VOLUME 123 NO. 11 NOVEMBER 2023
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The Southern African Institute of Mining and Metallurgy OFFICE BEARERS AND COUNCIL FOR THE 2023/2024 SESSION
PAST PRESIDENTS
Honorary President
* W. Bettel (1894–1895) * A.F. Crosse (1895–1896) * W.R. Feldtmann (1896–1897) * C. Butters (1897–1898) * J. Loevy (1898–1899) * J.R. Williams (1899–1903) * S.H. Pearce (1903–1904) * W.A. Caldecott (1904–1905) * W. Cullen (1905–1906) * E.H. Johnson (1906–1907) * J. Yates (1907–1908) * R.G. Bevington (1908–1909) * A. McA. Johnston (1909–1910) * J. Moir (1910–1911) * C.B. Saner (1911–1912) * W.R. Dowling (1912–1913) * A. Richardson (1913–1914) * G.H. Stanley (1914–1915) * J.E. Thomas (1915–1916) * J.A. Wilkinson (1916–1917) * G. Hildick-Smith (1917–1918) * H.S. Meyer (1918–1919) * J. Gray (1919–1920) * J. Chilton (1920–1921) * F. Wartenweiler (1921–1922) * G.A. Watermeyer (1922–1923) * F.W. Watson (1923–1924) * C.J. Gray (1924–1925) * H.A. White (1925–1926) * H.R. Adam (1926–1927) * Sir Robert Kotze (1927–1928) * J.A. Woodburn (1928–1929) * H. Pirow (1929–1930) * J. Henderson (1930–1931) * A. King (1931–1932) * V. Nimmo-Dewar (1932–1933) * P.N. Lategan (1933–1934) * E.C. Ranson (1934–1935) * R.A. Flugge-De-Smidt (1935–1936) * T.K. Prentice (1936–1937) * R.S.G. Stokes (1937–1938) * P.E. Hall (1938–1939) * E.H.A. Joseph (1939–1940) * J.H. Dobson (1940–1941) * Theo Meyer (1941–1942) * John V. Muller (1942–1943) * C. Biccard Jeppe (1943–1944) * P.J. Louis Bok (1944–1945) * J.T. McIntyre (1945–1946) * M. Falcon (1946–1947) * A. Clemens (1947–1948) * F.G. Hill (1948–1949) * O.A.E. Jackson (1949–1950) * W.E. Gooday (1950–1951) * C.J. Irving (1951–1952) * D.D. Stitt (1952–1953) * M.C.G. Meyer (1953–1954) * L.A. Bushell (1954–1955) * H. Britten (1955–1956) * Wm. Bleloch (1956–1957) * H. Simon (1957–1958) * M. Barcza (1958–1959) * R.J. Adamson (1959–1960)
Nolitha Fakude President, Minerals Council South Africa
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Gwede Mantashe Minister of Mineral Resources and Energy, South Africa Ebrahim Patel Minister of Trade, Industry and Competition, South Africa Blade Nzimande Minister of Higher Education, Science and Technology, South Africa
President
W.C. Joughin
President Elect E. Matinde
Senior Vice President G.R. Lane
Junior Vice President T.M. Mmola
Incoming Junior Vice President M.H. Solomon
Immediate Past President Z. Botha
Honorary Treasurer E. Matinde
Ordinary Members on Council W. Broodryk Z. Fakhraei R.M.S. Falcon (by invitation) B. Genc K.M. Letsoalo S.B. Madolo F.T. Manyanga K. Mosebi
M.C. Munroe S. Naik G. Njowa S.J. Ntsoelengoe S.M. Rupprecht A.T. van Zyl E.J. Walls
Co-opted Council Members M.A. Mello
Past Presidents Serving on Council N.A. Barcza R.D. Beck J.R. Dixon V.G. Duke I.J. Geldenhuys R.T. Jones A.S. Macfarlane
C. Musingwini S. Ndlovu J.L. Porter M.H. Rogers D.A.J. Ross-Watt G.L. Smith W.H. van Niekerk
G.R. Lane – TP Mining Chairperson Z. Botha – TP Metallurgy Chairperson K.W. Banda – YPC Chairperson S. Nyoni – YPC Vice Chairperson
Branch Chairpersons Botswana DRC Johannesburg Limpopo Namibia Northern Cape North West Pretoria Western Cape Zambia Zimbabwe Zululand
Vacant Not active N. Rampersad S. Zulu Vacant I. Tlhapi I. Tshabalala Vacant A.B. Nesbitt J.P.C. Mutambo (Interim Chairperson) Vacant C.W. Mienie
*Deceased
* W.S. Findlay (1960–1961) * D.G. Maxwell (1961–1962) * J. de V. Lambrechts (1962–1963) * J.F. Reid (1963–1964) * D.M. Jamieson (1964–1965) * H.E. Cross (1965–1966) * D. Gordon Jones (1966–1967) * P. Lambooy (1967–1968) * R.C.J. Goode (1968–1969) * J.K.E. Douglas (1969–1970) * V.C. Robinson (1970–1971) * D.D. Howat (1971–1972) * J.P. Hugo (1972–1973) * P.W.J. van Rensburg (1973–1974) * R.P. Plewman (1974–1975) * R.E. Robinson (1975–1976) * M.D.G. Salamon (1976–1977) * P.A. Von Wielligh (1977–1978) * M.G. Atmore (1978–1979) * D.A. Viljoen (1979–1980) * P.R. Jochens (1980–1981) * G.Y. Nisbet (1981–1982) A.N. Brown (1982–1983) * R.P. King (1983–1984) J.D. Austin (1984–1985) * H.E. James (1985–1986) H. Wagner (1986–1987) * B.C. Alberts (1987–1988) * C.E. Fivaz (1988–1989) * O.K.H. Steffen (1989–1990) * H.G. Mosenthal (1990–1991) R.D. Beck (1991–1992) * J.P. Hoffman (1992–1993) * H. Scott-Russell (1993–1994) J.A. Cruise (1994–1995) D.A.J. Ross-Watt (1995–1996) N.A. Barcza (1996–1997) * R.P. Mohring (1997–1998) J.R. Dixon (1998–1999) M.H. Rogers (1999–2000) L.A. Cramer (2000–2001) * A.A.B. Douglas (2001–2002) S.J. Ramokgopa (2002-2003) T.R. Stacey (2003–2004) F.M.G. Egerton (2004–2005) W.H. van Niekerk (2005–2006) R.P.H. Willis (2006–2007) R.G.B. Pickering (2007–2008) A.M. Garbers-Craig (2008–2009) J.C. Ngoma (2009–2010) G.V.R. Landman (2010–2011) J.N. van der Merwe (2011–2012) G.L. Smith (2012–2013) M. Dworzanowski (2013–2014) J.L. Porter (2014–2015) R.T. Jones (2015–2016) C. Musingwini (2016–2017) S. Ndlovu (2017–2018) A.S. Macfarlane (2018–2019) M.I. Mthenjane (2019–2020) V.G. Duke (2020–2021) I.J. Geldenhuys (2021–2022) Z. Botha (2022-2023)
Editorial Board S.O. Bada R.D. Beck P. den Hoed I.M. Dikgwatlhe R. Dimitrakopolous* B. Genc R Hassanalizadeh R.T. Jones W.C. Joughin A.J. Kinghorn D.E.P. Klenam J. Lake H.M. Lodewijks D.F. Malan R. Mitra* H. Möller C. Musingwini S. Ndlovu P.N. Neingo S.S. Nyoni M. Phasha P. Pistorius P. Radcliffe N. Rampersad Q.G. Reynolds I. Robinson S.M. Rupprecht K.C. Sole A.J.S. Spearing* T.R. Stacey E. Topal* D. Tudor* D. Vogt* *International Advisory Board members
Editor /Chairperson of the Editorial Board R.M.S. Falcon
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VOLUME 123 NO. 11 NOVEMBER 2023
Contents Journal Comment: Variety (at a high standard) is the spice of life by R.M.S. Falcon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Presidential Address: Innovation in the South African mining industry by W.C. Joughin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Erratum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Directory of Open Access Journals
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PROFESSIONAL TECHNICAL AND SCIENTIFIC PAPERS Carbothermic reduction of a willemite concentrate for use in the Waelz process by V.S. Coimbra, G.M. de Lima, V.A. Leão, R.F.M. de Souza, and V.A.A. Oliveira. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A willemite concentrate consisting mainly of willemite (55.3%) and dolomite (15.6%) was reduced in a tube furnace with charcoal as reductant. The calcium oxide generated through calcination of the dolomite promoted decomposition of the willemite, thus lowering the temperature at which reduction took place. The presence of CaO improved the zinc recovery at all temperatures studied. The best zinc recovery (93%) was obtained in the presence of 5% CaO, 20% charcoal reductant, and at a temperature of 1100°C. The results showed that the willemite concentrate studied has great potential to be used in the Waelz process. Cost modelling for dimension stone quarry operations by M.A. Raza, S. Raza, M.U. Khan, M.Z. Emad, K. Jalil, and S.A. Saki . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A production cost model for dimension stone mining using diamond wire sawing was developed based on data from a dolerite operation in Pakistan. A strong correlation of production cost with fuel, labour, and consumables costs was found. A production cost model based on the consumption cost of diamond wire is presented. The model may help field engineers in computing their dimension stone operational cost during the cutting phase. Employee engagement among women in technical positions in the South Africa mining industry by N. Mashaba and D. Botha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The factors that influence women’s engagement in technical positions in the South African mining industry were investigated using a convergent parallel mixed-methods research design. The three-factor structure of the Utrecht Work Engagement Scale was found to fit the sample data reasonably well. The results showed that employee engagement should be a core human resource function. Programmes should be developed that promote women employees’ absorption in and dedication to their work. Resistance of yielding rockbolts to multiple impact loads by A. Pytlik, D. O’Connor, and D.J. Corbett. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The resistance of yielding rockbolts to multiple impact loads was tested using a drop hammer. All the samples transferred double the gravitational potential energy of Ep = 50.85 kJ from the impact load of mass m = 2825 kg and impact velocity v = 6.0 m/s without failure. Subsequent impacts resulted in damage to the bolt-resin contact in the upper anchoring zone in the steel tube. As a result, the macro-deformed bolt exhibits additional yield, and its operation following the shearing of the resin bond is similar to that of a ‘cone bolt’.
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Copper Cobalt al
Journ
Variety (at a high standard) is the spice of life
ent
Comm
O
ne of the aims that an Editorial Board of an internationally accredited journal (such as that of the SAIMM) aspires to achieve is to present to its readers novel, high-quality scientific and technological information. This requires papers submitted to the journal to be vigilantly reviewed and evaluated and, once published, assessed in terms of the citations arising from them. The number of citations affects the journal’s Impact Factor and related publishing evaluation norms. The Impact Factor of the journal in turn directly affects the professional standing of academics associated with the papers printed in that journal. For a journal to be successful for all parties concerned, it is essential that it features only the highest level of research showing uniqueness, relevance, and previously unknown information. However, there comes a time when young professionals, whether in their final years of study or early in their professional lives, are obliged to submit papers in order to build their own reputations and, more relevantly, to meet the requirements for graduation. For example, a doctoral student is required to publish at least two papers in an internationally accredited journal in order to be awarded his or her degree, while a master’s student is required to produce one such paper. The question then arises as to where to submit such papers for publication and whether the papers meet the journal’s publication criteria. Given the high standards that journals set, and that senior students need to publish despite their limited experience or highly focused research topics, it is often difficult to reconcile these two requirements. However, the Editorial Board of this Journal believes it has found common ground in this dilemma by hosting an annual student conference at which senior students are invited to present their completed mining and metallurgical topics. From that event, the best papers are invited to be submitted for review. Once the papers have been reviewed and have met the criteria of the Journal they are selected for publication. On this basis, the SAIMM Journal has, for many years, published one or more of its monthly editions featuring such top student papers. Readers will note the wide variation in topics and the nature of the research, all of which address issues of concern within the greater mining and metallurgical value chains worldwide. In summary, may I refer to the previous month’s Commentary which called for industry to provide suitable research topics for senior mining and metallurgical students to undertake in order to meet the criteria for publication in journals such as this one. The Editorial Board looks forward to many more student-based research papers in future, papers that will benefit the industries and communities in which the students are destined to serve and which will enhance the students’ own professional careers. This month’s topics include an investigation of the ability of yielding rockbolts to resist multiple impact loads, which has considerable bearing on underground construction and safety. Research concerning the socioeconomic factors that influence women’s engagement on boards in the mining world led to significant recommendations based upon the findings. Another investigation found that the reduction of willemite in the presence of CaO showed considerable metallurgical benefit, with improved zinc extractions of up to 93%. In yet another paper a new model is presented for computing dimension stone operational costs during the cutting phase. This is significant as dimension stone is gaining rapidly in popularity because of its widespread use in construction. R.M.S. Falcon
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nt’s
Innovation in the South African mining industry
de Presi
er
Corn
I
have always been fascinated by innovation and the ever-evolving landscape of science and technology. The allure of innovation lies not only in the novelty of groundbreaking ideas but also in their transformative potential— how they reshape industries, elevate human experience, and address pressing global issues. Curiosity serves as a driving force, inspiring individuals and communities to push boundaries, challenge conventions, and actively pursue improvement. The terms ‘innovation’ and ‘invention’ are frequently used interchangeably, often leading to confusion. Invention is a term deeply rooted in creation— the act of conceiving and bringing something entirely new into existence. It represents the initial spark of inspiration that leads to the development of a unique or novel device, method, composition, idea, or process. Inventions are not necessarily useful, or in some cases, their uses have not yet been discovered. Innovation involves the practical implementation of an invention, or the adaptation of existing products or services to make a meaningful impact on society. Creating value is a defining characteristic of innovation. Incremental innovation is the continual refinement and improvement of products, services or processes based on the requirements of the beneficiaries. This is essential to remain competitive in business. Disruptive innovation occurs when a new product or service creates a new market and renders existing products or services obsolete. While disruptive innovation may be unwelcome, its early adoption often provides a strategic advantage, allowing pioneering individuals or businesses to capitalize on emerging trends and gain a competitive edge. Those who embrace disruptive technologies in their infancy can often position themselves as industry leaders and reap the benefits of being at the forefront of transformative change. The South African mining industry is associated with conventional labour-intensive methods, due to the narrow, tabular, shallow-dipping reefs in gold and platinum mines. It has been extremely difficult to adapt modern underground mining equipment for use in this harsh environment with confined spaces. These challenges necessitated a comprehensive industry research programme, which commenced in the 1960s, and is summarized in Brian Protheroe’s book entitled COMRO’s Legacy: Research and Development of Stoping Mining Machinery and Technologies, recently published by the SAIMM. This book describes numerous creative and innovative ideas that were conceived and put into practice. While some imaginative concepts could not be applied at the time, there is potential for their use with the aid of recently developed technologies. Regrettably, much of this research was terminated in the 1990s due to a cessation of industry funding. The global gold supply has since been dominated by international miners with more accessible orebodies. However, in South Africa we continue to operate platinum mines and deep gold mines, necessitating further innovation to stay competitive. Two former presidents of our Institute have proposed strategies for adapting mining machinery and embracing new technologies (Rod Pickering, 2007 and Jim Porter, 2014). More recently, the Mandela Mining Precinct has established a ‘Test Mine’ in Rustenburg, to provide an industry hub for research, development, and innovation. The Test Mine also serves as a platform for technology demonstration and testing. Cutting-edge technologies like drones and satellite imaging are enhancing geological and geotechnical surveys. Autonomous, GPS-denied drones are being used to accurately survey inaccessible underground cavities, using smart navigation and collision avoidance, providing essential data for production and
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President’s Corner (continued) geotechnical monitoring. Additionally, the adoption of real-time monitoring and sensor technologies has increased safety measures and optimized resource extraction. Furthermore, the integration of data analytics and artificial intelligence has the potential to predict equipment failures or provide early warning of instabilities in tailings storage facilities, slopes, and underground workings. This will enable mining companies to make informed and better decisions. The South African mining industry has also undergone a paradigm shift towards sustainability, recognizing the importance of environmental stewardship and community engagement. Companies are increasingly investing in eco-friendly technologies, renewable energy sources, and water recycling systems in order to minimize their ecological footprint. In addition, there is a growing emphasis on responsible mining practices, with a focus on biodiversity conservation and land rehabilitation post-extraction. This shift towards sustainability not only aligns with global environmental goals but also enhances the industry’s social license to operate, fostering positive relationships with local communities. In last month’s President’s Corner I emphasized the significance of diversity and inclusion, stressing that a diverse array of skills, experiences, and knowledge is essential for developing novel and improved ideas. Successful innovation relies on effective collaboration between mining operations, research institutions, government bodies, consultants, and technology providers. The SAIMM organizes forums and conferences as a platform for stakeholders to exchange ideas, showcase success stories, and address shared challenges. Pickering, R.G.B. 2007. Presidential address: Has the South African narrow reef mining industry learnt how to change? Journal of the Southern African Institute of Mining and Metallurgy, vol. 107, no. 9. pp. 557−565. https://www.saimm.co.za/Journal/v107n09p557.pdf Porter, J.L. 2014. Presidential Address: Are efforts to mechanize SA mines too focused on machinery rather than technology? Journal of the Southern African Institute of Mining and Metallurgy, vol. 114, no. 9. pp. 681−692. https://www.saimm.co.za/Journal/v114n09p681.pdf SAIMM Events: https://www.saimm.co.za/saimm-events/upcoming-events.
W.C. Joughin President, SAIMM
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Carbothermic reduction of a willemite concentrate for use in the Waelz process by V.S. Coimbra¹, G.M. de Lima², V.A. Leão³, R.F.M. de Souza⁴, and V.A.A. Oliveira¹
Affiliation:
1 Pyrometallurgy and Thermal Analysis
Laboratory, Department of Metallurgical and Materials Engineering, Universidade Federal de Ouro Preto, Ouro Preto, Minas Gerais, Brazil. 2 Coordination Chemistry Laboratory, Department of Chemistry, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil. 3 Bio&Hidrometalurgia Laboratory, Department of Metallurgical and Materials Engineering, Universidade Federal de Ouro Preto, Ouro Preto, Minas Gerais, Brazil. 4 Pyrometallurgy Research Group, Department of Chemical and Materials Engineering, Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil.
Correspondence to: V.A.A. Oliveira
Email:
victor@ufop.edu.br
Dates:
Received: 12 Dec. 2022 Accepted: 24 Aug. 2023 Published: November 2023
How to cite:
Coimbra, V.S., de Lima, G.M., Leão, V.A., de Souza, R.F.M., and Oliveira, V.A.A. 2023 Carbothermic reduction of a willemite concentrate for use in the Waelz process. Journal of the Southern African Institute of Mining and Metallurgy, vol. 123, no. 11. pp. 513–520 DOI ID: http://dx.doi.org/10.17159/24119717/2516/2023 ORCID: V.S. Coimbra http://orcid.org/0000-0003-1891-548X G.M. de Lima http://orcid.org/0000-0002-3816-0320 V.A. Leão http://orcid.org/0000-0001-9495-6529 R.F.M. de Souza http://orcid.org/0000-0002-3468-686X V.A.A. Oliveira http://orcid.org/0000-0003-2099-9459
Synopsis
A willemite concentrate consisting mainly of willemite (55.3%) and dolomite (15.6%) was reduced in a tube furnace with charcoal as reductant. The effects of temperature and varying reductant additions on zinc extraction were studied. A zinc recovery of 86% was achieved with 20% reductant in the charge at 1100°C. During reduction, the calcium oxide generated through calcination of the dolomite promoted decomposition of the willemite, thus lowering the temperature at which reduction took place. The presence of CaO improved the zinc recovery at all temperatures studied. The best zinc recovery (93%) was obtained in the presence of 5% CaO, 20% charcoal reductant, and at a temperature of 1100°C. The results show that the willemite concentrate studied has great potential to be used as a raw material for the Waelz process.
Keywords
willemite, carbothermic reduction, zinc smelting, Waelz process, non-sulphide zinc ore, calcium oxide.
Introduction Sphalerite (ZnS) is the main source of zinc, which is obtained through a roast-leach-electrowinning (RLE) process (Souza et al., 2007a; Sinclair, 2005; Safari et al., 2009). In general, in this process, the sphalerite concentrate is roasted in a fluidized bed furnace to obtain zinc oxide. The main solid products of roasting (ZnO and ZnFe2O4) are leached in tanks using sulphuric acid, and after purification, zinc-rich liquor is sent to the aqueous electrolysis stage to obtain zinc cathode (Special High-Grade Zinc – 99.995% Zn) (Sinclair, 2005; Oliveira et al., 2019). Other zinc minerals of economic importance are smithsonite (ZnCO3) and willemite (Zn2SiO4) (Souza et al., 2007b; Li et al., 2013). These minerals are constituents of secondary zinc deposits, called calamine deposits (Zhang et al., 2018; Boni and Mondillo, 2015). These minerals occur in non-sulphide zinc ores (Souza et al., 2007b). These ores are not processed by RLE for various reasons. Dehydration and/ or calcination is an endothermic reaction that will lead to higher energy consumption, in contrast to the exothermic roasting reaction (Zhang et al., 2019; Zhao et al., 2017; Xiong et al., 2012; Liu et al., 2012). The presence of acid-consuming minerals in the gangue (dolomite and calcite) will result in the consumption of large amounts of sulphuric acid during leaching (Santos et al., 2010). Acid leaching solubilizes a great deal of silica, which forms silica gel (Souza et al., 2007a; Xiong et al., 2012; Safari et al., 2009; Liu et al., 2012; Yin et al., 2010). Furthermore, non-sulphide zinc minerals pose greater challenges during the concentration stages (Zhao et al., 2017), hence, the zinc contents of the concentrates are lower than those obtained from sulphide ores. A possible alternative route for the extraction of zinc from these ores involves alkaline leaching (Santos et al., 2010). This would avoid the excessive consumption of acid reagents by the gangue minerals and the high energy demand associated with endothermic reactions (Zhang et al., 2014; Liu et al., 2012). Several alkaline reagents, such as NH4OH/NH4Cl and NaOH/NH4Cl, have been used in the leaching of these ores (Santos et al., 2010; Zhang et al., 2019; Li et al., 2013; Zhao et al., 2017; Liu et al., 2012; Yin et al., 2010). However, these reagents are considerably more expensive than sulphuric acid. In addition, the authors are not aware of any process that uses alkaline leaching of non-sulphide zinc ores on an industrial scale. A classic metallurgical process used for treating various zinc-bearing residues is the so-called Waelz process. This process has been extensively used and is a safe and reliable technology applied for the recovery of metals such as Pb, Cd, Ge, and particularly Zn, from electric arc furnace dust (EAFD) and other steel industrial residues (Chen, 2001; Mager et al., 2000; Antuñano, Arias, and Cambra, 2019, 2013; James and Bound,). EAFD is a waste, formed during steel production, which contains considerable amounts of zinc (Xiong et al., 2017). For zinc recovery from zinc-bearing residues, the Zn2+ cation is usually reduced in a rotary furnace (the Waelz furnace) at 1200°C, using a carbonaceous reducing agent. The reduction of zinc
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Carbothermic reduction of a willemite concentrate for use in the Waelz process oxide by carbon occurs at a temperature higher than the boiling point of the metal (907°C), and consequently the zinc vaporizes (Xiong et al., 2017; Antuñano, Arias, and Cambra, 2019):. [1] Due to the oxidizing atmosphere in the Waelz furnace the Zn metal that evaporates from the reduction reaction zone is oxidized in contact with this gaseous phase (Equations [2] and [3]), forming a very fine powder (ZnO) which is collected in the bag filter (Antuñano, Arias, and Cambra, 2019). [2]
crucible at 950°C for 40 minutes in a muffle oven. After fusion, all material was dissolved in an acid solution (HCl approx. 18% v/v). The solution was analysed by inductively coupled plasma optical emission spectrometry (ICP-OES, Varian model 725).
X-ray diffractometry X-ray diffractograms were obtained using a Shimadzu model XRD-6100 diffractometer equipped with a copper source operating at 45 kV and 40 mA and with a 1°/min scanning speed. The main phases in the samples were identified by comparison with standard diffractograms (ICSD patterns) using DIFFRAC.EVA. TOPAS 5.0 software was used to quantify the mineral phases present in the sample using the Rietveld method.
Thermogravimetric analysis [3] This powder is called Waelz oxide and, after purification (dehalogenation), it can be added to the acid leaching step of the RLE process. In this way, it is possible to recover zinc from secondary sources in an integrated way. A comprehensive review of the pyrometallurgical recovery of zinc from EAFD was presented by Wang et al. (2021). The fundamentals and operational parameters of the Waelz process , which is applied to the recovery of zinc and other volatile metals from secondary zinc resources, were described by Harris (1936). As well as being an important metallurgical approach for the treatment of non-sulphide zinc ores, the Waelz process is often used for the recovery of zinc from secondary sources. These sources usually have a lower zinc content (e.g. 22–28% Zn for EAFD) compared to oxidized ore concentrates (Xiong et al., 2017; Antuñano, Arias, and Cambra, 2019). It is noteworthy that the utilization of non-sulphide concentrates as feed to the Waelz process has received less attention than zinc-bearing residues. Many zinc-bearing residues are very heterogeneous in terms of their chemical composition and moisture content. For instance, many the raw materials used in the Waelz process often consist of a blend of different zinc-containing materials (Krupka et al., 2000; Mager et al., 2000; Harris, 1936). The study of the mineralogical changes under the typical operating conditions of the Waelz process can therefore contribute to a better understanding of the process in general. We studied the influence of temperature, the presence of CaO, and the amount of charcoal on the extraction of zinc from a willemite concentrate. Mineral transformations associated with the carbothermic reduction of this mineral and the gangue constituents were also investigated to determine chemical reactions that may occur if a willemite concentrate alone is fed to a Waelz furnace.
Materials and methods The willemite concentrate (CW) was supplied by Nexa Resources from a mine in the northwest region of the Brazilian state of Minas Gerais. The as-received sample had a moisture content of approximately 15% and particle size 100% less than 75 μm. All experiments were carried out had been samples that dried in an oven for 48 hours at 105°C.
Chemical analysis Approximately 0.150 g of the sample was homogenized with 4 g of a mixture of 1 part sodium tetraborate (Synth, 99.5%) to 3 parts sodium carbonate (F. Maia, 99.5%) and fused in a platinum 514
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Thermogravimetric curves were obtained using a heating rate of 10°C/min in an inert atmospere of N2 (White Martins, 99.9990%) at a flow rate of 50 ml/min. We used a Shimadzu model DTG 60 thermogravimetric analyser.
Scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) The sample was embedded in polyester resin and, after drying, the surface was polished using silicon carbide paper of different grain sizes (150 to 1500 grit). After sanding, the surface was polished with alumina paste (1 μm). The surface of the sample was metallized with gold using a sputter coater (Quorum model Q150R ES). The SEM images were generated using a Tescan model Vega 3 LMH and EDS mapping was performed using an Oxford INCA x-act 51-ADD0007 instrument.
Reduction experiments Charcoal (CV) ground to 100% less than 300 μm was used as reductant. Volatiles were removed by heating the ground charcoal sample in a closed crucible for 1 hour at 1000°C in a muffle furnace. Mixtures with different CW/(CW + CV) ratios were prepared and homogenized for the experiments, to evaluate the influence of CV on the reduction. The influence of calcium oxide on the reduction was assessed by adding different amounts of CaO to the CW/ (CW + CV) mixture. A crucible containing approximately 5 g of the reaction mixture was placed in a Jung tubular furnace with an automatic temperature controller, and a continuous flow (2 L/min) of N2 (99.9990%) was maintained inside the furnace throughout the experiment. After reduction, the crucible was heated in a muffle furnace at 800°C for 2 hours to remove residual carbon. Zinc extraction (Zn%) from CW was calculated according to Equation [4]: [4] where is the final mass of CW after reduction and removal of excess CV, is the initial mass of CW, and ZnO is the zinc oxide content in the CW sample. For the experiments where the influence of CaO was investigated, the mass of this reagent added at the beginning of the experiment was subtracted from the final mass after the removal of excess CV. All experiments were done in triplicate. Duplicates of the blank experiments were performed for all experimental conditions studied and the mass loss found for these experiments was added to the mass of .
Thermodynamic data HSC Chemistry V 4.1 software was used to construct the equilibrium diagrams. The Journal of the Southern African Institute of Mining and Metallurgy
Carbothermic reduction of a willemite concentrate for use in the Waelz process Table I
Chemical analysis of the willemite concentrate (CW) (%) Zn
Ca
Mg
Fe
Al
Pb
Cd
32.5
4.6
2.8
4.9
0.4
0.3
0.025
Results and discussion Characterization of willemite concentrate The chemical analysis of the concentrate is shown in Table I. The Zn content, 32.5% is considerably higher than the values reported by different authors for EAFD (20-28%) and other zinc-bearing materials (Mattich et al., 1998; Xiong et al., 2017). This is another attractive reason to use this material as feed to a Waelz furnace. Figure 1 shows both the X-ray diffractograms for the sample, one obtained by experiment and the other provided by the Rietveld method, revealing good concordance of results. Willemite (53.3%) is the main constituent, followed by dolomite (15.6%) (Table II). Table II also shows that three Zn-bearing minerals were identified: smithsonite (2.3%), hydrozincite (2.7%), and willemite (53.3%). Thus, 91.7% of the Zn present in the sample is in willemite, 3.5% in smithsonite, and 4.7% in hemimorphite. The minerals identified in the concentrate are typical minerals of this type of ore (Dill, 2010).
The difference between the zinc values found by ICP-OES (32.5%) and by the Rietveld method (34.1%) is less than 5%. Figure 2 shows the TGA and DTG curves for the decomposition of the CW sample in an inert atmosphere. The curves show two mass loss events in the temperature range between 478°C and 790°C. These events are identified as (i) and (ii) on the DTG curve. According to the mineralogical analysis, event (i) can be attributed to the thermal decomposition of smithsonite and hydrozincite according to Equations [5] and [6]: [5] [6] The mass loss shown in the TGA curve associated with the event (i) is 1.55%. According to the results obtained using the Rietveld method, for a sample containing 2.3% smithsonite and 2.7% hydrozincite (Table II), the expected mass losses will be 0.807% and 0.698%, respectively. Therefore, the total mass loss associated with the decomposition of smithsonite and hydrozincite will be approximately 1.5%, which is very close to that shown in the TGA curve. The temperature values found for the thermal decomposition of these minerals agree with the results of other authors (Wahab et al., 2008; Wang et al., 2021)). The event (ii) in the TGA curve is attributed to the thermal decomposition of dolomite according to Equation [7]: [7] The free energy values show that the temperature of thermal decomposition (calcination) of dolomite is 908K (635°C), considering the standard state (pCO2 = 1 atm.) and the activity of solid species equal to the unit. It is important to highlight that the experimental condition is not the standard state, but the calculated thermodynamic temperature of calcination is within the temperature range obtained experimentally. In addition, the values found are in accordance with the results of some research groups (Herce, Stendardo, and Cristóbal, 2015; Ptáček, Šoukal, and Opravil, 2021). The evidence for the decomposition of dolomite, hemimorphite, and smithsonite in the proposed temperature range
Figure 1—X-ray diffractogram for the CW sample
Table II
Mineralogical composition of the sample Mineral
Formula
Content (%)
Willemite
Zn2SiO4
53.3
Dolomite
CaMg(CO3)2
16.4
Chlorite
H4Mg3Si2O9
8.3
Nacrite
Al2(Si2O5)(OH)4
6.5
Quartz
SiO2
4.7
Hydrozincite
Zn5(CO3)2(OH)6
2.7
Smithsonite
ZnCO3
2.3
Kaolinite
Al4(Si4O10)(OH)8
2.0
Monticelite
CaMgSiO4
2.8
−
1.0
Others
The Journal of the Southern African Institute of Mining and Metallurgy
Figure 2—TGA curves and DTG of CW sample decomposition in an inert atmosphere (N2 50 ml/min) at a heating rate of 10°C/min VOLUME 123
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Carbothermic reduction of a willemite concentrate for use in the Waelz process
Figure 4—TGA and DTG curves for the reduction of willemite concentrate with charcoal (40% w/w) in an inert atmosphere at s heating rate of 10°C/min
Figure 3—SEM-EDS images for willemite concentrate sample. (W) willemite; (D) dolomite; (Q) quartz; (H) magnetite
could be confirmed by the disappearance of the diffraction peaks characteristic of these minerals when the sample was calcined in a muffle furnace at a temperature of 810°C (c.f. Figure 8). Finally, the results show that for a mass loss of 9.2%, the sample contains about 19.2% dolomite (c.f. Equation [7]). The dolomite content calculated through the TGA curve is very close to the value obtained using the Rietveld method for mineralogical quantification. Figure 3 shows a SEM image and EDS mapping for the CW sample. The main constituent minerals were identified through the association of phases identified in the X-ray diffractogram, with the elemental associations revealed by EDS mapping.
Carbothermic reduction of the willemite concentrate Thermogravimetry Figure 4 shows the thermogravimetric curve for the reduction of willemite concentrate. Two thermal events, A and B, can be identified. These events are due to (A) dolomite calcination, smithsonite calcination, and dehydration, and calcination of hemimorphite (Equations [5], [6], and [7]), and (B) the reduction of willemite. Equations [8] and [9] show two possible reactions of willemite reduction and Figure 5 shows the Ellingham diagram for these reactions. [8] [9] The results show that above 1291K (1018°C) the reduction of willemite, generating CO(g) as a reaction product becomes spontaneous. Therefore, this is one of the possible reactions 516
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Figure 5—Ellingham diagram for the carbothermic reduction of willemite
responsible for the second event on the TGA curve. It is also worth mentioning that, as shown in the diagram, this reaction will be thermodynamically more favourable than the reaction where CO2 is formed, at any temperature higher than 972K (699°C). Gaseous carbon monoxide, formed in situ, is a possible reducing agent playing a role in the extraction of Zn from willemite. Equations [10], [11], and [12] represent the possible reactions. [10] [11] [12] Figure 6 shows the variation of log(pCO/pCO2) as a function of temperature for willemite reduction. The diagram shows that the solid products are Zn and SiO2. These results indicate that SiO2 does not reduce in such conditions. In the TGA curve, the event attributed to the reduction of willemite starts at a temperature lower than that indicated by thermodynamic data (approx. 950°C) and, therefore, the observed mass loss for temperatures lower than 1018°C cannot be attributed to the reactions represented by Equations [9] and [10]. Thus, the The Journal of the Southern African Institute of Mining and Metallurgy
Carbothermic reduction of a willemite concentrate for use in the Waelz process
Figure 6—log(pCO2/pCO) as a function of temperature for the reduction of willemite
Figure 7—Ellingham diagram for willemite decomposition reactions
results suggest that the calcium oxide generated by the calcination of dolomite promotes the decomposition of willemite, generating different calcium silicates and zinc oxide. Equations [13] and [14] show some of the possible chemical reactions involved in willemite decomposition, and Figure 7 shows that these reactions are thermodynamically favourable throughout the studied range of temperature. Finally, the diagram also shows that the decomposition of willemite in the absence of these oxides is not thermodynamically favourable (blue line).
range, only diffraction peaks characteristic of a mixed calcium and magnesium silicate (CaMgSiO4, montcellite) could be identified. The Rietveld method was not applied to quantify the generated phases because the reaction between these basic oxides (CaO and MgO) and silica produces too many amorphous phases. The results show that the calcium oxide generated during the thermal decomposition of dolomite reacts with willemite forming ZnO and different calcium silicates. Note the presence of ZnO in the diffractograms in Figure 8. The zinc oxide formed is reduced by carbon and/or carbon monoxide according to Equations [15], [16], and [17]:
[13]
[15]
[14]
[16]
Figure 8 shows the X-ray diffractograms for the samples decomposed at 800°C and 1100°C. Diffraction peaks characteristic of zinc oxide and different calcium silicates can be identified. It is noteworthy that although the formation of different magnesium silicates is thermodynamically favourable in this temperature
[17] The standard free energy values for the reactions show that ZnO can be reduced by carbon at a temperature lower than willemite – 1229.5K (956°C), which justifies the low temperatures at the
Figure 8—X-ray diffractogram for the WC sample calcined at (A) 800°C and (B) 1100°C. (w) willemite – Zn2SiO4; (q) quartz – SiO2; (a) alite; (t) walstromite - CaSiO3; (lr) larnite - Ca2SiO4; (L) lime - CaO; (z) zincite – ZnO; (p) periclase - MgO; (Mt) montcelite - CaMgSiO4; (Ak) akermanite; (G) gehlenite; (b) Ca3SiO5 The Journal of the Southern African Institute of Mining and Metallurgy
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Carbothermic reduction of a willemite concentrate for use in the Waelz process beginning of the CW sample reduction. Figure 9 shows the log diagram of (pCO2/pCO) as a function of temperature for the zinc oxide reduction reaction, where it can be seen that this oxide will be reduced by a less reducing pCO2/pCO mixture than that required to reduce willemite. Since the presence of calcium oxide in the sample decreased the minimum temperature required for reduction, thermogravimetric carbothermic reduction assays in the presence of CaO (20% w/w) were performed to verify the influence of CaO on the process. Figure 10 shows the thermogravimetric curve of CW reduction in the presence of CaO, where one can observe the same events A and B, present in the TG curve for willemite concentrate reduction (Figure 4). The results show that in the presence of CaO, the mass loss was higher, suggesting the reduction of a greater amount of zinc oxide. Finally, in addition to events A and B, a new thermal event (event Y) could be observed in the TG and DTG curves when calcium oxide is added to the system. The authors believe that the mass loss observed in event Y can be attributed to the beginning of dolomite decomposition and to the reduction of metal oxides (Pb and Cd) that are always present in zinc ores. These reactions release CO2, which reacts with the calcium oxide (carbonation) forming calcium carbonate (Equation [18]), it is worth noting that calcium oxide carbonation is thermodynamically favourable at temperatures lower than 950°C.
Figure 9—Diagram of log(pCO2/pCO) as a function of temperature for the Zn-O-C system
Figure 10—TGA and DTG curves for the reduction of willemite concentrate with charcoal (40% w/w) in the presence of calcium oxide (20% w/w) in an inert atmosphere (N2 50 ml/min) at a heating rate of 10°C/min 518
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[18]
Experiments in a horizontal tube furnace Before being reduced in a horizontal tube furnace, CW samples were calcined at a temperature of 810°C. This eliminated the thermal event associated with dolomite calcination and ensured that, in the zinc extraction calculations, the mass loss values obtained could be attributed only to the reduction of zincite and willemite (Equations [1] and [9]). After verifying the minimum temperature for the reduction of the CW sample from the TGA curves, reduction experiments were carried out in a horizontal tube furnace at a temperature of 1100°C, varying the amount of CV added to the system. Figure 11 shows the zinc extraction values obtained in these experiments. As can be seen, the extraction values were constant when the amount of CV added was greater than 20%; it is important to stress that the stoichiometric amount required for the reduction would be approximately 11% (Equation [9]). The results also show that using 20% C at 1100°C it was possible to extract approximately 86% of the zinc present in the CW sample. The extraction value obtained is comparable to that found by Clay and Schoonraad (1976), who treated a blend of willemite concentrate and tailings using the Waelz process. They obtained a zinc extraction of approximately 90% at 1100°C using a 30% addition of reducing material (anthracite duff, coke breeze, and reclaimed reductant). According to Harris (1936), some industrial plants were able to treat calamine waste by adding only 10‒12% coke to the Waelz furnace, although the coke addition used in industrial processes typically ranges from 20‒35%. It is noteworthy that values as high as 45‒55% coke in feed material were reported in zinc production. After determining the optimum amount of CV needed to reduce willemite concentrate, experiments were carried out to determine the influence of temperature on zinc extraction (Figure 12). The results show that zinc extraction decreases with decreasing temperature, the highest extraction of 86% being obtained at 1100°C. Other authors who utilized different zinc-bearing materials have also reported this temperature as the optimal. Furthermore, the formation of accretions has been observed at temperatures exceeding 1200°C (Clay and Schoonraad, 1976). Industrial processes typically operate at temperatures close to 1100°C. (Krupka, Ochab, and Miernik, 2000; Harris, 1936).
Figure 11—Influence of charcoal addition on zinc extraction from the CW sample by carbothermic reduction (T =1100°C; time = 1 h) The Journal of the Southern African Institute of Mining and Metallurgy
Carbothermic reduction of a willemite concentrate for use in the Waelz process Assuming that the major mineral constituents of the sample (willemite and dolomite) were effectively reduced (Equation [9]) and calcined (Equation [7]), the estimated basicity (B) of the process, based on the experiments performed with varying quantities of CaO, ranges from 0.32 (0 % CaO) to 1.75 (40% CaO). This suggests that, besides enhancing the extraction of Zn, the addition of CaO will also contribute to better process control. Analysis of the slag generated at 1100°C, reaction time 1 hour, with with 5% CaO and 20% carbon yielded a calculated basicity of 0.38.
Conclusion
Figure 12—Influence of temperature on zinc extraction from CW sample by carbothermic reduction (20% C; time = 1 h)
As shown in the TGA curves (Figure 10), the presence of CaO in the concentrate promoted an increase in mass loss. Thus, reduction tests were performed in a tubular furnace aiming to evaluate the influence of CaO on zinc extraction (Figure 13). The results show that the presence of CaO significantly increased zinc extraction during carbothermic reduction at 1050°C. A CaO addition of only 5% increased zinc extraction by 34%. As discussed earlier, this increase can be ascribed to the promotion of the thermal decomposition of willemite by CaO (Equations [13] and ]14]). The effect of temperature on zinc extraction in reduction tests with CaO is shown in Figure 14. The addition of CaO improved zinc extraction at all temperatures (Figure 15). The best extraction (93%) was obtained at a temperature of 1100°C for 1 hour with 5% CaO addition and 20% carbon. The basicity of the slag generated by the Waelz process is determined by Equation [19]:
It was possible to obtain approximately 86% zinc extraction from a willemite concentrate using charcoal as a reducing agent at a temperature of 1100°C for 1 hour reaction time. The extraction values increased with increasing temperature, and the best results were obtained with 20% charcoal in the charge. During the reduction, the calcination of dolomite, present as a gangue constituentin the concentrate, promoted the formation of calcium oxide, which reacted with willemite to form zinc oxide and calcium silicates. The formation of zinc oxide allowed reduction of the concentrate to begin at a temperature 60°C lower than the minimum thermodynamic temperature for the reduction of willemite. The addition of only 5% CaO to the willemite concentrate improved the zinc extraction at all temperatures studied. At a temperature of 1100°C, with 20% C and 5% CaO, it was possible to extract approximately 93% Zn, 8% more than without addition of CaO under the same conditions.
[19] where %MO is the percentage of metallic oxide in the slag. Basicities between 0.2 and 0.5 denote an acid process, and values from 1.5 to 4 a basic process. The operational control of a Waelz plant between these two conditions is exceptionally challenging (Mager et al., 2000; Mattich et al., 1998). Figure 14—Influence of temperature on zinc extraction from willemite concentrate in the presence of CaO (time = 1 h; 5% CaO; 20% CV)
Figure 13— Influence of the amount of CaO addition on the extraction of zinc from the CW sample by carbothermic reduction (time = 1 h; 1050°C; 20% CV) The Journal of the Southern African Institute of Mining and Metallurgy
Figure 15—Zinc extraction from the CW sample in the presence and absence of CaO VOLUME 123
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Carbothermic reduction of a willemite concentrate for use in the Waelz process Acknowledgement This study was financed in part by the Fundação de Amparo à Pesquisa do Estado de Minas Gerais — Brazil (Fapemig) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) [Coordenação de Aperfeiçoamento de Pessoal de Nível Superior]. The authors are also grateful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the partnership and financial support throughout the research.
Credit author statement
VSC – Writing; Methodology; Investigation. GML – Writing; Funding acquisition; Reviewing. VAL – Validation; Resources; Funding acquisition. RFMS – Validation; Funding acquisition; Reviewing and Edition. VAO – C onceptualization; Methodology; Investigation; Supervision; Validation; Resources; Writing; Visualization; Funding acquisition.
Conflict of interest On behalf of all authors, the corresponding author states that the authors have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Zhang, Q., Wen, S., Wu, D., Feng, Q., and Li, S. 2019. Dissolution kinetics of hemimorphite in trichloroacetic acid solutions. Journal of Materials Research and Technology, vol. 8. pp. 1645–1652. https://doi.org/10.1016/j.jmrt.2018.11.010 Zhang, X., Chen, L., Sun, Y., Bai, Y., Huang, B., and Chen, K. 2018. Determination of zinc oxide content of mineral medicine calamine using near-infrared spectroscopy based on MIV and BP-ANN algorithm. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 193. pp. 133–140. https://doi. org/10.1016/j.saa.2017.12.019
Li, Q.X., Hu, H.P., Zeng, D.W., and Chen, Q.Y. 2013. Solubility of hemimorphite in ammonium sulfate solution at 25°C. Transactions of Nonferrous Metals Society of China, vol. 23. pp. 2160–2165. https://doi.org/10.1016/S1003-6326(13)62712-0
Zhang, Y., Deng, J., Chen, J., Yu, R., and Xing, X. 2014. A low-cost and large-scale synthesis of nano-zinc oxide from smithsonite. Inorganic Chemistry Communications, vol. 43. pp. 138–141. https://doi.org/10.1016/j. inoche.2014.02.032
Liu, Z., Liu, Z., Li, Q., Cao, Z., and Yang, T. 2012. Dissolution behaviour of willemite in the (NH4)2SO4–NH3–H2O system. Hydrometallurgy, vol. 125–126. pp. 50–54. https://doi.org/10.1016/j.hydromet.2012.05.006
Zhao, D., Yang, S., Chen, Y., Tang, C., He, J., and Li, H. 2017. Leaching kinetics of hemimorphite in ammonium chloride solution. Metals, vol. 7. pp. 237. https:// doi.org/10.3390/met7070237 u
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Cost modelling for dimension stone quarry operations by M.A. Raza¹, S. Raza¹, M.U. Khan¹, M.Z. Emad¹, K. Jalil2, and S.A. Saki¹
Affiliation:
1 University of Engineering and
Technology (UET) Lahore, Pakistan.
2 Khawar Jalil Mining Consultants
(KJMC), Pakistan.
Correspondence to: M.U. Khan
Email:
usman@uet.edu.pk
Dates:
Received: 21 Mar. 2021 Accepted: 29 Aug. 2023 Published: November 2023
How to cite:
Raza, M.A., Raza, S., Khan, M.U., Emad, M.Z., Jalil, K., and Saki, S.A. 2023 Cost modelling for dimension stone quarry operations. Journal of the Southern African Institute of Mining and Metallurgy, vol. 123, no. 11. pp. 521–526 DOI ID: http://dx.doi.org/10.17159/24119717/1578/2023 ORCID: M.A. Raza http://orcid.org/0000-0001-5373-8795 M.U.Khan http://orcid.org/0000-0002-6260-6679 M.Z. Emad http://orcid.org/0000-0001-8537-8026
Synopsis
Dimension stone mining is Increasing because of growing demand from the building and construction industries. Diamond wire saw cutting is a popular dimension stone mining technique around the world. Estimation of the production cost for this method is critical for these operations. In this research a production cost model was developed for the mining of granite using a diamond wire saw. Cost and production data were collected from a granitic dolerite operation in Pakistan for a 4.5-year period, and analysed to identify the cost components. Fuel (34%), labour (15%), consumables (40%), and maintenance (5%) were found to be the four major cost components in this operation. A regression-based dimension stone production cost model incorporating statistically significant variables was developed. The data presented a strong correlation of production cost with fuel, labour, and consumables costs. Finally, a production cost model based on the consumption cost of diamond wire is presented. The model was verified using actual production cost data, which indicated 95% (R2 = 0.95) variance in the data between the predicted and actual production cost values. The model may help field engineers in computing their dimension stone operational cost during the cutting phase.
Keywords
dimension stone, diamond wire saw, modelling, production cost, granite mining.
Introduction Dimension stone is a technical and commercial term for all natural stones that can be quarried in blocks of different dimensions and processed by cutting or splitting, and which possess the technical and aesthetic properties required for use in the building and construction industries (PERC, 2021). Traditionally, dimension stone has been mined using common surface mining and rock-breakaging techniques such as splitting using explosives and cutting using various types of saw (Rehman et al., 2018; Ashmole and Motloung, 2008; Mamasaidov, Mendekeev, and Ismanov, 2004. Sawing is becoming more popular as this results in less wastage and a product with fewer cracks (Mendekeev, 2004). Of the various cutting techniques, diamond wire sawing, is the most widely used, and has become increasingly popular during the last three decades (Careddu, Perra, and Masala, 2019). A typical production cycle of this technique consists of five phases: (1) drilling, (2) cutting, (3) block dropping, (4) block slicing. and (5) loading. During the drilling phase, three mutually perpendicular holes are drilled in the rock mass with a common termination point, as illustrated in Figure 1. The cutting phase involves cutting a block in three planes using diamond wire. Other cutting techniques, such as disc cutting, may also be employed. The principle for diamond wire cutting involves pulling a continuous loop of wire, fitted with diamond-bonded steel beads, in a plane. The diamond wire is passed through two drill-holes, forming a closed loop and running over the wire saw pully which is connected to a track-mounted motor. The wire cuts through the plane while tension is maintained in the wire by continuously propelling the motor on the track as shown in Figure 2. Water is continuously fed during cutting to cool the wire. Once one plane is cut, the same procedure is repeated to cut the block in the other two planes. The block is then available for excavation. The remaining three phases of extraction are related to the excavation and loading of the block. During block dropping, the block is separated from the parent rock mass for easier processing. For some benches the block dropping phase may be omitted. During block slicing, smaller slices are cut from the larger block for loading and transportation. The diamond wire is a multi-strand steel wire with equally spaced steel beads (commonly 25 to 50 per metre based on the cutting requirements) with diamond abrasive. The wire is crimped at intervals to make it resistant to unwinding. The common wire types are manufactured for marbles and granites, both for dry and wet cutting (Tantussi, Lanzetta, and Romoli, 2003; Diamond Pauber, 2023).
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Cost modelling for dimension stone quarry operations stone extraction. The research was conducted within the specific context of granitic rocks. The outcomes will enable the industry and engineers to realistically estimate the cost and forecast probable production outputs for the incurred costs, thus assisting the planners to prepare realistic feasibility studies for dimension stone mining projects.
Methodology
Figure 1—A schematic of block cutting for dimension stone mining. Three orthogonal drill-holes define three planes of cutting. The drill-holes terminate at a common point
Block cutting is the primary cost component for a diamond wire operation in dimension stone mining, as observed in the field and in this research, and therefore should be studied for cost-benefit analysis. The performance of the wire saw machine is critical for optimizing the operations (Jain and Rathore, 2011). The wear of the diamond beads on the wire and the operational parameters are the primary factors that govern the cost and performance of a diamond wire cutting operation (Bortolussi et al., 1995; Korre and Durucan, 2000; Mikaeil et al., 2018; Almasi et al., 2017; Mosch et al., 2011; and Ulyakov, 2015). The wear rate of the diamond wire is higher for harder rocks such as granite than for soft rocks such as marble (Careddu and Marras, 2015). Pakistan is endowed with large deposits of granite and marble which present good potential for supplying the dimension stone market across the globe. However, a lack of technology and skilled labour, and shortage of area-specific mining knowledge, are major barriers to converting these resources into meaningful revenue and contribution to the country’s GDP (Business Recorder, 2012; Express Tribune, 2019). Cost estimation is one of the critical aspects of any dimension stone operation. Unfortunately, little research has been done to estimate and model the costs incurred in the use of diamond wire cutting technology for stone extraction. This paper presents a cost model based on statistical analysis of the cost centres for a dimension stone quarry that may be useful for similar operations in the area or elsewhere. The cost centres were established after a detailed analysis of different cost components of
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Results and discussion Based on the data collected from the field, percentage costs were generalized for the broader implications (i.e., for all granitetype rocks) as presented in Figure 3 as a pie chart of various cost components. Consumable cost (C) was the highest incurred cost during bench cutting phase, at 39% of total cost, while fuel cost (F) was 34%, labour cost (L) 15%, and maintenance cost (M) was 5%. Overhead expenses (O) were computed at 7% of the total cost. Overhead expenses, although marginally higher than the maintenance cost, were ignored for the purpose of cost modelling as the focus of this research was to investigate the relationship between operating costs and stone production. Overhead are not standardized costs and may vary considerably based on factors such as equipment care policies and dealership support. Maintenance costs, however, contribute to the overall operating costs and are therefore included in the cost modelling.
Figure 2—Diamond wire saw machine on surface track 522
Data was collected from M/S Indus Mining (Private) Limited (IML), which mines dolerite (termed commercially ‘black granite’) in Tehsil Oghi, district Mansehra of Pakistan. The deposit is located at approximately 72°55E 34°26ʹ N. The stone is excavated using diamond wire cutting on one active level, yielding blocks as the primary product and boulders as byproduct. One 41 kW wire saw machine (Marini) and a compatible 207 kVA generator operate in two 8-hour shifts. A diamond wire with injected vulcanized rubber is used for cutting the dolerite. This wire has 40 sintered beads per metre with an external bead diameter of about 12 mm. Figure 2 shows the diamond wire saw machine on track at the IML site. A 4.5-year (January 2013 to June 2017) data-set for stone production and costs was used for this study. In the first step, the collected data was studied and organized for various cost heads. After a thorough examination the cost data was divided into two major components – operating costs and overhead costs. The operating cost was further subdivided into four cost centres: fuel (F), labour (L), maintenance (M), and consumables (C). Other minor costs, such as equipment depreciation and insurance, were grouped collectively as overhead expenses (O). Fuel cost (F) included direct diesel and lubrication expenses. Labour cost (L) included salaries, bonuses, and expenses related to on-site facilities for workers such as food and laundry. Consumable cost (C) included diamond wire and machine jointing costs. Maintenance cost (M) included all expenses incurred for preventative maintenance and breakdowns of generators and wire saw machines. The maintenance cost was estimated based on the costs for parts and technicians’ salaries. Once the cost data was organized, the data was statistically analysed using SPSS (R-17) software using the cost centres identified in the first phase. SPSS is a popular commercial software package for data analysis. The software was chosen due to its user-friendly interface and robust algorithm for statistical data analysis. SPSS has a facility for importing data from Excel, which was handy in this research, and offers multiple tools for data analysis and model creation.
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Figure 3—Cost breakdown for bench cutting at IML
Diamond wire was the primary consumable item used in the cutting phase, and which mostly defined the consumables cost. Monthly requirements for diamond wire depend on multiple factors such as abrasiveness and hardness of the rock, the wire saw machine’s operational parameters, number of working horizons, bench dimensions, and total production. Fuel consumption was a little more than one-third of the total cost. Fuel consumption was dependent on cutting time, which further depended on factors such as motor power, cuttability of the rock, and speed. Cutting time could be a key reason for higher fuel cost. Wire saw operations require high skill levels. The operator needs to manually adjust the parameters such as tension on the wire, cutting speed, and water flow rate, as these have direct impact on machine health and longevity as well as production. These parameters are adjusted onthe-go during cutting and require high skill levels. Small personal and operational errors during operation may lead to severe losses or fatalities. For example, an inexperienced operator trying to achieve higher cutting rates may apply too much tension and use a higher speed, resulting in breaking of the diamond wire which can cause accidents. Highly skilled operators cost more in terms of salaries and other allowances, resulting in higher labour costs compared with other surface mining operations. Maintenance and overheads costs were almost equal for this operation. A regression model was developed to study correlations between the production and cost centres. Pearson’s correlation coefficient was used to find the correlation between total production (tons) and identified cost (PKR) components. For both correlation and regression analyses, a p-value (significance level) of 0.05 was fixed as the benchmark. This is a common standard value for significance testing. Only statistically significant variables were included in the final regression model.
The regression analyses were conducted in SPSS, with production cost as the dependent variable and various cost components as independent variables, resulting in Equation [1], where β0 is a constant and B1, B2, B3, and B4 are unstandardized regression coefficients associated with different cost variables. [1] where Pc is the production cost and F, L, C, and M are independent variables for fuel cost, labour cost, consumable, and maintenance cost respectively. Table I gives the Pearson’s correlation coeficients between production (dependent variable) and IL, C, and M (independent variables) incurred during the bench cutting phase. As depreciation and insurance costs (overheads) are fixed costs, and do not affect the operating cost, these cost components were excluded from the remaining analysis. In Table I, the p-values for correlations of production with fuel cost, labour cost, and consumable cost are zero, which suggests that each correlation is significant at the 0.01 level. However, we could not establish any causality between variables on this basis alone. The p-value for correlation between production and maintenance is 0.0031, which is insignificant. Strong correlations were observed between production and fuel cost (r = 0.974), between production and consumable cost (r = 0.951), and between production and labour cost (r = 0.786). A weak correlation was observed between production and maintenance cost (r = 0.779). The r values were positive in all cases, indicating that an increase (decrease) in one variable will cause an increase (decrease) in the other.
Table I
Correlation of production and production cycle costs in bench cutting phase (N=54)
Production
Fuel cost (F)
Labour cost (L)
Consumable cost (L)
Maintenance cost (M)
Pearson correlation I
0.974**
0.786**
0.951**
0.294**
Sig. (2-tailed) p-value
0.000
0.000
0.000
0.031
**Correlation is significant at the 0.01 level (2-tailed) The Journal of the Southern African Institute of Mining and Metallurgy
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Cost modelling for dimension stone quarry operations Table II
Regression analysis results Unstandardized coefficients
Model
1
Standardized coefficients T
Sig. (p-value)
‒4.340
0.000
6.809
0.000
4.499
0.000
0.312
4.012
0.000
–0.007
–0.149
0.749
Beta (βi)
B
Std. error
(Constant)
‒574.570
121.838
Fuel
0.001
0.000
‒0.565
Labour
0.003
0.001
0.165
Consumable
0.001
0.000
Maintenance
0.000
0.001
Adjusted R2 = 0.970
Dependent variable: Production
Table III
Regression analysis of statistically significant variables Unstandardized coefficients
Model
1
Standardized coefficients
T
Sig. (p-value)
–5.048
0.000
6.817
0.000
0.168
4.622
0.000
0.313
3.969
0.000
B
Std. error
(Constant)
–575.678
118.0081
Fuel
0.001
0.000
0.564
Labour
0.003
0.001
Consumable
0.001
0.000
Beta (βi)
Adjusted R2 = 0.970
Dependent variable: Production
Table IV
Regression analysis of statistically significant variables Unstandardized coefficients
Model
1
B
Std. error
(Constant)
-211.027
42.817
Consumable
0.002
0.000
Dependent variable: Production
Table II shows the relationship between production and bench cutting cost components obtained through regression analysis. Here again, the p-values for F, L, and C, are 0.000, which is considerably less than 0.05. This suggests that the relationships of these variables with production are statistically significant. In the case of maintenance cost, the p-value is 0.458 which is considerably higher than 0.05. This suggests that the relationship of maintenance cost with production is statistically insignificant. The adjusted R2 value for this analysis is 0.97, which means that the model explains 97% of the variance in the data. There is still a need to omit the statistically insignificant variable of maintenance cost from the optimum cost model. Table III shows the regression analysis results after omitting the statistically insignificant variable of maintenance cost. The adjusted R2 value for the new cost model is again 0.967, which means that this model too describes nearly 97% of the variance in data. However, this model contains all statistically significant independent variables only. 524
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Standardized coefficients Beta (βi)
0.951
T
Sig. (p-value)
-4.929
0.000
22.072
0.000
Adjusted R2 = 0.904
Equation [2] represents the cost model for different cost factors that are involved in bench cutting. [2] Positive B values for both independent variables suggest a direct relationship between production and the independent variables. The B values define the coefficients for Equation [2] and establish the relationship between production and component costs. Similarly, the standardized coefficients (βi) suggest variations in the standard deviations. The beta coefficient values also suggest that fuel cost has an approximately 3.5 times stronger influence on production than does labour cost , while consumables cost has approximately 2 times stronger influence. The above model presents the predictive cost model for diamond wire saw production in terms of labour, fuel, and consumables costs. This theoretical model is not ideal for practical use by the estimation engineers, as many combinations of F, L, The Journal of the Southern African Institute of Mining and Metallurgy
Cost modelling for dimension stone quarry operations and M can exist. Furthermore, in our field observation we found that there is more need to estimate production based on diamond wire consumption, i.e., production per unit cost of diamond wire (consumable cost in our case). Therefore, a cost model was derived based on consumables cost only. Table IV presents the regression analysis between P and C only. [3]
Acknowledgment The researchers are thankful for the support of Indus Mining (Pvt.) Limited, Pakistan for provision of data for this project.
References Almasi, S.N., Bagherpour, R., Mikaeil R., and Ozcelik, Y. 2017. Developing a new rock classification based on the abrasiveness, hardness, and toughness of rocks and pa for the prediction of hard dimension stone sawability in quarrying. Geosystem Engineering, vol. 20. pp. 295–310.
The model is simpler, practical, and still explains 95% of the variance in the data.
Ashmole, I. and Motloung, M. 2008. Dimension stone: The latest trends in exploration and production technology. Proceedings of Surface Mining 2008. Southern African Institute of Mining and Metallurgy, Johannesburg. pp. 5–8.
Model validation
Bortolussi, A., Ciccu, R., Manca, P.P., and Massacci, G. 1995. Computer simulation of diamond-wire cutting of hard and abrasive rock. International Journal of Rock Mechanics and Mining Sciences & Geomechanics abstracts, | vol. 32. -Doi: 0.1016/0148-9062(95)90156-Y
The production cost values were estimated using the model presented in Equation [3]. These values were plotted against the actual production values as a function of consumables, as shown in Figure 4. An R2 value of 0.951 was obtained between the actual and predicted production. The strong correlation proves the validity of the model.
Conclusions Dimension stone mining practice in Pakistan is experience-based and there is shortage of technical knowledge and expertise in this field. As a result, current operations are conducted using less economical or low productivity techniques. We analysed 4.5 years of historical data from a working stone quarry in Pakistan. The analysis revealed four major cost centres for dimension stone production using diamond wire sawing. A detailed statistical analysis showed that three cost components (fuel, labour, and consumables in the form of diamond wire cost) were statically significant and responsible for 97% of the variance in the data. A predictive production cost model for the diamond wire saw based on the consumables costs, which largely comprise the cost of diamond wire, is presented and verified using actual production data. The cost model predicted 95% of the cost variance at the selected operation. Although the current production cost model has been developed for a specific operation, it is expected that it should be applicable to similar operations. It is planned to verify the moder on data from a larger pool of dimension stone quarries in Pakistan. Furthermore, the model was based on the cost of diamond wire, which is variable. It could be better to base the model on diamond wire consumption. This will require the relevant data to be recorded at the mine. This is planned for future research as well.
Careddu, N. and Marras, G. 2015. Marble processing for future uses of CaCO3microfine dust: a study on wearing out of tools and consumable materials in stoneworking factories. Mineral Processing and Extractive Metallurgy Review, vol. 36. pp. 183–191. Careddu, N., Perra, E.S., and Masala, O. 2019. Diamond wire sawing in ornamental basalt quarries: Technical, economic and environmental considerations. Bulletin of Engineering Geology and the Environment, vol. 78. pp. 557–568. Diamond pauber. 2023. Data sheet. Https://www.Diamondpauber.It/stoneproducts Express tribune. 2019. Pakistan's marble sector declining due to lack of attention. Karachi. Https://tribune.Com.Pk/story/2055198/pakistans-marble-sectordeclining-due-lack-attention Busines recorder. 2012. Issues, problems faced by marble sector highlighted, Karachi. Https://fp.Brecorder.Com/2012/08/201208171228736/ Jain, S.C. and Rathore, S.S. 2011. Prediction of cutting performance of diamond wire saw machine in quarrying of marble: A neural network approach. Rock Mechanics and Rock Engineering, vol. 44. pp. 367–371. Korre, A. and Durucan, S. 2000. The effects of granite microstructure on the sawing performance of diamond wires. International Journal of Surface Mining, Reclamation and Environment, vol. 14. pp. 87–102. Mamasaidov, M.T., Mendekeev, R.A., and Ismanov, M.M. 2004. Generalized model of technology for article production from stone massif. Journal of Mining Science, vol. 40. pp. 521–527. Mendekeev, R.A. 2004. Analysis of raw material losses in sawing stone blocks into facing products. Journal of Mining Science, vol. 40. pp. 515–520. Mikaeil, R., Haghshenas, S.S., Ozcelik, Y., and Gharehgheshlagh, H.H. 2018. Performance evaluation of adaptive neuro-fuzzy inference system and group method of data handling-type neural network for estimating wear rate of diamond wire saw. Geotechnical and Geological Engineering, vol. 36. pp. 3779–3791. Mosch, S., Nikolayew, D., Ewiak, O. and Siegesmund, S. 2011. Optimized extraction of dimension stone blocks. Environmental Earth Sciences, vol. 63. pp. 1911–1924. Perc. 2021. Pan-European Standard for the Public Reporting of Exploration Results, Mineral Resources and Reserves. Appendix a. Reporting of Exploration Results, Mineral Resources and Mineral Reserves for Dimension Stone, Ornamental and Decorative Stone. Pan-European Reserves and Resources Reporting Committee, brussels. Https://percstandard.Org/wp-content/uploads/2021/09/ PERC_REPORTING_STANDARD_2021_RELEASE_01Oct21_full.Pdf Pershin, G.D. and Ulyakov, M.S. 2015. Enhanced dimension stone production in quarries with complex natural jointing. Journal of Mining Science, vol. 51. pp. 330–334. Rehman, Z.U., Hussain, S., Mohammad, N., Raza, S., Sherin, S., Khan, M., Tahir, M., and Khan, M. 2018. Comparative analysis of different techniques used for dimension stone mining. Journal of Himalayan Earth Science, vol. 51. pp. 23–33.
Figure 4—Predicted production values versus actual production values as a function of consumables cost The Journal of the Southern African Institute of Mining and Metallurgy
Tantussi, G., Lanzetta, M., and Romoli, V. 2003. Diamond wire cutting of marble: state of the art, modeling and experiments with a new testing machine. Proceedings of the 6th International Conference of the Italian Association of Mechanical Technology, Enhancing the Science of Manufacturing. pp. 113–126. https://arpi.Unipi.It/retrieve/handle/11568/190631/17498/artperlinefin.Pdf u VOLUME 123
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Associate / Full Professor – Mining Engineering King Fahd University of Petroleum & Minerals (KFUPM), College of Petroleum Engineering & Geosciences (CPG) invites applications for senior level faculty position (Associate Professor or Professor) in the field of Mining Engineering in a newly established Mining Engineering program. We seek an outstanding individual to boost the program’s reputation for cutting-edge research, dedicated teaching, and university and professional service. This four-year degree program will prepare the graduates to serve the Mining industry and the Kingdom of Saudi Arabia for next several decades to come. As identified by the Kingdom of Saudi Arabia Vision 2030, the Minerals sector is expected to be the 3rd Pillar of Saudi Arabia’s economy, along with Oil and Gas, and Petrochemicals. The new program in Mining Science & Engineering is well supported by the government and private sector including Ma’aden, one of the fastest-growing mining companies in the world and the largest multi-commodity mining and metals company in the Middle East. KFUPM has a strong tradition and international reputation in applied undergraduate and graduate education. KFUPM ranks 4th globally in the 2023 QS World University Rankings by subject category of Petroleum Engineering. The university also ranks 9th globally by subject category of Minerals and Mining Engineering. State-of-the-art engineering research and analytical facilities are housed in CPG, including most instrumentation necessary for cutting-edge petroleum and mining engineering, and mineral exploration research. The Mining Science & Engineering program is enhanced through close collaboration with the Department of Petroleum Engineering, the Department of Geosciences and the Center for Integrative Petroleum Research within the College, and with other departments on campus. Information about KFUPM, CPG, CIPR, and the Department can be found at http:// cpg.kfupm.edu.sa. Responsibilities: The successful candidate will be expected to develop a strong and vibrant research program and establish or build on an international reputation through publications, in addition to teaching at the undergraduate level, design and development of instructional and research laboratories, planning and supervising field trips, development of graduate programs, directing graduate research, and supervising thesis projects. Qualifications: Candidates must possess a doctoral degree in the field of Mining Engineering or closely related engineering discipline. The successful candidate will have demonstrated success for high-quality basic and applied research and scholarship. Candidates should have research focus in one or more of these areas: Cooperative projects between science and mining engineering with high-level knowledge of a combination of subjects that include surface and underground mine operations and mine design, mine planning and evaluation, soil and rock mechanics, mine ventilation, and mine production technologies with environmental stewardship and sustainability. Candidates having experience on course development and curriculum design with teaching a broad range of subjects within and/or bridging the disciplines of materials science and engineering and mining engineering are preferred. Candidates are expected to advance KFUPM mission of being a leading Global R&D Center in Mining and Mineral Exploration and Processing. Applicants should demonstrate the potential for successful teaching and possess strong interpersonal and communication skills. Previous industry experience will be viewed positively. Compensation: Salary and benefits will be commensurate with qualifications and experience. KFUPM and CPG provide competitive benefits package including free furnished on-campus housing, fully paid health insurance, dependent education aid, and paid tickets for annual repatriation holidays. The annual contract includes two months of paid summer holiday. How to Apply: Applicants must send a letter of interest, a full curriculum vitae containing Scopus statistics (h-index and citations), a statement of teaching and research interests, and the names and contact information for a minimum of three references to: College of Petroleum Engineering & Geosciences, Human Resources Office, KFUPM, Dhahran 31261, Saudi Arabia. Preference is for email submissions to cpg-jobs@kfupm.edu.sa. Further Information: Further questions by qualified potential applicants can be addressed to Dr. Dhafer Al Shehri, Chairman, alshehrida@kfupm.edu.sa, and/or Prof. Shirish Patil, patil@kfupm.edu.sa, Petroleum Engineering Department. For more information about College of Petroleum Engineering and Geosciences, please scan the QR Code below:
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Employee engagement among women in technical positions in the South Africa mining industry by N. Mashaba1 and D. Botha1
Affiliation:
1 North-West University, Potchefstroom,
South Africa.
Correspondence to: D. Botha
Email:
Doret.Botha@nwu.ac.za
Dates:
Received: 12 Aug. 2022 Revised: 3 Sept. 2023 Accepted: 4 Sept. 2023 Published: November 2023
How to cite:
Mashaba, N. and Botha, D. 2023 Employee engagement among women in technical positions in the South Africa mining industry. Journal of the Southern African Institute of Mining and Metallurgy, vol. 123, no. 11. pp. 527–538 DOI ID: http://dx.doi.org/10.17159/24119717/2269/2023 ORCID: D. Botha http://orcid.org/0000-0003-2787-8107 N. Mashaba http://orcid.org/0000-0001-6629-5786
Synopsis
The aims of this study were to investigate the factors that influence women’s engagement in technical positions in the South African mining sector and to determine what could be done to promote their successful participation. A convergent parallel mixed-methods research design was used to ascertain the factors that facilitate, inhibit, and influence engagement. In the quantitative phase of the study, questionnaires were circulated to women employeees; and in the qualitative phase, semistructured interviews were conducted with employer representatives, most of whom were human resource personnel. Confirmatory factor analysis showed that the three-factor structure (vigour, dedication, and absorption) of the Utrecht Work Engagement Scale fit the sample data reasonably well. Although there is room for improvement, respondents demonstrated acceptable levels of engagement in their work. On the other hand, the qualitative findings showed that employee engagement is impacted by unfavourable working conditions, work–life balance, and the mining industry’s male-dominated work culture. The findings showed that employee engagement should be elevated to a core human resource function. To increase the participation of women in mining, human resource professionals are encouraged to collaborate with mine supervisors, managers, and employees to develop programmes that promote employees’ absorption in and dedication to their work.
Keywords
employee engagement, South Africa, technical mining positions, women in mining.
Introduction One of the major challenges in the mining industry is introducing and fully integrating women into the traditionally male-dominated sector (Zungu, 2011, p.4). A male-dominated industry is defined as one that has 25% or fewer women participating in it (Catalyst, 2013). Equal participation of both men and women is critical for a country’s economic growth to be effective and sustainable (Bayeh, 2016, p. 39). One of the reasons for women’s underrepresentation in the mining industry is the challenge of engaging women in technical positions (AHRC, 2013, p. 3; Botha, 2013, p. 200; Campbell, 2007, p. 8; Ledwaba, 2017, p. 17; Masvaure, Ruggunan, and Maharaj, 2014, p. 488). Technical positions in mining are held by employees with some form of tertiary qualification in the frontline tasks of exploration, quantification, development, , and processing of mineral resources (Terrill, 2016, p. 16). Engaged employees are essential for an organization – having engaged employees leads to reduced turnover, opportunities to recruit new talent, expansion of employees’ knowledge base, and a competitive edge over organizations with disengaged employees (Albrecht et al., 2015, p. 7). Employee engagement is crucial for staff retention (Kundu and Lata, 2017, p. 718). For the mining industry to become a driver of inclusive economic growth, gender considerations and women’s empowerment should be prioritized (BSR, 2017, p. 3). Gender equality is a human rights issue and a precondition for, and an indicator of, sustainable development (Alvarez, 2013, p. 13). Considering that women account for most of the world’s poor population, prioritizing their inclusion in the workplace, especially where they are less represented, would liberate them from a life of poverty and could contribute to countries’ economic growth. To achieve this, the mining industry must implement relevant measures to ensure that current employees are engaged to their fullest potential (Hughes, 2012, p. 39). Employee engagement is therefore significant for the viability and success of an organization because of its potential to positively influence the productivity, loyalty and retention of employees (Muthuveloo et al., 2013, p. 1546). There is a gap in the literature on research into women's engagement in technical mining jobs. Previous research (Lord and Eastham, 2011; MCA, 2005; MCSA, 2019) focused primarily on the topic of attracting and retaining women in the mining industry in general, but did not consider the importance of engagement as a factor that could influence women’s retention. These studies were conducted in Australia, not in the
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Employee engagement among women in technical positions in the South African mining industry South African context. Furthermore, other studies (AWRA, 2014; Bailey-Kruger, 2012; Botha, 2013; Hutchings, e Cieri, and Shea, 2011; Khoza, 2015; Ledwaba, 2017; Nyabeze, Espley, and Beneteau, 2010; Ozkan and Beckton, 2012; van der Walt, 2008) focused on women in mining, in general, and in all occupational categories rather than only those in technical positions. Diverting attention to women employed in technical mining positions is imperative given their underrepresentation in the industry. As a result, this research sought to fill the gap in existing knowledge. The paper begins with a theoretical framework of employee engagement and the factors that influence women’s engagement in the mining industry. The research methodology, empirical results, and findings are then presented, followed by a discussion of these. Finally, key conclusions and practical recommendations for enhancing women’s engagement in technical mining positions and their successful participation in the mining industry are given.
Literature review A theoretical framework of employee engagement Since 2002, various definitions of engagement have been proposed (Kuok and Taormina, 2017, p. 262; Leiter and Maslach, 2017, p. 55, Schaufeli et al., 2002). When Schaufeli et al. (2002) operationalized(2002) operationalised their three-factor engagement model, they noticed little attention was paid to concepts concerning the antithesis of burnout. They noted that while Kahn (1990) provided a theoretical model of the psychological presence of engagement, he did not propose an operationalization of the concept. However, Maslach and Leiter (1997) developed a theory based on the assumption that engagement is defined by three dimensions, namely energy, involvement, and efficacy, which are considered the opposites of the three burnout dimensions (exhaustion, cynicism, and lack of professional efficacy). According to Maslach and Leiter (1997, p. 17), employees become exhausted when they are overburdened emotionally and physically. When employees are cynical, they tend to be cold and distant towards their work and co-workers. Inefficacy is characterized by decreased feelings of competence and productivity at work (Maslach and Leiter, 2007, p. 368). It develops in response to an emotional exhaustion overload and is initially self-protective – an emotional buffer of detached concern (Maslach and Leiter, 2007, p. 368). This causes employees to reduce their involvement at work and even abandon their ideals (Maslach and Leiter, 1997, p. 18). According to Maslach and Leiter (1997, p. 23), burnout is an erosion of job engagement, as what starts as important, meaningful, and challenging work turns into unpleasant, unfulfilling, and meaningless work. Employees’ sense of engagement begins to diminish because of burnout, and there is a corresponding shift from these positive feelings to their negative counterparts. As a result, energy becomes exhaustion, involvement becomes cynicism, and efficacy becomes ineffectiveness (Maslach and Leiter, 1997, p. 24). Focusing on engagement signifies focusing on the energy, involvement, and effectiveness that employees bring to a job and develop through their work (Maslach and Leiter, 1997, p. 102). As a result, engagement is the positive pole, while burnout is the negative pole (Moshoeu, 2017,p. 149). Maslach, Schaufeli, and Leiter (2001, p. 417) define employee engagement as a persistent, positive affective-motivational state of fulfilment characterized by high levels of activation and pleasure. In 2002, Schaufeli et al. developed a new perspective on engagement based on Maslach and Leiter’s (1997) burnout theory. Schaufeli et al.’s (2002, p. 74) three-factor engagement model 528
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contends that burnout and engagement are conceptually distinct aspects that are not endpoints of some underlying continuum. Engagement is viewed through the lens of optimal human function, stressing that it is a positive, fulfilling, work-related state of mind characterized by vigour, dedication, and absorption (Moshoeu, 2017, p. 164; Schaufeli et al., 2002, p. 74). High energy levels, mental resilience, willingness to put effort into the work, and persistence when faced with challenges are demonstrated by vigour. Dedication can be described as a sense of significance, enthusiasm, inspiration, and pride in working for a particular organization. Absorption is attributed to a pleasant association with one’s work, where time passes rapidly without one experiencing challenges with detaching oneself from work (Schaufeli and Bakker, 2004, p. 295). As a result, vigour and dedication are seen as the opposites of exhaustion and cynicism (Schaufeli and Bakker, 2004, p. 295). Vigour and exhaustion have been labelled as energy or activation, while dedication and cynicism have been labelled as identification. According to Schaufeli and Bakker (2004, p. 3), while burnedout employees are exhausted and cynical, engaged employees are energized and enthusiastic about their work. Professional inefficacy was omitted from the definition of engagement, as Schaufeli and Bakker’s (2004, p. 5) research showed that exhaustion and cynicism are at the core of burnout, while professional efficacy seemed to play a smaller role. They noted that prior research had shown that engagement, rather than efficacy, is best defined by being immersed and happily absorbed in one’s work – a state of absorption. As a result, absorption is a distinct dimension of work engagement that is not synonymous with professional inefficacy (Schaufeli and Bakker, 2004, p. 295). Schaufeli et al. (2002) developed the Utrecht Work Engagement Scale (UWES) based on the assumptions of their theory. This scale was formulated based on the underlying assumption that engagement is the positive antithesis of burnout. Consequently, it is argued that the assessment of engagement and burnout should employ distinct measurement approaches. Schaufeli and Bakker (2004, p. 3) argued that assessing burnout and engagement with the same questionnaire has two drawbacks. First, they argued that it is impractical to expect both concepts to be inversely correlated. If employees are not burned out, it does not necessarily indicate that they are engaged in their work, and vice versa. Second, the relationship between burnout and engagement cannot be empirically studied when measured with the same questionnaire. Therefore, both constructs cannot be incorporated into the same model to study their concurrent validity. As a result, the UWES assesses the three dimensions of engagement (vigour, dedication, and absorption). The UWES was used in this study to measure the engagement levels of women employed in technical positions in mining in South Africa. The application of this scale is explained in detail in the Tools and data collection section.
A contextualization of women employed in mining The mining industry is perceived as male-dominated and often not a common or preferred field that women pursue (Botha, 2013, p. 179; Fernandez-Stark, Couto, and Bamber, 2019, p. 3). FernandezStark, Couto, and Bamber (2019, p. 3) estimate that globally, women occupy approximately between 5 and 10% of jobs in the mining industry – one of the lowest levels of participation of women across all economic sectors. This has been attributed to its traditionally masculine culture, accompanied by the physically intensive labour required (Botha, 2016, p. 252). The Journal of the Southern African Institute of Mining and Metallurgy
Employee engagement among women in technical positions in the South African mining industry Historical laws, policies, and traditional customs played a role in perpetuating the underrepresentation of women in mining. In May 1937, the International Labour Organization (ILO) effected the Underground Work (Women) Convention 45 of 1935, which prohibited women of all ages from being employed in any mine for underground work under article 2 (ILO, 2017). While this legislation has been revised and repealed, the ILO played a critical role in establishing labour standards. The Act was the only available template for some countries, especially European countries concerned with women’s work in mining (Lahiri-Dutt, 2019, p. 5). This propagated discrimination against women in mining. Even after the abolishment of discriminatory laws, women remain underrepresented globally. Although the mining industry is a key driver of economic growth in most countries, employment does not benefit all members of society, as it remains highly maledominated (Armah et al., 2016, p. 471; Baah-Boateng, Baffour, and Akyeampong, 2016, p. 9; Chichester, Pluess, and TaylorTaylos, 2017). Women in mining seldom occupy core occupations that often present more employment opportunities (Abrahamsson et al., 2014, p. 20; Segerstedt and Abrahamsson, 2019, p. 617). The same applies to managerial positions, as very few women are in decision-making roles (Catalyst, 2019). In other countries, women are better equipped, as they possess the relevant qualifications and skill sets, yet they are still not permeating the industry (Daley et al., 2018, p. 91, Fernandez-Stark, Couto, and Bamber, 2019, p. 16, Purvee, 2019). This is partly due to the industry’s masculine image, lack of opportunities for advancement, work environments that do not accommodate a work–life balance, and sexual harassment that prevails in the industry and is a deterrent for attracting more women, among other reasons (Cane, 2014, p. 188; Fernandez-Stark, Couto, and Bamber, 2019, p. 19; MiHR, 2016, p. 14). In South Africa, the mining industry supports a vast number of communities through employment. At least two other jobs are created in allied industries for every direct mining job, while each mining employee supports between five and 10 dependents (MCSA, 2020). Considering the role assumed by mining in South Africa’s communities, there is a notion that the industry remains of crucial importance to address the country’s triple challenge of poverty, unemployment, and inequality (Fabricius, 2019, p. 2). However, the industry’s progression towards achieving gender equality has been slow, as it remains male-dominated (MQA, 2020, p. 23). Currently, 17% of employees in mines are women (MQA, 2021, p. 18). Most of these women (52%) are employed in clerical support positions, and 19% are in top and senior management (MQA, 2019, pp. 13–14). Despite efforts by the Mining Charter to promote the participation of women in the industry and their advancement into management echelons, women remain a minority in non-core mining occupations, particularly in technical positions. Despite the issue of underrepresentation, the challenges faced by South African women working in mining are similar to those faced globally. Over the years, the need to reach gender parity and holistic inclusion of women has gained prominence in the mining industry. Gender parity is adjudged as a fundamental component of sustainable development (Nayak and Mishra, 2005, p. 1). In line with the United Nations sustainable goal of achieving gender equality and empowerment of all women and girls, there is a belief that a society cannot remain healthy and achieve adequate economic well-being without the full participation of women in the different economic sectors, including mining (Nayak and Mishra, 2005, p. 2). The Journal of the Southern African Institute of Mining and Metallurgy
Factors influencing employee engagement of women in mining The above section revealed that cultural and organizational norms in the mining industry have contributed to the underrepresentation of women in mining. The experiences of women already employed in the industry can either motivate or demotivate other women aspiring to enter the sector (Kaggwa, 2019, p. 1). The factors that influence the engagement of women employed in mining are discussed in the following subsections.
Compensation and benefits Compared to other sectors of the economy, the mining industry is known for paying its employees higher wages than the average remuneration (Pactwa, 2019, p.10). Attractive salaries and benefits motivate women to remain engaged in their work in the mining industry (van der Walt, 2008, p. 41). In his study on job demands, job resources, burnout, and engagement of employees in the mining industry in South Africa, van der Walt (2008, p. 6) found that poor salaries and benefits could contribute to employee burnout and disengagement from work. Salaries occasionally serve as a motivating factor for employees in need of money (Ntsane, 2014, p. 26).
Career development opportunities There is a strong association between career development and employee engagement (Guest, 2014, p. 146). Hlapho (2015:71) found that human resource development practices – such as training and development, employee feedback, career development opportunities, employee welfare schemes, and reward and recognition schemes – are key drivers of employee engagement. This assertion is supported by Ledwaba (2017, p. 60), who established that inadequate training and development prospects for women affect their morale and leave them without hope as regards growing in the mining industry. Organizations with high levels of engagement provide employees with opportunities to develop their abilities to acquire new skills and knowledge and to realize their potential (Simha and Vardhan, 2015, p. 5). Employees are more likely to commit to organizations that provide them with opportunities that facilitate career improvement (Aguenza and Som, 2012, p. 90). A lack of growth opportunities could lead to disengaged employees (van der Walt, 2008, p. 40).
Work–life balance Work–life balance employment practice involves providing employees with an environment where they can balance what they do at work with responsibilities and interests outside the workplace (Almaaitah et al., 2017, p. 26). The mining industry has not been unsusceptible to the challenges of fostering work– life balance for employees. Work–life balance is important for employee engagement (Lockwood, 2007, p. 4). Employees are most likely to be engaged in and attached to their organizations if they recognize that their employers consider their family life (Simha and Vardhan, 2015, p. 6). The study by van der Walt (2008, p. 40) on the engagement of employees in the mining industry in South Africa revealed that a lack of work–life balance was one of the factors that led to disengaged employees. Women in mining are most likely to take advantage of employment outside the mining industry that offers them more family-friendly work environments and arrangements that provide them with less physical, more comfortable jobs with higher salaries and higher social status (Botha, 2013, p. 200). VOLUME 123
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Employee engagement among women in technical positions in the South African mining industry Gender stereotyping and workplace culture Workplace culture plays a role in employee engagement (Lockwood, 2007, p. 4; Moletsane, Tefera, and Migiro, 2019, p. 128). For employees to be engaged, an organization needs to establish its employees’ feelings about their work environment (Moletsane, Tefera, and Migiro, 2019, p. 128). Effective engagement is also likely to depend on the type of organizational culture that is perceived by employees (Guest, 2014, p. 153). The overt prejudice, discrimination, and resistance towards women in mining could result in disengaged employees. The disengagement and alienation of women in mining are largely due to unequal workplace culture, the low perceived value by men, and lack of respect (AWRA, 2014). This assertion was corroborated by Hlapho (2015, p. 71), who found that the work environment and relationships with colleagues significantly affect employee engagement.
Hazardous working conditions and safety risks The hazardous working conditions and safety risks affect women’s perceptions and lead to the disengagement of those employed in the mining industry, which ultimately results in them leaving the industry as a whole (Bailey-Kruger, 2012, p. 15; Botha, 2014, p. 439; Simha and Vardhan, 2015, p.:5). Simha and Vardhan (2015, p. 5) highlight that the engagement levels of employees are affected if they do not feel secure or safe while working. Yuan, Li, and Tetrick (2015, p. 169) found that social interactions (co-worker support) and perceptions of safety practices (organizational commitment to safety) can collectively lead to high levels of engagement and safety behaviours. Therefore, organizations must implement appropriate measures to ensure equal health and safety measures for the engagement of women in mining.
Research methodology The research was conducted from a relational epistemology perspective (the premise that relationships in research are best established through what the researcher considers appropriate for the study), a non-singular reality ontology (the assumption that there is no single reality and that all individuals have their own and unique interpretations of reality), a mixed-methods research design (integrating quantitative and qualitative research methods), and value-laden axiology (conducting research that benefits people) (see Kivunja and Kuyini, 2017, p. 35).
Sampling Women employed in technical positions across various mining companies in South Africa were the target population for the quantitative phase of the study, while the qualitative phase focused on mining company representatives who were well-versed in issues of employee engagement. Convenience sampling (also known as availability sampling) was used to select the respondents for the quantitative phase of the study. The inclusion criteria were as follows: women who possessed some form of tertiary qualification in the frontline tasks of exploration, quantification, development, extraction and ,processing of mineral resources. This included women who were employed in positions requiring technical skills within the mining value chain, such as in geology, mining engineering, metallurgical engineering, chemical engineering, electrical engineering, analytical chemistry, mine surveying, and jewellery design and manufacturing. The exclusion criteria were women who were employed in administrative and supportive positions, such as clerical, secretarial, catering, and nursing and health work. In addition, purposive and convenience sampling was used to select the participants for the qualitative phase of the 530
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research. Purposive sampling is adopted when the researcher targets individuals with specific traits that are of interest or relevant to the study (Turner, 2019, p. 11). Moreover, non-probability sampling was used; thus the sample size could not be determined in advance. A total of 282 women in technical mining positions completed the structured questionnaire. Tthis sample size is comparable to previous studies conducted on women in mining (Botha, 2013 [156]; de Klerk, 2012 [100]; Mangaroo-Pillay, 2018 [165])1. In addition, 11 employer representatives participated in the qualitative data collection phase.
Tools and data collection Quantitative data was collected using a web-based, self-constructed coded questionnaire. The questionnaire included two sections. Section A contained biographical questions, including age, highest qualification, marital status, having children, the requirement to work shifts, duration of employment in the mining organization, and industry and work committee involvement. For Section B, the original 17-item UWES was used to measure the women’s level of engagement in their organizations. Wilmar Schaufeli provides permission on his website to use the UWES (Carnahan, 2013, p. 43). This is the commonly used measurement scale for employee engagement (Schaufeli and Bakker, 2004, p. 295). The UWES contains 17 questions in total: six that measure vigour, five that measure dedication, and six that measure absorption (Carnahan, 2013, p. 43). Since as early as 1999, studies have been conducted using the UWES and have shown that the scale is a valid tool that can be used to measure employee engagement (Carnahan, 201, p. 43). According to Schaufeli and Bakker (2004), the UWES is reliable and internally consistent, with a Cronbach’s alpha coefficient ranging between 0.80 and 0.90. The questionnaire was distributed through different channels. Among them was Women in Mining South Africa, which distributed the questionnaire’s link to women in technical mining positions in South Africa via their LinkedIn page. The questionnaire was also distributed to employees of various mines by human resource personnel, the Minerals Council South Africa, and the National Union of Mineworkers. In addition, semi-structured interviews were conducted, using an interview schedule. with employer representatives (who consisted mostly of human resource personnel) knowledgeable about employee engagement. The qualitative research participants were identified with the assistance of different mines, the MQA, and the National Union of Mineworkers. Owing to Covid-19 restrictions, participants were encouraged to participate in the interviews via video meeting platforms such as Zoom, Microsoft Teams, or Skype. Participants also had the option to respond to the interview in written format.
Data analysis and reporting The following statistical analyses were applied in the study to provide meaning to the collected data: descriptive statistics (frequency distributions, means, and standard deviation [SD]), multivariate analysis (exploratory and confirmatory factor analysis [CFA]), comparison tests (independent t-test and analysis of variance [ANOVA]) and correlation tests (the Pearson product-moment correlation). For the qualitative analysis, thematic content analysis was done to identify and analyse patterns or themes across data sets (see Wilson and MacLean, 2011, p. For the qualitative analysis, thematic content analysis was done to identify and analyse patterns or themes across data-sets (see Wilson and MacLean, 2011, p. 551). 1The square brackets indicate the sample size achieved The Journal of the Southern African Institute of Mining and Metallurgy
Employee engagement among women in technical positions in the South African mining industry Table I
Biographical information Item
Province currently employed
Mining subsector employed
Age
Highest qualification
Duration of employment in present position
Duration of employment in mining organisation
Duration of employment in the mining industry
Employment at the mine Requirement to work night shifts
Marital status
Children
Category
N
%
Free State Gauteng KwaZulu-Natal Limpopo Mpumalanga North-West Northern Cape Western Cape Cement, lime, aggregates and sand Coal mining Diamond mining Diamond processing Gold mining Jewellery manufacturing Other mining (includes the mining of iron ore, chrome, manganese, copper, phosphates and salt) Platinum group metals (PGM) mining 20–29 30–39 40–49 50–59 60 and older No schooling Less than high (secondary) school Completed some high (secondary) school Standard 10 / Grade 12, NATED 3 / NCV Level 3 National / Higher Certificate Advanced Certificate Diploma Advanced diploma Bachelor’s degree Honour’s degree Master’s degree Doctoral degree and/or postdoctoral degree Less than a year 1–3 years 4–6 years 7–9 years 0 10 years or more Less than a year 1–3 years 4–6 years 7–9 years 10 years or more Less than a year 1–3 years 4–6 years 7–9 years 10 years or more Underground On the surface Underground and on the surface No Yes Married Cohabiting/Living together Single Separated No Yes
4 51 6 29 46 109 29 4 6 49 13 1 23 2 65 119 91 127 47 14 1 3 1 4 48 16 8 25 46 32 59 32 2 43 125 41 31 37 3 86 61 28 55 32 86 61 28 55 54 154 69 197 84 87 31 145 18 100 181
1.4 18.1 2.1 10.3 16.3 38.7 10.3 1.4 2.1 17.4 4.6 0.4 8.2 0.7 2.0 42.2 32.3 45.0 16.7 5.0 0.4 1.1 0.4 1.4 17.0 5.7 2.8 8.9 16.3 11.3 20.9 11.3 0.7 15.2 44.3 14.5 11 13.1 11.3 30.5 21.6 9.9 19.5 11.3 30.5 21.6 9.9 19.5 19.1 54.6 24.5 69.9 29.8 30.9 11.0 51.4 6.4 35.5 64.2
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Employee engagement among women in technical positions in the South African mining industry Ethical considerations The Basic and Social Sciences Research Ethics Committee of the Faculty of Humanities, North-West University, granted permission to conduct the research (ethics number NWU-01007-20-A7). The researcher adhered to the following ethical standards: voluntary participation, informed consent, anonymity, confidentiality, privacy, respect, no harm, and protection from undue risks (Gravetter and Forzano, 2009, p. 107; Wilson and MacLean, 2011, pp. 599, 611). Data was collected face -o-face, and all the necessary Covid-19 protocols were adhered to (e.g., permission to access the location, wearing masks, sanitizing, physical distancing, safety toolkit for fieldwork, clean and disinfected equipment, and self-monitoring for symptoms).
Limitations of the study It was expected that the study would be subject to certain limitations. One of the limitations encountered pertained to the process of data collection. The data was gathered during the peak of the Covid-19 pandemic’s lockdown restrictions. This had a significant impact on the approach, timing, and duration of data collection. At the outset, data was intended to be collected through direct interpersonal interaction. However, owing to the lockdown restrictions, not all data could be gathered through this particular method. Supplementary data collection strategies were employed, including the use of social media platforms. Owing to the system of multiple work shifts in the mines, some difficulties were encountered collecting data face-to-face. To address this challenge, appointments were scheduled to accommodate respondents with busy schedules. The data collection process was facilitated by the assistance of human resource personnel at the mines where data was collected during respondents’ designated lunch breaks, when they were reporting for work, and during knock-off periods. In addition, to increase the number of respondents who participated in the study, the Mining Qualifications Authority (MQA) encouraged their registered companies to participate and assisted the researcher in obtaining access to the mines. Furthermore, the use of the non-probability sampling technique imposed limitations as regards generalizing findings to the broader population under investigation (women occupying technical mining positions in South Africa). Consequently, the results and findings of the study are limited to the individuals who participated in the research.
Most respondents (45%; N = 127) fell in the age group 30–39, followed by those in the 20–29 age group (32.3%; N = 91). Only a few respondents (1.1%; N = 3) stated that they had not attended school. Post-standard 10 comprised 78% (N = 220) of those with qualifications. Most of this cohort had an honours degree (20.9%; N = 59) or an advanced diploma (16.3%; N = 46). Just over half (51.4%; N = 145) of the respondents indicated that they were single. The majority of respondents (64.2%; N = 181) indicated that they had children and had worked for their organizations for the past one to three years (30.5%; N = 86). About a quarter (25.9%, N = 72) were involved in a work committee. Slightly more than half of respondents (54.6%; N = 154) worked on the surface and were not required to work night shifts (69.9%; N = 197).
Validity and reliability of employee engagement A CFA was conducted to test the structure and relationships between the latent variables that underlay the data. The results of the CFA for the measurement model with standardized regression weights and correlations are depicted in Figure 1.
Empirical results: Quantitative analysis Biographical information The structured questionnaire was completed by 282 women in technical mining positions, although some did not complete all sections. These questionnaires were not disregarded entirely. Only sections that were satisfactory and contained valuable and useful information were retained. As a result, the quantity of responses varied between questions. Table I presents the biographical results from the respondents. The respondents were from eight provinces of South Africa, with the majority (38.7%; N = 109) employed in the NorthProvince. The Free State and the Western Cape had the least respondents (both at 1.4%; N = 4). The subsectors represented were coal mining, gold mining. platinum group metal (PGM); other mining (including iron ore, chrome, manganese, copper, phosphates. and salt), cement, lime, aggregates and sand; diamond mining and processing, and jewellery manufacturing. PGM mining had the highest representation (42.2%; N = 119), and only one respondent (0.4%) represented diamond processing. 532
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Figure I—Confirmatory factor analysis results for the measurement model with standardized regression weights and correlations The Journal of the Southern African Institute of Mining and Metallurgy
Employee engagement among women in technical positions in the South African mining industry The results depicted in Figure I satisfactorily support the measurement of vigour by six items, dedication by five items, and absorption by six items. All factor loadings were statistically significant at the 0.05 level. The factor loadings for vigour ranged from 0.533 to 0.874, for dedication from 0.611 to 0.866, and for absorption from 0.575 to 0.850. The commonly accepted factor loadings are those greater than 0.30 (Field, 2009, p. 631). The higher the factor loading, the greater the contribution of the variable to the factor (Yong and Pearce, 2013, pp. 80–81). The results of the goodness-of-model-fit indices (chi-square statistic divided by degrees of freedom [CMIN/DF], Comparative Fit Index [CFI] and root mean square error of approximation [RMSEA]) yielded values that indicated an acceptable fit between the measurement model and the sampled data. The CMIN/DF obtained a value of 3.610, which is satisfactory according to Carmines and McIver (cited by Shadfar and Malekmohammadi, 2013, pp. 585–586) and Mueller (1996). The CFI was 0.910, indicating a good fit (Hair et al., 2010; Mueller, 1996; Paswan cited by Shadfar and Malekmohammadi, 2013, p. 2010; Mueller, 1996; Paswan, cited by Shadfar and Malekmohammadi, 2013, p. 585). The RMSEA value was 0.906 with a 90% confidence interval of 0.087 (low) and 0.106 (high), showing an acceptable fit (Blunch, 2008). The Cronbach’s alpha coefficient values for vigour, dedication and absorption were 0.881, 0.887, and 0.860, respectively. This showed good reliability and internal consistency
since Cronbach’s alpha was greater than the recommended threshold of 0.70 (Child, 2006; Hair et al., 2010; Kaiser, 1974). The descriptive statistics of employee engagement are presented in Table II. The response categories consisted of the following: 1 = almost never or a few times a year or less; 2 = rarely or once a month or less; 3 = sometimes or a few times a month; 4 = often or once a week; and 5 = very often or a few times a week. The research results indicate that all three factors obtained mean scores of more than 3.6. Dedication obtained the highest mean score (3.79), followed by vigour (3.66) and absorption (3.61). This indicates that the respondents showed acceptable levels of engagement (feelings of dedication, vigour, and absorption); however, there is still room for improvement.
Table II
Descriptive statistics of employee engagement N
Minimum
Maximum
Mean
*SD
Vigour
278
1.00
5.00
3.6605
0.5091
Dedication
278
1.00
5.00
3.7935
1.01791
Absorption
278
1.0
5.00
3.6116
0.93487
* Standard deviation
Table III
Association between shift work, having children and work committee involvement, and employee engagement among women employed in technical mining positions Independent samples test
Group statistics Factor
N
Mean
*SD
Yes No Yes No Yes No
83 195 83 195 83 195
3.54 3.71 3.63 3.86 3.54 3.64
0.97 0.94 1.09 0.98 0.99 0.91
Yes
178
3.72
0.97
No
100
3.56
0.92
Yes
178
3.84
0.99
No
100
3.72
1.06
Yes
178
3.72
0.90
No
100
3.43
0.98
Yes
72
3.79
0.98
No
206
3.61
0.94
Yes
72
4.03
0.95
No
206
3.71
1.03
Yes
72
3.74
0.94
No
206
3.57
0.93
P-value
Effect size
Shift work
Vigour Dedication Absorption Having children Vigour Dedication Absorption Work committee involvement Vigour Dedication Absorption
0.1
0.18
0.09
0.23
0.39
0.11
0.20
0.16
0.35
0.12
0.01
0.31
0.18
0.19
0.02
0.32
0.17
0.19
* Standard deviation d = 0.2: small effect size; d = 0.5: medium effect size; d = 0.8: large effect size The Journal of the Southern African Institute of Mining and Metallurgy
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Employee engagement among women in technical positions in the South African mining industry In addition to the validity and reliability analysis, the association between the biographical variables and employee engagement was explored. The results are discussed below.
Association between biographical variables and employee engagement Independent samples t-tests and ANOVA tests were conducted on various biographical variables to determine whether there was an association between these variables and employee engagement factors. The results of the t-tests are depicted in Table III. Table III shows that there was no association between the requirement to work shifts and employee engagement; the p-values measured above 0.5 and the effect sizes ranged from negligible to small for all the engagement factors. The results of the t-tests showed no significant differences between the mean scores of respondents with and without children for vigour and dedication. However, significant differences between the mean scores were found for absorption (p-value = 0.01). Respondents with children (M = 3.72) scored higher on absorption than those without children (M = 3.43); the effect size (d = 0.31) showed a small to medium effect. Therefore, respondents with children appeared to recognize absorption (a pleasant state of association with one’s work in the workplace) more as a factor affecting employee engagement than respondents who did not have children. The results of the t-tests further showed no significant differences between the mean scores of respondents involved in a work committee and those that were not for vigour and absorption. However, significant differences between the mean scores were found for dedication (p-value = 0.02). Respondents who were involved in a work committee (M = 4.03) scored higher on dedication compared to those who were not (M = 3.71); the effect size (d = 0.32) showed a small to medium effect. This implies that respondents who were involved in a work committee were more likely to show traits of dedication (having a sense of significance, enthusiasm, inspiration, and pride in working for a particular organization) than those not in a work committee. The ANOVA test showed no significant differences between the mean scores of the marital status categories for all the employee engagement factors; the p-values measured above 0.5, and the effect sizes ranged from negligible to small.
Table IV presents the results of the correlation tests between age, highest qualification, and duration of employment in the mining organization and industry, and engagement. Table IV shows a small negative correlation between the duration of employment in an organization and dedication (p-value = 0.008; r = -0.163). This implies that the lomger that respondents had been employed in a specific organization, the less dedicated they were to their organizations.
Empirical results: Qualitative analysis The qualitative findings that emerged from the semi-structured interviews are presented in themes derived from transcripts. The qualitative research aimed to provide detailed information on factors that affect women's engagement in technical mining positions from the perspective of employers. Eleven semi-structured interviews were conducted. Most of the research participants (10) were human resource personnel, except for one, who was a rock engineering superintendent. The participants were mainly from the PGM subsector,. After gauging the participants’ understanding of employee engagement, the researcher read the study’s definition of the term to channel responses contextualized within the study’s conceptualization.
Factors affecting employee engagement The main factor affecting employee engagement was the lack of career development opportunities. Three participants (P1, P2, and P4) said there were few career development opportunities, such as being promoted to higher positions. They asserted that women had to work twice as hard as men to be considered for promotion. The following comments illustrate these points: Growth opportunities within the company. But for a female, for a mother, it’s a bit difficult. That person will have to almost work twice as hard as the male to get to be seen to be considered for the next level. (P1, PGM subsector) Having few career development opportunities affects women’s drive in the workplace. Career development becomes an issue. (P2, PGM subsector) Their career growth takes longer than that of men. (P4, PGM subsector)
Table IV
Correlations between age, highest qualification and duration of employment in the mining organization and industry, and engagement Age
Highest qualification
Duration of employment in current position
Duration of employment in the organization
Duration of employment in the mining industry
0.020 0.739
−0.01 0.827
0.00 0.977
−0.074 0.236
0.038 0.538
N 277 273.00 274.00 Pearson correlation 0.015 0.01 -0.09 Sig. (2-tailed) 0.806 0.899 0.128 N 277 273.00 274.00 Absorption Pearson correlation 0.108 −0.04 0.01 Sig. (2-tailed) 0.074 0.490 0.894 N 277 273.00 274.00 ** Correlation is significant at the 0.01 level (2-tailed) * Correlation is significant at the 0.05 level (2-tailed) (a) small effect: r = 0.1; (b) medium effect: r = 0.3; (c) large effect: r > 0.5
259 −0.163** 0.008 259 −0.060 0.334 259
261 −0.019 0.763 261 0.104 0.094 261
Factor
Vigour
Pearson correlation Sig. (2-tailed)
Dedication
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Employee engagement among women in technical positions in the South African mining industry Other factors that were mentioned were unfavourable working conditions, work–life balance, and workplace culture (P1, P4, and P5). Women had to balance household responsibilities with work duties; sometimes, they did not even have time for themselves. In addition, the male-dominated work culture was described as intimidating, and women had to adapt and adjust to it. Some of these sentiments were expressed as follows: Unfavourable working conditions. (P4, PGM subsector) The mining environment is not easy for a woman. She is a mother, she’s a breadwinner, and she needs to take care of the kids and the husband. They have responsibilities at home. That’s demotivating in the sense that there is so much that they need to compromise for them to be able to work here and be a mother at home and to take care of responsibilities there, to the extent where you don’t even have time for yourself. (P1, PGM subsector) Male domination, the work culture of mining affects women’s engagement. (P5, Other mining) I think it is quite intimidating … and say you need to adapt … and you need to adjust to the way things are being done and the culture around here. (P1, PGM subsector)
Measures implemented by mining organizations to keep women engaged Participants P1, P4, and P5 said their organizations provided platforms for women to express their concerns and challenges. Women used these platforms to communicate concerns they were facing at work and to raise issues that needed to be addressed to create a more suitable work environment for women. The availability of such platforms is thought to create a haven for women and make them feel valued. The following quotes indicate some of the participants’ assertions of measures implemented by mining organizations to keep women engaged: First of all, you need to recognizerecognise that you have women in he workplace. You need to give them a voice. By giving them a voice, they feel appreciated. (P1, PGM subsector) We have created platforms where women can feel safe to talk when encountering challenges. (P4, PGM subsector) The mine has an open platform where women can talk about issues that affect them whilst working here. (P5, Other mining subsector) Furthermore, women were said to be protected from any form of sexual harassment (P1 and P5). Sexual harassment was not tolerated under any circumstances, and those who were found guilty of it were dismissed. The following comments demonstrate these points: The company is going an extra mile to protect the women. In this company, for example, we recently had a sexual harassment incident from a manager’s level. That person is no longer working here. We do not protect perpetrators in this environment. (P1, PGM subsector) They are also taking legal actions against men that contravene these policies. You can even lose your job because of that. If you are a man and harassing women. (P5, Other mining subsector) There were also initiatives in place aimed at getting women into leadership roles (P1, P3, P4, P5, P6, P8, and P11). These were implemented through programmes that encouraged employees to study further to enhance their skills. In addition, one participant (P1) stated that managers were discouraged from assigning women to night shifts to allow for work–life balance and to ensure that women were safe at work. The following assertions demonstrate these points: The Journal of the Southern African Institute of Mining and Metallurgy
ecause this is a 24/7 operation, we discourage managers to put B our women on night shift because of safety reasons and because we understand that they’ve got responsibilities at home. (P1, PGM subsector) Women are progressing in technical management positions. (P4, PGM subsector) There are programmes and learnerships offered in the company and skills development. (P8, PGM subsector)
Discussion The results show that the three-factor structure (vigour, dedication, and absorption) of the UWES fit the sample data reasonably well. Cronbach’s alpha coefficients showed good reliability and internal consistency for the three factors. Two goodness-of-modelfit indices (CMIN/DF and CFI) indicated a good fit, while the RMSEA indicated an acceptable fit. The mean scores of all three factors were greater than 3.6, indicating relatively acceptable levels of engagement (feelings of dedication, vigour, and absorption); however, there is still room for improvement. The t-test and ANOVA revealed no significant differences between the mean scores of the different categories (Yes/No) for the requirement to work night shifts and marital status for the engagement factors. However, the results of the t-test and effect size revealed that respondents with children were more absorbed in their work (i.e., they had a pleasant state of association with their work in the workplace) than without children. they had a pleasant state of association with their work in the workplace) than those without children. Furthermore, the t-test and effect size showed that respondents who were involved in a work committee were more likely to exhibit traits of dedication (having a sense of significance, enthusiasm, inspiration, and pride in working for a particular organization) (Schaufeli and Bakker, 2004, p. 295) than those who were not part of a work committee. The results of the Pearson product-moment correlation revealed a small negative correlation between the duration of employment in an organization and dedication. This indicates that the more years respondents had been employed in a specific organization, the less dedicated they were to that organizations. This confirms Bakar’s (2013, p. 206) finding that employees who had worked in an organization for a shorter period tendedtend to be more engaged than those who had worked there for a longer period. According to Bakar (2013, p. 206), individuals may be more excited about their work in the first few years at a company, resulting in higher engagement levels than those who have been in the organization longer. These results also align with Boikanyo’s (2012, p. 73) finding that employees with zero to two years’ experience were the most engaged. The qualitative research indicated that the dearth of career development opportunities for women, such as promotion opportunities, is the major factor affecting employee engagement. The participants asserted that women had to work ‘twice as hard as men’ to be considered for promotion. There is a significant relationship between career development and employee engagement, as evidenced by the literature (Guest, 2014, p. 146). Hlapho (2015, p. 71) discovered that employee engagement is influenced by practices such as training and development and career advancement possibilities. Therefore, a lack of career development may result in disengaged employees (van der Walt, 2008, p. 40). Other factors affecting engagement, according to the participants, included unfavourable working conditions, such as being required to work in hazardous or labour-intensive conditions. VOLUME 123
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Employee engagement among women in technical positions in the South African mining industry Botha (2013, p. 439) and Simha and Vardhan (2015, p, 5) emphasize that employees’ engagement levels will suffer if they do not feel secure or safe at work. Yuan, Li, and Tetrick, p. (2015:169) support this assertion, stating that a positive perception of safety practices (an organization’s commitment to safety) is one of the factors that can contribute to high levels of workplace engagement. Another issue affecting employee engagement is work–life balance. Participants indicated that women were expected to balance household responsibilities with work obligations, leaving little time for themselves. According to Lockwood (2007, p. 4), work–life balance is critical for employee engagement. Employees are more likely to be engaged and attached to their employers if they understand that their employers acknowledge the value of their family life (Simha and Vardhan, 2015, p. 6). Previous research on women in mining in South Africa (Botha, 2013; van der Walt, 2008) identified a lack of work–life balance as a factor contributing to disengaged employees. The lack of engagement may result in women leaving the mining industry for industries that provide more family-friendly work environments and less physically demanding jobs (Botha, 2013, p. 200). In addition, the male-dominated work culture, to which women must adapt, affects women’s engagement in technical mining positions. Women in mining are reported to feel disengaged and alienated due to unequal workplace culture, men’s low perceived value of women, and a perceived lack of respect for them (AWRA, 2014). As a result, overt bias, discrimination, and resistance against women in mining may result in disengaged women employees.
Conclusion and recommendations The study respondents, on average, showed fairly high levels of engagement (feelings of dedication, vigour, and absorption), although there is still room for improvement. The qualitative research revealed that the lack of career development opportunities, unfavourable working conditions, gender stereotyping, work–life balance, and mining’s male-dominated work culture all affect engagement. These factors corresponded to those identified in the literature. It is recommended that employee engagement be elevated to a core human resource function. Human resource professionals should collaborate with mine supervisors and managers to develop programmes encouraging employees to be more absorbed in and dedicated to their work. The emphasis, however, should not be solely on absorption and dedication. The programmes t could be constructed using Schaufeli et al.’s (2002) conceptualization of engagement, which views engagement through a positive lens, resulting in a workforce marked by a positive, fulfilling, workrelated state of mind characterized by vigour, dedication, and absorption. Employees (both new and existing) should also be involved in developing these programmes and should be monitored regularly. Mining organizations should accord high priority to enhancing working conditions for women and adopting work arrangements that foster a healthy work–life balance. It is advisable for mining organizations to proactively address any unfavourable working conditions that may impede women's engagement levels in the workplace, and consider the adoption of flexible working arrangements, even though mining typically has predefined systems of operation. This can be achieved using technological advancements that effectively minimize the need for manual labour. Moreover, it would be advantageous to implement daycare facilities specifically tailored for mothers with young children at mining sites. If deemed practicable, it may also be worthwhile to consider 536
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tlimiting the amount of night shift work undertaken by female employees. Moreover, mining organizations should prioritize career development to enhance women's engagement. To achieve this, it is recommended that mining companies implement measures to facilitate study assistance, mentoring, coaching, and participation in training and development programmes. By addressing these aspects, the industry can enhance its appeal to women, foster their engagement, and contribute to the mitigation of the maledominated work culture prevalent in mining. It is recommended that human resource managers undergo training to acquire the necessary skills to effectively manage employee engagement and address any barriers that impede it.
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Employee engagement among women in technical positions in the South African mining industry down on the SA economy. https://www.mineralscouncil.org.za/downloads/ send/68-covid-19/946-economic-impact-of-covid-19-lock-down-on-the-saeconomy [accessed 23 July 2020]. MiHR (Mining Industry Human Resources Council). 2016. Strengthening mining’s talent alloy: Exploring gender inclusion. https://mihr.ca/wp-content/ uploads/2020/03/MiHR_Gender_Report_EN_WEB.pdf [accessed 2 May 2020]. Moletsane, M., Tefera, O., and Migiro, S. 2019. The relationship between employee engagement and organisational productivity of sugar industry in South Africa: The employees’ perspective. African Journal of Business and Economic Research, vol. 14, no. 1. pp. 113–134. https://doi:10.31920/17504562/2019/v14n1a6 Moshoeu, A.N. 2017. A model of personality traits and work-life balance as determinants of employee engagement. PhD dissertation, University of South Africa, Pretoria. https://uir.unisa.ac.za/bitstream/handle/10500/23247/thesis_ moshoeu_an.pdf?sequence=1&isAllowed=y [accessed 3 October 2021]. MQA (Mining Qualifications Authority). 2019. Analysis of the 2019 workplace skills plan and annual training. Johannesburg. MQA (Mining Qualifications Authority). 2020. Women in mining: understanding factors that influence access and mobility in and within occupational structures in the MMS. Johannesburg. MQA (Mining Qualifications Authority). 2021. Sector Skills Plan for the mining and minerals sector submitted by the Mining Qualifications Authority (MQA) to the Department of Higher Education and Training 2020–2025. Johannesburg. Mueller, R.O. 1996. Basic Principles of Structural Equation Modeling: An Introduction to LISREL and EQS. Springer, New York. Muthuveloo, R., Basbous Khalit, O., Ping Ai, T., and Long Sang, C. 2013. Antecedents of employee engagement in the manufacturing sector. American Journal of Applied Sciences, vol. 10, no. 12. pp. 1546–1552. https://doi:10.3844/ ajassp.2013.1546.1552 Nayak, P. and Mishra, S.K. 2005. Gender and sustainable development in mining sector in India. https://www.researchgate.net/profile/Purusottam-Nayak/ publication/23745146_Gender_and_Sustainable_Development_in_Mining_ Sector_in_India/links/0fcfd5066823e5d918000000/Gender-and-SustainableDevelopment-in-Mining-Sector-in-India.pdf?origin=publication_detail [accessed 2 May 2020]. Ntsane, M.M. 2014. Factors influencing employee turnover and engagement of staff within branch network in Absa (central region). MBA dissertation, University of the Free State, Bloemfontein. https://scholar.ufs.ac.za/bitstream/ handle/11660/715/NtsaneMM.pdf?sequence=1&isAllowed=y [accessed 28 January 2019]. Nyabeze, T., Espley, S., and Beneteau, D. 2010. Gaining insights on career satisfaction for women in mining. CIM, ICM. https://internationalwim.org/ wp-content/uploads/2020/06/Tech-Paper_MEMO_2010_Beneteau_Espley_ Nyabeze_Gaining-Insights-on-Career-Sati.pdf [accessed 17 July 2020]. Ozkan, U.R. and Beckton, C. 2012. The pathway forward: creating gender inclusive leadership in mining and resources. Carleton University, Ottawa, Ontario.. https://www.bcctem.ca/sites/default/files/the_pathway_forward.pdf [accessed 17 May 2020].
Pactwa, K. 2019. Is there a place for women in the Polish mines? Selected issues in the context of sustainable development. Sustainability, vol. 11. pp. 1–14. https://doi:10.3390/su11092511 Purvee, A. 2019. Women in engineering in Mongolia. Proceedings of World Engineers Convention 2019. https://www.wec2019.org.au/wp-content/uploads/ pdfs/presentation_668.pdf [accessed 2 June 2020]. Schaufeli, W.B. and Bakker, A.R. 2004. Job demands, job resources, and their relationship with burnout and engagement: A multi-sample study. Journal of Organizational Behaviour, vol. 25, no. 3. pp. 293–315. https://doi:10.1002/job.248 Schaufeli, W.B., Salanova, M., González-Romá, V., and Bakker, A.B. 2002. The measurement of engagement and burnout: a two sample confirmatory factor analytic approach. Journal of Happiness Studies, vol. 3, no. 1. pp. 71–92. Segerstedt, E. and Abrahamsson, L. 2019. Diversity of livelihoods and social sustainability in established mining communities. The Extractive Industries and Society, vol. 6. pp. 610–619. https://doi:10.1016/j.exis.2019.03.008 Shadfar, S. and Malekmohammadi, I. 2013. Application of structural equation modeling (SEM) in restructuring state intervention strategies toward paddy production development. International Journal of Academic Research in Business and Social Sciences, vol. 3, no. 12. pp. 576–618. https://doi:10.6007/IJARBSS/ v3-i12/472 Simha, B.S. and Vardhan, B.V. 2015. Enhancing “performance and retention” through employee engagement. International Journal of Scientific and Research Publications, vol. 5, no. 8. pp. 1–6. Terrill, J.L. 2016. Women in the Australian mining industry: Careers and families. PhD thesis, UQ Business School, University of Queensland, Brisbane. https://espace.library.uq.edu.au/view/UQ:406948/s42717773_final_thesis.pdf [accessed 24 May 2019]. Turner, D. 2019. Sampling methods in research design. American Headache Society, vol. 60, no. 1. pp. 8–12. https://doi:10.1111/head.13707 Van der Walt, M. 2008. Job demands, job resources, burnout and engagement of employees in the mining industry in South Africa. Honours. dissertation, North-West University, Potchefstroom. https://repository.nwu.ac.za/bitstream/ handle/10394/5072/vanderwalt_m%281%29.pdf?sequence=1 [accessed 29 April 2019]. Wilson, S. and MacLean, R. 2011. Research Methods and Data Analysis for Psychology. McGraw-Hill, London. Yong, A.G. and Pearce, S. 2013. A beginner’s guide to factor analysis: Focusing on exploratory factor analysis. Tutorials in Quantitative Methods for Psychology, vol. 9, no. 2. pp. 79–94. https://doi:10.20982/tqmp.09.2.p079 Yuan, Z., Li, Y., and Tetrick, L.E. 2015. Job hindrances, job resources, and safety performance: the mediating role of job engagement. Applied Ergonomics, vol. 51. pp. 163–171. https://doi:10.1016/j.apergo.2015.04.021 Zungu, L.I. 2011. Women in the South African mining industry: An occupational health and safety perspective. Inaugural lecture, University of South Africa. Unisa. http://uir.unisa.ac.za/bitstream/handle/10500/5005/Inaugurallecture_ Women%20in%20the%20SAMI_LIZungu_20October2011.pdf?sequence=1 [accessed 30 January 2019]. u
Erratum- June 2008 It has come to our attention that some numbering in the paper entitled: 'Application of modified Hoek-Brown transition relationships for assessing strength and post yield behaviour at both ends of the rock competence scale' by T.G. Carter*, M.S. Diederichs†, and J.L. Carvalho* was listed incorrectly. The paper was published in SAIMM Journal vol. 108, no. 6, pp. 325-338. For the correct numbering on page 333 in the paragraph: This suggests that intact properties should account for nearly 50% of the rock mass behaviour. Adjustment according to the transition function then results in the following modified H-B parameter values: s* = 0.445; a* = 0.747; mb* = 2.691 mb* in the second sentence should be 1.68 and not 2.691. and in the paragraph below: Comparing these modified values with the conventionally calculated H-B values the most significant change occurs in s, (namely, s = 0.000138 by conventional calculation to s* = 0.445 through the transition relationship). As the s value provides the main control on strength under very low to no confinement, this change has a significant impact on the computed extent of the plastic zone. Pushing the envelope to linearization by taking a* = 0.747 versus a = 0.544 and increasing mb from 0.4 to mb* = 2.7 results also in an increase in friction angle of about 15° at confinements mb* in the last sentence should be 1.7 and not 2.7. 538
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Resistance of yielding rockbolts to multiple impact loads by A. Pytlik¹, D. O’Connor¹, and D.J. Corbett¹
Affiliation:
Główny Instytut Górnictwa - Pan’stwowy Instytut Badawczy, Zakład Badan’ . Mechanicznych i Inzynierii Materiałowej, Katowice.
Correspondence to: A. Pytlik
Email:
apytlik@gig.eu
Dates:
Received: 23 Jan. 2019 Revised: 16 Mar. 2020 Accepted: 3 Nov. 2023 Published: November 2023
How to cite:
Pytlik, A., O’Connor, D. and Corbett, D.J. 2023 Resistance of yielding rockbolts to multiple impact loads. Journal of the Southern African Institute of Mining and Metallurgy, vol. 123, no. 11. pp. 539–556 DOI ID: http://dx.doi.org/10.17159/24119717/776/2023 ORCID: A. Pytlik http://orcid.org/0000-0003-0899-0590 D. O'Connor http://orcid.org/0000-0001-8346-4035 D.J. Corbett http://orcid.org/0000-0002-8534-5344
Synopsis
The resistance of yielding rockbolts to multiple impact loads was tested by means of a drop hammer. The methodology was based on the ASTM D7401-08 standard as well as the requirements specified for rockbolts by Luossavaara-Kiirunavaara Aktiebolag (LKAB – a Swedish mining company) and the Safety In Mines Research Advisory Committee of South Africa (project number GAP 423). During the tests, the loading force and bolt elongation were measured with a sampling frequency of fs = 19.2 kHz. In order to analyse the phenomena involved, the tests were recorded using two independent high-speed video cameras (600 and 1000 frames per second) and one thermal camera (128 frames per second). The tests demonstrated that all the samples transferred double the gravitational potential energy of Ep = 50.85 kJ from the impact load of mass m = 2825 kg and impact velocity of v = 6.0 m/s without failure. Damage to the bolt-resin contact in the upper anchoring zone of the bolt in the steel tube occurred after subsequent impacts. As a result, the macro-deformed bolt exhibits additional yield, and its operation following the shearing of the resin bond is similar to that of a ‘cone bolt’. Only one test resulted in damage to the threaded bolt rod-nut coupling, during the fourth impact; however, no damage to the bolt-resin contact zone was observed.
Keywords
yielding rockbolts, dynamic impact drop test, multiple impact loads, consecutive impacts, thermovision analysis.
Introduction The necessity of conducting mining operations at increasing depths results in significantly greater hazards related to seismic events, such as rockbursts (strain bursts and fault-slip bursts) (Guntumadugu, 2013; Li, 2017a, 2017b; Li et al., 2019). Dynamic loading, caused by the impact of masses of rock that intrude into a working as a result of a rockburst is particularly hazardous to the mining support and its stability, which is the primary factor determining safety in a working. An intensification of the rockburst phenomenon is observed in deep metalliferous mines (in hard and strong rock), particularly at depths greater than 1000 m, which results in severe intrusion of rocks into the workings (Li, 2017b). Yielding support is often used in order to secure the workings against static and dynamic loading originating from the rock mass. In underground mining, the most commonly employed types of yielding support include: ➤ Yielding steel arch support (passive) – commonly employed in hard coal mines (Horyl and Šňupárek, 2007; Pytlik, 2020a; Zhao et al., 2015; Sun et al., 2018) ➤ Yielding rockbolt support (active) – worldwide application, typically in metalliferous mines, for the purposes of rock mass reinforcement under conditions of great rock mass stresses accompanied by rockbursts in hard and strong rock (Li, 2017b) ➤ Mixed support, e.g. with yielding steel arches and rockbolts – commonly employed in Polish, German, Czech, and Chinese hard coal mines (Pytlik, 2019). Steel mesh is another important support element for absorbing energy under dynamic loads (Eriksson, 2020), and it is used in combination with both arch support systems and rockbolts. Damage to steel weldmesh typically occurs at an impact energy of about 2 kJ (Villaescusa, 2009; Pytlik, 2015b). Though no standardized definition or evaluation criteria of a ‘yielding support’- can be found, it may be stated that yield is a key property of the support, by which the rock mass surrounding the working can undergo significant deformation (at a minimum support load capacity determined by the designer) with no resulting damage to the support elements. Therefore, compared to standard support, a yielding support operating under identical rock mass deformation and load can be expected to retain its integrity. Consequently, yielding support units improve the stability of a working and increase worker safety. In the
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Resistance of yielding rockbolts to multiple impact loads case of a yielding steel arch support, the condition of its elements can often be assessed relatively quickly by visual examination or technical means. However, a problem arises in the case of rockbolt support, since the condition of the bolts installed in the rock mass (by means of resin, grout, or expandable anchors) is difficult to determine quickly. A question that is particularly important in the context of rockbursts is: what is the condition of the bolts, and consequently what is the level of safety in the working, not only after the first rock impact, but also following the subsequent impact loading of the bolts? The problem of the maximum rockbolt support deformation (as determined by the designer), which is meant to ensure unobstructed access to and stability of the working, is closely related to this. In the case of rockbolt support in a blocky rock mass (Cała, Flisiak, and Tajduś, 2001; Li, 2017b), the dynamic displacement of a loose block of rock into a working may occur during rockbursts. The support units responsible for bearing the load and absorbing the impact energy are tendons, usually in the form of steel bars or cables. Under in-situ conditions, the bolts are subjected to complex states of loading, occurring primarily as a result of tension (normal stress) and shearing (shear stress) (Figure 1). Comparative shear tests of threaded bolts under dynamic loads (Pytlik, 2020b) demonstrated that the bolt’s energy absorption capacity was considerably lower than that of bolts subjected exclusively to tension. This is understandable considering that, practically speaking, shearing results only in bolt diameter deformation, and it is the level of deformation that is the primary factor influencing bolt yield. For example, during the shear tests, bolts produced from threaded bars with a core diameter of 21.7 mm (effective bolt rod diameter De = 22.1 mm), formed from steel with a strength of Rm = 830 MPa and elongation of A = 19%, absorbed energy at a level of Wd = 1.269 ± 0.062 kJ. However, during tensile tests under dynamic loading, the same type of bolt can absorb an energy of Wd = 29.5 kJ without failure. A schematic diagram of a gallery working driven in a blocky rock mass, secured by means of rockbolt support and exposed to the dynamic influence of blocks of rock as a result of rockbursts, is depicted in Figure 1. Similar problems with maintaining the stability of workings exposed to dynamic loads generated by rockbursts are present in mines all over the world (Li, 2010). An example of the major problems regarding this issue can be found in ultra-deep gold mines (extraction at a depth of nearly 4000 m) in South Africa (Sengani, 2018). Increasing work safety is possible only by the utilization of rock mass destressing, correct support design, and testing of the support unit technical parameters under laboratory conditions (static and dynamic tests) and underground (static tests).
Rockbolt test methodologies and standards are specified in many countries in Europe, North and South America, and Australia. For example, detailed standardization regarding the mechanical elements of bolts is included in Polish (PN-G-15091:1998 and PNG-15092:1999), German (DIN 21521 Teil 1:1990 and DIN 21521 Teil 2:1993), USA (ASTM F 432-13, ASTM D 7401-08), British (BS 7861-1:2007), Canadian (CAN/CSA-M430-90), and South African (SANS 1408:2002) standards. The only example of a standard that specifies the methodology for bolt tests under dynamic loading is ASTM D7401-08, according to which the tensile impact loading of bolts is performed by means of a drop hammer (ram). Tests of bolts under dynamic loading based on ASTM D7401-08 are conducted by internationally renowned laboratories in Australia, Canada, South Africa, and Sweden. There are many publications in the international literature that provide test results from laboratories (Hadjigeorgiou and Potvin, 2007, 2011) such as CANMET-MMSL (Labrie, Doucet, and Plouffe, 2008; Plouffe, Anderson, and Judge, 2008), the Western Australian School of Mines (WASM) (Player, Thompson, and Villaescusa, 2008; Player, Villaescusa, and Thompson, 2008; Potvin, Wesseloo, and Heal, 2010; Villaescusa, 2009), the SRK drop weight test facility (SIMRAC Project GAP 423 (Ortlepp and Stacey, 1998)), and New Concept Mining in Canada and South Africa (Bosman, Cawood, and Berghorst, 2018; Knox and Berghorst, 2018; Knox, Berghorst, and Crompton, 2018; Knox, Berghorst, and de Bruin, 2018) and SINTEF, and the Norwegian University of Science and Technology (NTNU) in Trondheim (Hagen et al., 2020). Recently, the Central Mining Institute in Poland (GIG) has been conducting dynamic tests of bolts according to ASTM D7401-08. The current capabilities of the GIG test facility enable the testing of bolts with a maximum length of 4.0 m by means of an impact mass of m = 6000 kg dropped from a height of 3 m. This makes it possible to load the bolt with an impact energy of Ep= 176.6 kJ and impact velocity of v = 7.67 m/s. Other kinds of tests conducted at the GIG facility include the impact testing of hydraulic props (Pytlik, 2015a, 2018; Prusek et al., 2016), mining chains (Michalak et al., 2012), shaft hoist ropes, and cable bolts (Pytlik, Prusek, and Masny, 2016) with a maximum impact energy of Ep = 500 kJ (m = 20 000 kg, h = 2.5 m). The above test facilities make it possible to simulate impact loads across broad ranges of impact energy and velocity, which are observed in situ. For example, during tests that were conducted in iron ore mines (Shirzadegan, Nordlund, and Zhang, 2016a, 2016b) belonging to LKAB (Sweden), the measured maximum PPV (peak particle velocity) was 7.5 m/s. Rockburst simulations performed under gold mine conditions (Haile and le Bron, 2001; Milev et al., 2001; Milev and Spottiswoode, 2005) in South Africa also revealed high PPV values, reaching up to 3.3 m/s. Direct and indirect
Figure 1—Example diagram of working load and deformation in a blocky rock mass (Cała, Flisiak, and Tajduś, 2001; Li, 2017) under rockburst conditions 540
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Figure 2—Test facility: (a) schematic; (b), (c) testing and measuring equipment
estimates (Ortlepp and Stacey, 1998) of rock ejection velocities range from 3 to 10 m/s or even higher. This article presents a methodology for the laboratory testing of yielding bolts via dynamic tensile impact loading exerted by means of a drop hammer, and attempts to determine the resistance of yielding rockbolts to multiple impact loads. The methodology is based on ASTM D7401-08 as well as the test methodology and requirements specified for rockbolts by LKAB and the Safety in Mines Research Advisory Committee – Project Number: GAP 423 (Ortlepp and Stacey, 1998). In order to determine the resistance of yielding rockbolts to multiple impact loads, yielding bolts with high load capacity and elongation capability were selected for the tests. The tests adopted a higher impact energy and velocity than the typical values specified for bolts by LKAB (E = 30 kJ and v = 5 m/s). The impact energy during testing was E = 50.85 kJ (drop hammer mass of m = 2825 kg), providing an impact velocity of v = 6 m/s (at a ram free fall height of h = 1.835 m). During the tests, the loading force and the bolt elongation were measured with a sampling frequency of fs = 19.2 kHz. The tests were recorded using two independent high-speed video cameras (600 and 1000 frames per second) and one thermal camera (128 frames per second).
Yielding bolt test methodology using multiple impact loads The objective of testing yielding bolts under multiple impact loads is to conduct relatively simple and repeatable tests, the results of
which could be used by bolt manufacturers and rockbolt support designers, as well as for the purposes of confirming compliance with safety requirements in the process of product certification. The tests make it possible to determine the technical condition of the yielding bolt elements and connections. The methodology also enables comparison of the load capacity, elongation, and energy absorbed by various types of bolt; the determination of sensitive zones in the tested bolts and zones of thermal energy accumulation; and the definition of the maximum number of impacts that can be sustained beforw damage occurs to the elements of the bolt, the threaded coupling, and the resin anchor. The primary objective of the tests was to determine whether a bolt can be safely utilized in underground mines susceptible to rockbursts, where the support is exposed to a series of loads exerted as a result of roof caving and rockbursts. The test facility is illustrated in Figure 2. Rams with various masses adapted to the selected impact energy were used during the tests. The bolt test method is based on the free fall of a ram with a mass m from a given height h, giving the selected impact velocity v. The ram strikes the bolt, exerting load upon it according to the two load cases presented in Figure 3. According to the ASTM D7401-08 standard, bolt impact energy Ep and impact velocity v are calculated from the following formulae: [1]
Figure 3—Dynamic load diagram: (a) load case 1 (split tube – LC1); (b) load case 2 (continuous tube – LC2) The Journal of the Southern African Institute of Mining and Metallurgy
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Resistance of yielding rockbolts to multiple impact loads [2] where m – ram mass, m = 2825 kg g – gravitational acceleration, 9.81 m/s2 h – ram height of fall, m. During the test, the impact of a drop mass m against an impact plate initially results in an inelastic collision (leading to bolt elongation), after which the periodic rebounding of the mass from the plate can be observed (Figure 4a), which indicates an elastic collision. This is a typical phenomenon that occurs under real conditions when two bodies undergo an elasto-plastic collision of an intermediate character. The rebound height periodically reached by the drop mass is low enough to have only a slight influence on the degree of bolt deformation. Based on the post-process analysis of paths Fd(t) and Ld(t), which are depicted in a simplified form in Figures 4a and 4b, the following values are determined: ➤ Maximum load Fmax registered during the test ➤ Temporary maximum bolt displacement Lmax registered during the first impulse of the force, corresponding to the point of the lowest position of the impact mass, which comes into an elasto-plastic collision with the impact plate (Figure 3) ➤ Final maximum displacement LF measured after the test. The value of the energy Wd absorbed by the bolt is calculated to determine bolt energy absorption during the test (Figures 4c and 4d). It is a basic parameter that is useful for both comparing different bolts and aiding the rockbolt support design process, as it is calculated and provided in literature by research laboratories for various types of bolts. The total value of the energy Wd absorbed by the bolt, which corresponds to the energy consumed during the elasto-plastic deformation of the bolt bar material (equal to the work done on the deformed bolt) is calculated by integrating the Fd = f(Ld) path using the following formula (Chrysochoos and Martin 1989; Maj, 2007):
[3] where We – energy consumed for the elastic (reversible) deformation. Energy We is released as the bolt is unloaded (path Fdr in Figures 4b and 4c) during the first load impulse (Figure 4a) Wp – energy consumed for the plastic (irreversible) deformation. The total energy Wd absorbed for the deformation is calculated by integrating the Fd = f(Ld) path: [4] Once the bolt is unloaded as a result of the elasto-plastic rebound of the ram mass (during the first impact), the energy Wp consumed for the plastic deformation is calculated using the following formula: [5] The absolute value of the second element of Equation [5] corresponds to the energy We consumed for the elastic deformation: [6] where Lmax – maximum elasto-plastic elongation of the bolt during the first load peak, corresponding to the lowest position of the ram relative to the facility foundation. Ldr – p lastic bolt elongation after reducing the force from a value of Fdr = f(Lmax) to zero. By using a high-speed thermal camera it is possible to record the temperature variations of the tube with the grouted bolt rod as well as of the steel rod with a sampling frequency of 128 Hz. Average bolt rod temperature rise ∆Ta is calculated from the following formula: [7]
Figure 4—Typical Fd(t), Ld(t), Fd(Ld), and Wd(Ld) paths (using sample 3 as an example) during the first impact 542
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Resistance of yielding rockbolts to multiple impact loads Ta1 – average bolt rod section temperature before the test (°C) Ta2 – final average bolt rod section temperature after the test (°C) There are certain technical differences between the methodologies provided by the ASTM D7401-08 standard (2008), LKAB, and SIMRAC, but they share a common method of exerting dynamic loads by means of the free fall of a drop mass. The ASTM D7401-08 standard (2008) assumes a single dynamic load case in the form of the direct loading of the bolt washer and nut by means of a free falling drop mass. Typical test parameters include an input energy of 16.01 kJ and impact velocity of 5.425 m/s. The LKAB test methodology, though based on ASTM D740108, introduces an additional load case in the form of a bolt mounted in a split tube. The load is exerted indirectly on the bolt by loading the lower section of the tube (according to the LC1 diagram in Figure 3). This makes it possible to test the yielding part of the bolt. Typical requirements adopted by LKAB in terms of the kinetic energy of the load include 19 kJ for a bolt in a continuous tube, 30 kJ for a bolt mounted in a split tube, impact velocity of 5 m/s, and maximum elongation greater than 140 mm for a 2.1 m long bolt. The methodology adopted by the Safety In Mines Research Advisory Committee of South Africa, described in the GAP 423 project report (Ortlepp and Stacey, 1998), is also based on the principle of the dynamic loading of a bolt by means of a free-falling drop mass. The bolts are grouted directly into steel tubes or into tubes filled with a binding agent simulating rock, to a length of 0.6 to 2.4 m (depending on the type of bolt). Before testing, the bolt is statically loaded with an 820 kg beam, which is then impacted by a ram with a mass of 1048 kg or 2706 kg. The adopted impact velocity is 3–10 m/s. The impact velocity during the test depends on the ram drop height. A single bolt is subjected to multiple impacts until failure. An increase in the force and energy absorbed by the bolt was observed over the course of the subsequent impacts. Typical threaded bolts formed from rebars and smooth bars with a diameter of 16 mm were used during the tests. Furthermore, the authors concluded that the smooth bar bolts absorbed significantly more energy than the rebar bolts, and plastic deformation was uniform along the entire length of the bolt. A partial slip of the bolt from the smooth bar occurred following the failure of the bolt-grout interface, which resulted in the absorption of additional impact energy, while progressive debonding further secured the bolt from rupture.
Test procedure Secura yielding bolts, which are a threaded bolt variant formed from smooth bars that end with a thread, were selected for the cyclic impact load tests. The mechanical properties of the bar material are the main factor influencing the yield of this bolt. The yielding section of the bolt, formed from a 25 mm diameter smooth bar, is primarily responsible for absorbing impact energy. Cyclic impact load tests performed on the same bolt reveal the bolt's ability to absorb tensile load energy, determine whether there are any indications of imminent failure, and establish how many times a bolt can be loaded before failure. Weak points in the bolt structure and the bolt-grout interface can also be identified based on the tests. Bolts with yielding sections formed from smooth bars are available on the market, similar to the Secura bolt (Cai, Champaigne, and Kaiser, 2010; Charette et al., 2014; Doucet and Voyzelle, 2012; Guntumadugu, 2013; Li, Stjern, and Myrvang, 2014; Ghorbani et al., 2020; Nguyen, Cai, and Challagulla, 2018; Raju, Mitri, and Thibodeau, 2011; Yokota et al., 2020), such as the cone bolt, D-bolt, Garford solid bolt, and others. This is why the The Journal of the Southern African Institute of Mining and Metallurgy
Figure 5—Example of a cone bolt (Player, Thompson, and Villaescusa, 2008)
experience gained during the dynamic testing of Secura bolts could be utilized for other types of threaded bolts that are subjected to dynamic loading by means of tensile axial force. Gaudreau, Aubertin, and Simon (2004) carried out cyclic impact testing on an NTC impact test rig, using impact masses of 750 kg and 1000 kg. During the testing of one of the cone bolt type bolts named MCB, it was found that the bolts would not fail even after four impacts, while the most common reason for failure was rod or nut thread shearing. Tests of various types of bolts under similar conditions were also conducted by Player, Thompson, and Villaescusa (2008) at the Western Australian School of Mines (WASM) and at CANMET – MMSL (2008). Analysis of the tests reveals that cone bolt type bolts (Figure 5) achieve very similar results in terms of the absorption of energy greater than 50 kJ (at a maximum force of over 200 kN and deformation greater than 300 mm) compared to the Secura bolt (yielding section formed from a smooth bar). This is in line with the test results from numerous laboratories that were compared by Hadjigeorgiou and Potvin (2011) as well as Potvin, Wesseloo, and Heal (2010). The cone bolt mode of operation is similar to conventional two-point anchored bolts as well as other bolts such as Garford bolt, Roofex, Yield-Lok (Li, Stjern, and Myrvang, 2014) and the Secura bolt. This was confirmed by both thermal imaging-assisted tests and geometric bolt measurements carried out after cyclic impact testing, which revealed a uniform deformation of the bolt rod along its length and diameter between the two anchor points: the profiled section. The t Secura-type bolts, tested are depicted schematically in Figure 6. The Secura bolt rod is formed from a smooth bar with a length of L = 350+1900+150 = 2400 mm (profiled section length + yielding section length + thread). Other technical parameters of the bolts and installation are: ➤ Size: Dia = 25.0 mm diameter smooth bar ➤ Steel grade: manganese-steel alloy ➤ Thread specification: DIN 405–26 mm (left-hand thread) ➤ Hex nut: 36AF × 30H (heat treated) ➤ Resin: fast-setting resin (at the anchor end of the hole) – colour code green. Minova Africa Lokset resin capsule, 30 mm diameter, Type A; setting time 60 seconds; slow resin (for the balance of the length) – colour code yellow, setting time 5–10 minutes. Minimum shear strength when tested per SANS 1534:2018 is 23 MPa ➤ Installation: 250–300 r/min rotation (after each installation the produced specimen was left for 1 minute to harden, then removed). Prior to dynamic testing, the quasi-static load-deformation characteristics of the steel bolts themselves, and of the bolts resin-grouted into steel pipes, were determined by tensile testing VOLUME 123
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Figure 6—Structural diagram and photographs of the Secura yielding bolt rod
at the Mechanical Engineering Laboratory of the South African Council for Scientific and Industrial Research (CSIR). The tests were displacement-controlled at 90 mm/min (O’Connor, 2018). The load-deformation curves of the bolts by themselves and the grouted bolts were quantitatively similar, indicating that the behaviour was dominated by the deformation of the bolts alone, not the relative displacement between the bolts and the resin grout. The results also reveal the good mechanical properties of the rod under static loading as well as a great energy absorption capacity. Example load elongation Fs = f(Ls) and work elongation Ws = f(Ls) paths are presented in Figure 7. During the tests, the maximum force was Fsmax = 391.3 kN, elongation was Lsmax = 404.8 mm, while work until rod rupture was 111 kJ. The diagrams demonstrate that the yield point of the bolt rod (with a length of 1650 mm) is Re = 400 MPa, whereas the ultimate strength reaches a value of Rm = 800 MPa (which is also the point of rod rupture) at a relative elongation of A = 24.5%. The dynamic bolt testing procedure was as follows. 1. Mount a bolt grouted into a 2.1 m long tube in the test facility (Figure 3a or 3b). 2. Determine the impact energy Ep and the impact velocity v from Equations [1] and [2]. 3. Raise the drop mass m to a height h corresponding to the selected impact energy Ep and load velocity v Ep = 50.85 kJ and v = 6.0 m/s – m = 2825 kg, h = 1.835 m (LC 1 and LC 2).
4. Allow the free fall of the mass m from a height h onto: • the washer of the bolt grouted into a continuous tube • the washer welded to the tube, 5 cm above its end. 5. Monitor the force F loading the bolt and the bolt displacement L against time, with a sampling frequency of fs = 19.2 kHz. Based on the measurement data, the following paths are determined: Fd = f(t), Ld = f(t), and Fd = f(Ld), which serve as the basis for further analysis and the determination of the energy balance. In order to eliminate noise typical of paths determined under impact loading, the force and elongation paths are subjected to smoothing by means of 2nd- and 4thorder Savitzky-Golay filters. 6. Each bolt rod is tested multiple times (at 10- to 15- minute intervals) until the bolt fails or loses its functional properties, i.e. its load capacity. After the bolt fails, the ram is intercepted by two buffers (equipped with springs and a liquid elastomer) that protect the test facility from damage. 7. After the tests, an opening is made by milling in the upper section of the tube, where the upper section of the bolt – known as the Secura deformed section – is grouted. The displacement LR of the rod within the resin is measured. The force measurements were carried out by means of a strain gauge sensor (accuracy class 0.5), whereas the displacement measurements were carried out using a laser sensor (resolution of 0.5 mm). The sensors were connected to an HBM MGCplus-
Figure 7—Example of a static load-deformation curve for a grouted bolt (lLC 1, split tube) (O’Connor, 2018): (a) CSIR report chart; (b) paths of static loading force Fs and work Ws as a function of elongation Ls 544
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Resistance of yielding rockbolts to multiple impact loads Table I
Bolt resistance to single impacts conducted according to LC2 Bar diameter (after the test) Dia (mm)
Total elongation (after the test) LF (mm)
Energy absorbed by the bolt Wd, (J)
Post-test sample condition
The bolt did not fail; The nuts were free-running after the test
Test No.
Sample ID
Max. load Fmax (kN)
1 2 3 4 5
1 2 3 4 5
416.3 371.8 355.5 388.9 401.4
23.6 23.7 23.5 23.5 23.6
202 203 211 207 208
55184 52745 54240 53153 53631
average standard deviation
86.8
23.6
206.2
53791
23.9
0.1
3.7
958
Table II
Results of bolt resistance tests to single impacts conducted according to LC1 Bar diameter (after the test) Dia (mm)
Total elongation (after the test) LF (mm)
Energy absorbed by the bolt Wd, (J)
Post-test sample condition
The bolt did not fail; The nuts were free-running after the test
Test No.
Sample ID
Max. load Fmax (kN)
6 7 8 9 10
6 7 8 9 10
378.1 377.5 392.8 367.3 380.4
23.8 23.7 23.5 23.5 23.4
201 206 205 204 212
53074 52759 53118 53298 52323
average standard deviation
379.2
23.6
205.6
52915
9.1
0.2
4.0
383
type measuring amplifier (accuracy class 0.03), which worked in conjunction with the computer that registered the measurement data. Each test was recorded using one or two high-speed cameras to register damage-susceptible points on the bolt or the moment and manner of damage. One of the cameras was typically used to record the general view of the entire bolt, while the other was pointed at an area that was particularly susceptible to damage. The videos were recorded at a rate of 600 frames per second (Casio EX-F1) and 1000 frames per second (Sony RX10 IV). Additionally, the tests were recorded using a high-speed thermal camera, the purpose of which was to register the variations in temperature across the entire length of the bolt or at its yielding section. Zones exhibiting significant temperature increases typically represent points where damage, significant deformation (internal friction in the steel bar), or heat accumulation as a result of friction (e.g. at the tube-resin or rod-resin interface) occur. The high-speed thermal camera (Optris PI 230) was operated at a rate of 128 frames per second. Its exchangeable lenses with various angles of view made it possible to record portions of the bolt and the entire bolt.
impact according to LC 2 (Figure 3). The results are presented in Table I. The tests were continued according to l LC 1 using five different bolts, in order to investigate their resistance to a single impact against the yielding section of the bolt (the middle part of the bolt at the junction between the upper and lower parts of the tube). The results are presented in Table II. Photographs of the bolts after the single impact resistance tests are presented in Figure 8. The results exhibit high repeatability for both maximum force and elongation. This was confirmed by visual inspection and photographs of the samples after testing (Figure 8). Also, frame-byframe analysis of the videos recorded by the high-speed cameras
Results and discussion Testing began by investigating the resistance of five bolts to a single The Journal of the Southern African Institute of Mining and Metallurgy
Figure 8—Bolts after a single impact: (a) :C 2; (b) LC 1 VOLUME 123
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Resistance of yielding rockbolts to multiple impact loads revealed no sensitive zones that would indicate bolt damage. The threaded coupling with the nut, as well as the resin connection with the tube, were not shorn. Although the measured bolt rod diameter was smaller than the initial bolt diameter (pre-test), the diameter deformation was uniform across the entire length of the elongated section. The nut remained free-running after the test. A comparison of the full paths of the tests according to LC1 and LC2 is shown in Figure 9. As can be seen, in the case of LC1 there is a faster damping of the impact energy, which manifests in a smaller number of vibrations and a shorter time for their stabilization. This is influenced by the yielding section B, which has a beneficial effect on the impact energy damping. The load and elongation paths were similar for tests conducted according to LC 1 and LC 2. Following the first impulse of the force, the bolt undergoes temporary elongation to Lmax (as a result of elasto-plastic deformation), after which the vibrations of the entire ram-bolt system undergo damping, and the bolt attains a final elongation LF related to the plastic deformation. As an example, a comparison of the first impulse of the force and the elongation during tests of samples 1 and 8 according to LCs 1 and 2 respectively is presented in Figure 10. A significant similarity between the measured load and elongation paths as functions of time can be observed. During the first load (impact) stage, the force is about 400 kN and the bolt begins elongating until it reaches a temporary maximum value Lmax, which is accompanied by minor sinusoidal damped vibrations of the force within a range of 200 to 300 kN. After the ram-bolt system exceeds the value of Lmax = 30 mm, an
elastic rebound of the ram ensues, which results in a decrease in the load to nearly zero, whereas the bolt itself undergoes plastic deformation and minor elasto-plastic vibrations. Since the measured characteristics of load and deformation as functions of time were very similar for all of the tests conducted according to LCs s1 and 2, and since no deformations were observed in the upper sections of the tubes, it was inferred that no displacement of the bolt had occurred in the upper section of the tube (i.e. relative to the embedding resin). In order to investigate the bolt-resin interface in the upper section of the tube, longitudinal openings were cut in randomly selected samples (no. 5, 6, and 7). These exposed the upper sections of the bolts (section A). No bolt displacement LR from the resin was found during tests conducted according to LCs 1 and 2 (see Figures 11a and 11b). Subsequent impact tests, from 2 up to 5 impacts, were conducted on previously tested samples, using the thermal camera in order to inspect the temperature distribution across the entire length of the tubes into which the bolts were grouted. A compilation of the results is included in Tables III and IV. It was observed that, compared to the first bolt impact tests, the force Fmax increased, reaching up to 517.7 kN during the second impact, whereas the final maximum bolt elongation LF decreased to about 140 mm (during the first bolt impact tests, the average elongation LF was about 206 mm). Additionally, no deformation of the tubes into which the bolts were grouted was noted, but there were further deformations of the bolts themselves. All nuts remained free-running after the tests. Figures 12 and 13 present comparisons between the loading force and displacement as functions of time during the second impact for LCs 1 and 2.
Figure 9—Comparison of the full load curves of the bolt according to LC 1 and LC 2 during the first impact: (a) sample 8 (LC 1); (b) sample 1 (LC 2)
Figure 10—Comparison of the first impulse of the loading force according to LC 1 and lLC 2 during the first impact: (a) sample 8 (LC 1); (b) sample 1 (LC 2) 546
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Figure 11—View of samples 5 and 7 after the first impact – the resin interface in the upper bolt section was not shorn
Table III
Compilation of bolt test results according to LC2 under multiple loads Max. load Fmax (kN)
Total elongation (after the test) LF (mm)
Total displacement from the resin (after the test) LR (mm)
Energy absorbed by the bolt Wd, (J)
Post-test sample condition
514.4
140
−
56715
The bolt did not fail. The nuts were free- running after the test
516.5
363
−
30183
365.4
>160
566
25646
Displacement of the bolt from the upper section of the tube. Bar diameter after the tests: 22.8 mm. The ram rested on the buffers
504.8
139
−
57083
The bolt did not fail. The nuts were free- running after the test
526.1
199
−
56259
509.5
78
−
53022
The bolt did not fail. The nuts were free- running after the test. There was a displacement of the bolt from the upper section of the tube
518.0
104
209
52211
Bar diameter after the tests: 21.7 mm
502.5
145
0
51128
556.0
119
0
55556
520.5
-
0
35194
517.7
143
−
55415
22
1 – 2nd drop 1 – 3rd drop 1 – 4th drop 2 – 2nd drop 2 – 3rd drop 2 – 4th drop 2 – 5th drop 3 – 2nd drop 3 – 3rd drop 3 – 4th drop 4 – 2nd drop 4 – 3rd drop
546.1
117
−
55077
23
4 – 4th drop
507.5
>560
3
11887
Test No.
11 12 13 14 15 16 17 18 19 20 21
Sample ID
During the tests according to LC 1, the maximum loads in the first phase of the impulse were lower compared to the tests according to LC 2 (Figure 3). This was confirmed by the tests conducted on different samples (Figure 13). Minor sinusoidal damped vibrations of the force within a range of 300 to 400 kN, can be observed on the charts. After the ram-bolt system exceeds the value LF =170 mm, an elastic rebound of the ram ensues, which results in a decrease in the load to nearly zero, whereas the bolt undergoes plastic deformation and minor elastoplastic vibrations, similarl to those during the first impact tests. An example comparison of consecutive impact tests is depicted in Figure 14. Each consecutive impact test conducted on each bolt resulted in increased load and decreased bolt elongation, which can be observed in Figures 14a–c. Pioneering work by John Hopkinson and his son Bertram Hopkinson revealed that the dynamic yield point of steel is nearly twice as great as the static yield point. Fundamental tests regarding The Journal of the Southern African Institute of Mining and Metallurgy
The bolt did not fail. The nuts were free- running after the test Thread shearing of the nut. Bar diameter after the tests: 22.0 mm The bolt did not fail. The nuts were free- running after the test The bolt did not fail. The nuts were free- running after the test Displacement of the rod from the tube. Bar diameter after the tests: 22.2 mm. The ram rested on the buffers
the phenomena in solids during impact were presented by Taylor (1954) and Campbell (1953). A number of test results were also presented in the book edited by Kinslow (1970). The concept of the dynamic stress-deformation path presented therein by R.B. Pond and C.M. Glass demonstrates the significant increase in the yield point and deformation energy (the crosshatched part marked A) relative to the static curve (Figure 15a). The phenomenon of steel strength increasing together with the rate of elongation is typical (Jurczak, 2007; Kinslow, 1970) and is confirmed in numerous studies. Figure 15b presents example stress curves as functions of elongation of steel with 0.2% C content. This phenomenon was also described by Ortlepp and Stacey (1998). In the case of sample 9 during the 4th impact, the bolt-resin interface was shorn, which resulted in additional bolt yield and protected the bolt from rupturing. The protective reaction of the bolt was thus confirmed, proving that failure is prevented by the absorption of a part of the impact energy, which is a consequence of the bolt’s sliding (Ortlepp and Stacey, 1998). VOLUME 123
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Resistance of yielding rockbolts to multiple impact loads Table IV
Compilation of bolt test results according to LC1 under multiple loads Max. load Fmax (kN)
Total elongation (after the test) LF (mm)
Total displacement from the resin (after the test) LR (mm)
Energy absorbed by the bolt Wd, (J)
445.2
141
−
50151
25
8 – 2nd drop 8 – 3rd drop
500.9
115
−
53101
26
8 – 4th drop
429.8
>189
189
30092
27
466.5
141
−
56898
525.0
115
−
54696
522.5
>220
320
38574
405.8
133
−
51128
31
9 – 2nd drop 9 – 3rd drop 9 – 4th drop 10 – 2nd drop 10 – 3rd drop
439.6
126
−
52885
32
10 – 4th drop
535.5
103
−
53133
33
10 – 5th drop
454.2
>208
215
32952
Test No.
24
28 29 30
Sample ID
Post-test sample condition
The bolt did not fail. The nuts were free- running after the test Displacement of the bolt from the from the tube. Bar diameter after the tests: 22.2 mm. Ram on the buffers The bolt did not fail. The nuts were free- running after the test Bar diameter after the tests: 22.1 mm. Ram on the buffers The bolt did not fail. The nuts were free- running after the test The bolt did not fail. The nuts were free- running after the test. There was a displacement of the bolt from the upper section of the tube Displacement of the bolt from the tube. Bar diameter after the tests: 21.6 mm. Ram on the buffers
Figure 12—Load and displacement curves for the second impact and post-test sample photographs: (a) sample 8 (PC 1); (b) sample 1 (LC 2)
Figure 13—Load and displacement curves for the second impact: (a) sample 9 (lLC); (b) sample 2 (LC 2)
No bolt damage or deformation of the upper section of the tube (the portion of the tube into which the bolt is anchored by the ‘Secura’ deformations) was observed in bolt tests during the 2nd and 3rd impacts. Deformation of the upper tube section occurred 548
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only as a consequence of the 4th impact, which was confirmed by paths of the force as a function of time (Figures 14a, 14c) and by the thermal camera photographs presented in Figure 16. The tests demonstrated that bolts 8 and 9 (LC 1) transferred The Journal of the Southern African Institute of Mining and Metallurgy
Resistance of yielding rockbolts to multiple impact loads
Figure 14—Load and displacement curves for consecutive impacts: (a) 1st; (b) 2nd; (c) 3rd; (d) 4th (sample 9, LC 1)
Figure 15—(a) Dynamic stress-deformation path concept (dotted line) demonstrating the increase in energy relative to the static curve (solid line) (Pond and Glass in Kinslow, 1970); (b) stress curves as functions of elongation of steel with 0.2% C content. (1) static load; (2) dynamic load (Jurczak, 2007)
Figure 16—Sample 9 during consecutive impacts: (a) 2nd impact; (b) 3rd impact; (c) 4th impact; (d) opening in the upper tube section – section A The Journal of the Southern African Institute of Mining and Metallurgy
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Resistance of yielding rockbolts to multiple impact loads a load with an impact energy of 50 kJ a maximum of three times without slipping from the upper tube section. By the fourth impact during the testing of bolts 8 and 9, the rods had already undergone displacement inside the tube. Bolt 10 transferred the load twice and underwent displacement in the tube during the third and fourth impacts, whereas by the fifth impact, the rod slipped out of the tube. The paths of load as a function of time and displacement demonstrate that despite slipping out of the tube, the bolt continued to retain a high load capacity. The reason for this is that the rodgrout-tube interface forms a kind of friction connection similar to a wedge (Figure 17), which leads to significant resistance to motion and the emission of great amounts of heat during the displacement of the rod. Thermal measurements did not reveal any local points of bolt temperature increase that could indicate the beginning of failure. This was confirmed by tests carried out on sample 8. Since the thermal camera utilized a telephoto lens, it was possible to precisely determine the increase and distribution of bolt temperature in the visible part of the yielding section during the second and third impacts. Thermal images taken during the second impact against sample 8 are presented in Figure 18. The maximum average temperature increase during testing was Ta = 8.0°C. No points of excess heating were observed along the embedded tube, only uniform heating of the tube as a result of heat emission by the bolt rod from the time of the previous test. The bolt section between tubes 1 and 2 (Figure 3) exhibits uniform heating along its entire length. There is also no ‘necking’ that would result in a local temperature increase, which would indicate a risk of bolt rupture. Thermal images taken during the third impact against sample 8 are presented in Figure 19. The maximum average temperature increase during testing was Ta = 7.4°C. No points of excess heating were observed along the embedded tube, only uniform heating of the tube as a result of heat emission by the bolt rod from the time of the previous test. The bolt section between tubes 1 and 2 exhibits uniform heating along its entire length, and there is also no ‘necking’ that would indicate a risk of bolt rupture. Comparisons of the energy We consumed for the elastic deformation and energy Wp consumed for the plastic deformation of bolt 8 during impacts 1 to 4 are presented in the paths displayed in Figure 20. Sample 8 transferred three impacts without bolt failure and shearing of the resin connection in the upper part of the tube embedment. However, the fourth impact resulted in the shearing of the resin connection at the rod-grout interface, which led to the pulling out of the bolt rod (Figure 21). Analysis of the thermal image (Figure 21c) revealed that after the rod was pulled out of the grout; its upper part exhibited a maximum temperature of Tmax = 26°C, while for the lower part it was Tmax = 36°C, which indicates a clear boundary between the
embedded section in tube 1 and the yielding section between tubes 1 and 2. The pulling out occurred approximately 40 ms following impact, and as can be observed, the post-test rod temperature did not increase over this time. There was no further increase in the plasticity of the rod in the yielding section, and the force with which the bolt was pulled out was primarily a result of friction between the sliding rod and the grout. Another instance of a bolt subjected to multiple impact loads is depicted in Figure 22, presenting sample 2, which was subjected to load tests according to lLC 2. The compilation includes five test paths during impacts 1 to 5. Figure 23 presents five Fd Ld paths obtained during the tests after impacts 1 to 5. The bolt-resin interface was shorn during the third impact, but the bolt retained its operational properties and was still capable of transferring the load during the fourth and fifth impacts. No breaking of the bolt continuity or shearing of the bolt thread and nut were observed after testing (Figure 24). However, heating of the upper section of the bolt rod was observed in thermal images. Heating began during the third impact and progressed over the fourth and fifth impacts, which can be seen in Figures 25a-d. At the end of the test series, the tubes were opened in the upper sections. Figure 25e presents a section of the tube with a visible bolt displacement of LR = 209 mm.
Figure 18—Thermal images of sample 8 before and after the second impact
Figure 19—Thermal images of sample 8 before and after the third impact
Figure 17—Sample 6 after one impact: (a) the resin connection in section A was not shorn; (b) profiled section A after removal from the tube, diameter D = 25-31 mm 550
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Figure 20—Comparison of energy consumed during elastic (We) and plastic (Wp) deformation of bolt 8 during the 1st (a), 2nd (b), 3rd (c), and 4th (d, e) impacts
Figure 21—Bolt 8 during the fourth impact: (a) thermal image before testing; (b)bolt after testing; (c) thermal image after testing; (d) opening in the upper tube section – section A
Figure 22—Comparison of sample 2 load curves (LC 2) during five consecutive impacts
Sample 1 exhibited a similar behaviour, which can be observed in the thermal images depicted in Figures 26a-c and in the photograph of the milled-open tube after testing (Figure 26d). The only instance of damage to a mechanical element of the bolt was noted during a test conducted on sample 3. The bolt transferred three impact loads without damage, but the thread on the bolt-nut interface was sheared during the fourth impact, which resulted in a sudden drop in force and a loss of the bolt’s functional quality. The paths of these tests are depicted in Figure 27. For the same sample, the thermal images in Figures 28a-c show no bolt displacement in the upper section, as indicated by the absence of temperature increase in the bonding zone. An opening The Journal of the Southern African Institute of Mining and Metallurgy
cut in the upper tube section also revealed no bolt displacement, and the resin connection was intact (Figure 28e). Despite the significant elongation and constriction of the bolt, bolt rod rupture did not occur (Figure 28d). The measured diameter of the nonthreaded part of the bolt rod averaged about 22.0 mm (the pre-test diameter was 25.0 mm). The diameter was practically uniform across the entire section of the bolt rod, and no characteristic local constriction in the form of a ‘neck’ that would indicate the beginning of bolt rupture was observed. However, it is likely that the shearing of the bolt thread in the nut was due to the reduction in the diameter of the thread, which after the test measured approximately 24.9 mm. There was no VOLUME 123
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Resistance of yielding rockbolts to multiple impact loads
Figure 23—Comparison of energy consumed during elastic (We) and plastic (Wp) deformation of bolt 2 during impacts 1–5
Figure 24—Photographs of bolt 2 (load case 2) after the fifth impact
Figure 25—Sample 2 after consecutive impacts 2 (a) to 5 (d); -€ opening in the upper tube section – Secura deformed section
bolt yield resulting from the displacement of the bolt in the upper tube section. This (often unfavourable) phenomenon, which leads to a loss of load capacity due to shearing of the bolt rod-resin connection, in this case gives the bolt further yielding potential, the effects of which are similar to a friction coupling. It can be observed 552
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that the style of the Secura bolt macro-deformations initiates the formation of a kind of wedge, the functionality of which is similar to that of a ‘cone bolt’. We suspect that the behaviour of the Secura deformed section (A) as a frictional yielding element can only occur if the steel has The Journal of the Southern African Institute of Mining and Metallurgy
Resistance of yielding rockbolts to multiple impact loads
Figure 26—Sample 1 after consecutive impacts 2 (a) to 4 (c); (d) opening in the upper tube section – Secura deformed section
Figure 27—Comparison of sample 3 load charts (LC 2) during consecutive impacts 1: (a) to 4 (d)
Figure 28—Sample 3 during consecutive impacts 2 (a) to 4 (d); (e) opening in the upper tube section – Secura deformed section
first undergone internal deformation. The reduction in the diameter of the steel results in debonding from the resin and ensures that all the load is applied to the (short) resin interface in the Secura deformed section. If the steel did not decrease in diameter first, it would still exhibit good contact with the resin over the entire length of the bolt, which would probably result in rupture of the bolt. Earlier-generation yielding bolts, such as the cone bolt, that relied on relative movement between an anchoring section of the bolt and the surrounding grout, incorporated a debonding layer over most of the length of the bolt.
Summary and conclusions The Secura-type yielding rockbolts transferred double the gravitational potential energy Ep = 50.85 kJ from the impact of a load of mass m = 2825 kg at an impact velocity v = 6.0 m/s without failure. Damage to the bolt-resin interface in the bonding zone occurred only as a result of multiple impacts. The test methodology confirmed the rupture of the resin interface, both on the basis of bolt force and elongation paths as functions of time, as well as the analysis of videos recorded by a high-speed thermal camera. Only one test (test no. 20, sample 3) The Journal of the Southern African Institute of Mining and Metallurgy
resulted in damage to the threaded bolt-nut coupling on the fourth impact. Since during all the remaining tests the bolts retained their functionality and were capable of continued impact load transfer, the evaluation of the test results should be given more thought. Additional bolt yield due to the displacement of the bolt’s deformed section in relation to the resin can be beneficial, resulting in the formation of a kind of tapered frictional coupling in the upper section of the opening for bolt installation. The tests also confirmed the findings of Taylor (1954) and Taylor and Tadros (1956), who compared such factors as the static and dynamic stress- deformation characteristics of soft steel (0.17% C), medium-carbon steel (0.31% C), and silico- manganese (SiMn) alloy steel with a carbon content of 0.55%. Their tests also utilized the dynamic impact drop method to exert dynamic loading, while the dynamic yield point was achieved over a time of 0.18 to 1 ms. All the tests exhibited increases in dynamic yield point together with shorter loading times, and an explanation for this phenomenon can be found in the theory of dislocation formation in steel under dynamic loads (Campbell, 1953). There is insufficient time for these dislocations to move, which inhibits deformation and thereby results in an increased yield point during the rapid build-up of stress. VOLUME 123
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Resistance of yielding rockbolts to multiple impact loads In the future, yielding bolt tests under multiple impact loads should be performed for different mechanical configurations of the bolts and at various values of energy and impact velocity. It is envisaged that these tests will investigate the shear strength and adhesion of the resins and grouts under dynamic impact loading.
Acknowledgements
The authors would like to thank Mr Dariusz Modliński and Mr Tadeusz Wosik of MINOVA ARNALL Sp. z o.o. for their assistance in preparing the test facility and the samples for testing, as well as their valuable advice concerning the structure of the test facility.
conditions. International Journal of Mining Science and Technology, vol. 10, no. 5. pp. 555–572. Guntumadugu, D.R. 2013. Methodology for the design of dynamic rock supports in burst prone ground. Doctoral dissertation, McGill University. Hagen, S.A., Larsen, T., Berghorst, A., and Knox, G. 2020. Full-scale rockbolt testing in the laboratory: Analysis of recent results. Journal of the Southern African Institute of Mining and Metallurgy, vol. 120, no. 1. pp. 1–6. Haile, A.T. and Le Bron, K. 2001. Simulated rockburst experiment - evaluation of rock bolt reinforcement performance. Journal of the South African Institute of Mining and Metallurgy, August 2001. pp. 247–252.
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Cała, M., Flisiak, J., and Tajduś, A. 2001. Mechanizm współpracy kotwi z górotworem o zróżnicowanej budowie. [The mechanism of interaction between anchors and a rock mass with diverse construction]. Instytut Gospodarki Surowcami Mineralnymi i Energią PAN, Kraków. Cai, M., Champaigne, D., and Kaiser, P.K. 2010. Development of a fully debonded cone bolt for rockburst support. Deep Mining 2010: Proceedings of the Fifth International Seminar on Deep and High Stress Mining. Van Sint Jan, M. and Potvin, Y. (eds). Australian Centre for Geomechanics, Perth. pp. 392–342. CAN/CSA-M430-90. Roof and rock bolts, and accessories. Canadian Standards Association, toronto. Charette, F.C., Hyett, A.J., Voyzelle, B., and Anderson, T. 2014. Loaddeformation behaviour of a deformable rockbolt and accessories under dynamic loading. Proceedings of the Seventh International Conference on Deep and High Stress Mining. Australian Centre for Geomechanics, Perth. pp. 253–262. Chrysochoos, A. and Martin, G. 1989. Tensile test microcalorimetry for thermomechanical behaviour law analysis. Materials Science and Engineering A, vol. 108. pp. 25–32. DIN 21521.1990. Teil 1 – Gebirgsanker für den Bergbau und den Tunnelbau – Begriffe. [German Standard: Rock bolts for mining and tunnelling; terms]. German Institute for Standardization, Berlin. DIN 21521:1993. Teil 2 – Gebirgsanker für den Bergbau und den Tunnelbau – Allgemeine Anforderungen für Gebirgsanker aus Stahl – Prüfungen, Prüfverfahren. [German Standard: Rock bolts for mining and tunnel support; general specifications for steel-bolts; tests, testing methods]. Doucet, C. and Voyzelle, B. 2012. Technical information data sheets. CanmetMINING, Ottawa. https://www.workplacesafetynorth.ca/sites/default/ files/resources/CanmetMINING-Technical-Data-Sheets- September-2012_1.pdf Eriksson, F. 2020. Assessment of static performance of LKAB´s welded mesh: Laboratory testing and analysis. Master’s thesis, Luleå University of Technology. Gaudreau, D., Aubertin, M., and Simon, R. 2004. Performance assessment of tendon support systems submitted to dynamic loading. École polytechnique de Montréal. Ghorbani, M., Shahriar, K., Sharifzadeh, M., and Masoudi, R. 2020. A critical review on the developments of rock support systems in high stress ground 554
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Knox, G. and Berghorst, A. 2018. Increased agility for the research and development of dynamic roof support products. New Concept Mining, Johannesburg. pp. 1-6. https://www.ncm.co.za/downloads/papers_ presentations/Knox_Berghorst-2018-Increased_agility_for_the_research_and_ development_of_dynamic_roof_support_products.pdf [accessed 27 May 2019] Knox, G., Berghorst, A., and Crompton, B. 2018. The relationship between the magnitude of impact velocity per impulse and cumulative absorbed energy capacity of a rock bolt. AusRock 2018: Proceedings of the Fourth Australasian Ground Control in Mining Conference, Sydney, NSW, 28–30 November 2018. Australasian Institute of Mining and Metallurgy, Melbourne. pp. 160–169. https://www.ncm.co.za/downloads/papers_presentations/Knox_Crompton_ Berghorst(2018)- The_relationship_between_the_magnitude_of_impact_ velocity_per_impulse_&_cumulative_absorbe d_energy_capacity_of_a_rock_ bolt-Paper.pdf [accessed 27 May 2019] Knox, G., Berghorst, A., and de Bruin, P. 2018. An empirical comparison between new and existing laboratory-based dynamic sample configurations. Caving 2018. Proceedings of the Fourth International Symposium on Block and Sublevel Caving. Potvin, Y. and ]Jakubec, J. (eds). Australian Centre for Geomechanics, Perth. pp. 775-786. https://www.ncm.co.za/downloads/papers_presentations/ Knox_Berghorst_DeBriun_2018_An_empiri cal_comparison_between_ new&existing_laboratory-based_dynamic_sample_configurations- Paper.pdf [accessed 27 May 2019] Labrie, D., Doucet, Ch., and Plouffe, M. 2008. Design guidelines for the dynamic behaviour of ground support tendons. Phase I and II. CANMET-MMSL, Vald'Or, Quebec. Li ,C.C. 2017a. Rockbolting: Principles and Applications. Butterworth-Heinemann. Li, C.C. 2017b. Principles of rockbolting design. Journal of Rock Mechanics and Geotechnical Engineering, vol. 9, no. 3. pp. 396–414. Li, C.C. 2010. Field observations of rock bolts in high stress rock masses. Rock Mechanics and Rock Engineering, vol. 43, no. 4. pp. 491–496. Li , C.C., Mikula, P., Simser,, B., Hebblewhite, B., Joughin, W., Feng, X., and Xu, N. 2019. Discussions on rockburst and dynamic ground support in deep mines. Journal of Rock Mechanics and Geotechnical Engineering, vol. 11, no. 5. pp. 1110–1118. Li, C.C., Stjern, G., and Myrvang, A. 2014. A review on the performance of conventional and energy-absorbing rockbolts. Journal of Rock Mechanics and Geotechnical Engineering, vol. 6, no. 4. pp. 315–327. The Journal of the Southern African Institute of Mining and Metallurgy
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Resistance of yielding rockbolts to multiple impact loads PARTNERSHIPS IN PRACTICE
Wear liner manufacturer Tega hosts conclave Tega Industries Africa CEO Vishal Gautam, together with his team, hosted a conclave on 16 November at the Maslow, Times Square Pretoria. Experts from four continents gave technical presentations that covered topics including innovations in mill liners, optimization and maintenance, and the influence of design and operating variables on mill performance. The reccurring themes included safety, reliability, time saving, energy efficiency, and durability. Ernesto Mori, Marketing and Production Director, mentioned that a reduction in injuries has been reported by mines where AG-SAG mill liners produced by Tega have been installed. For over 45 years Tega Industries has lived by its philosophy of working together with its clients to enhance productivity through innovative and effective solutions. The company has announced the founding of Teg McNally, a new branch of Tega that will bring an offering of future technology and high-quality products. The product line includes apron feeders, jaw crushers, ring granulators, and mobile crushing units. The announcement of the new Tega McNally carries the promise of high-quality durable products that will increase productivity and ultimately profits.
Tega Industries factory open day Conclave attendees were invited to an open day at the Tega Industries factory in Brakpan. This was held on 17 November 2023 and hosted by the company CEO, Mr Vishal Gautam. Delegates were greeted by security personnel who conducted the necessary safety checks. PPE and safety equipment was provided for the visitors, followed by a 15-minute safety briefing. This underlines the importance of minimizing safety incidents in the work environment. Tega Industries showcased a streamlined process, making use of highquality raw materials. The company prides itself on minimal wastage and is currently intending to install an alternative energy source, solar panels, to replace the coal currently used to produce energy, thus, reducing the company’s carbon footprint. Mr Gautam has confirmed that the organization continues to source raw materials both internationally and nationally, guaranteeing the supply.
Elastocer Liners Polyurethane Liners
Metal Back Rubber Liners
The staff at Tega Industries are knowledgeable and answered all question from attendees. Tega Industries has a quality guarantee and service promise, and will not sell its products in areas where they cannot provide after-sales services to clients.
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NATIONAL & INTERNATIONAL ACTIVITIES 2023 7 December 2023 — GMG Underground Communications Infrastructure Workshop 239 Montée Principale Grand Sudbury, Canada Website: https://www.eventbrite.ca/e/undergroundcommunications-infrastructure-workshop-in-sudbury-tickets751301060697?aff=oddtdtcreator 14 December 2023 — GMG Operation Readiness and Deployment in Autonomous Mining (Virtual held in Spanish) Website: https://www.eventbrite.ca/e/taller-sobreimplantacion-de-sistemas-autonomos-tickets757905143687?aff=oddtdtcreator Until 31 December 2023 — ICMS Mine, Connect, Empower Operations with Virtual WMC 2023 Access to the WMC 2023 Congress Platform and all virtual sessions Website: https://icmsaust.eventsair.com/26th-world-miningcongress/virtualplatformpurchase/Site/Register
2024 12-13 March 2024 — GMG Kiruna Forum | Tomorrow’s Mining: Innovating to Improve the Way We Mine Contact: Camielah Jardine Website: https://gmggroup.org/gmg-kiruna-forumtomorrows-mining-innovating-to-improve-the-way-we-mine/ 13-14 March 2024 — Southern African Pyrometallurgy 2024 International Conference Sustainable Pyrometallurgy - Surviving Today and Thriving Tomorrow Misty Hills Conference Centre, Johannesburg, South Africa Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 19-25 April 2024 — World Tunnel Congress 2024 Shenzhen, China Website: https://www.wtc2024.cn/ 21-23 May 2024 — The 11TH World Conference of Sampling and Blending 2024 Hybrid Conference Misty Hills Conference Centre, Johannesburg, South Africa Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za
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27-31 May 2024 — Nickel-Cobalt-Copper Lithium-Battery Technology-REE 2024 Conference and Exhibition Perth, Australia Website: https://www.altamet.com.au/conferences/alta-2024/ 11-13 June 2024 — 15TH International Conference on Industrial Applications of Computational Fluid Dynamics Trondhedim, Norway E-mail: Jan.E.Olsen@sintef.no Website: https://www.sintef.no/projectweb/cfd2024/ 18-20 June 2024 — Southern African Rare Earths 2ND International Conference 2024 Swakopmund Hotel and Entertainment Centre, Swakopmund, Namibia Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 3-5 July 2024 — 5TH School on Manganese Ferroalloy Production Decarbonization of the Manganese Ferroalloy Industry Boardwalk ICC, Gqeberha, Eastern Cape, South Africa Contact: Gugu Charlie Tel: 011 538-0238 E-mail: gugu@saimm.co.za Website: http://www.saimm.co.za 21-22 August 2024 — Mine Closure Conference 2024 Johannesburg, South Africa Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 5-8 August 2024 — 2nd Battery Materials Conference 2024 The Arena, Emnotweni Casino, Mbombela, Mpumalanga Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za 1-3 September 2024 — Hydrometallurgy Conference 2024 Hydrometallurgy for the Future Hazendal Wine Estate, Stellenbosch, Western Cape, South Africa Contact: Camielah Jardine Tel: 011 538-0237 E-mail: camielah@saimm.co.za Website: http://www.saimm.co.za
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Company affiliates The following organizations have been admitted to the Institute as Company Affiliates 3M South Africa (Pty) Limited A and B Global Mining (Pty) Ltd acQuire Technology Solutions AECOM SA (Pty) Ltd AEL Mining Services Limited African Pegmatite (Pty) Ltd Air Liquide (Pty) Ltd Alexander Proudfoot Africa (Pty) Ltd Allied Furnace Consultants AMEC Foster Wheeler AMIRA International Africa (Pty) Ltd ANDRITZ Delkor(pty) Ltd Anglo Operations Proprietary Limited Anglogold Ashanti Ltd Anton Paar Southern Africa (Pty) Ltd Arcus Gibb (Pty) Ltd ASPASA Aurecon South Africa (Pty) Ltd Aveng Engineering Aveng Mining Shafts and Underground Axiom Chemlab Supplies (Pty) Ltd Axis House Pty Ltd Bafokeng Rasimone Platinum Mine Barloworld Equipment -Mining BASF Holdings SA (Pty) Ltd BCL Limited Becker Mining (Pty) Ltd BedRock Mining Support Pty Ltd BHP Billiton Energy Coal SA Ltd Blue Cube Systems (Pty) Ltd Bluhm Burton Engineering Pty Ltd Bond Equipment (Pty) Ltd Bouygues Travaux Publics Caledonia Mining South Africa Plc Castle Lead Works CDM Group CGG Services SA Coalmin Process Technologies CC Concor Opencast Mining Concor Technicrete Council for Geoscience Library CRONIMET Mining Processing SA Pty Ltd CSIR Natural Resources and the Environment (NRE) Data Mine SA DDP Specialty Products South Africa (Pty) Ltd Digby Wells and Associates DRA Mineral Projects (Pty) Ltd DTP Mining - Bouygues Construction Duraset ▶ viii
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EHL Consulting Engineers (Pty) Ltd Elbroc Mining Products (Pty) Ltd eThekwini Municipality Ex Mente Technologies (Pty) Ltd Expectra 2004 (Pty) Ltd Exxaro Coal (Pty) Ltd Exxaro Resources Limited Filtaquip (Pty) Ltd FLSmidth Minerals (Pty) Ltd Fluor Daniel SA ( Pty) Ltd Franki Africa (Pty) Ltd-JHB Fraser Alexander (Pty) Ltd G H H Mining Machines (Pty) Ltd Geobrugg Southern Africa (Pty) Ltd Glencore Gravitas Minerals (Pty) Ltd Hall Core Drilling (Pty) Ltd Hatch (Pty) Ltd Herrenknecht AG HPE Hydro Power Equipment (Pty) Ltd Huawei Technologies Africa (Pty) Ltd Immersive Technologies IMS Engineering (Pty) Ltd Ingwenya Mineral Processing (Pty) Ltd Ivanhoe Mines SA Kudumane Manganese Resources Leica Geosystems (Pty) Ltd Loesche South Africa (Pty) Ltd Longyear South Africa (Pty) Ltd Lull Storm Trading (Pty) Ltd Maccaferri SA (Pty) Ltd Magnetech (Pty) Ltd MAGOTTEAUX (Pty) Ltd Malvern Panalytical (Pty) Ltd Maptek (Pty) Ltd Maxam Dantex (Pty) Ltd MBE Minerals SA Pty Ltd MCC Contracts (Pty) Ltd MD Mineral Technologies SA (Pty) Ltd MDM Technical Africa (Pty) Ltd Metalock Engineering RSA (Pty)Ltd Metorex Limited Metso Minerals (South Africa) Pty Ltd Micromine Africa (Pty) Ltd MineARC South Africa (Pty) Ltd Minerals Council of South Africa Minerals Operations Executive (Pty) Ltd MineRP Holding (Pty) Ltd Mining Projections Concepts Mintek MIP Process Technologies (Pty) Limited MLB Investment CC VOLUME 123
Modular Mining Systems Africa (Pty) Ltd MSA Group (Pty) Ltd Multotec (Pty) Ltd Murray and Roberts Cementation Nalco Africa (Pty) Ltd Namakwa Sands(Pty) Ltd Ncamiso Trading (Pty) Ltd Northam Platinum Ltd - Zondereinde Opermin Operational Excellence OPTRON (Pty) Ltd Paterson & Cooke Consulting Engineers (Pty) Ltd Perkinelmer Polysius a Division of Thyssenkrupp Industrial Sol Precious Metals Refiners Rams Mining Technologies Rand Refinery Limited Redpath Mining (South Africa) (Pty) Ltd Rocbolt Technologies Rosond (Pty) Ltd Royal Bafokeng Platinum Roytec Global (Pty) Ltd RungePincockMinarco Limited Rustenburg Platinum Mines Limited Salene Mining (Pty) Ltd Sandvik Mining and Construction Delmas (Pty) Ltd Sandvik Mining and Construction RSA(Pty) Ltd SANIRE Schauenburg (Pty) Ltd Sebilo Resources (Pty) Ltd SENET (Pty) Ltd Senmin International (Pty) Ltd SISA Inspection (Pty) Ltd Smec South Africa Sound Mining Solution (Pty) Ltd SRK Consulting SA (Pty) Ltd Time Mining and Processing (Pty) Ltd Timrite Pty Ltd Tomra (Pty) Ltd Trace Element Analysis Laboratory Traka Africa (Pty) Ltd Trans-Caledon Tunnel Authority Administarator Ukwazi Mining Solutions (Pty) Ltd Umgeni Water Webber Wentzel Weir Minerals Africa Welding Alloys South Africa Worley
The Journal of the Southern African Institute of Mining and Metallurgy
FOUNDED 1894
THE SOUTHERN AFRICAN INSTITUTE OF MINING AND METALLURGY
The Southern African Institute of Mining and Metallurgy in collaboration with the SAIMM Western Cape Branch is hosting the
HYDROMETALLURGY CONFERENCE 2024
Hydrometallurgy for the Future 1-3 SEPTEMBER 2024
HAZENDAL WINE ESTATE, STELLENBOSCH, WESTERN CAPE, SOUTH AFRICA
T
he world’s dependency on metals has become more evident with the growing demand for metals required to drive advancements in the technological and digital landscape and, the energy transition for a carbon neutral future. This growing demand however, implies that the metal extraction industry will need to play a significant role in providing the world with vast quantities of metals crucial in the building of the necessary infrastructure. Furthermore, energy and water are two critical inputs in the hydrometallurgical process flowsheets and their increasing shortage suggests the need for the development of processes that take such challenges into consideration. A circular hydrometallurgy approach focusing on innovative research and developments around energy and resource efficient processes based on closing materials and resources loops can therefore, play an important role if the metal extraction sector is to meet the current and future global metal demands. In addition, advancements in the field of artificial intelligence can also allow for the use of innovative tools such as machine learning to better understand, predict and optimise hydrometallurgical processes in a smarter and sustainable manner. The SAIMM Hydrometallurgy conference, 2024, will bring together internationally and locally recognized scientists and engineers from mining and metal producing companies, project design and implementation entities, equipment and reagent suppliers, research and academic institutions to discuss and share innovative technologies that can assist the global world in meeting the current and future metal demands.
FOR FURTHER INFORMATION, CONTACT:
Camielah Jardine, Head of Conferencing
E-mail: camielah@saimm.co.za Tel: +27 11 530 0238 Web: www.saimm.co.za
2 BATTERY MATERIALS ND
CONFERENCE 2024 5 AUGUST 2024 - WORKSHOP 6 -7 AUGUST 2024 - CONFERENCE 8 AUGUST 2024 - TECHNICAL VISIT
THE ARENA, EMNOTWENI CASINO, MBOMBELA, MPUMALANGA
The intensified search over the past decade for alternatives to fossil fuels as sources of energy, has led to the development of a number of renewable energy technologies. A major issue with renewable energy sources is its intermittency which requires energy storage. This requirement has led to an exponential growth in the demand for batteries and research into battery technologies. The largest application by far has been in transportation, followed by the balancing of electrical distribution grids. Of the raw materials required for battery manufacture, metals such as cobalt, manganese, vanadium and to a lesser extent nickel are concentrated in southern Africa. The supply of lithium, on the other hand, is mainly concentrated in Australia, Chile and Argentina with only Zimbabwe boasting significant resources in Africa. These activities have created both opportunities and challenges. Opportunities such as new value chains for the associated raw materials, with several production companies with battery-material metals in their plant feedstocks undertaking research towards producing battery-grade products. Challenges such as the means for recycling these batteries once they reach the end of their (first) life. The aim of this conference is to provide the opportunity for thought leaders in the global battery value chain to exchange ideas on recent
developments in the fields of: • Materials and high-purity intermediates for battery components – Novel battery chemistries • Flow-battery electrolytes • Processes for the recycling of batteries • Market outlook and legislative implications – New projects and entrepreneurship in the battery industry • Related case studies. An even sharper focus can be provided by addressing the following questions and hypotheses: • Will future battery developments and applications in southern Africa centre more around bulk energy storage by drawing on regional metal resources and addressing local bulk energy shortages? • Will lithium-ion batteries continue to dominate most battery applications, with other battery technologies serving only niche applications? • What (exactly) are the criteria and specifications for battery materials, intermediates and electrolytes required to achieve the envisaged performance and life of the batteries? – What impact will South Africa’s electrical supplyissueshaveonthelocalmotormanufacturing industry and the market for EVs?
FOR FURTHER INFORMATION CONTACT: Camielah Jardine: Head of Conferencing E-mail: camielah@saimm.co.za
Web: www.saimm.co.za Tel: +27 11 538-0237