ACID DRAINAGE FROM MINES AND ITS RELATEDPROBLEMS

ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS PREDICTION, QUANTIFICATION AND IMPLEMENTATION OF MITIGATION MEASURES ARE THE KEY FOR ENHANCEMENT OF ENVIRONMENTAL STANDARD

Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blogs/Websites: http://miningandblasting.wordpress.com/ , http://saferenvironment.wordpress.com Abstract Acid Mine Drainage (AMD), is the outflow of acidic water from mining operations including waste rock, tailings, and exposed surfaces in open pits and underground workings. ARD forms as a result of the dissolution of sulphides, mainly pyrite (FeS2) and pyrrhotite (FeS) under oxidizing conditions in air and water. This oxidation releases H+ ions and lowers the surrounding pH to acidic levels. Acidic drainage will subsequently leach additional metal ions from the adjacent rocks and deposit them.

AMD is a problem because the vast majority of natural life is designed to live and survive at, or near, pH 7 (neutral). The drainage acidifies the local watercourses and so either kills or limits the growth of the river ecology.

Mining operations lacking sufficient neutralizing carbonate minerals are at greatest risk of environmental degradation and usually require engineering intervention to minimize the problem. Although prevention of AMD is the most desirable option, a cost-effective prevention method is not yet available. The most effective method of control is to minimize penetration of air and water through the waste pile using a cover, either wet (water) or dry (soil), which is placed over the waste pile. Despite their high cost, these covers cannot always completely stop the oxidation process and generation of AMD. Application of more than one option might be required. Early diagnosis of the problem, identification of appropriate prevention/control measures and implementation of these methods to the site would reduce the potential risk of AMD generation. AMD prevention/control measures broadly include use of covers, control of the source, migration of AMD, and treatment.

INTRODUCTION Acid mine drainage (AMD) in general refers to the outflow of acidic water from metal mines or coal mines (including abandoned mines). AMD is one of the most perpetual pollution problems which occur world-wide in the mining areas. It refers to the distinctive type of wastewater that originates from the weathering and leaching of sulphide minerals present in coal and metal ore bodies.

In fact, AMD from abandoned coal mines affects the quality of both groundwater and surface water. Drainage results from various mining methods performed in the watershed. These methods include underground mining, strip mining, and auger mining. The mining process exposes iron Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, 1 E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

sulfide (pyrite) and unremoved coal contained in the sandstone overburden to air and water.

These oxidizing conditions result in an increase of acidity, which subsequently decreases the pH and increases the concentrations of dissolved metals. These consequences lead to an overall degradation of water quality and the inability to support aquatic life.

Mineral production is an important component of the economy for many countries, and in some cases it can be the major source of international revenue. However, mining and mineral production operations that are not well managed can contaminate groundwater and surface water in the form of AMD, and can adversely affect the health of nearby communities that rely on this source for drinking-water or agriculture. Extractive industries include mining of mineral deposits (principally metal-bearing ores and coal deposits), oil and natural gas production, and quarrying for building and road-making materials. Poorly operated or abandoned mine sites are often significant sources of water contamination; contaminants of particular health concern from these sources include heavy metals, and mineral-processing chemicals, such as cyanide. Water pumped from abandoned mine shafts and open-cut pits is often used for water supply, and is generally safe and reliable. However, these water sources may sometimes be contaminated by mineral processing chemicals, acid mine drainage (AMD) and waste disposal. These risks must be considered and assessed to determine whether such water sources are safe to be used for drinkingwater supply.

PRODUCING ACID FROM ROCK Acid mine drainage (AMD) is produced by the chemical reaction of sulfide ore and associated minerals with air and water. This reaction (as shown below) illustrates how sulfuric acid(H 2 SO4) and iron sulfate (FeSO4) are produced when the iron sulfide mineral pyrite (FeS2) reacts with water: FeS 2 + H 2 O + 3.5O 2 = H 2 SO 4 + FeSO 4 The iron sulfate and sulfuric acid continue to react with water and air through several steps to produce iron hydroxide (Fe[OH] 3 ) and additional sulfuric acid.

The sulfuric acid is responsible for leaching metals from mine dumps as well as significantly lowering the pH in streams. The iron hydroxide is responsible for the characteristic reddish color associated with AMD. Although operating more slowly, the reactions described above do affect natural outcroppings of sulfide ore minerals, resulting in a characteristic reddish stain that is referred to as a ‘gossan’. The color of the gossan is so distinctive that it can be seen for miles. Early mineral exploration made use of gossans as an indicator of where potential ore deposits might be found.

DISCUSSION ON ACID DRAINAGE AND RELATED ASPECTS a. Acid Rock Drainage and Acid Mine Drainage - Acid rock drainage (ARD) is a natural process in which sulfuric acid is produced when sulfides in rocks—for example, pyrite (FeS 2 ) — are exposed to air and water. This is an explanation of the natural weathering process of mineral (such as gold, copper, zinc etc.) bearing rocks exposed to atmosphere. This occurs along outcrops or scree slopes where sulfide-bearing rock is naturally weathered. Acid Rock Drainage occurs where there are large quantities of sulphur- containing rock minerals and has been observed associated with road building, construction (including construction at an airport) and at mines.

Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

Acid mine drainage (AMD) is essentially the same process as ARD only greatly magnified. In general, rocks that contain valuable metals usually contain sulfides (metals combined with sulfur). The reason for this marriage (metal deposits with sulfide or sulfur) is that thermal waters are typically responsible for depositing many types of metallic ore. These thermal waters travel along fractures or small channels in the host rock. As a result, the thermal waters also change the mineralogy of the host rock along these fractures, creating bodies of rock referred to as hydrothermal alteration zones, which may be many times larger than the economically-defined ore zones or veins that fill the fracture.

b. Mineral Deposits associated with AMD - Gangue minerals are the non-valuable minerals closely associated with the valuable ore deposits. They generally include minerals like quartz or calcite. During mining activities, the gangue material is commonly discarded as waste rock or low-grade ore in an effort to extract more valuable ore minerals found in the veins. AMD is typically associated with these types of hard rock mines across the world.

Another major form of AMD is associated with coal mines, where acid is formed by the oxidation of sulfur occurring in the coal and the rock or clay found above and below the coal seams.

Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

When the minerals in the rock were deposited millions of years ago, they were formed at high temperatures and pressures. This makes these mineral deposits (including the gangue material) unstable under surface conditions when exposed to oxygen and water. Most sulfide minerals react with oxygen (oxidation) and water (hydration). Some sulfides, especially those containing iron and copper, generate sulfuric acid in the process. Pyrite (commonly called "fool's gold"), the most common sulfide mineral, reacts with oxygen and water to form ferrous iron and sulfuric acid in solution.

Laboratory studies have shown that exposing sulfide minerals to oxygen and water produces sulfuric acid, but scientists found that the rate of generation is so slow that it would take decades to oxidize a significant proportion of sulfide. Observations of AMD and other natural systems clearly demonstrate that acid production occurs in a short time period, from months to years. This is because some common strains of bacteria present in almost all environments increase the reaction rate by orders of magnitude.

Once the acid is formed it leaches other metals, such as copper, zinc, cadmium, nickel, arsenic, lead, and mercury, from the mineralized vein. High concentrations of these metals are dissolved by the acid and carried away in solution. As the acid solution flows away from the mine, the pH changes and affects the chemistry of the solution such that different metals begin to precipitate out of solution.

Color changes typical of creeks affected by AMD start as orange, red, or yellow-brown as the ferrous iron solution is diluted. The pH rises as the AMD mixes with the receiving stream, causing the ferrous iron to precipitate out as ferric iron. Farther downstream, the stream is white as aluminum oxide deposits along rocks and the streambed. The iron and aluminum deposits tend to form a sludge-like material, which inhibits algae, insect, and fish growth, and damages their habitat.

Benthic (bottom-dwelling) organisms are particularly sensitive to this type of pollution.

Following the orange iron and white aluminum deposits, the streams can then take on turquoiseblue or green colors as copper and other metals begin to precipitate from solution.

Depressed food supplies, gill clogging, and smothering by iron or aluminum precipitates, along with direct toxicity from ingested metals, contribute to the significant decline of fish, insect, and benthic communities in streams polluted by metal oxides. With their food supply diminished, fish populations can be limited even when degradation is not severe enough to cause direct poisoning of individual fish. c. Is Mine Drainage always Acidic? - Not all mine drainage is acidic. It is possible in areas where the geology is rich in carbonates or lime that the effluent will become closer to neutral.

Often these neutral waters are also saline. Whilst this tends to suggest that the drainage will be less of a problem (after all, the acid is responsible for at least some of the environmental degradation) this drainage too requires treatment.

CHEMISTRY AND ROLE OF WATER IN ACID DRAINAGE Acid mine drainage is an extremely acidic iron and sulphate rich drainage that forms under natural conditions when certain coal seams are mined and the associated strata are exposed to a new oxidizing environment. During this process, a variety of iron sulphides are exposed to the atmosphere and oxidize in the presence of oxygen and water to form soluble hydrous iron Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

sulphates. These compounds usually appear as yellow and white crusts along certain horizons on the exposed surfaces of the pyritic material in coal mines.

Some of the oxidation products have been identified as melanterite (white crystals of FeSO4), copiapite (yellow crystals of ferric sulpahte Fe2(SO4)3, halotrichite (white crystals of iron and/ or magnesium aluminium sulpahte), and alunogenite (white crystals of aluminum sulphate). These minerals are present in the hydrated form, the amount of water varying with the mode of formation. Following reactions represent the oxidation of FeS2 and production of acid (H+): 2FeS2(S) + 7O2 + 2H2 = 2Fe2+ + 4 SO24 + 4H+

(1)

Further oxidation of Fe+2 (ferrous iron) to Fe+3 (ferric iron) occurs when sufficient oxygen is dissolved in the water or when the water is exposed to sufficient atmospheric oxygen.

Fe2+ + ¼ O2 + O2 + H+ = Fe3+ + ½ H2O

(2)

Ferric iron can either precipitate as Fe(OH)3 , a red-orange precipitate seen in waters affected by acid rock drainage, or it can react directly with pyrite to produce more ferrous iron and acidity (as shown in equation 3 and 4).

Fe3+ + 3H2O = Fe(OH)3(S) + 3H+

(3)

FeS2(S) + 14Fe3++ 8H2O = 15Fe2+ + 2 SO 24 + 16H+

(4)

When ferrous iron is produced (equation 4) and sufficient dissolved oxygen is present the cycle of reactions 2 and 3 is perpetuated. Without dissolved oxygen equation 4 will continue to completion and water will show elevated levels of ferrous iron.

The rates of chemical reactions (equations 2, 3, and 4) can be significantly accelerated by bacteria, specifically Thiobacillus ferrooxidans. Another microbe, Ferroplasma Acidarmanus, has been identified in the production of acidity in mine waters.

Hydrolysis reactions of many common metals also form precipitates and in doing so generate H+.

These reactions commonly occur where mixing of acidic waters with substantial dissolved metals blend with cleaner waters resulting in precipitation of metal hydroxides on stream channel substrates (Equations 5 through 8).

Al+3 + 3H2O <–> Al(OH)3(s) + 3H+

(5)

Fe+3 + 3H2O <–> Fe(OH)3(s) + 3H+

(6)

Fe+2 + 0.25 O2 + 2.5 H2O <–> Fe(OH)3(s) + 2H+

(7)

Mn+2 + 0.25 O2 + 2.5 H2O <–> Mn(OH)3(s) + 2H+

(8)

Metal sulfide minerals in addition to pyrite may be associated with economic mineral deposits and some of these minerals may also produce acidity and SO4-2. Oxidation and hydrolysis of metal sulfide minerals pyrrhotite (Fe1-xS), chalcopyrite (CuFeS2), sphalerite ((Zn, Fe)S) and others release metals such as zinc, lead, nickel, and copper into solution n addition to acidity and SO4-2 .

Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

Secondary reactions also take place between iron sulphates, sulphuric acid and the compounds in nearby clays, limestones, sandstones and various organic substances that are present in mines or streams to produce the variety of chemicals found in mine drainage.

Moreover, water appears to be essential for this chemical reaction. The rate of pyrite oxidation increases with water vapour pressure until at 100% relative humidity, the rate becomes equal to that for immersed pyrite. It has been suggested that water may not necessarily be a reactant; it may act as a medium for the transfer of oxidation products from reaction sites in view of the fact that the rate of the oxidation reaction increases as the concentration nears saturation state.

MICROBIAL ASPECTS OF ACID MINE DRAINAGE (Role of Bacteria in AMD) The formation of acid mine water may be attributed to non-biological and biological oxidation of sulphur and iron sulphide in a mine in the presence of moisture and oxygen. Microbial oxidation plays a more important role than non-biological oxidation. The possible involvement of bacteria in the formation of AMD was first reported in 1919 by Powell and Parr, who found that coal inoculated with an unsterilised sulphate solution produced drainage with higher concentration of sulphate than did sterile controls. Colmer et al. demonstrated that bacteria play a role in iron oxidation in acid mine water, based on the observations on iron oxidation that occurred in water samples freed from bacteria by filtration through Scitz filter/millipore filter or treatment with bactericidal agents.

Conditions for microbial oxidation - The important requirements in the microbial oxidation of sulphide minerals are (i) an energy source and (ii) adequate supply of O2, CO2 and essential nutrients. In mines, appreciable percentages of CO2, O2, N2, etc. are present. These gases help in the growth of bacterial cells. Bacteria assimilate CO2 as the sole carbon source at the expense of energy available from the oxidation of Fe2+ and sulphide minerals. The energy derived from the oxidation of FeSO4 can support the growth of only a few species of bacteria.

FACTORS INFLUENCE THE QUALITY OF MINE DRAINAGE Primary, secondary, tertiary and downstream factors influence the quality and quantity of mine drainage. * Primary factors influencing the amount and quality of acidic water are the relative amount of water and oxygen in the environment. In order for pyrite to oxidize, both oxygen and water must be present. Water serves not only as a reactant, but also as a reaction medium and a producttransport solvent. * A secondary factor is the neutralization of acids by the alkalinity released from the carbonate minerals in the mine waste and surrounding stratum. * Tertiary factors include the physical characteristics of mining waste, the spatial relationship between wastes, and the hydrologic regime. * Downstream factors may impact the quality and quantity of acid drainage. Physical processes such as dilution and precipitation and chemical processes such as neutralization will permit a stream to assimilate acid drainage, but not without incurring a great deal of acid damage to the preceding stream area.

Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

IMPACTS FROM MINING OPERATION ON WATER QUALITY Typically, mining operation includes a number of phases that can have different impacts on water quality; these are listed below: * Exploration. Exploration for mineral and petroleum resources involves field surveys, drilling programmes and exploratory excavations. Some water contamination can be produced at this stage from land clearing; for example, if clearing exposes a layer with high content of heavy metals, leading to contamination of stormwater by the heavy metals and by waste disposal from exploration camps. Unfilled exploration boreholes can allow contaminants from the surface to be washed into groundwater without being attenuated in the soil profile. * Project development. The development of a mining site and supporting infrastructure causes extensive land clearance. Also, groundwater and surface water contamination can be caused by spills and leaks from fuel storage tanks, and from waste disposal. * Mine operation. The type of operations can include pumping from boreholes (oil and natural gas, solution mining), heap leaching of rock piles, underground mining, open cuts and surface dredging. Oxidation and leaching of minerals from mining spoil and other waste products can contaminate groundwater and surface water. * Beneficiation. Processing of minerals using a variety of mechanical and chemical treatment processes can be the most significant source of water contamination at a mine site. The major sources of contamination from mineral processing are leaks from storage ponds holding processing liquors, and leakage from tailings dams used to separate and recover processing liquids from fine solid wastes. * Mine closure. Closure and rehabilitation of a mine site to mitigate environmental impacts (e.g. stabilisation and revegetation of waste rock and tailings) can contaminate groundwater if not well managed. Sources of contamination include continued seepage from waste rock and tailings if these are not well stabilised; salinisation of groundwater by evaporation from abandoned open pits and the excessive use of fertilizers in rehabilitation programmes.

Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

* Effects of mining on water quality - The type of water contamination produced by a mining operation depends to a large extent on the nature of the mineralization and on the processing chemicals used to extract or concentrate minerals from the host rock. The water contaminants of most concern are summarized below: Type of mine Wastewater generated Characteristics of Chemicals possibly wastewater contained Open-cut and Acid mine drainage Low pH (< 4.5, Arsenic, antimony, underground mining of from waste rock heaps possibly as low as 2) barium, cadmium, base metal sulfide and ammonium nitrate- of water in springs, chromium, cobalt, deposits, precious fuel oil explosive used seeps, open cuts and fluoride, lead, mercury, metal deposits or for rock blasting streams draining from molybdenum, nickel, uranium deposits with the mine site. nitrate, selenium, sulfide minerals, Extensive vegetation sulfate, uranium (radon may be of sulfide rich heavy death, yellow or white concern where mineral sands, coal salt crusts on the soil there are high uranium deposits surface, pale blue cloudy appearance of concentrations) surface water Base metal and Flotation agents used Depends on the type of precious metal deposits to concentrate minerals mineralization â&#x20AC;&#x201D; from ore; the main contaminants from sources of flotation agents of contamination are health concern include seepage from chromium, processing mills and cresols, cyanide tailings dams compounds, phenols and xanthates Gold deposits Chemicals used to High pH of water (up Arsenic, free cyanide, extract gold from ore to pH 10) when weak acid (cyanide and mercury), cyanide is used dissociable cyanide, particularly from mercury tailings dams Uranium deposits Acid leaching Low pH of water, high Arsenic, antimony, (especially sulfuric sulfate concentrations barium, cadmium, acid) used to extract in water chromium, cobalt, uranium from ore fluoride, lead, mercury, molybdenum, nickel, radon, selenium, sulfate, uranium Petroleum and natural Disposal of brines High salinity of water, Boron, fluoride, gas associated with high concentrations of hydrocarbons, uranium petroleum hydrogen sulfide, hydrocarbons methane or detectable hydrocarbon odours in water AMD is probably the most severe environmental problem that occurs on mine sites. It happens where mineral and coal deposits contain sulfide minerals, particularly pyrite (FeS2). When waste rock containing sulfides is exposed to air, these minerals are oxidized, releasing sulfuric acid. The process is accelerated by bacteria such as Thiobacillus ferrooxidans that obtain energy from the oxidation reaction for their growth. The release of acid can cause the pH of surface water and Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

groundwater to become very low (as low as 2). Under these very acidic conditions, metal concentrations in water can become very high due to the dissolution of elements from waste rock.

Acidic water at mine sites often kills vegetation, and may cause fish deaths in rivers. Apart from low pH, visual indicators of AMD at mine sites include the following: * Large areas where vegetation has died due to acidic runoff and shallow acidic groundwater; * The presence of abundant yellow or white salt crusts on waste rock and at the surface of the soil. The crusts comprise alum-like sulfate minerals containing variable amounts of sodium, potassium, iron and aluminium, such as the mineral jarosite. They are often very soluble in water, releasing acid and precipitating ferric hydroxides; * Surface water bodies on the mine sites often appear to have a milky blue-white cloudy appearance due to the presence of flocs of aluminium hydroxide. If the water is extremely acidic (< pH 3), it may appear to be crystal clear due to the precipitation of the flocs.

Of the chemicals used to process ores, cyanide may be the most problematic due to its toxicity and the complexity of its chemical behaviour in groundwater. Cyanide degrades rapidly into nontoxic chemical compounds when exposed to air and sunlight, but in groundwater it may persist for long periods with little or no degradation. Cyanide (usually in the form of potassium or sodium cyanide) is used to extract gold from its ore, but in the subsurface it can react with minerals in soil and rock to form a wide range of metal cyanide complexes, many of which are very toxic.

Abandoned pits and mine shafts are commonly used for water supply after mine closure.

Depending on the type of mining activity, water from these sources could pose a risk to human health from high dissolved metal or cyanide concentrations.

EFFECTS OF MINE DRAINAGE AND METALS ON ENVIRONMENT AND AQUATIC RESOURCES Mine drainage is a complex of elements that interact to cause a variety of effects on aquatic life that are difficult to separate into individual components. Toxicity is dependent on discharge volume, pH, total acidity, and concentration of dissolved metals. pH is the most critical component, since the lower the pH, the more severe the potential effects of mine drainage on aquatic life. The overall effect of mine drainage is also dependent on the flow (dilution rate), pH, and alkalinity or buffering capacity of the receiving stream. The higher the concentration of bicarbonate and carbonate ions in the receiving stream, the higher the buffering capacity and the greater the protection of aquatic life from adverse effects of acid mine drainage. Alkaline mine drainage with low concentrations of metals may have little discernible effect on receiving streams. Acid mine drainage with elevated metals concentrations discharging into headwater streams or lightly buffered streams can have a devastating effect on the aquatic life. Secondary effects such as increased carbon dioxide tensions, oxygen reduction by the oxidation of metals, increased osmotic pressure from high concentrations of mineral salts, and synergistic effects of metal ions also contribute to toxicity. In addition to chemical effects of mine drainage, physical effects such as increased turbidity from soil erosion, accumulation of coal fines, and smothering of the stream substrate from precipitated metal compounds may also occur.

Benthic (bottom-dwelling) macroinvertebrates are often used as indicators of water quality because of their limited mobility, relatively long residence times, and varying degrees of sensitivity to pollutants. Unaffected streams generally have a variety of species with representatives of all insect orders. Like many other potential pollutants, mine drainage can cause a reduction in the diversity and total numbers, or abundance, of macroinvertebrates and changes Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

in community structure. Moderate pollution eliminates the more sensitive species. Severely degraded conditions are characterized by dominance of certain taxonomic representatives of pollution-tolerant organisms, such as earthworms (Tubificidae), midge larvae (Chironomidae), alderfly larvae (Sialis), fishfly larvae (Nigronia), cranefly larvae (Tipula), caddisfly larvae (Ptilostomis), and non-benthic insects like predaceous diving beetles (Dytiscidae) and water boatmen (Corixidae). While these tolerant organisms may also be present in unpolluted streams, they dominate in impacted stream sections. pH - Most organisms have a well defined range of pH tolerance. If the pH falls below the tolerance range, death will occur due to respiratory or osmo-regulatory failure. Low pH causes a disturbance of the balance of sodium and chloride ions in the blood of aquatic animals. At low pH, hydrogen ions may be taken into cells and sodium ions expelled. The primary causes of fish death in acid waters are loss of sodium ions from the blood and loss of oxygen in the tissues.

Metals - Heavy metals can increase the toxicity of mine drainage and also act as metabolic poisons. Iron, aluminum, and manganese are the most common heavy metals which can compound the adverse effects of mine drainage. Heavy metals are generally less toxic at circumneutral pH. Trace metals such as zinc, cadmium, and copper, which may also be present in mine drainage, are toxic at extremely low concentrations and may act synergistically to suppress algal growth and affect fish and benthos.

Sedimentation - Drainage water from acid mine drainage is initially clear but turns a vivid orange colour as it becomes neutralised because of the precipitation of iron oxides and hydroxides. This precipitate, often called ochre, is very fine and smothers the river bed with avery fine silt. Thus, small animals that used to feed on the bottom of the stream or ocean (benthic organisms) can no longer feed and so are depleted. Because these animals are at the bottom of the aquatic food chain, this has impacts higher up the food chain into fish.

Assessing the impact - When assessing the impact of industrial discharges on receiving waters, the most critical characteristics are: * The types of chemicals discharged â&#x20AC;&#x201D; this depends on the type of industries and processes used; * The amount and concentration of chemicals in the effluent â&#x20AC;&#x201D; these vary over time depending on the operation mode of both manufacturing and wastewater treatment processes employed (e.g. hourly, daily, weekly, monthly and seasonal variations).

Solid wastes and/or gaseous emission generated from industrial sources also contribute to the amount and concentration of chemicals in the effluent if they are treated with water or they have any contact with water.

MITIGATING THE PROBLEM OF ACID DRAINAGE a. Acid Mine Drainage Remediation at the Source - A number of factors influence the development of acid mine drainage directly at the source and along the pathway. Besides the neutralization potential based on the chemistry of the minerals, the long term availability and the amount of reactants during the process of weathering are crucial for the quantity of water getting access to the reactive phases and for the quality of the outflow. Reduction of the accessibility of the material and limiting the amount of water and oxygen infiltration will have the strongest influence on AMD generation. Besides technical remediation efforts, natural processes such as clogging of pores, formation of hardpans or cemented layers, and generation of capillary barriers on the basis of grain size contrasts, are most effective to withdraw cells of the heap from further weathering. b. AMD treatment - The formation and treatment of acid mine drainage is the biggest environmental problems relating to mining and processing activities in the worldwide. Various methods are used for the sulphates and heavy metals removal from acid mine drainage in the Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, 10 E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

world. There are two approaches to controlling Acid Mine Drainage. The first is to reduce or eliminate the source of the AMD. One method for source elimination seeks to prevent oxidation by replacing the air within the mine with groundwater. This air-with-water replacement is brought about by sealing any mine openings with an impermeable grouting material. One such material under investigation is flue gas desulferization (FGD) material, a by-product from coal-fired power plants. This material is composed of primarily calcium sulfate (gypsum). Another source elimination strategy is to fill the mine with a solid (e.g., FGD or a clay slurry) in order to eliminate the oxidation reaction.

The second primary method for mitigating Acid Mine Drainage involves treating the AMD itself in order to remove the negative impact to the watershed. Chemical, biological, or physical treatments may be used in AMD abatement. Chemical treatments primarily seek to neutralize the acid through the addition of an alkali (e.g., soda ash) with a subsequent sedimentation basin in order to retain metal precipitates after the pH adjustment. Biological treatments use constructed wetlands, as one example, for natural attenuation of biological nutrient additions in order to accelerate indigenous activity. Physical treatment seeks to alleviate the impact through re-routing of streams to circumvent possible problematic geological formations.

In environments where groundwater has been contaminated by waste water and acid mine drainage, microbial sulfate reduction can be exploited in subsurface permeable reactive barriers.

A permeable reactive barrier is a passive, in-situ technique: groundwater treatment proceeds within the aquifer and long-term maintenance of the installation is unnecessary. This method consists of installing an appropriate reactive material into the aquifer, so that contaminated water flows through the material (see figure below). The reactive material induces chemical reactions that remove the contaminants from the water or otherwise cause a change that decreases the toxicity of the contaminated water. For the treatment of water contaminated with acid mine drainage, a number of studies have shown the effectiveness of this method.

Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

Acid mine drainage is a global problem. Cleanup of abandoned mine sites is difficult because of their remote locations and because these problems will go on for hundreds of years until the mineralized rock is leached free of sulfides and metals. Typical cleanup strategies for addressing AMD include the following: * Flooding the acid-producing rock or tailings with water; * Constructing wetlands or treatment ponds containing large quantities of organic material, from which sulfide-reducing bacteria react with the metals and cause them to precipitate; * Using plants to take up the metals from the soil or sediment; and * Using concrete or cement to solidify the acid-producing material into an inert block.

To be effective in eliminating or significantly reducing AMD, it is necessary to remove one of the three factors that produce it: WATER, OXYGEN, OR BACTERIA. c. Underground Mine Sealing - The AMD problems associated with older underground mines can be aggravated by inadequate barrier pillars between mines, inadequate outcrop barriers, and hydraulic interconnection of adjacent mine complexes. While AMD problems associated with some of these older mines can be addressed by re-mining the abandoned mine complex, this option is not economical for most abandoned mine complexes.

Mine sealing can minimize the AMD pollution associated with abandoned underground mines.

The primary factor affecting the selection, design and construction of underground mine seals is the anticipated hydraulic pressure that the seal will have to withstand when sealing is completed.

A dry mine seal is a wall across a mine entrance where water does not drain from the entrance. A wet mine seal is a wall across a draining mine entrance that allows water flow through the seal but prevents air from entering the mine. Production of AMD can be inhibited to the extent that the seal raises the water level in the mine and inundates the workings. The placement and construction of mine seals must be carefully planned and executed.

Surface access seals (or dry seals) are installed in entries where little or no hydrostatic pressure will be exerted on the seals. The primary functions of these seals are to eliminate access to the mine and to decrease AMD production by limiting movement of air and water into the deep mine.

Dry seals are typically constructed of concrete block, masonry, or concrete-flyash mixtures, and are often backfilled from the front side of the seal.

Due to the leaking or collapse of many wet seals, hydraulic mine seals are being constructed in most current wet sealing situations. This type of mine seal serves as a structural bulkhead and acts as a water tight dam capable of withstanding the maximum hydrostatic head that may develop as a result of flooding the mine complex.

Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

PREDICTION, QUANTIFY AND MANAGEMENT OF MINE DRAINAGE CHEMISTRY Accurate prediction of acidic drainage from proposed mines is recognized by both industry and government as a critical requirement of mine permitting and long-term operation. Substantial emphasis has been placed on prediction of acid drainage associated with coal development in the Eastern U.S. (Pennsylvania DEP 1998; Skousen and Ziemkiewicz, 1996), and metal mining in the Western U.S. and in Canada (MEND 2001). The standard protocols for evaluating geologic materials for their ability to produce AMD are generally agreed upon within the scientific community, yet much uncertainty remains in the ability of scientists and engineers to predict the ultimate drainage quality years in the future, as many complex variables influence acid generation and neutralization.

The backbone of predicting acid generating potential from any geologic formation is the ability to characterize the presence and quantity of both acid-forming minerals and neutralizing minerals in the geologic materials to be unearthed during mining operations. Typically samples are collected by drilling during exploration, analyzed and interpreted with respect to their risk of acid formation.

Managing mine drainage water quality is a critical concern for all mining operations because discharges must typically meet stringent water quality standards set by local, regional and national governments. Acidic drainage remains the most significant issue due to high concentrations of metals, and costs of treatment to achieve acceptable levels. However, in the past decade or so, awareness of leaching under non-acidic conditions has greatly increased.

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

Accurate prediction of leaching effects, and design of practical and proven control measures, is often critical to the feasibility of the projects. These issues are encountered during permitting of new mines, optimisation of existing operations, development of closure plans and remediation of abandoned mines.

Remediation of acid drainage is difficult and expensive. Many companies use hydrated lime, sodium hydroxide, sodium carbonate, or ammonia to treat acid mine water, with each chemical offering the advantage of neutralizing acidity. Bactericides including antibiotics, heavy metals, detergents, and food preservatives have also been found to reduce acid mine drainage, however, antibiotics and heavy metals are too costly and also too dangerous to the surrounding aquatic life to be effectively used. Alconox, an inexpensive commercial detergent, and sodium lauryl sulfate both are found to reduce acid production in mine drainage.

Crushed limestone is a common material used to neutralize acid drainage. The limestone reacts with acidic water in the following manner: The natural bicarbonate in limestone neutralizes the hydrogen ions, but the metals in solution may not be simultaneously removed by the process. The resulting, neutralized water is typically still high in iron and sulfate content.

Because chemical treatment is so expensive, biological alternatives are currently being researched and implemented. The use of built wetlands, a method developed by the USBM, precipitates metals and neutralizes acidity through biological activity.

The first wetlands were planted with a plant called Sphagnum in an attempt to simulate natural bog-type wetlands. The large surface areas of aquatic plants and algae serve as substrate to support bacteria. The filtering and settling mechanisms effectively remove suspended solids that do not normally settle. The decaying biomass of plants and algae provide anaerobic conditions and nutrients to the sulfate reducing bacteria. The large surface area of leaves enhance evapotranspiration and help dispose of excess water.

Open limestone channels are an important innovation in acid mine drainage treatment. The channels are created by filling drains or lining stream beds with high quality limestone.

Results from field sites show that acid and metals in acid drainage were reduced by 25 to 40% even when the limestone became coated by iron and aluminum.

Some Methods to Prevent Acid Mine Drainage - In preventing acid drainage, water and air contact with the acidic material must be eliminated. Prevention effectiveness depends on the nature of the mine and the strata's geological characteristics.

Preventing water from reaching underground mines involves the use of diversion ditches and pipes to divert water from acidic areas. Another method to prevent acid drainage is to prevent the material from oxidizing. By burying mine waste, or covering the waste with an impermeable liner, pyrite cannot oxidize and sulfuric acid cannot form. Some mines use a method in which an asphalt emulsion of polyurethane sealant encapsulates the mine waste.

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

a. Qualitative procedure i.e., ‘Acid Base Accounting’ (ABA), of quantification - The cornerstone of any approach to understand and quantify release of acid drainage is controlled by geological conditions. AMD potential is also affected by local climatic conditions. Although, prediction and quantification of acid mine drainage (AMD) from a given rock unit is in its infancy; ‘Acid Base Accounting’ (ABA) is the current procedure. It is a useful screening procedure and is designed to indicate whether a rock unit will or will not produce acid. In this sense, Acid Base Accounting is qualitative. Researchers at West Virginia University have developed a prediction method to estimate how much acid will be produced over the life of a rock unit's AMD production. The AMD prediction procedure can also evaluate the required rates and effectiveness of various AMD control amendments.

ABA is mechanism for assessing post-mining water quality. Its utility is amplified when used in conjunction with other pre-mining information including baseline water quality, examination of adjacent and previous mining, and evaluation of geologic and hydrologic conditions. Acid-Base Accounting was developed at West Virgmia University by Richard M. Smith and coworkers (Skousen et al., 1990). The approach grew from early attempts at classifying mine spoils for revegetation potential, based principally on acidity or alkalinity, and rock type. From these broad classifications, the need for lime and suitability for plant species could be assessed.

ABA consists of measuring the acid generating and acid neutralizing potentials of a rock sample.

These measurements of Maximum Potential Acidity (MPA) and Neutralization Potential (NP) are subtracted to obtain a Net Neutralization Potential (NNP), or net Acid-Base balance for the rock: Net Neutralization Potential (NNP) = NP - MPA The results are customarily reported in tons per thousand tons of overburden or parts per thousand. The measurements and calculations of NP, MPA, and NNP are based on the following assumed stoichometry (Cravotta et al., 1990): FeS2 + 2CaCO3 + 3.75O2 + 1.5H2O → 2SO42- + Fe(OH)3 + 2 Ca2+ + 2CO2 For each mole of pyrite that is oxidized, two moles of calcite are required for acid neutralization.

On a mass ratio basis, for each gram of sulfur present, 3.125 grams of calcite are required for acid neutralization. When expressed in parts per thousand of overburden, for each 10 ppt of sulfur (equal to 1 percent sulfiur content) present, 3 1.25 ppt of calcite is required for acid neutralization.

Computation methods for NNP imply that acid generation from MPA and acid neutralization from NP take place concurrently and at equal rates. In fact, acid generation can proceed more rapidly and is catalyzed by Thiobacillusferrooxidans bacteria. Carbonate mineral dissolution is a hction of pH and partial pressure of carbon dioxide and does not occur as rapidly.

Acid-Base Accounting has been applied to the prediction of overburden and water quality properties on mined land for about more than a couple decades. An extensive institutional knowledge base and "rules of thumb" have developed on the interpretation of ABA data, and have been supplemented with a few formal studies. Carbonate or NP content exerts major control over the post-mining water quality. b. Procedural application - Following is a description of how the procedure would be applied to a new mining operation, one which is still in the planning stage. The procedure consists of three components: Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

* IDENTIFY AMD PRODUCING ROCKS in the overburden and refuse. This is done by examining cores, taking samples of representative lithic units and subjecting them to accelerated weathering cycles in the laboratory. This step identifies which rocks units require special attention. * APPLY THE SSPE/PSM MODEL to the resulting data indicating the duration of AMD production expected from each type material. * IDENTIFY REQUIRED AMOUNTS OF PHOSPHATE. AMD producing rock units identified in steps 1st and 2nd above, are then treated with rock phosphate or other amendments in the laboratory and subjected to accelerated weathering. This task identifies the cost of controlling AMD in each of the problematic rock units.

THE SSPE/PSM MODEL FOR PREDICTING AMD A mathematical model (SSPE/PSM) has been developed that relates AMD production and elimination rates and provides valuable insight into the long range behavior of refuse sites. The model predicts such field information as AMD producing longevity and water quality predictions. Two input variables are needed for the model: alpha, the oxidation rate constant for rock's pyrite and beta, the rate at which acid forming salts leach from the rock.

Probability simulation, where a generation-discharge scenario could be simulated and brought under the governing principle of the Bateman equation was devised. This technique employed probability distributions of field data and utilized queue theory to simulate the sulfate ion generation-elimination phenomenon. This technique became known as PSM (Probability Simulation Modeling) . The end result was a technique known as SSPE/PSM modeling.

Through this process the cost of controlling AMD production can be estimated with reasonable reliability. Three outcomes are possible: A. Acid producing rock is widely disseminated through the overburden.

B. Acid producing rock is concentrated in the refuse.

C. No significant AMD is produced from any of the rock units.

If outcome A pertains then it is unlikely that it will be possible to handle the overburden so as to prevent AMD production. if outcome B is indicated then refuse can be treated with rock phosphate or another amendment as it leaves the prep plant on the conveyor belt. Outcome C needs no explanation. c. Assessment of Acid Rock Drainage and Metals Release - Canadaâ&#x20AC;&#x2122;s Mine Environment Neutral Drainage (MEND) Program was implemented to develop and apply new technologies to prevent and control acid drainage. In 2005, MEND released a report titled List of Potential Information Requirements in Metal Leaching/Acid Rock Drainage Assessment (ML/ARD) and Mitigation Work (Price 2005). The purpose of this document is to improve the assessment and mitigation of metal leaching/acid rock drainage. The information required for the purpose are summarized in the following statements: (i) General site characteristics: location, access, climate, ecology, history of previous mining, waste materials, geology, hydrology, mineralogy, descriptions of all materials that will be excavated or exposed, soils, reclamation objectives, end land uses, data tables, relevant figures, and other pertinent information.

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

(ii) Specific material characterization and predictions of ML/ARD: The ability to accurately predict the potential for ML/ARD requires a careful and complete characterization of all materials and waste types under the probable weathering (oxygen, bacteria, moisture, volumes of materials, etc.) conditions. Representativeness and adequacy of samples collected, measures of variability and uncertainty, and analytical procedures selected need to be appropriate. Industry-regulatory quality assurance and quality control procedures need to be followed. To be complete, predictions and assessments are to be made pre-mining (baseline data), during the operational phase, postmining, and long-term. The document defines specific tests to define the geological and mineralogical properties of materials. (iii) Static and kinetic tests: Static tests require appropriate sampling intensity, sample preparation, determinations of elemental concentrations (total and water soluble), and full acidbase accounting. Kinetic tests are recommended to evaluate reaction rates and to predict and measure drainage chemistry. Humidity cell, column test and actual field verification tests should be conducted. Monitoring of site drainage (seeps, mine drainage, pit lakes, etc.) should include parameters to be evaluated and the frequency of monitoring during and post-mining. (iv) Assessments of waste materials: Waste materials may include waste rock, tailings, treatment wastes, low grade ore and overburden materials. All media require assessments and predictions for acid drainage and releases of metals. Post-disposal weathering of waste piles, including changes in pH, carbonate content, soluble weathering products (acid water and metals). Thermal properties, pore gas composition, and oxygen concentrations may be significant parameters in the assessments of long-term water quality degradation. d. Water Quality and AMD: Pre-mine Predictions and Post-mine Comparisons - A major and unique study (Kuipers et al. 2006) was conducted comparing predicted and actual water quality at several mines in the United States. The overall purpose of this study was to examine the reliability of pre-mining water quality predictions at hard rock mining operations. The approach included reviews of the history and accuracy of water quality predictions in Environmental Impact Statements (EISs) for major hard rock mines and then examined and compared actual water quality to the predictions postulated in the EISs. In the report comparing predicted and actual water quality at hard rock mines (Kuipers et al.

2006), the authors identified two types of characterization failures that led to differences between predicted water quality as speculated in EIS documents and the actual water quality either during or after mining began. The two characterization failure types were: 1) insufficient or inaccurate characterization of the hydrology, and 2) insufficient or inaccurate geochemical characterization of the proposed mine. Inaccurate pre-mining characterization and interpretation can, therefore, result in a failure to recognize or predict water quality impacts. The authors reported primary causes of hydrologic characterization failures as follows: overestimations of dilution, lack of hydrological characterization, overestimations of discharge volumes, and underestimations of storm size. The primary causes of geochemical characterization failures were identified as: lack of adequate geochemical characterization, in terms of sample representativeness and sample adequacy.

TREATMENT OF ACID MINE DRAINAGE Water treatment for elevated metal levels and acidity is a common outcome of acid mine drainage. The effectiveness and feasibility of water treatment is highly variable depending on the treatments employed and unique site characteristics. Water treatment installations may include both passive and active systems. Passive water treatment systems, typically wetlands, operate without chemical amendments and without motorized or mechanized assistance. In contrast active Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, 17 E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

water treatment systems are highly engineered water treatment facilities commonly employing chemical amendment of acid mine water to achieve a water quality standard specified in a discharge permit. It requires a constant maintenance of the system, supplying, e.g., lime for neutralisation and transport of wastes away from the site.

The standard treatment is to pump the water and add lime to precipitate the iron before it enters rivers and streams. The residual solids are voluminous and present a disposal problem. This solution is not sustainable in economic or environmental terms. Each discharge tends to be highly variable and requires tailored treatment. In virtually all cases however the discharge will have highly polluting effects on rivers and streams. It is difficult to predict where discharges will occur once a mine is abandoned and pumping stops.

RECOMMENDATIONS FOR ACIDIC DRAINAGE MINIMIZATION Acidic drainage from mines is observed at many mine sites and the undesirable consequences of acidification are well known. Every effort should be employed to minimize the causes of acid generation. Because mineralogy and other factors (particle size, reactivity of NP and presence of oxidizers) that influence AMD formation are highly variable from one mine to another, and among different geologic materials within a proposed mine site, accurate prediction of future acid generation is difficult at best. There are two primary approaches to addressing AMD: circumvent mining sulfide rich ore deposits with high AMD potential, and implementing mitigation measures to limit potential AMD impacts. It is noted that avoiding mining of sulfide ores with the potential to form AMD may be difficult because they are most often associated with the mineral resource of interest.

ACID MINE DRAINAGE MANAGEMENT SYSTEM As discussed above, the term AMD as used refers to the potential environmental impacts that could result from the oxidation of sulphide minerals such as pyrite. The emphasis is on timely and thorough analysis of the risks, early identification and implementation of control (management) strategies and thorough integration of controls with mine planning and operational activities.

Guidelines of AMD management system are discussed below: a. Planning * Identify and document the geological setting and the mineralogy of sulphide containing rocks, adjacent lithologies and unconsolidated sediments that will be disturbed or exposed in order to support AMD potential and prediction studies. * Assess the AMD potential of any new development as part of exploration, order of magnitude, pre-feasibility and feasibility studies, due-diligence reviews for acquisitions, and also for changes in process and/or mineralogy. Ensure that realistic AMD management costs are estimated and included in project financial evaluations. * Undertake appropriate environmental baseline studies for AMD before the commencement of a development project or any significant expansions of existing operations. * Due diligence studies as part of potential project acquisitions must include an assessment of the projectâ&#x20AC;&#x2122;s current and potential AMD issues and liabilities. * Maintain an AMD prediction program for forecasting the short-term and long-term behaviour under local weathering conditions of sulphide-bearing materials such as: i) The rocks and unconsolidated sediments exposed in open pits and underground mines; ii) Ore, waste rock, block cave rubble, acid sulphate soils and other materials that have been disturbed; and iii) Tailings, spent heap leach ore and other process wastes that have been generated.

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

* Ensure the AMD prediction program reduces uncertainty about potential risk and liability to a level which permits a decision to be made to either reject the project or initiative, or to put in place effective mining and waste management strategies. * Ensure that recognised AMD experts are consulted for the initial assessment to determine whether there is an AMD issue at the site, design of the prediction program, the interpretation of its results, and the development of the management plan. * Develop an AMD management plan, commensurate with the AMD potential of mineral wastes and products and in line with the AMD prediction program, addressing as a minimum: i) a summary assessment of the AMD setting, hazards and potential impacts; ii) the discharge limits and receiving environment objectives; iii) the AMD management strategy designed to meet the environmental objectives in a reliable and cost effective manner during operation and after closure; iv) the procedures and responsibilities for implementing the management strategy on an ongoing basis under actual field conditions; v) ongoing AMD characterisation, monitoring and data collection requirements; and vi) contingency measures for response to unplanned conditions or unexpected impacts. b. Implementation and operation * Implement the AMD management plan and make sure that it is integrated with mine and processing design, waste scheduling, closure planning, relevant operational procedures, and the business plan. * Maintain an inventory comprising quantities, location and representative characteristics of materials extracted from a mine or exposed to oxidation with respect to their abilities to generate or mitigate AMD. * Assign accountabilities at each affected operation for undertaking the AMD prediction program and for developing and implementing the AMD management plan. * Ensure that induction, general awareness and job specific training contains additional elements relating to AMD risks and how they are managed, where AMD is a significant issue for the operation. In such operations, the management team must have an appropriate knowledge of AMD prediction and control. c. Performance management * Maintain a monitoring procedure appropriate to the potential AMD impacts, which, as a minimum, allows adequate early warning of unacceptable impacts, facilitates management decisions, supports the ongoing prediction program and confirms assumptions used in the management plan. * Arrange for independent review of the AMD management plan at regular intervals (at least every four years, or more frequently when operational or environmental conditions so dictate).

The review must be carried out by an AMD expert and produce an independent document attesting the status of the prediction program and control strategies in place and indicating any potential threats to the operation.

MAJOR ENVIRONMENTAL INCIDENTS CAUSED BY ACID MINE DRAINAGE Releases of acid mine waters containing elevated metal and cyanide concentrations with resulting impacts to landscapes and waterways have been documented by several organizations (UNEP 2002). Fish kills resulting from the uncontrolled release of acid and metals from mine wastes into receiving streams have been reported from world wide areas in which hard rock mining, milling, and smelting activities have occurred.

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

* In 1998, a mine flood incident in Spain deposited some 6 million m3 of acid water over the banks of the Guadiamar River with metal and sulfide rich sediments. * The U.S. EPA described 66 incidents in which environmental injuries from mining activities are detailed (EPA 1995). Nordstrom and Alpers (1999) reported that millions, perhaps billions, of fish have been killed from mining activities in the U.S. during the past century. * In 1989, a large fish kill (> 5000 salmonids) in Montanaâ&#x20AC;&#x2122;s Clark Fork River resulted when acid, metalliferous tailings and efflorescent metal salts were flushed into the river during a thunderstorm event. Within 20 minutes, the acidity of the river water was reduced by several orders of magnitude, and copper concentrations rose dramatically. Fish gill tissue copper levels indicated acute toxicity (Munshower et al. 1997). * The Sacramento River in California has experienced several fish kills due to sudden releases of acid water from upstream mine areas; more than 20 fish kills were reported since 1963, and in 1967, at least 47,000 fish died (Nordstrom et al. 1977). * In the UK there has also been some experience with acid mine drainage. One of the major incidents was the Wheal Jane AMD pollution incident. In this case the mine produced metals (rather than coal) and the drainage contained high levels of zinc and cadmium as well as the ubiquitous iron. It was the presence of the iron that made the headlines as this metal turns a bright orange and the plume of orange pollution was highly visible to onlookers. The metals impacted on the local Fal Estuary which has received similar waters from the local mining industry over much of the last two centuries. It was likely the result of the visual impact, rather than the threat of zinc and cadmium contamination, which stimulated the public outcry and encouraged swift Government intervention.

CONCLUSION Of the huge amount of money spent on acid mine drainage each year, the major portion is spent on treatment. But treatment is not the best solution to most acid mine drainage problems.

Treatment has the disadvantage of being necessary for as long as the acid discharge continues and thus requires manpower, surface facilities, and sludge disposal areas indefinitely.

Since acid drainage results from the oxidation of pyrite associated with coal and overburden strata, limiting the rate of pyrite oxidation would reduce the amount of acid formed. T. ferrooxidans normally catalyzes the pyrite oxidation and accelerated the initial acidification of freshly exposed coal and overburden. Inhibiting bacterial activity through the application of bactericides, therefore, would limit the rate of acid production and, in combination with proper reclamation, would reduce substantially the total amount of acid produced.

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

McGuire, M. M., K.J. Edwards, J.F. Banfield, and R.J. Hamers (2001). "Kinetics, surface chemistry, and structural evolution of microbially mediated sulfide dissolution." Geochimica et Cosmochimica Acta 65(8): 1243-1258.

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Munshower, F. F., D.R. Neuman, S.R. Jennings and G.R. Phillips (1997). “Effects of Land Reclamation Techniques on Runoff Water Quality from the Clark Fork River Floodplain, Montana.” Washington, DC, EPA Office of Research and Development: 199-208.

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Nordstrom, D. K., and C. N. Alpers (1999). "Negative pH, efflorescent mineralogy, and consequences for environmental restoration at the Iron Mountain Superfund site, California." Proc. Natl. Acad. Sci. USA 96(7): 3455-3462.

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96 (7): 3455-3462.

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Perry, E. F., M.D. Gardner, and R.S. Evans (1997). “Effect of acid material handling and disposal on coal mine drainage quality.” Fourth International Conference on Acid Rock Drainage, Vancouver, B.C. Price, W. A. (2005). MEND. “List of potential information requirements in metal assessment and mitigation work.” CANMET Mining and Mineral Sciences Laboratories, Natural Resources Canada.

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Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

Schmidt, T. S., D. J. Soucek, and D. S. Cherry (2002). "Modification of an ecotoxicological rating to bioassess small acid mine drainage-impacted watersheds exclusive of benthic macroinvertebrate analysis."

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Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

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Partha Das Sharma, Acid Mine Drainage (AMD) and its control, (http://knol.google.com/k/partha-dassharma/acid-mine-drainage-amd-and-its-control/oml631csgjs7/44 )

-------------------------------------------------------------------------------------------------------Author’s Bio-data: Partha Das Sharma is Graduate (B.Tech – Hons.) in Mining Engineering from IIT, Kharagpur, India (1979) and was associated with number of mining and explosives organizations, namely MOIL, BALCO, Century Cement, Anil Chemicals, VBC Industries, Mah. Explosives etc., before joining the present organization, Solar Group of Explosives Industries at Nagpur (India), few years ago.

Author has presented number of technical papers in many of the seminars and journals on varied topics like Overburden side casting by blasting, Blast induced Ground Vibration and its control, Tunnel blasting, Drilling & blasting in metalliferous underground mines, Controlled blasting techniques, Development of Non-primary explosive detonators (NPED), Hot hole blasting, Signature hole blast analysis with Electronic detonator etc.

Author’s Published Books: 1. "Acid mine drainage (AMD) and It's control", Lambert Academic Publishing, Germany, (ISBN 978-3-8383-5522-1).

2. “Mining and Blasting Techniques”, LAP Lambert Academic Publishing, Germany, (ISBN 978-3-8383-7439-0).

3. “Mining Operations”, LAP Lambert Academic Publishing, Germany, (ISBN: 978-3-8383-8172-5).

4. “Keeping World Environment Safer and Greener”, LAP Lambert Academic Publishing, Germany. ISBN: 978-3-8383-8149-7.

Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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ACID DRAINAGE FROM MINES AND ITS RELATED PROBLEMS - Prediction, quantification and implementation of mitigation measures are the key for enhancement of environmental standard

5. “Man And Environment”, LAP Lambert Academic Publishing, Germany. ISBN: 978-38383-8338-5.

6. “ENVIRONMENT AND POLLUTION”, LAP Lambert Academic Publishing, Germany.

ISBN: 978-3-8383-8651-5 Currently, author has following useful blogs on Web: • http://miningandblasting.wordpress.com/ • http://saferenvironment.wordpress.com • http://www.environmentengineering.blogspot.com • www.coalandfuel.blogspot.com Author can be contacted at E-mail: sharmapd1@gmail.com, sharmapd1@rediffmail.com, ------------------------------------------------------------------------------------------------------------------Disclaimer: Views expressed in the article are solely of the author’s own and do not necessarily belong to any of the Company.

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Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering, E.mail: sharmapd1@gmail.com, Blog: http://miningandblasting.wordpress.com/

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