Origin of acid mine drainage in Enugu

Mine flooding is a serious problem in the Enugu Coal Mines and has led to the abandonment of two of the four mines. About 1800 m³ of water is pumped out daily from the mines into the nearby streams. The source of this enormous volume of water has been established based on the hydrodynamics and hydrology of the area. It is shown that although two prolific aquifers—an unconfined and a confined system—overlie the mines, the mine water is derived principally from the unconfined aquifer. The pathway of flow is, however, provided by the numerous fractures connecting the two aquifers and the mine tunnel.The major hydrochemical activity resulting in pollution of the mine water occurs within the sumps in the floor of the longwalls. These sumps act as oxidation chambers where groundwater from the fractures is mixed and subsequently reacted with sulfur-rich solutes released by coal mining.Contrary to general belief, the mine drainage has not seriously degraded the chemistry of receiving streams. The pH, electric conductivity and, thus, the dissolved ions were increased less than 10% of the values in the unaffected region.     

Investigation of pyrite oxidation and acid mine drainage characterization associated with Razi active coal mine and coal washing waste dumps in the Azad shahr–Ramian region,northeast Iran

Acid mine drainage (AMD) pollution is considered to be the most serious water pollution problem in mining areas. AMD containing iron sulfates and other components can affect the receiving water bodies. Pyrite oxidation and AMD generation can be considered as important processes that may take place in the wastes produced by coal mining and coal washing operations in the Golestan province (northeast Iran). The study area is characterized by appropriate atmospheric conditions that favor pyrite oxidation and the presence of a large amount of water bodies. This study attempts to consider pyrite oxidation and AMD generation in the Azad shahr–Ramian region. The impact of AMD on the quality of the surface water bodies was investigated by taking samples and analyzing them for hydro-geochemical parameters. Stiff and Piper diagrams were used to represent chemical analyses of water samples. The coal samples taken from different depths at four points on two different coal waste dumps were analyzed to find the fraction of pyrite that remained in the waste particles to investigate the pyrite oxidation process. A computational fluid dynamic package called PHOENICS was used to model pyrite oxidation process numerically. The results obtained from the geochemical analyses of water and coal samples and numerical simulation show pyrite oxidation and acid generation in the region. However, the presence of carbonate rocks raised the pH of the water samples. The drainages of the Razi mine may be recognized as natural alkaline mine drainages.     

Geochemical response of acid groundwater to neutralization by alkaline recharge

Solute transport and chemical neutralization (pH 3 to 7) within a shallow heterogeneous aquifer producing acid mine drainage (AMD) are examined at an abandoned surface coal mine in West Virginia. The aquifer is undergoing partial neutralization by mixing with alkalinity from a leaking sludge disposal pond, extending in preferential zones controlled by aquifer heterogeneity. Hydraulic heads interpolated from wells indicate leakage from a central alkaline (pH 7.1, 0.72 meq/L alkalinity) sludge pond is a principal source of recharge. Chemically-conservative sodium, added to AMD during treatment and leaked into the aquifer with the sludge, develops a dispersion plume over a restricted portion of the aquifer that correlates with pH, hydraulic head, and dissolved metals distributions. Concentrations of aluminum, iron, sulfate and acidity display higher concentrations downgradient from the pond as sludge alkalinity is consumed along flow paths. Before reaching springs, most dissolved iron is oxidized and hydrolyzed, likely precipitating in the aquifer as a ferric hydroxide or hydroxysulfate phase. The spatial pattern of iron and aluminum concentrations suggests accelerated oxidation caused by gas transport along the outer slopes of the spoil. Dissolved aluminum concentrations increase with total acidity, suggesting that dissolution of silicate minerals results from acidity released by iron hydrolysis. Neutralization reactions and higher pH are favored in more highly permeable portions of the spoil, where ferrihydrite and aluminum hydroxysulfate minerals (such as basaluminite) are supersaturated. In acid-producing zones at pH < 4.5, jurbanite is near equilibrium and an aluminum-sulfate phase with similar properties may limit aluminum concentrations, but become undersaturated in zones of advancing neutralization. At this particular site, ferrous iron produced by pyrite oxidation is almost completely oxidized over short transport distances, allowing hydrolysis of iron and aluminum should sufficient alkalinity be added to these acid waters.     

Geochemical response of acid groundwater to neutralization by alkaline recharge

Solute transport and chemical neutralization (pH 3 to 7) within a shallow heterogeneous aquifer producing acid mine drainage (AMD) are examined at an abandoned surface coal mine in West Virginia. The aquifer is undergoing partial neutralization by mixing with alkalinity from a leaking sludge disposal pond, extending in preferential zones controlled by aquifer heterogeneity. Hydraulic heads interpolated from wells indicate leakage from a central alkaline (pH 7.1, 0.72 meq/L alkalinity) sludge pond is a principal source of recharge. Chemically-conservative sodium, added to AMD during treatment and leaked into the aquifer with the sludge, develops a dispersion plume over a restricted portion of the aquifer that correlates with pH, hydraulic head, and dissolved metals distributions. Concentrations of aluminum, iron, sulfate and acidity display higher concentrations downgradient from the pond as sludge alkalinity is consumed along flow paths. Before reaching springs, most dissolved iron is oxidized and hydrolyzed, likely precipitating in the aquifer as a ferric hydroxide or hydroxysulfate phase. The spatial pattern of iron and aluminum concentrations suggests accelerated oxidation caused by gas transport along the outer slopes of the spoil. Dissolved aluminum concentrations increase with total acidity, suggesting that dissolution of silicate minerals results from acidity released by iron hydrolysis. Neutralization reactions and higher pH are favored in more highly permeable portions of the spoil, where ferrihydrite and aluminum hydroxysulfate minerals (such as basaluminite) are supersaturated. In acid-producing zones at pH < 4.5, jurbanite is near equilibrium and an aluminum-sulfate phase with similar properties may limit aluminum concentrations, but become undersaturated in zones of advancing neutralization. At this particular site, ferrous iron produced by pyrite oxidation is almost completely oxidized over short transport distances, allowing hydrolysis of iron and aluminum should sufficient alkalinity be added to these acid waters.     

Coal mining‐derived ochres in the UK: a potential selenium trap

Thanks to the pioneering research of Paul Younger over the past 20 years, acid mine drainage in the UK has been recognized as a major environmental issue. Acid mine drainage and hydrous ferric oxide deposition are environmental hazards resulting from centuries of extensive coal mining activities across the UK. Oxidative weathering of pyrite in coal from spoil heaps and exposed bedrock can liberate trace elements, releasing them into local water systems. In addition to posing an environmental threat through water and ground contamination, ochres can also act as a remediation material, trapping elements such as selenium. Trace elements with a close association to iron oxides, such as selenium, may fix to the fine‐grained ochre materials, resulting in hyper‐enriched ochres. Selenium in coals has been known to cause an environmental issue in areas of North America but is also an important commodity for solar cells and nanotechnologies. Coal‐bearing areas of the UK, such as Northumberland, are known to contain a high selenium content, and coal‐derived ochres in these regions also contain significant selenium. The widespread occurrence of ochres in UK coal‐mining regions may therefore present a unique ‘E tech’ trace element source and prevent a toxicity problem for which they were once thought to be responsible.     

Origin of high manganese concentrations in coal mine drainage, eastern Tennessee

The origin of high dissolved manganese concentrations in slightly acidic mine runoff from a surface mine operated by the Cumberland Coal Company in eastern Tennessee was investigated. Mineralogical and chemical analyses were performed on 31 samples of sandstone, shale, coal, and mudstone from the mine to identify the sources and stratigraphic distribution of high extractable manganese contents in the spoil materials. The samples were analyzed for their bulk mineral content by X-ray diffraction, net acid-base potential, and reaction to 2 or 4 chemical extraction procedures. A limited number of samples were analyzed for petrographic characteristics, clay mineral composition by X-ray diffraction, and mineral compositions by electron microprobe. Analysis of the data and consideration of the geochemical conditions at the mine were used to identify probable sources for the high extractable manganese contents.The results indicate 2 prominent, independent sources of extractable manganese. The first source is exchangeable manganese on clay minerals (mainly illite + muscovite and chlorite) and is concentrated in shale and mudstone rock types. The second and more significant source is manganese in siderite concretions and cement, mainly in shale and mudstone. Comparison to other coal-bearing strata indicates that manganese-rich siderite is common in fresh- to brackish-water subaqueous sediments that overlie coal. This is especially the case for coals formed in wet, tropical environments.Ratios of manganese to calcium and magnesium in mine runoff suggest that manganese from siderite is the major cause of the high dissolved manganese contents. A conceptual model is developed to explain the high manganese contents of the mine runoff. Oxidation of pyrite creates mildly acidic waters that are subsequently partially neutralized by reaction with impure siderite. Solubilized manganese remains dissolved in the slightly acidic runoff water, whereas dissolved iron precipitates as ferric hydroxide or goethite. Consideration of data from other coal mining regions suggests that similar reactions involving impure siderite may be responsible for high manganese concentrations in acidic to slightly acidic mine runoff. Geochemical reaction path modeling of pyrite and impure siderite with rainwater illustrate how resulting water compositions may vary depending on pyrite to siderite ratios in spoil materials. Spoil water compositions from the Cumberland mine are largely consistent with reaction of pyrite and impure siderite in proportions observed in the sediments; however, deviations may be explained by minor mixing with waters that reacted only with impure siderite or clay mineral exchange reactions.     

硅藻土、石英砂和钾离子促进微生物转化酸性矿山废水中亚铁成次生矿物的研究

嗜酸性氧化亚铁硫杆菌(Acidithiobacillus ferrooxidans)能够在低pH值条件下,迅速将Fe2+氧化并产生大量次生羟基硫酸铁沉淀,从而除去水中可溶性Fe2+。这为富含Fe2+的酸性矿山废水(acid mine drainage,AMD)处理提供了新的思路。本文从晶种刺激和阳离子诱导两个方面,分别研究了固定化载体(硅藻土、石英砂)和具有强诱导能力的成矾离子(K+)对微生物转化酸性体系中Fe2+成次生矿物的影响。结果表明,3种材料均有明显促进可溶性Fe2+向次生矿物转化的作用,且总铁(TFe)沉淀率与3种材料的添加量呈正相关关系。在起始Fe2+浓度为160mmol/L,硅藻土、石英砂和钾离子最大添加量分别为10 g、10 g和80 mmol/L时,经过72 h反应后,TFe沉淀率分别比对照增加了8%、24%和20%。矿物中的Fe、K和S元素含量与溶液中的起始K+浓度有非常密切的关系,随着K+浓度的增大,矿物中的K和S含量逐渐增加,而Fe含量则相应减少。     

Production of acid water in a lead-zinc mine,Coeur d'Alene,Idaho

The Bunker Hill Mine in Idaho's Coeur d'Alene mining district produces approximately 10 m³/minute of acid water containing high concentrations of heavy metals. Field and laboratory studies indicate that much of the acid water is produced in a single ore body in the upper part of the mine. The ore of this body contains mainly sphalerite, galena, and pyrite in a siderite-quartz gangue. Ground water recharges this ore body through a near-vertical zone of high permeability, which is the result of mining by the caving technique. Ore samples from the caving area contained oxidized forms of iron and produced acid in a laboratory leaching test. Leaching experiments with several ore samples from the mine also indicated that the ratio of pyrite to calcite in the samples strongly controlled the resultant pH values. Oxidation of pyrite to sulfuric acid and compounds of iron is apparently responsible for the production of acid water in the mine. In contrast, dissolution of calcite in water results in a basic solution, with pH around 8.3, that can neutralize the acid produced by the oxidation process. Methods for prevention of acid mine drainage in this and other similar mines are noted.     

Effect of acid mine drainage on a karst basin: a case study on the high-As coal mining area in Guizhou province,China

Acid mine drainage (AMD) is a common pollution in mining areas due to the oxidation of pyrite and associated sulfide minerals at mines, tailings and mine dumps. Elevated metals (Fe, Mn, Al) and metalloids (As, Hg) in AMD would deteriorate the local aquatic environment and influence the water supply. A carbonate basin with deposits of high-arsenic coal in Xingren County, southwestern China, was chosen to study the behavior of As and other chemical constituents along a river receiving AMD. Heavy metals (Fe, Mn) and major ions such as (Ca²⁺, Mg²⁺, Cl⁻, SO₄ ²⁻) in surface water, and As in sediment and surface water were analyzed. It was found that high concentrations of SO₄ ²⁻ (1,324–7,560 mg/L) and Fe (369–1,472 mg/L) in surface water were mainly controlled by the interactions between water and rocks such as the oxidation of pyrite in the local coal seams, precipitation and adsorption of iron minerals. Although ubiquitous carbonate minerals in the bedrock and the riverbeds, low pH (<3) water was maintained until 2 km downstream from the AMD source due to the Fe(hydro)oxide minerals coating on the surface of carbonate minerals to restrain the neutralization of acidic water. Moreover, the formation of Fe(hydro)oxide precipitations absorbed As was dominated the attenuation of As from water to sediment. Whereas, the dilution also played an important role in decrease of As in river water.     

Stable isotope geochemistry of acid mine drainage: Experimental oxidation of pyrite

Sulfate and water from experiments in which pyrite was oxidized at a pH of 2.0 were analyzed for sulfur and oxygen stable isotopes. Experiments were conducted under both aerobic and anaerobic sterile conditions, as well as under aerobic conditions in the presence of Thiobacillus ferrooxidans, to elucidate the pathways of oxidation. Oxygen isotope fractionation between SO^2?₄ and H₂O varied from +4.0 %. (anaerobic, sterile) to + 18.0 %. (aerobic, with T. ferrooxidans.). The oxygen isotope composition of dissolved oxygen utilized in both chemical and microbially-mediated oxidation was also determined (+11.4 %., by T. ferrooxidans; +18.4 %., chemical). Contributions of water-derived oxygen and dissolved oxygen to the sulfate produced in the oxidation of pyrite could thus be estimated. Water-derived oxygen constituted from 23 to ~ 100 percent of the oxygen in the sulfate produced in the experiments, and this closely approximates the range of contribution in natural acid mine drainage. Oxidation of sulfides in anaerobic, water-saturated environments occurs primarily by chemical oxidation pathways, whereas oxidation of sulfides in well-aerated, unsaturated zone environments occurs dominantly by microbially mediated pathways.     

Geochemistry and stable isotope investigation of acid mine drainage associated with abandoned coal mines in central Montana,USA

The Great Falls-Lewistown Coal Field (GFLCF) in central Montana contains over 400 abandoned underground coal mines, many of which are discharging acidic water with serious environmental consequences. Areas of the mines that are completely submerged by groundwater have circum-neutral pH and relatively low concentrations of metals, whereas areas that are only partially flooded or freely draining have acidic pH (< 3) and high concentrations of metals. The pH of the mine drains either decreases or increases after discharging to the surface, depending on the initial ratio of acidity (mainly Al and Fe²⁺) to alkalinity (mainly HCO₃^?). In acidic, Fe-rich waters, oxidation of Fe²⁺ after exposure to air is microbially catalyzed and follows zero-order kinetics, with computed rate constants falling in the range of 0.97 to 1.25 mmol L^? 1 h^? 1. In contrast, Fe²⁺ oxidation in near-neutral pH waters appears to be first-order with respect to Fe²⁺ concentration, although insufficient data were collected to constrain the rate law expression. Rates of Fe²⁺ oxidation in the field are dependent on temperature such that lower Fe²⁺ concentrations were measured in down-gradient waters during the day, and higher concentrations at night. Diel cycles in dissolved concentrations of Zn and other trace metals (Mn, Ni) were also noted for down-gradient waters that were net alkaline, but not in the acidic drains.The coal seams of the GFLCF and overlying Cretaceous sandstones form a perched aquifer that lies ~ 50 m above the regional water table situated in the underlying Madison Limestone. The δD and δ¹⁸O values of flooded mine waters suggest local derivation from meteoric water that has been partially evaporated in agricultural soils overlying the coal mines. The S and O isotopic composition of dissolved sulfate in the low pH mine drains is consistent with oxidation of biogenic pyrite in coal under aerated conditions. A clear distinction exists between the isotopic composition of sulfate in the acid mine waters and sulfate in the adjacent sedimentary aquifers, making it theoretically possible to determine if acid drainage from the coal mines has leaked into the underlying Madison aquifer.     

The potential formation of acid mine drainage in pyrite-bearing hard-coal tailings under water-saturated conditions: an experimental approach

 Annually, an amount of approximately 13 million cubic meters of hard-coal tailings must be disposed of in the German Ruhr Valley. Besides the waste of land in a densily populated region, the disposal of the pyrite-bearing material under atmospheric conditions may lead to the formation of acid mine drainage (AMD). Therefore, alternative disposal opportunities are of increasing importance, one of which being the use of tailings under water-saturated conditions, such as in backfilling of abandoned gravel pits or in the construction of waterways. In this case, the oxidation of pyrite, and hence the formation of AMD, is controlled by the amount of oxygen dissolved in the pore water of tailings deposited under water. In case the advective percolation of water is suppressed by sufficient compaction of the tailings, oxygen transport can be reduced to diffusive processes, which are limited by the diffusive flux of dissolved oxygen in equilibrium with the atmospheric pO₂. Calculations of the duration of pyrite oxidation based on laboratory experiments have shown that the reduction of oxygen is mainly controlled by the content of organic substance rather than the pyrite content, a fact that is supported by results from oxidation experiments with nitrate. A "worst case" study has lead to the result that the complete oxidation of a 1.5-m layer of hard-coal tailings deposited under water-saturated conditions would take as much as several hundred thousand years. Received: 6 May 1996 · Accepted: 2 August 1996     

Estimation of potential pollution of waste mining dumps at Peña del Hierro (Pyrite Belt,SW Spain) as a base for future mitigation actions

Peña del Hierro is an abandoned mine site located in the catchment area of the Tinto river (Pyrite Belt, SW Spain). As leaching from the spoils affect the quality of the stream water, the waste dumps have been characterized for mineralogy, geochemistry and granulometry to obtain an estimate of the potential pollution. Waste rock dumps in Peña del Hierro are very heterogeneous and are mainly composed of acid volcanic tuffs > gossan > shales > roasted pyrite ashes > floated pyrite. The volcanic tuffs, the gossan and the shales coexist in the same piles. The roasted pyrite ashes and the floated pyrite form more homogeneous dumps. The dissolution of pyrite concentrated in pyrite ashes and floated pyrite units can generate acid mine drainage. Nevertheless, acid volcanic tuffs, which are rich in pyrite and have no neutralizing minerals, are the main source of these acidic effluents. Only muscovite might partially neutralize the acidity, but the dissolution of this mineral is too slow to compensate for acidity. The occurrence of jarosite in the <2 mm fraction indicates that extreme acid mine drainage occurs. The gossan and roasted pyrite ashes have high contents of trace elements. According to their concentration, As (46–1710 ppm), Pb (113–3455 ppm) and Hg (0–53) are some of the most important toxic trace elements in these wastes. In dumps mainly composed of volcanic tuffs most of the trace elements derive from the gossan mixed in the piles. Gossan is stable in an oxidizing environment, but acidic effluents (pH < 2) can dissolve Fe oxyhydroxides from them and release high amounts of trace elements to the stream water. This research contributes to estimating the production of acid mine drainage and the actual contamination risk of potentially toxic elements in soils and waters of this area, and could be the base for possible future mitigation actions in other areas affected by mining wastes.     

Hydrogeochemistry and microbiology of mine drainage: An update

The extraction of mineral resources requires access through underground workings, or open pit operations, or through drillholes for solution mining. Additionally, mineral processing can generate large quantities of waste, including mill tailings, waste rock and refinery wastes, heap leach pads, and slag. Thus, through mining and mineral processing activities, large surface areas of sulfide minerals can be exposed to oxygen, water, and microbes, resulting in accelerated oxidation of sulfide and other minerals and the potential for the generation of low-quality drainage. The oxidation of sulfide minerals in mine wastes is accelerated by microbial catalysis of the oxidation of aqueous ferrous iron and sulfide. These reactions, particularly when combined with evaporation, can lead to extremely acidic drainage and very high concentrations of dissolved constituents. Although acid mine drainage is the most prevalent and damaging environmental concern associated with mining activities, generation of saline, basic and neutral drainage containing elevated concentrations of dissolved metals, non-metals, and metalloids has recently been recognized as a potential environmental concern. Acid neutralization reactions through the dissolution of carbonate, hydroxide, and silicate minerals and formation of secondary aluminum and ferric hydroxide phases can moderate the effects of acid generation and enhance the formation of secondary hydrated iron and aluminum minerals which may lessen the concentration of dissolved metals. Numerical models provide powerful tools for assessing impacts of these reactions on water quality.     

Net alkalinity and net acidity 2: Practical considerations

The pH, alkalinity, and acidity of mine drainage and associated waters can be misinterpreted because of the chemical instability of samples and possible misunderstandings of standard analytical method results. Synthetic and field samples of mine drainage having various initial pH values and concentrations of dissolved metals and alkalinity were titrated by several methods, and the results were compared to alkalinity and acidity calculated based on dissolved solutes. The pH, alkalinity, and acidity were compared between fresh, unoxidized and aged, oxidized samples.Data for Pennsylvania coal mine drainage indicates that the pH of fresh samples was predominantly acidic (pH 2.5–4) or near neutral (pH 6–7); ≈ 25% of the samples had pH values between 5 and 6. Following oxidation, no samples had pH values between 5 and 6.The Standard Method Alkalinity titration is constrained to yield values >0. Most calculated and measured alkalinities for samples with positive alkalinities were in close agreement. However, for low-pH samples, the calculated alkalinity can be negative due to negative contributions by dissolved metals that may oxidize and hydrolyze.The Standard Method hot peroxide treatment titration for acidity determination (Hot Acidity) accurately indicates the potential for pH to decrease to acidic values after complete degassing of CO₂ and oxidation of Fe and Mn, and it indicates either the excess alkalinity or that required for neutralization of the sample. The Hot Acidity directly measures net acidity (= −net alkalinity). Samples that had near-neutral pH after oxidation had negative Hot Acidity; samples that had pH < 6.3 after oxidation had positive Hot Acidity. Samples with similar pH values before oxidation had dissimilar Hot Acidities due to variations in their alkalinities and dissolved Fe, Mn, and Al concentrations. Hot Acidity was approximately equal to net acidity calculated based on initial pH and dissolved concentrations of Fe, Mn, and Al minus the initial alkalinity. Acidity calculated from the pH and dissolved metals concentrations, assuming equivalents of 2 per mole of Fe and Mn and 3 per mole of Al, was equivalent to that calculated based on complete aqueous speciation of Fe^II/Fe^III. Despite changes in the pH, alkalinity, and metals concentrations, the Hot Acidities were comparable for fresh and most aged samples.A meaningful “net” acidity can be determined from a measured Hot Acidity or by calculation from the pH, alkalinity, and dissolved metals concentrations. The use of net alkalinity = (Alkalinity_measured − Hot Acidity_measured) to design mine drainage treatment can lead to systems with insufficient Alkalinity to neutralize metal and H⁺ acidity and is not recommended. The use of net alkalinity = −Hot Acidity titration is recommended for the planning of mine drainage treatment. The use of net alkalinity = (Alkalinity_measured − Acidity_calculated) is recommended with some cautions.     

Acid mine drainage at a coal mine in the eastern Transvaal, South Africa

 Several mines in the Witbank coalfield in South Africa are affected by acid mine drainage. This has led to a deterioration in the water quality in many surface streams. The Loubert Mine is one such mine. Hence, an initial investigation was carried out to determine the source of acid mine drainage pollution and the associated hydrogeological conditions. The investigation showed that most of the acid mine drainage is emanating from old opencast workings which have been backfilled. Most of the water from the backfilled area drains into control reservoirs. Unfortunately their capacity is limited, which means that water overspills and seeps from them. This water finds its way into a nearby stream, the water of which accordingly has an unacceptably low pH value and high sulphate content. The proposals advanced to control the problem basically involve inhibiting the amount of water infiltrating the backfilled opencast area on the one hand and reducing the amount of water entering the control reservoirs on the other. Received: 5 March 1997 · Accepted: 17 June 1997     

铜陵矿山酸性排水及固体废弃物中的重金属元素

在调查中国铜陵凤凰山铜矿和新桥硫铁矿两种不同类型矿山固体废弃物特征的基础上,研究了矿山尾矿和废石产生酸性排水的可能性及其差异以及矿山固体废弃物中重金属元素的赋存形式。结果表明,凤凰山铜矿的尾矿基本不产生矿山酸性排水,而新桥硫铁矿采矿废石产生矿山酸性排水,并且凤凰山铜矿的尾矿和新桥硫铁矿采矿废石中重金属元素的赋存形式也有差异,前者重金属Cu、Pb、Zn、Cd、As、Hg主要赋存于硅酸盐态中,而后者在还原态中有较高的含量,这反映了在地表条件下尾矿中大量重金属元素已经发生了迁移,而采矿废石已经开始氧化,且酸性排水的存在更有利于废石中重金属元素的迁移和扩散,进而导致矿区周围环境的污染。     

Evaluation of the long term groundwater pollution by the open cast lignite mine Jänschwalde (Germany)

The reconstruction of the hydrogeochemical composition of the dumps in the active Lusatian lignite mining region is necessary to forecast the acid mine drainage into the residual lakes and the natural groundwater systems. Therefore, a three-dimensional geochemical model of the Jänschwalde dump was developed. By analysing the geological situation and the mining technology, it is possible to calculate the pyrite oxidation in different parts of the mine (groundwater lowering in front of the mine, natural and dump slopes, marginal pits and the dump surface).Only 4% of the total pyrite content is oxidised during the mining process within its time of operation (43 years). The major fraction (about 60%) is oxidised on the surface of the dumps, whereas the other zones contribute less to the production of acidity (groundwater lowering 5.4%, short term exposed slopes (1.2% natural slopes; 7.4% dump slopes) and 22.4% inclusion of O₂ during the tipping). It may be concluded that the technology of conveyor belt bridges, combined with the selective tipping of loamy sediments on the surface is very favourable to minimise the oxidation of pyrite. It is also shown that in the open cast mine of Jänschwalde the buffer capacity of the carbonate dominates over the produced acid.     

西藏巴达铜金矿床黄铁矿原位主微量元素特征及其环境效应

黄铁矿在自然环境中极易发生氧化,造成严重生态环境问题。为了研究自然条件下不同粒度和晶形黄铁矿化学成分的差异对黄铁矿氧化速率的影响,本文对巴达铜金矿床黄铁矿进行了LA- ICP- MS原位主微量元素分析和矿物面扫描分析。测试结果表明粗粒黄铁矿S、Fe含量较高,成分更纯;微量元素As、Co、Ni和Pb、Cu、Zn分别以类质同象方式和包裹体形式更多地存在于细粒黄铁矿中,二者均能促使细粒黄铁矿氧化速率加快;粗粒黄铁矿中Cr和Ti元素含量较高,其氧化后生成致密氧化膜可抑制黄铁矿被进一步氧化。本文认为对于本矿床中粗粒黄铁矿和细粒黄铁矿氧化污染问题应采用两种不同的治理措施,对于不易被氧化的粗粒黄铁矿,使其处于常温常压的干燥避光环境中即可防止发生氧化;对于易氧化的细粒黄铁矿,其氧化产物造成污染对环境压力较大,应采用源头治理和末端治理相结合的措施进行处理,以达到更科学的治理效果。