary atomistic modelling studies planned here will lead to a deeper understanding of the relevant processes occurring on calcite surfaces on an atomistic length scale. After a careful test of their applicability, it is envisaged to investigate the interactions between molecules and surfaces »in silico« before carrying out complex experiments. The quantitative interpretation of spectroscopic investigations will also be based on atomic models as well.

The four subprojects of RECAWA are to a large extent experimentally as well as analytically oriented and will generate fundamental data with respect to the dynamics of surface reactivity during trace element incorporation and during the formation of surface structures by selective interaction of inorganic and organic additives with distinct surface sites.

The experimental data will be complemented by molecular modelling studies, which will provide the basis for a conceptual model regarding the reactivity of calcite surfaces. All parts of the project involve close collaboration with industrial partners, which intend to use the scientific results in various ways.

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Figure 2: RECAWA concept showing the connection of fundamental research works with technical applications. A suite of analytical as well as computational techniques will be applied to work on the different research topics

2.1 Sub-project A »Immobilization of environmental-relevant trace elements at calcite surfaces« (FZK-INE, UF-IfG, Rheinkalk Akdolit GmbH & Co. KG) The sequestration of dissolved contaminants at calcite surfaces occurs via adsorption, ion exchange processes and/or by co-precipitation.

Many studies have demonstrated a significant site selectivity in trace element incorporation during calcite crystal growth. Factors such as charge and ionic size of the impurity introduced and the crystallographic orientation of the calcite surfaces play a major role in this process.

The adsorption and retention of divalent cations by calcite surfaces has been extensively studied with various analytical techniques.

Reeder (1996) studied the incorporation of Co, Zn, Cd and Ba during calcite crystal growth. The author used synchrotron µXRF and demonstrated that these trace metals exhibit different preferences for incorporation among multiples surface sites present on calcite face during spiral growth. Chada et al.

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(2005) investigated the uptake of Cd and Pb using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The authors showed that the uptake of Cd by calcite was greater than that of Pb. EXAFSstudies demonstrate that Cu(II) and Zn(II) ions coordinate at the Ca sites on the calcite surface, forming mononuclear inner-sphere adsorption complexes (Elzinga & Reeder 2002). The effect of dissolved Zn, Co, Pb, Mg, and Ca on the uptake of Cd at CaCO3-surfaces has been investigated by Koehler et al.

(2007). The study showed that Cd removal occurs by surface precipitation of otavite. The other divalent metals have a significant effect on the removal of Cd. Especially Pb and Zn outcompete Cd for the dissolving carbonate ions and thus decrease significantly the Cd removal rates.

Anions can also be bound to calcite surfaces.

Because of the high toxicity of As, the immobilization of arsenate and arsenite ions, the most abundant aqueous species, from water

are of major concern. Calcite, in particular, may significantly control the mobility of arsenite in water and soils by adsorption processes.

The location and orientation of arsenite incorporated at the calcite surface from aqueous solution was investigated by Cheng et al.

(1999). The study shows that arsenite is located at the carbonate position. Furthermore, EXAFS investigations by Alexandratos et al.

(2007) suggest the presence of arsenate, in both adsorption and co-precipitation samples as a tetrahedral AsO43– complex. However, synchrotron µXRF investigations from Alexandratos et al. (2007) show an inhomogeneous distribution of AsO43– complexes at the calcite surface. The –vicinal faces of the crystal plane are distinctively enriched in arsenate compared to the +vicinal faces. The results imply that bulk partition coefficients for As(V) depend on the availability of different calcite surface sites.

The element Se is also potentially hazardous to human health. The uptake of selenite from dilute aqueous solutions onto calcite cleavage surface was studied with XPS (Cheng et al.

1997). Selenite was found to selectively adsorb at the calcite surface forming a solidsolution of the form Ca(SeO3)x(CO3)1–x.

The mentioned studies demonstrate that calcite can not only be a very efficient material in trace element fixation, but also that the application of surface sensitive analytical methods lead to an molecular level understanding of the reactivity at calcite/ water interfaces.

Therefore, we intend to investigate the molecular level processes at calcite/water interfaces via an integrated approach using a suite of analytical as well as computational techniques (AFM, µXRF, µXANES, µEXAFS, GIXAFS). The research will focus on selected cationic and anionic trace elements of environmental importance (Cd, Pb, As, Se, U). The goal is to develop, also by using additives, optimal conditions for the efficient and sustainable trace element uptake by calcite surfaces and applying this knowledge to water treatment procedures.

2.2 Sub-project B »Fixation and phase transformation of phosphate at calcite surfaces« (UKA-IMG, UF-IfG, Rheinkalk Akdolit GmbH & Co. KG) Eutrophication of water bodies is one the most severe environmental problems in Germany and Worldwide. Eutrophication results through the discharge of nutrient rich waters from urban, agricultural and industrial sources. It is well known that the availability of phosphate, as the limiting nutrient, is crucial for increased primary production. As a consequence, in many countries, which obtain their drinking water mainly from lakes and reservoirs, the supply of clean drinking water without expensive water treatment is threatened. Therefore, the immobilization of dissolved phosphate in eutrophic water bodies is a promising approach to solve this problem.

The mineral calcite has a point of zero charge at pH 10, while many other minerals have negative surfaces already at pH values <7.

Therefore, in most waters calcite exhibits a positive surface charge and can be used for anion adsorption. In the past, calcite was used successfully for the remediation of eutrophied water to immobilize dissolved phosphate (Babin et al. 1994, Prepas et al. 1997, Hart et al. 2003). In comparison to other remediation measures, e.g. application of aluminium and iron minerals, ventilation of water bodies or clearing of nutrient rich mud from lakes, the calcite application is an environmental friendly and inexpensive measure. Laboratory tests demonstrate the success of this measure and show that a calcite barrier can reduce the phosphate flux from nutrient-rich sediments to the water body by up to 90% (Fig. 3). The mechanism of phosphate fixation at the calcite surface is decisive for the efficiency and sustainability of this measure (Berg et al. 2004).

The mechanism and capacity of the P-fixation is controlled by the calcite saturation of the water. The P-fixation occurs via adsorption, coprecipitation and/or crystal growth. Adsorption processes take place, if the water is in equilibrium or slightly supersaturated with respect to

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Figure 3: Effect of calcite capping to reduce the phosphate flux from anoxic sediments into the water column derived from column experiments

calcite. Under these conditions P can also be co-precipitated with CaCO3. During conditions of calcite sub-saturation, the mineral dissolves and thus the Ca2+ activity rises, leading to the precipitation of a Ca-P-phase at the calcite surface (Berg et al. 2004).

A further calcite application exists in the recuperation of phosphate from wastewater and sewage sludge. Frequently, sewage sludge is mineralized by wet oxidation and hydrolysis.

Phosphate can be sequestered from this solution and processed as a valuable fertilizer resource. Depending upon the hydrochemical conditions the uptake of phosphate by calcite takes place as surface adsorption or via co-precipitation. The efficiency and capacity of phosphate uptake by calcite is crucially for the quality of the fertilizer product.

Recent laboratory tests show that the fixation of phosphate on calcite surfaces depends strongly on its solute concentration and takes place as a multi-stage process (Eiche et al.

2008). Depending on the residual P-concentration in solution, the sigmoidal shaped isotherms can be divided into three sections indicating different processes responsible for the P-fixation on calcite surfaces. Adsorption

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prevails in equilibrium with lowest residual Pconcentrations. The inflection of the isotherm at moderate residual P-concentrations suggests that precipitation and transformation of a Ca-P compound becomes dominant. This is supported by characteristic Ca/P-ratios for different Ca-P-compounds (β-Tri-Calcium-Phosphate, Octa-Calcium-Phosphate). On the new surface phosphate ions again are fixed by adsorption. The kind of P-bonding is crucial for sustainable phosphate immobilization on calcite surfaces. While pure adsorption processes are reversible, the development of a thermodynamically stable Ca-P-phase, like hydroxylapatite, will lead to a lasting immobilization of phosphate (Steefel & van Cappellen 1990, Staudinger et al. 1990, House 1999).

Until now, the suggested mechanisms of phosphate fixation and its transformation at the calcite surface are based only on results of macroscopic experiments. A detailed understanding of the molecular processes is an important task of this subproject.

In order to study the interaction of dissolved phosphate and calcite surfaces in detail, macroscopic sorption experiments will be carried out under various hydrochemical conditions (concentration of solute phosphate and

suspended calcite, calcite saturation of water, physical properties of calcite grains). Calcite surfaces will be investigated by surface sensitive analytical techniques, such as AFM, µXRF, µXAS, µXRD, which allows the quantification of phosphate concentration and the characterisation of the phosphate speciation at the mineral surface. In addition, in situ AFM experiments will be carried with changing phosphate concentration and calcite saturation of the water. These experiments allow observing the structural changes of the surface during the phosphate uptake.

The experimental results will be systematized by molecular model calculations. This leads to a molecular level understanding of phosphate fixation mechanisms and phase transformation of phosphate at the calcite surface. With this knowledge calcite can be applied more efficiently to remediate eutrophic waters and to accumulate phosphate from waste water under variable hydrochemical conditions.

2.3 Sub-project C »Surface modification of PCC crystals« (UKA-IMG, FZK-INE, UF-IfG, Schaefer Kalk GmbH & Co. KG) The industrial application of PCC (precipitated calcium carbonate) depends to a large extent on the morphology and size of the calcite crystals (Fig. 4). The control and design of a desired crystal morphology and crystal size can be achieved by introducing inorganic and organic additives during crystal growth. Crystal growth is controlled via selective interaction

(e.g. adsorption) of additives with distinct surface sites (e.g. kink sites).

Here, we intend to control crystal growth of calcite by inorganic and organic additives within an integrated approach. As a prerequisite, the molecular level reaction mechanisms need to be unravelled. This will be achieved by a combination of modern state-of-the-art spectroscopic and microscopic methods as well as molecular modelling and classical crystallisation techniques. Furthermore, it is intended to study experimentally as well as numerically the stabilisation/aggregation of micro crystals (<1 µm).

Precipitation processes in aquatic systems are in general quite complex and numerous reactions can take place on a molecular level. In most cases it is therefore not possible to develop a molecular level process understanding on the basis of macroscopic empirical observations.

Calcite surfaces can also be functionalised in order to optimize their wetting behaviour in aqueous and organic liquids and melts. Further interesting applications include the dispersion of fillers/pigments, the incorporation of calcite in a polymer matrix and the use of calcite as a carrier in the pharmaceutical industry This part of the project can be structured in 5 steps: (1) Selection of relevant additives: It is intended to study polymeric inhibitors (e.g. poly

Figure 4: SEM-image of precipitated calcium carbonates (PCCs). Schaefer Precarb 200 is a typical PCC-product used as filler material by the paper industry

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(2)

(3)

(4)

(5)

acrylic acid/sodiumpolyaccrylate, poly aspartic acid, phosphonates), non-ionic polymers (polyvinylalcohol), carboxylic acids (e.g. citric acid, tartaric acid), polyelectrolytes (polystyrensulfonate), sodiumpolyphosphate, saccharide, and saccharite-derivates, chelators such as EDTA. The description of the macroscopic crystal morphology as a consequence of distinct additives will be investigated systematically.

This will provide a first indication of specific interactions with carbonate surfaces.

Furthermore, PCC compounds will be characterized by XRD with respect to crystallite size and strain.

The quantification of the precipitation kinetics is also a key information for further studies. For such experiments it has to be ensured that precipitation occurs exclusively under surface reaction controlled conditions (in contrast to transport/diffusion controlled conditions).

On the basis of these macroscopic observations, the main focus will be on the nanotopography of calcite surfaces during crystal growth using atomic force microscopy. Here we will study the reactivity of molecular steps as well as the surface roughness. This information provides unambiguous indications for specific interactions between additives and distinct surface sites. The characterisation of the atomic calcite / water interface structure will be another important aspect within this part of the project. Modern x-ray diffraction techniques using a synchrotron xray source allow such in-situ investigations.

As a consequence, relaxation as well as potential surface reconstructions can be identified. The nanotopography as well as the atomic surface structure provides key information with respect to the effect of the selected additives. Furthermore, this information represents base-line information for molecular modelling procedures.

The transferability of the molecular level process understanding to conditions for industrial PCC production will be demonstrated. Potentially new optimized crystal

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morphologies will be evaluated for industrial applications (paper, paint). Furthermore the achieved developments can be used for new applications.

2.4 Sub-project D ÂťReactivity of calcite surfaces during cement processingÂŤ (UKA-IfMB, UKA-IMG, Lafarge Zement GmbH) Calcium carbonates are one of the basic raw materials for the industry of building materials.

Apart from their use as a natural limestone carbonate minerals are the prerequisite for the production of cement and lime and cannot be substituted by other minerals. During the production of cement carbonates as well as clay and further additives will be processed under high temperature to highly reactive, hydraulically compounds, such as calcium silicates and -aluminates. The physical and chemical reactions of cement processing including hydration reactions of the different mineral phases involved have been examined in detail and documented in the literature (e.g. Taylor 1990, Bye 1983).

With respect to climate protection larger quantities of limestone are added more frequently to the Portland cement production because energy consumption can be substantially reduced. Regarding to the hydration of the cement it is assumed that calcium carbonate is chemically inert. Calcium carbonate should account only as a conservative compound responsible for purely mechanical stabilization resulting in high strength of the concrete. However recent investigations (Matschie & Glaser 2006) contradict such an aspect.

They give clear implications that the surfaces of the carbonates are reactive in the high-alkaline environment of the fresh concrete at pH values >13 and contribute to the hydration reactions. Such participation will change not only the flow characteristics of the cement and its solidification process but also the physical properties of the solid concrete.

Furthermore, the geological provenance of limestone is important concerning the processing of the cement. This counts in particu-

lar for the simultaneous use of limestone with modern superplasticizer on the basis of polycarboxylatether. The consequence of incompatibilities between components of the mixture results in a loss of the workability of the fresh concrete, which can lead to larger damage on the structural component to be manufactured.

So far only few publications exist on the reactivity of calcium carbonate minerals with polymers in high alkaline solutions. Therefore the purposeful application of organic additives to cements with limestone compounds is until now not possible, but is in particular from concrete-technological view urgently necessarily.

On the other hand methods to modify the reactivity of calcite are not used to optimize the processing of cements, because the effects on the final product concrete are so far unknown and unexplored. Therefore, a detailed knowledge about the reactivity of calcite surfaces in high alkaline solutions and with respect to organic additives is substantial to improve the processing of cement.

This aspect is particular important regarding to the improvement of the eco-balance of cements if larger portions of carbonate phases can be introduced to the energetically complex manufactured cement. However, the application of limestone must not decrease the quality of concrete, which could be already proven for some cement mixtures (Herold & Müller 2003).

Therefore, this project will investigate the reactivity between different modern superplasticizer and calcite surfaces in high-alkaline solution in batch experiments. The surface reactivity will be observed in situ by using the fluid low cell of the AFM at INE. In particular atomic force microscopy (AFM), scanning electron microscopy and transmission electron microscopy (TEM) will be applied to clarify whether dissolution and precipitation reactions occur at the calcite surface. Supplementing investigations with synchrotron-based nano-XRD and µ-XAS (µXANES and µEXAFS) will give infor-

mation about the modification of the calcite surface and on the accumulation of additives on the surface, like the preferential accumulation of superplaticizer molecules.

After the identification and characterisation of the reactions on the calcite surface, the physical properties of the cement suspension (rheologic parameter) and the physical properties of the solid concrete will be examined in macroscopic experiments. A goal of these investigations is the control of rheologic features and strength of the concrete by calcite surfaces modifications in connection with a reduction of the primary energy need and a decreased CO2 output as possible.

3. References Alexandratos V., Elzinga E.J. & Reeder R.J. (2007) Arsenate uptake by calcite: Macroscopic and spectroscopic characterization of adsorption and incorporation mechanisms. Geochimica et Cosmochimica Acta 71: 4172–4182.

Babin J, Preaps E.E., Murphy T.P., Serediak M., Curtis P.J., Zhang Y. & Chambers P.A. (1994) Impact of lime on sediment phosphorus release in hardwater lakes: The case of hypertrophic Halfmoon Lake, Alberta. Lake Reserv.

Manag. 8: 131–1432.

Berg U., Neumann T., Donnert D., Nüesch R. & Stüben D. (2004) Sediment capping in eutrophic lakes – efficiency of undisturbed calcite barriers to immobilze phosphorus. Applied Geochemistry 19: 1759–1771.

Bye G. C. (1983) Portland Cement. Pergamon Press. Oxford.

Chada V.R.C., Hausner D.B., Strongin D.R., Rouff A.A. & Reeder R.J. (2005) Divalent Cd and Pb uptake on calcite (1014) cleavage faces: An XPS and AFM study. J. Colloid and Interfacial Sci. 288: 350–360.

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Cheng L., Fenter P., Sturchio N.C., Zhong Z. & Bedzyk M.J. (1999): X-ray standing wave study of arsenite incorporation at the calcite surface.

Geochimica et Cosmochimica Acta 63: 3153–3157.

Cheng L., Lyman P., Sturchio N.C. & Bedzyk M.J. (1997) X-ray standing wave investigation of the surface of selenite anions adsorbed on calcite. Surface Science 382: 690–695.

Eiche E., Berg U., Song Y. & Neumann T. (2008) Fixation and phase transformation of phosphate at calcite surfaces – implications for eutrophic lake restoration. Proceedings of the Ninth International Congress for Applied Mineralogy 2008, Brisbane Australia.

Elzinga E.J. & Reeder R.J. (2002) X-ray absorption spectroscopy study of Cu2+ and Zn2+ adsorption complexes at the calcite surface: Implications for site-specific metal incorporation preferences during calcite crystal growth. Geochimica et Cosmochimica Acta 66: 3943–3954.

Hart B., Roberts R., Taylor J., Donnert D. & Furrer R. (2003) Use of active barriers to reduce eutrophication problems in urban lakes. Water Sci. Technol. 47: 157–163.

Herold G. & Müller H.S. (2003) Dauerhaftigkeit von CEM II/A-L- im Vergleich zu CEM I-Zementen. 15. Internationale Baustofftagung IBAUSIL, Weimar, ISBN 3-00-010932-3, Band 2: 905.

House W.A. (1999) The physico-chemical conditions for the precipitation of phosphate with calcium. Environ. Technol. 20: 727–733.

Koehler S.J., Cubillas P., Rodriguez-Blanco J.D., Bauer C. & Prieto M. (2007) Removal of cadmium from wastewaters by aragonite shells and the influence of other divalent cations.

Env. Sci. Technol. 41: 112–118.

Matschei T. & Glaser F.P. (2006) Zum Einfluss von Kalkstein auf die Zementhydratation. ZKG International 59 (12): 78 – 86.

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Prepas E.E., Murphy T.P., Dinsmore W.P., Burke J.M., Chambers P.A. & Reedyk S. (1997) Lake Management based on lime application and hypolimnetic oxygenation: the experience in eutrophic hardwater lakes in Alberta. Water Qual. Res. J. Canada 32: 273–293.

Reeder R.J. (1996) Interaction of divalent cobalt, zinc, cadmium, and barium with the calcite surface during layer growth. Geochimica et Cosmochimica Acta 60: 1543–1552.

Staudinger B, Peiffer S. Avnimelech Y & Berman T. (1990) Phosphorus mobility in interstitial waters of sediments in Lake Kinneret, Israel. Hydrobiologia 207: 167–177.

Steefel C.I. & van Cappellen P. (1990) A new kinetic approach to modeling water-rock interaction: The role of nucleation, precursors, and Ostwald ripening. Geochimica et Cosmochimica Acta 54: 2657–2677.

Taylor H. F. W. (1990) Cement Chemistry. Academic Press Limited, London.

Author’s Index

A Agné T. . . . . . . . . . . . . . . . . . . . . . . 89 Altermann W. . . . . . . . . . . . . . . . . . 58 Azzam R. . . . . . . . . . . . . . . . . . . . . 46 B Bäppler K. . . . . . . . . . . . . . . . . . . . . 46 Bosbach D. . . . . . . . . . . . . . . . . . . 122 Burghardt D. . . . . . . . . . . . . . . . . . . 34 D Daus B. . . . . . . . . . . . . . . . . . . . . . . 25 Diedel R. . . . . . . . . . . . . . . . . . . 3, 117 Driehaus W. . . . . . . . . . . . . . . . . . . 25 Dultz S. . . . . . . . . . . . . . . . . . . . . . . 13 E Engels, M. . . . . . . . . . . . . . . . . . . . . 89 F Feinendegen M. . . . . . . . . . . . . . . . 46 Fernandez-Steeger T. M. . . . . . . . . . 46 Fischer C. . . . . . . . . . . . . . . . . . . . . 70 Fischer H. . . . . . . . . . . . . . . . . . . . 108 Fischer R. . . . . . . . . . . . . . . . . . . . 101 Fischer U. . . . . . . . . . . . . . . . . . . . 122 G Geisler T . . . . . . . . . . . . . . . . . . . . . 79 Geiß P. L. . . . . . . . . . . . . . . . . . . . 117 Gemming S. . . . . . . . . . . . . . . . . . 108 Grefhorst C. . . . . . . . . . . . . . . . . . . . 3

H Haderlein S. . . . . . . . . . . . . . . . . . . 25 Heckl W. M. . . . . . . . . . . . . . . . . . . 58 Herold G. . . . . . . . . . . . . . . . . . . . 122 Hopf J. . . . . . . . . . . . . . . . . . . . . . . 79 J Janneck E. . . . . . . . . . . . . . . . . . . . . 34 Jennissen H. . . . . . . . . . . . . . . . . . 108 Jordan G. . . . . . . . . . . . . . . . . . . . . . 3 K Kappler A. . . . . . . . . . . . . . . . . . . . 25 Kersten M. . . . . . . . . . . . . . . . . . . . 25 Kothe E. . . . . . . . . . . . . . . . . . . . . . 79 L Langenhorst F. . . . . . . . . . . . . . . . . 79 Latief O. . . . . . . . . . . . . . . . . . . . . . 89 Lüttge A. . . . . . . . . . . . . . . . . . . . . 70 M Meyer J. . . . . . . . . . . . . . . . . . . . . . 34 Müller-Mai C. . . . . . . . . . . . . . . . . 108 N Neumann T. . . . . . . . . . . . . . . . . . 122 O Obst U. . . . . . . . . . . . . . . . . . . . . . 101 P Peiffer S. . . . . . . . . . . . . . . . . . . . . . 34 Pentcheva R. . . . . . . . . . . . . . . . . . . 34 Peschard A. . . . . . . . . . . . . . . . . . . . 46

131

Pinka J. . . . . . . . . . . . . . . . . . . . . . . 34 Plöhn J. . . . . . . . . . . . . . . . . . . . . . 122 Pollok K. . . . . . . . . . . . . . . . . . . . . . 79 Post C. . . . . . . . . . . . . . . . . . . . . . . 46 Pralle N. . . . . . . . . . . . . . . . . . . . . . 46 Putnis A. . . . . . . . . . . . . . . . . . . . . . 79 Putnis C. V. . . . . . . . . . . . . . . . . . . . 79 R Rezende J. L. L. . . . . . . . . . . . . . . . . 89 Rolland W. . . . . . . . . . . . . . . . . . . . 34 S Schäfer T. . . . . . . . . . . . . . . . . . . . . 70 Schellhorn M. . . . . . . . . . . . . . . . 3, 13 Schenk M. K. . . . . . . . . . . . . . . . . . 13 Schlömann M. . . . . . . . . . . . . . . . . . 4 Schmahl W. . . . . . . . . . . . . . . . . 3, 34 Schmilewski G. . . . . . . . . . . . . . . . . 13 Schwartz T. . . . . . . . . . . . . . . . . . . 101 Seifert G. . . . . . . . . . . . . . . . . . . . 108 Seifert J. . . . . . . . . . . . . . . . . . . . . . 34 Stanjek H. . . . . . . . . . . . . . . . 3, 25, 46 Stark R. W. . . . . . . . . . . . . . . . . . . . 58 Strobel J. . . . . . . . . . . . . . . . . . . . . . 58 V Vucak M. . . . . . . . . . . . . . . . . . . . 122 Vuin A. . . . . . . . . . . . . . . . . . . . . . . 89 W Wennrich R. . . . . . . . . . . . . . . . . . . 25 Wiacek C. . . . . . . . . . . . . . . . . . . . . 34 Winkler B. . . . . . . . . . . . . . . . . . . . 122 Wittwer W. . . . . . . . . . . . . . . . . . . . 17

132

Wolff H. . . . . . . . . . . . . . . . . . . . . . . 3 Wolkersdorfer Ch. . . . . . . . . . . . . . 58 Z: Ziegler M. . . . . . . . . . . . . . . . . . . . . 46 Zwick O. . . . . . . . . . . . . . . . . . . . . . . 2

GEOTECHNOLOGIEN Science Reports – Already published/Editions

No. 1 Gas Hydrates in the Geosystem – Status Seminar, GEOMAR Research Centre Kiel, 6–7 May 2002, Programme & Abstracts, 151 pages.

No. 2

No. 3

No. 4

No. 5

No. 6

Information Systems in Earth Management – Kick-Off-Meeting, University of Hannover, 19 February 2003, Projects, 65 pages.

Observation of the System Earth from Space – Status Seminar, BLVA Munich, 12–13 June 2003, Programme & Abstracts, 199 pages.

Information Systems in Earth Management – Status Seminar, RWTH Aachen University, 23–24 March 2004, Programme & Abstracts, 100 pages.

Continental Margins – Earth’s Focal Points of Usage and Hazard Potential – Status Seminar, GeoForschungsZentrum (GFZ) Potsdam, 9–10 June 2005, Programme & Abstracts, 112 pages.

No. 7

Gas Hydrates in the Geosystem – The German National Research Programme on Gas Hydrates, Results from the First Funding Period (2001–2004), 219 pages.

No. 8

Information Systems in Earth Management – From Science to Application, Results from the First Funding Period (2002–2005), 103 pages.

No. 9

1. French-German Symposium on Geological Storage of CO2, Juni 21./22.

2007, GeoForschungsZentrum Potsdam, Abstracts, 202 pages.

No. 10 Early Warning Systems in Earth Management – Kick-Off-Meeting, Technical University Karlsruhe, 10 October 2007, Programme & Abstracts, 136 pages.

No. 11 Observation of the System Earth from Space – Status Seminar, 22–23 November 2007, Bavarian Academy of Sciences and Humanities, Munich, Programme & Abstracts, 194 pages.

Investigation, Utilization and Protection of the Underground – CO2-Storage in Geological Formations, Technologies for an Underground Survey Areas – Kick-Off-Meeting, Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) Hannover, 22–23 September 2005, Programme & Abstracts, 144 pages.

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Notes

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