Contaminant Attenuation Processes at Mine Sites

The global imprint of acid drainage problems at mine sites is a clear reminder that generally, natural processes do not adequately ameliorate the acidity and metal contamination produced by oxidizing sulfide minerals. Yet at nearly all such sites, natural attenuation processes occur and may contribute to site remediation. Biogeochemical processes can be particularly important in controlling the transport and fate of certain metal and metalloid contaminants, under specific environmental conditions. This paper identifies the major natural attenuation processes that have been documented at mine sites around the world and discusses how monitored natural attenuation is sometimes used in combination with active treatment technologies to achieve site-specific remediation objectives.     

Acid Mine Drainage at the Abandoned Kettara Mine (Morocco): 1. Environmental Characterization

The Kettara site (Morocco) is an abandoned pyrrhotite ore mine in a semi-arid environment. The site contains more than 3 million tons of mine waste that have been deposited on the surface without concern for environmental issues. Tailings were stockpiled in a dyke and pond and in piles, over an area of about 16 ha, and have generated acid mine drainage (AMD) for more than 24 years. The mine waste and secondary precipitates from this mine were characterized using geochemical and mineralogical techniques. The Kettara wastes contain 1.6–14.5 wt% sulfur, mainly sulfide minerals (e.g., pyrrhotite, pyrite, chalcopyrite, galena, and sphalerite). The main gangue minerals were goethite, quartz, chlorite-serpentine, talc, muscovite, and albite. Carbonates occur at very low quantities (less than 1 wt%). The most abundant heavy metals were Cu, Zn, Cr, Pb, Co, As, Cd, and Ni. Acid–base accounting static test results showed that all the samples have low values of acid-neutralizing potential (NP) (0–9 kg CaCO3/t). The mine waste has high acid-producing potential (AP) (51–453 kg CaCO3/t). Abundant secondary mineralogy is present, consisting mainly of halotrichite, goethite, jarosite-hydroanion, hydroniumjarosite, starkeyite, gypsum, alunite, copiapite, butterite, and coquimbite. Hardpans, which can prevent water infiltration to fresh tailings beneath and thereby lessen the rate of sulfide reactivity, were observed during sampling of the fine tailings. Mineralogical analysis indicated that the cementitious phase of the hardpan is mainly goethite. The alteration observed in the tailings pond does not extend more than 5–15 cm.     

Acid Mine Drainage at the Abandoned Kettara Mine (Morocco): 2. Mine Waste Geochemical Behavior

Weathering and humidity cell tests were used to predict the potential for acid mine drainage (AMD) and to estimate the mineral reaction rates and depletion of fine and coarse tailings from the abandoned Kettara mine, Morocco. The geochemistry of the fine and coarse mine wastes was similar and, as expected by static tests, the wastes produced significant amounts of AMD. The sulfate production rate of both fine and coarse tailings was very high (2,000–8,000 and 2,400–560 mg SO₄/kg/week, respectively) during the first weeks of kinetics tests. After 9 weeks, sulfate release became low, ranging between 600 and 78 mg SO₄/kg/week for fine tailings and 500–120 mg SO₄/kg/week for coarse tailings. Effluent water samples had low pH (2.9–4.2) and elevated concentrations of acidity, sulfate, iron, copper, and zinc. Most or all of the dissolved K, Na, Al, Mg, and Si in the AMD result from the acidic dissolution of silicates (chlorite, talc, muscovite, and albite). Fine tailings produce much higher concentrations of acidity and sulfate than coarse tailings. However, due to greater transport of oxygen and water within the coarse waste, coarse tailings could be of greater environmental significance than fine tailings. The coarse waste continued to release acid after 378 days of leaching, whereas the fine tailings naturally passivates. These laboratory results agree with field observations; the upper profile of the coarse waste rock dam is highly oxidized (75 cm) whereas oxidation in the fine tailings does not extend more than 5–15 cm beneath the surface. A comparison between weathering and humidity cell tests indicated that the general trend of dissolution of metals was essentially similar for both methods. However, sulfate depletion rates were higher for the weathering cell tests. These tests indicate that the Kettara tailings piles and dam will continue to release acid for a long time unless remedial action is taken.     

Acid Mine Drainage Flowing from Abandoned Gas Wells

Abstract  In northwestern Pennsylvania (USA), numerous abandoned natural gas wells are producing artesian flows of Fe-contaminated water. The origin of the polluted water has been generally assumed to be brines from the gas-producing sands. We sampled 20 artesian discharges where iron staining was conspicuous. The waters were not brines, but were more characteristic of acid mine drainage (AMD). The dominant cations were Fe, Ca, and Mg, while the dominant anion was sulfate. The study area has a long history of coal mining in the lower Allegheny formation; however, the coal beds are generally at higher elevations than the discharges. We propose that AMD formed in the coal mines is infiltrating into lower aquifers, moving outside the lateral limits of mining, and using abandoned gas wells as conduits to the surface. While flowing through the underlying sandstones, the AMD chemistry is modified by contact with siderite, the dominant carbonate mineral in this stratigraphy. This would suggest that current remediation strategies that emphasize plugging the pollution-producing gas wells may be ill-advised because the source of the polluted water is more shallow than currently assumed.     

我国报废煤矿瓦斯抽采利用现状及潜力

随着我国煤炭开采强度的持续加大,以及东部经济发达省份煤炭资源的日益枯竭,报废煤矿的数量将会越来越多,报废煤矿瓦斯抽采利用在我国具有巨大的潜力.本文首先全面对比分析了美国、英国和德国等发达国家以及我国报废煤矿瓦斯抽采利用现状,然后探讨了我国报废煤矿瓦斯抽采利用潜在可行性技术方案,最后提出了促进我国报废煤矿瓦斯抽采利用产业发展的对策建议.     

Potential for Passive Treatment of Coal Mine-derived Acid Mine Drainage in Abandoned Stream Channels

Mine Water and the Environment - Passive treatment of coal mining derived acid mine drainage (AMD) utilizes natural processes to neutralize acidity and remove dissolved metal contaminants. In some...     

废弃矿井瓦斯抽放与利用现状及发展趋势

废弃矿井瓦斯抽放与利用旨在抽取和利用聚存于废弃矿井中的洁净能源。在简述国内外废旧矿井瓦斯资源量、预测与评价理论、抽放方法与利用的基础上,分析了我国废弃矿井瓦斯抽放与利用的可行性及发展趋势。     

废弃矿井瓦斯抽放与利用坝状及发展趋势

废弃矿井瓦斯抽放与利用旨在抽取和利用聚存于废弃矿井中的洁净能源。在简述国内外废旧矿井瓦斯资源量、预测与评价理论、抽放方法与利用的基础上，分析了我国废弃矿井瓦斯抽放与利用的可行性及发展趋势。     

Performance of a Natural Wetland Treating Acid Mine Drainage in Arid Conditions

Abstract  A wetland naturally formed in the discharge from a copper mine tailing impoundment in Rajasthan, India. The wetland is abundantly vegetated. This study investigated changes that occurred in the seepage as it travelled 180 and 380 m (P₁ and P₂) through the wetland. The pH increased from 6.17 to 7.10 at P₁ and 7.34 at P₂ in the pre-monsoon season, 6.53 to 7.36 at P₁ and 7.77 at P₂ in the post-monsoon season, and from 6.20 to 6.63 at P₁ and 6.89 at P₂ in the winter. Contaminant removal at P₂ ranged from 40 to 95%.     

A Comparison Between Kinetic Test Results and Natural Weathering: The Abandoned Kettara Mine Tailings Pond

More than three million tons of sulfide tailings were discarded without any protection for more than 36 years at the since-abandoned Kettara mine. The impact of these tailings as well as the coarse wastes disorderly dumped on the surface site is highlighted by the elevated sulfate levels in the wells downstream of the wastes. Kinetic tests carried out on these sulfide tailings over 10 years ago, showed similar trends in metal dissolution despite large difference in test duration (21 and 53 weeks for the weathering and humidity cell tests, respectively). 40% of the sulfate release occurred in the first 3 weeks of the humidity test. However, in this study, the elevated sulfate levels in the groundwater was shown not be linked to the tailings, where the original sulfide material is still present under an oxidized layer of 10 cm–1.2 m. Thus, kinetic test results should not be extrapolated to field scale without accounting for site-specific factors, especially particle size and climate.     

寺家庄煤矿瓦斯抽放可行性研究

通过对寺家庄煤矿煤层透气性系数和钻孔瓦斯流量衰减系数等基础参数的现场实测,对矿井瓦斯抽放的可行性进行了论证,得出了寺家庄煤矿需要建立瓦斯抽放系统的结论,为寺家庄煤矿的瓦斯防治工作指明了方向,为邻近矿井的瓦斯防治工作提供参考.     

高抽巷瓦斯抽放技术在天池煤矿的应用

通过对瓦斯来源的分析,设计采取煤层顶板走向高抽巷瓦斯抽放技术治理上邻近层瓦斯,经生产实践证明效果良好,有效的防止了采煤工作面瓦斯超限,保证了高产高效综放工作面的安全生产。     

废弃矿区建筑可持续利用研究

本文首先探讨了废弃矿区建筑可持续利用的意义,论述了废弃矿区建筑可持续利用的策略,最后通过案例探讨了废弃矿区建筑可持续利用效果。     

A Geotechnical Solution to Reduce Acid Mine Drainage Generation at Recreio Mine

Coal mining is frequently associated with acid mine drainage (AMD) generated by tailings and waste dumps containing sulphide minerals. A practical and economical alternative to minimise AMD generation is to avoid the contact between water and waste dumps using a compacted soil cover. This study evaluates the use of distinct raw materials as cover layers. The study area was an open pit coal mine in the south of Brazil. Geotechnical characterization, physical, chemical and mineralogical analyses were carried out on two different soils from this mine. Hydraulic conductivity tests were performed using Flexible-Wall Permeameter. The results obtained from the hydraulic conductivity tests for two compacted soils suggest their applicability as impermeable layers. Considering the operational aspects at the mine and the characteristics determined for the soils a new construction scheme for the dump site was suggested.     

Geochemical Characterisation of Seepage and Drainage Water Quality from Two Sulphide Mine Tailings Impoundments: Acid Mine Drainage versus Neutral Mine Drainage

Seepage water and drainage water geochemistry (pH, EC, O₂, redox, alkalinity, dissolved cations and trace metals, major anions, total element concentrations) were studied at two active sulphide mine tailings impoundments in Finland (the Hitura Ni mine and Luikonlahti Cu mine/talc processing plant). The data were used to assess the factors influencing tailings seepage quality and to identify constraints for water treatment. Changes in seepage water quality after equilibration with atmospheric conditions were evaluated based on geochemical modelling. At Luikonlahti, annual and seasonal changes were also studied. Seepage quality was largely influenced by the tailings mineralogy, and the serpentine-rich, low sulphide Hitura tailings produced neutral mine drainage with high Ni. In contrast, drainage from the high sulphide, multi-metal tailings of Luikonlahti represented typical acid mine drainage with elevated contents of Zn, Ni, Cu, and Co. Other factors affecting the seepage quality included weathering of the tailings along the seepage flow path, process water input, local hydrological settings, and structural changes in the tailings impoundment. Geochemical modelling showed that pH increased and some heavy metals were adsorbed to Fe precipitates after net alkaline waters equilibrated with the atmosphere. In the net acidic waters, pH decreased and no adsorption occurred. A combination of aerobic and anaerobic treatments is proposed for Hitura seepages to decrease the sulphate and metal loading. For Luikonlahti, prolonged monitoring of the seepage quality is suggested instead of treatment, since the water quality is still adjusting to recent modifications to the tailings impoundment.     

Lime Treatment of Mine Drainage at the Sarcheshmeh Porphyry Copper Mine,Iran

Laboratory and field treatment tests were performed to evaluate the effectiveness of lime treatment for mitigation of environmental effects of acid mine drainage (AMD) at the Sarcheshmeh porphyry copper mine. AMD associated with the rock waste dumps is contaminated with Al (>36,215 μg/L), Cd (>105 μg/L), Co (>522 μg/L), Cu (>53,250 μg/L), Mn (>42,365 μg/L), Ni (>629 μg/L), and Zn (>12,470 μg/L). The concentrations of other metals (Fe, Mo, Pb, and Se) are low or below detection limits (As, Cr, and Sb). Due to the very high Al and Mn content and the low concentration of Fe, a two-stage lime treatment method was chosen for the laboratory tests. In the first stage, the AMD was treated at four pH set points: 7.5, 8.9, 9, and 10. In the second stage, after removing the sludge at pH 9, treatment was continued at pH 10 and 11. The results indicated that a two-stage treatment method was not necessary because elements such as Al, Cu, Co, and Zn were easily treated at pH 7.5, while complete removal of Cd, Mn, and Ni only required a pH of 10. Increasing pH during the treatment process only caused a slight increase in Al. Field treatment tests support the laboratory results. Lime treatment of highly contaminated AMD from dump 11, using simple low density sludge pilot scale equipment, show that contaminant metals are treatable using this method. The mean treatment efficiency for contaminant metals was 99.4% for Al, % for Cd, 99.6% for Co, 99.7% for Cu, 98.5% for Mn, 99.7% for Ni, 99% for U, and 99.5% for Zn. The optimum pH for AMD treatment by lime was in the range of 9–10. The produced sludge in the treatment process was highly enriched in the contaminant metals, especially Cu (>7.34%), Al (>4.76%), Mn (>2.94%), and Zn (>1.25%). A correlation coefficient matrix indicates that the distribution pattern of the contaminant metals between soluble and precipitated phases is consistent with the hydrochemical behavior of the metals during the lime treatment process.     

保德煤矿采空区瓦斯抽放试验研究

较为详尽地介绍了神华集团保德煤矿采空区瓦斯抽放情况,针对不同条件共采用了六种采空区瓦斯抽放方法,通过对其进行总结分析,从而为其它类似工作面的瓦斯抽放积累宝贵的经验。     

Abandoned Mine Drainage in the Swatara Creek Basin, Southern Anthracite Coalfield, Pennsylvania, USA: 2. Performance of Treatment Systems

A variety of passive and semi-passive treatment systems were constructed by state and local agencies to neutralize acidic mine drainage (AMD) and reduce the transport of dissolved metals in the upper Swatara Creek Basin in the Southern Anthracite Coalfield in eastern Pennsylvania. To evaluate the effectiveness of selected treatment systems installed during 1995–2001, the US Geological Survey collected water-quality data at upstream and downstream locations relative to each system eight or more times annually for a minimum of 3 years at each site during 1996–2007. Performance was normalized among treatment types by dividing the acid load removed by the size of the treatment system. For the limestone sand, open limestone channel, oxic limestone drain, anoxic limestone drain (ALD), and limestone diversion well treatment systems, the size was indicated by the total mass of limestone; for the aerobic wetland systems, the size was indicated by the total surface area of ponds and wetlands. Additionally, the approximate cost per tonne of acid treated over an assumed service life of 20 years was computed. On the basis of these performance metrics, the limestone sand, ALD, oxic limestone drain, and limestone diversion wells had similar ranges of acid-removal efficiency and cost efficiency. However, the open limestone channel had lower removal efficiency and higher cost per ton of acid treated. The wetlands effectively attenuated metals transport but were relatively expensive considering metrics that evaluated acid removal and cost efficiency. Although the water-quality data indicated that all treatments reduced the acidity load from AMD, the ALD was most effective at producing near-neutral pH and attenuating acidity and dissolved metals. The diversion wells were effective at removing acidity and increasing pH of downstream water and exhibited unique potential to treat moderate to high flows associated with storm flow conditions.     

Metal Loadings and Alkaline Mine Drainage from Active and Abandoned Mines in the Ivo River Basin Area of Southeastern Nigeria

Discharges from 11 active and abandoned mines were investigated in the Lokpaukwu-Ishiagu mining areas of Nigeria. The discharges had very high concentrations of TDS, hardness, chloride, calcium, conductivity, turbidity, and unacceptable levels of some metals. A conservative estimate is that nearly 33 million L of untreated circumneutral-alkaline drainage and effluents find their way into the Ivo River watershed annually, including about 710,000 kg of dissolved solids and 586 kg of potentially toxic metals. These discharges exceed national (FEPA) and international (EU, WHO, and USEPA) permissible standards for domestic water use and discharge into aquatic sources, and national groundwater protection standards for permitted concentrations of toxic substances in industrial effluents. Our study also revealed that wetlands that serve as sinks for this mine drainage become sources of continuous polluted recharge to both surface and groundwater. We recommend that a task force be established to investigate the environmental operations of mining companies in Nigeria, that mine sites be closely monitored by state agencies, and that host communities receive environmental education.     

鞍山铁矿露天采坑废弃地的土壤动物群落研究

鞍山市大孤山露天铁矿山已有80多年的开采历史，矿山开采对周边和采坑的土地造成了不可避免的生态环境影响。近年来，关于矿山采坑废弃土地的生态环境受到了广泛的关注，而其中土壤动物的种类和数量问题却没有得到应有的重视。通过对鞍山市大孤山铁矿露天采坑不同段阶上废弃地土壤动物的调查研究，查明了自然恢复过程中土壤动物演替的基本生态特征，并对比研究了在人工扰动条件下和自然恢复过程中，土壤动物丰度的特点，总结了自然恢复条件下土壤动物演替的规律性。