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1.
The behavior of heavy metals in acid mine drainage (AMD) is mainly controlled by pH values. Therefore, a quantitative estimation of factors affecting pH values in AMD is very important in predicting the behavior of those metals. Many different factors cause pH changes in streams affected by AMD and we quantitatively estimated those factors by making simple equations from geochemical data collected from the Dalsung mine. In a stream from that mine, the pH values decrease as the stream flows downstream from the AMD source, which is different from normal streams affected by AMD. The stream shows low pH ranges (4.04–5.96), high electrical conductivity (1,407–1,664 μS/cm), and sulfate concentration (680–854 ppm). Most ion concentrations decrease or do not show noticeable changes mainly due to dilution. The change of the iron content is most significant, even though the concentration of iron is relatively low compared with other ions. The iron concentration (13.4 ppm) becomes almost 0 ppm due to precipitation. Schwertmannite is the dominant precipitated phase downstream and whitish basaluminite is observed in the upstream. From our pH estimation, precipitation is the most important process lowering pH values from 5.96 to 4.04. The dilution factor was calculated by the concentration changes in sulfate ions. Dilution increases pH values, but compared with the precipitation factor, the contribution of the dilution factor to pH is relatively small. Alkalinity is the main factor that buffers hydrogen, which is released by precipitation. The redox changes, which were calculated from the pH and Eh values, also affect pH at each sampling site. The trend of estimated pH changes is almost identical to the observed ones, but the values are slightly different. Some errors are expected mainly due to the uncertainty in the observed Eh values and the chemistry of the added water for dilution.  相似文献   

2.
Biological reduction of iron-sulfate minerals, such as jarosite, has the potential to contribute to the natural attenuation of acid mine drainage (AMD) sites. Previous studies of AMD attenuation at Davis Mine, an abandoned pyrite mine in Rowe Massachusetts, provided evidence of iron and sulfate reduction by indigenous bacteria. Jarosite is a large component of the sediment at Davis Mine and may play a role in AMD attenuation. In this study, microcosms were constructed with groundwater and sediment from Davis Mine and amended with glycerol, nitrogen and phosphorus (GNP) and naturally formed natrojarosite. Over time, higher total iron, sulfate, pH and sodium concentrations and lower oxidation–reduction potentials were observed in microcosms amended with GNP and jarosite, compared with unamended microcosms and killed controls. Geochemical modeling predicted jarosite precipitation under microcosm conditions, suggesting that abiotic processes were unlikely contributors to jarosite dissolution. SEM imaging at the jarosite surface showed microbial attachment. Microbial community composition analysis revealed a shift to higher populations of Clostridia, which are known to reduce both iron and sulfate. The results show that jarosite may be utilized as an electron acceptor by iron and/or sulfate reducing bacteria at Davis Mine and its presence may aid in the attenuation of AMD.  相似文献   

3.
Water is one of the basic and fundamental requirements for the survival of human beings. Mining of the sulphide mines usually produce a significant amount of acid mine drainage (AMD) contributing to huge amounts of chemical components and heavy metals in the receiving waters. Prediction of the heavy metals in the AMD is important in developing any appropriate remediation strategy. This paper attempts to predict heavy metals (Cu, Fe, Mn, Zn) from the AMD using backpropagation neural network (BPNN), general regression neural network (GRNN) and multiple linear regression (MLR), by taking pH, sulphate (SO4) and magnesium (Mg) concentrations in the AMD into account in Shur River, Sarcheshmeh porphyry copper deposit, southeast Iran. The comparison between the predicted concentrations and the measured data resulted in the correlation coefficients, R, 0.92, 0.22, 0.92 and 0.92 for Cu, Fe, Mn and Zn ions using BPNN method. Moreover, the R values were 0.89, 0.37, 0.9 and 0.91 for Cu, Fe, Mn, and Zn taking the GRNN method into consideration. However, the correlation coefficients were low for the results predicted by MLR method (0.83, 0.14, 0.9 and 0.85 for Cu, Fe, Mn and Zn ions, respectively). The results further indicate that the ANN can be used as a viable method to rapidly and cost-effectively predict heavy metals in the AMD. The results obtained from this paper can be considered as an easy and cost-effective method to monitor groundwater and surface water affected by AMD.  相似文献   

4.
The subsurface acid mine drainage (AMD) environment of an abandoned underground uranium mine in Königstein/Saxony/Germany, currently in the process of remediation, is characterized by low pH, high sulfate concentrations and elevated concentrations of heavy metals, in particular uranium. Acid streamers thrive in the mine drainage channels and are heavily coated with iron precipitates. These precipitates are biologically mediated iron precipitates and related to the presence of Fe-oxidizing microorganisms forming copious biofilms in and on the Fe-precipitates. Similar biomineralisations were also observed in stalactite-like dripstones, called snottites, growing on the gallery ceilings.The uranium speciation in these solutions of underground AMD waters flowing in mine galleries as well as dripping from the ceiling and forming stalactite-like dripstones were studied by time resolved laser-induced fluorescence spectroscopy (TRLFS). The fluorescence lifetime of uranium species in both AMD water environments were best described with a mono-exponential decay, indicating the presence of one major species. The detected positions of the emission bands and by comparing it in a fingerprinting procedure with spectra obtained for acid sulfate reference solutions, in particular Fe(III) - SO42− - UO22+ reference solutions, indicated that the uranium speciation in the AMD environment of Königstein is dominated in the pH range of 2.5-3.0 by the highly mobile aquatic uranium sulfate species UO2SO4(aq) and formation of uranium precipitates is rather unlikely as is retardation by sorption processes. The presence of iron in the AMD reduces the fluorescence lifetime of the UO2SO4(aq) species from 4.3 μs, found in iron-free uranium sulfate reference solutions, to 0.7 μs observed in both AMD waters of Königstein and also in the iron containing uranium sulfate reference solutions.Colloids were not observed in both drainage water and dripping snottite water as photon correlation spectroscopy analyses and centrifugation experiments at different centrifugal accelerations between 500g and 46000g revealed. Thus transport and uranium speciation at the investigated AMD sites is neither influenced by U(IV) or U(VI) eigencolloids nor by uranium adsorbed on colloidal particles.This study shows that TRLFS is a suitable spectroscopic technique to identify the uranium speciation in bulk solutions of AMD environments.  相似文献   

5.
Treatment of acid mine drainage (AMD) highly rich in sulfate and multiple metal elements has been investigated in a continuous flow column experiment using organic and inorganic reactive media. Treatment substrates that composed of spent mushroom compost (SMC), limestone, activated sludge and woodchips were incorporated into bacterial sulfate reduction (BSR) treatment for AMD. SMC greatly assisted the removals of sulfate and metals and acted as essential carbon source for sulfate-reducing bacteria (SRB). Alkalinity produced by dissolution of limestone and metabolism of SRB has provided acidity neutralization capacity for AMD where pH was maintained at neutral state, thus aiding the removal of sulfate. Fe, Pb, Cu, Zn and Al were effectively removed (87–100%); however, Mn was not successfully removed despite initial Mn reduction during early phase due to interference with Fe. The first half of the treatment was an essential phase for removal of most metals where contaminants were primarily removed by the BSR in addition to carbonate dissolution function. The importance of BSR in the presence of organic materials was also supported by metal fraction analysis that primary metal accumulation occurs mainly through metal adsorption onto the organic matter, e.g., as sulfides and onto Fe/Mn oxides surfaces.  相似文献   

6.
The acid mine drainage (AMD) discharged from the Hejiacun uranium mine in central Hunan (China) was sampled and analyzed using ICP-MS techniques. The analyzing results show that the AMD is characterized by the major ions FeTotal, Mn, Al and Si, and is concentrated with heavy metals and metalloids including Cd, Co, Ni, Zn, U, Cu, Pb, Tl, V, Cr, Se, As and Sb. During the AMD flowing downstream, the dissolved heavy metals were removed from the AMD waters through adsorption onto and co-precipitation with metal-oxhydroxides coated on the streambed. Among these metals, Cd, Co, Ni, Zn, U, Cu, Pb and Tl are negatively correlated to pH values, and positively correlated to major ions Fe, Al, Si, Mn, Mg, Ca and K. The metals/metalloids V, Cr, Se, As and Sb are conservative in the AMD solution, and negatively-correlated to major ions Na, Ca and Mg. Due to the above different behaviors of these chemical elements, the pH-negatively related metals (PM) and the conservative metals (CM) are identified; the PM metals include Cd, Co, Ni, Zn, U, Cu, Pb and Tl, and the CM metals V, Cr, Se, As and Sb. Based on understanding the geochemistry of PM and CM metals in the AMD waters, a new equation: EXT = (Acidity + PM)/pH + CM × pH, is proposed to estimate and evaluate extent of heavy-metal pollution (EXT) of AMD. The evaluation results show that the AMD and surface waters of the mine area have high EXT values, and they could be the potential source of heavy-metal contamination of the surrounding environment. Therefore, it is suggested that both the AMD and surface waters should be treated before they are drained out of the mine district, for which the traditional dilution and neutralization methods can be applied to remove the PM metals from the AMD waters, and new techniques through reducing the pH value of the downstream AMD waters should be developed for removal of the CM metals.  相似文献   

7.
黄钾铁矾是酸性矿山废水（AMD） 中常见的次生矿物,能有效吸附AMD中Cu、Pb、Zn、Gd、As等重金属元素。不 同条件下形成的黄钾铁矾微形貌不同,其吸附能力也不同。文章通过化学法和微生物法合成了黄钾铁矾,并在粤北大宝山 矿酸性矿山废水中采集了含黄钾铁矾的泥样。利用扫描电镜-能谱分析（SEM） 和X光衍射（XRD）,对三种不同条件下形 成的黄钾铁矾进行鉴定和微形貌特征观察,并分析黄钾铁矾的形成条件。结果表明,常温条件下,pH值2.0~2.5时能够化 学合成黄钾铁矾,其晶体粒径约2~10 μm,且晶形呈板状;而在65℃时,可在pH2.0~3.0之间化学合成黄钾铁矾,但晶形 差。微生物法合成黄钾铁矾pH范围是2.0~5.0,其晶形完好,呈菱面体且晶体大小比较均匀,而约为2~4 μm。酸性矿山废 水中的黄钾铁矾形成的pH值为2.5~3.5,晶形为菱面体形,单个晶体大小多为1~2 μm。根据其形成条件和微形貌特征,文 章推测酸性矿山废水中形成的黄钾铁矾可能是微生物成因。  相似文献   

8.
黄钾铁矾是酸性矿山废水（AMD） 中常见的次生矿物，能有效吸附AMD中Cu、Pb、Zn、Gd、As等重金属元素。不 同条件下形成的黄钾铁矾微形貌不同，其吸附能力也不同。文章通过化学法和微生物法合成了黄钾铁矾，并在粤北大宝山 矿酸性矿山废水中采集了含黄钾铁矾的泥样。利用扫描电镜-能谱分析（SEM） 和X光衍射（XRD），对三种不同条件下形 成的黄钾铁矾进行鉴定和微形貌特征观察，并分析黄钾铁矾的形成条件。结果表明，常温条件下，pH值2.0~2.5时能够化 学合成黄钾铁矾，其晶体粒径约2~10 μm，且晶形呈板状；而在65℃时，可在pH2.0~3.0之间化学合成黄钾铁矾，但晶形 差。微生物法合成黄钾铁矾pH范围是2.0~5.0，其晶形完好，呈菱面体且晶体大小比较均匀，而约为2~4 μm。酸性矿山废 水中的黄钾铁矾形成的pH值为2.5~3.5，晶形为菱面体形，单个晶体大小多为1~2 μm。根据其形成条件和微形貌特征，文 章推测酸性矿山废水中形成的黄钾铁矾可能是微生物成因。  相似文献   

9.
Feasibility of using straw as sole substrate for in situ bioremediation of acidic mine drainage (AMD) was studied. The result showed that straw was more suitable than woodchips, which had been successfully used for bioremediating AMD at the source, for establishing bioremediation layer. The sulfate removal rate of rice straw treatment was almost two times higher than that of the woodchips treatment when the initial pH of the synthetic AMD was set to 3.0. Straw treatment may be more efficient at reducing sulfate than woodchips treatment under stressful conditions. The sulfate removal rate of the rice straw treatment increased from 8.67 to 21.77 mg L−1 day−1 when initial pH increased from 1 to 7 while the removal rate of woodchips treatment increased from 3.80 to 11.95 mg L−1 day−1. The sulfate removal rate of the rice straw treatment decreased from 13.93 to 9.91 mg L−1 day−1 when temperature decreased from 25 to 5°C while the removal rate of woodchips treatment decreased from 7.43 to 4.98 mg L−1 day−1. Differences in soluble organic carbon release between rice straw and woodchips led to the differences in bioremediation efficiency. Concentrations of Cu2+ maintained at low level in the column effluent during the whole bioremediation period. Cu2+ was removed by forming sulfide precipitates. Microbial community analysis showed that sulfate reducing bacteria in the bioremediation layer together with microorganisms capable of degrading rice straw caused the bioremediation of AMD. These findings have significant environmental implications in terms of in situ bioremediation of AMD using straw as sole substrate.  相似文献   

10.
Mine-drainage water from coal mines of Kerman region,Iran   总被引：1，自引：0，他引：1  
Two types of mine-drainage water were recognized in Kerman coalfield, namely neutral to alkaline and acid (AMD). Both types contain a high level of trace-metal concentrations with a higher level in AMD. Trace metals from the coal-mine waters of Kerman coalfield are mainly present as adsorption on Fe and Mn oxide and hydroxide particles, and to a lesser extent as sulfate, simple metal ions and as metal sorption on clay particles and hydrous aluminum oxides.  相似文献   

11.
煤矿酸性水水化学特征及其环境地球化学信息研究   总被引：19，自引：0，他引：19  
以水化学数据为依据,应用相关分析,结合地质、水文勘探资料,对煤矿酸性矿排水 (AMD)的水化学特点及其成因进行了研究。煤矿AMD在一定的物质条件和环境条件下形成,只要条件适宜,不管是高硫煤还是低硫煤均可产生酸性水;低pH、高Eh、高TDS及高硬度是煤矿AMD的重要特征,水中的SO32-与其EC之间以及Fe3+/Fe2+比值与其Eh值走势具有良好的一致性,水中微量元素及重金属来源较复杂,如Ni、Cu、Co、Zn等来源于黄铁矿的氧化溶解,但Pb、Sr等主要来自AMD对煤系地层中煤及岩石中矿物的淋滤作用。   相似文献   

12.
自2002年9月14日至2004年9月28日，在天山乌鲁木齐河源1号冰川积累区雪坑中连续观测取样，频率为1次/周。对表层雪样品和粒雪坑样品的pH值和电导率进行了分析。结果表明，表层雪的pH值和电导率具有明显的季节变化趋势，与本区域的主导山谷风风向NE和ENE密切相关。在春季，由于尘暴发生频率的增加，表层雪的pH值呈现较强碱性，电导率达到最大值；在冬季，由于原生气溶胶向次生气溶胶的转化，pH值呈现较弱碱性，电导率达到最小值。在后沉积过程中（2003年10月4日至2004年9月8日），雪坑中不同时期的pH值和电导率呈现不同的季节变化特征和淋溶过程。电导率的峰值P1进入粒雪冰的时间比与它相对应的大粒径（直径>10 μm）微粒的浓度峰值提前40天左右；在有的雪坑中，pH值和电导率的峰值出现在污化层附近，与污化层的位置有较好的一致性，说明污化层对可溶性离子的淋溶作用可能有一定的影响。相关分析表明，Ca2+是影响表层雪中pH值和电导率变化的最主要离子。  相似文献   

13.
The purpose of this work is to characterize the hydrochemical behavior of acid mine drainages (AMD) and superficial waters from the Adoria mine area (Northern Portugal). Samples of superficial and mine drainage water were collected for one year, bi-monthly, with pH, temperature, Eh, conductivity and HCO3 determined in situ with chemical analyses of SO4, Ca, K, Mg, Na, Cl, Ag, As, Bi, Co, Cu, Fe, Mn, Ni, Pb, Zn and Cd. In the mine, there are acidic waters, with low pH and significant concentrations of SO4, and metals (Fe, Mn, Zn, Cu, Pb, Cd and Ni), while in the superficial natural stream waters outside the mine, the pH is close to neutral, with low conductivity and lower metal concentrations. The stream waters inside the mine influence are intermediate in composition between AMD and natural stream waters outside the mine influence. Principal Component Analysis (PCA) shows a clear separation between AMD galleries and AMD tailings, with tailings having a greater level of contamination.  相似文献   

14.
The chemical characteristics, formation and natural attenuation of pollutants in the coal acid mine drainage (AMD) at Xingren coalfield, Southwest China, are discussed in this paper based on the results of a geochemical investigation as well as geological and hydrogeological background information. The chemical composition of the AMD is controlled by the dissolution of sulfide minerals in the coal seam, the initial composition of the groundwater and the water–rock interaction. The AMD is characterized by high sulfate concentrations, high levels of dissolved metals (Fe, Al, Mn, etc.) and low pH values. Ca2+ and SO4 2− are the dominant cation and anion in the AMD, respectively, while Ca2+ and HCO3 − are present at significant levels in background water and surface water after the drainage leaves the mine site. The pH and alkalinity increase asymptotically with the distance along the flow path, while concentrations of sulfate, ferrous iron, aluminum and manganese are typically controlled by the deposition of secondary minerals. Low concentrations of As and other pollutants in the surface waters of the Xingren coalfield could be due to relatively low quantities being released from coal seams, to adsorption and coprecipitation on secondary minerals in stream sediments, and to dilution by unpolluted surface recharge. Although As is not the most serious water quality problem in the Xingren region at present, it is still a potential environmental problem. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

15.
Spent mushroom compost (SMC) is widely used as reactor matrix in passive bioreactor involving sulfate reducing bacteria (SRB) for acid mine drainage (AMD) treatment. Follow-up our previous report, recent work has been established the extent of activity, sustained organic carbon availability, and the biochemical events of successive alkalinity producing system-based chemo-bioreactor for continuous performance using SMC. Removal of iron and sulfate from influent was over 77 and 90%, respectively, for first 13 weeks, while sulfate removal efficiency suddenly dropped down to 31% thereafter. Ahead of 13th week, process failure was beginning to be noticed when available dissolved organic carbon (DOC) value dropped down to 50 mg/L. SRB population was mostly affected with DOC drought at this stage. Sulfur was one of the major elements found with other tested metals in blackish green effluent precipitate. Sulfide compounds of the tested metals were formed on both exhausted chemo-bioreactor bed and precipitate. FTIR analysis indicated that SMC was responsible for metal binding and available nutrients supply. The present study revealed the feasibility of SMC as a host for treating AMD by this chemo-bioreactor that will assist in designing the continuous treatment practice.  相似文献   

16.
Spent mushroom compost (SMC) is commonly used as a carbon source for passive treatment systems in South Korea; however, it has some drawbacks, such as sulfate release from itself. Consequently, investigations to identify effective substitutes for SMC are necessary. In this study, batch experiments were conducted for 27 days to evaluate the efficiency of rice wine waste (RWW) for reducing sulfate and removing dissolved metals within synthetic acid mine drainage (AMD). The results showed that RWW could be more suitable than SMC, which even released sulfate in the early stage of the experiment, for sulfate reduction by sulfate-reducing bacteria. Both materials produced similar results with respect to the removal of dissolved metals, such as Fe and Al. Furthermore, a mixture of SMC and RWW showed the greatest efficiency in sulfate removal. Overall, both RWW and the mixed carbon source showed comparable performance to SMC, which indicated that RWW had a great potential for use as a carbon source for AMD treatment.  相似文献   

17.
Under stagnant conditions, the ability of 15 earth materials (non-lime) including various inorganic 2:1 and 1:1 layer silicates, an amorphous oxide, and two 'whole' soils were tested for their pH-buffering efficiency in an acid mine drainage (AMD) water. The purpose was to decrease AMD acidity to a level where sulfate-reducing bacteria (SRB) placed in it may be activated. Of all materials, a whole soil (a high cation-exchange capacity clayey mollisol containing 40% clay, and 4% soil organic matter) caused the greatest pH increases from 2.5 up to 5.5 units after 10 days in the AMD water. Influent AMD was then ameliorated at various speeds through an SRB driven bioreactor using a 50/50 weight over weight (w/w) combination of the mollisol and ryegrass (MR) as the pH buffer substrate. This substrate combination decreased the SRB acclimatisation period (from 50 days in a previous experiment utilising sludge + ryegrass) to <10 days in the present experiment. After causing pH increases from 2.8 to >6 units in 5 days, the buffer reduced the hydraulic retention time (HRT) of the constant-flow reactor from 12 days at flow speeds of 100 ml/day to 2 days at 25 ml/day, respectively. After 10 days, soluble Fe, Al and sulfate were all decreased >1,800-, >40- and 3-fold, respectively. This was a more efficient performance than the no-flow bioreactor of a previous experiment using sludge + ryegrass. This method of AMD rehabilitation is an alternative for localities that lack cheap sources of calcium compounds for chemical treatment, but have a similar soil type and copious quantities of fresh decomposable plant wastes.  相似文献   

18.
玉龙雪山浅冰芯pH值对冰川作用区降水量变化的响应   总被引：7，自引：0，他引：7  
玉龙雪山10.10 m浅冰芯的pH和电导率(EC)变化分析以及与Ca2 、 Mg2 、 K 和Na 浓度的对比表明, 玉龙雪山主要受局地碱性陆源物质的控制.与丽江气象台站的降雨量资料比较发现, 在海洋性冰川区浅冰芯pH和电导率的变化与降雨量和周围地表可溶性离子的输入量关系密切, 并与降雨量呈显著的负相关关系.结合玉龙雪山主要由局地来源补给的特征, 引入TSP(总悬浮颗粒物)作为局地可溶盐补给能力的代用指标分析玉龙浅冰芯pH值对降水量年际变化的响应.在相对湿润年, pH值较低, 若TSP值较高, 则pH值相对较高, TSP值较低, 则pH值较低.在相对干旱年, pH值较高, 若TSP值较高, pH值较高, 若TSP值较低, 则pH值相对较低;在海洋性冰川区, 浅冰芯pH和电导率的变化, 并结合TSP能够有效的反映出冰川作用区干湿的年际变化, 是大气环境状况的敏感指示器.  相似文献   

19.
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.  相似文献   

20.
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.  相似文献   

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