Chemical characteristics and acid drainage assessment of mine tailings from Akara Gold mine in Thailand

Acid Mine Drainage (AMD) is a great concern in many abandoned mines because of its adverse effect on the environment. In mining processes, many kinds of wastes are produced. These wastes may become eventually sources of environmental degradation. The focus of this study is the geochemical characterization of the end-processed tailings generated by Akara Gold Mine, the biggest gold mine in Thailand. Tailing samples were systematically collected for analyses of chemical and mineralogical compositions. As a result, their quantitative chemical analyses are slightly different from place to place, but mineral components cannot be clearly differentiated. For instance, it may be assumed that the end-processed tailings, which were a mixture between high and low grade concentrates, would have similar mineral components. However, the little variation of chemical composition may be caused by the ore refining processes that are somehow varied in proportion to chemical additives, alkali cyanide and quick lime in particular. In addition, clay composition in ore-bearing layers may also influence alumina content of tailings, accordingly. Distribution of the tailings is not related to depth and distance of the tailing storage pond because the disposal has sped them over the pond during operation. Total heavy metals of the tailing samples were analyzed on the basis of the EPA 3052 method. Consequently, the most toxic elements (e.g., Co, Cu, Cd, Cr, Pb, Ni and Zn) were found falling within the standard of Thailand Soil Quality Standards for Habitat and Agriculture. Only Mn appears to have higher content than the standard. In addition, leaching tests proved that these tailings contain low metal concentrations. As a result, at pH 2, Mn can leach out exceeding the Thailand Surface Water Quality Standard for Agricultural (Mn <1 ppm) and the Thailand Industrial Effluent Standard (<5 ppm). Although leachate at pH 4 and neutral conditions contains lower Mn than the Industrial Effluent Standard it still exceeds the surface water quality standard. Interestingly, Pb can be leached out exceeding both standards (0.2 ppm for the industrial effluent standard and 0.05 ppm for the surface water quality standard). For Ni leaching, its concentration is lower than the Industrial Effluent Standard at all pH conditions but still exceeds the Surface Water Standard at pH 2 and 4. This information should be taken into consideration for further environmental monitoring. Acid generating potential of the tailings was estimated using acid–base accounting (ABA) and net acid generation (NAG) tests. The results of ABA and NAG tests show that the tailing samples contain a high amount of sulfur. However, they also contain high acid neutralization capacity. Consequently, these tailings may not have potential to generate acid drainage; in the other words, they can be classified as a non-acid forming (NAF) material. However, since these tailings contain some heavy metals (e.g., Ni, Mn and Pb) that are observed in leachates exceeding the standards at low pH, the AMD conditions may lead to heavy metal release. Therefore, prevention of oxidizing process and dissolution should be considered with great care. In addition, Mn and Pb can also be leached at neutral conditions. Barrier of air and water, clay layer for example, should be placed over the tailings pound before covering by topsoil for re-vegetation. Growing native grass is recommended for stabilization of the surface and reducing erosion rate. Monitoring of water quality should also be carried out annually.     

Geochemical and mineralogical aspects of sulfide mine tailings

Tailings generated during processing of sulfide ores represent a substantial risk to water resources. The oxidation of sulfide minerals within tailings deposits can generate low-quality water containing elevated concentrations of SO₄, Fe, and associated metal(loid)s. Acid generated during the oxidation of pyrite [FeS₂], pyrrhotite [Fe_(1−x)S] and other sulfide minerals is neutralized to varying degrees by the dissolution of carbonate, (oxy)hydroxide, and silicate minerals. The extent of acid neutralization and, therefore, pore-water pH is a principal control on the mobility of sulfide-oxidation products within tailings deposits. Metals including Fe(III), Cu, Zn, and Ni often occur at high concentrations and exhibit greater mobility at low pH characteristic of acid mine drainage (AMD). In contrast, (hydr)oxyanion-forming elements including As, Sb, Se, and Mo commonly exhibit greater mobility at circumneutral pH associated with neutral mine drainage (NMD). These differences in mobility largely result from the pH-dependence of mineral precipitation–dissolution and sorption–desorption reactions. Cemented layers of secondary (oxy)hydroxide and (hydroxy)sulfate minerals, referred to as hardpans, may promote attenuation of sulfide-mineral oxidation products within and below the oxidation zone. Hardpans may also limit oxygen ingress and pore-water migration within sulfide tailings deposits. Reduction–oxidation (redox) processes are another important control on metal(loid) mobility within sulfide tailings deposits. Reductive dissolution or transformation of secondary (oxy)hydroxide phases can enhance Fe, Mn, and As mobility within sulfide tailings. Production of H₂S via microbial sulfate reduction may promote attenuation of sulfide-oxidation products, including Fe, Zn, Ni, and Tl, via metal-sulfide precipitation. Understanding the dynamics of these interrelated geochemical and mineralogical processes is critical for anticipating and managing water quality associated with sulfide mine tailings.     

Colloid formation and metal transport through two mixing zones affected by acid mine drainage near Silverton,Colorado

Stream discharges and concentrations of dissolved and colloidal metals (Al, Ca, Cu, Fe, Mg, Mn, Pb, and Zn), SO₄, and dissolved silica were measured to identify chemical transformations and determine mass transports through two mixing zones in the Animas River that receive the inflows from Cement and Mineral Creeks. The creeks were the dominant sources of Al, Cu, Fe, and Pb, whereas the upstream Animas River supplied about half of the Zn. With the exception of Fe, which was present in dissolved and colloidal forms, the metals were dissolved in the acidic, high-SO₄ waters of Cement Creek (pH 3.8). Mixing of Cement Creek with the Animas River increased pH to near-neutral values and transformed Al and some additional Fe into colloids which also contained Cu and Pb. Aluminium and Fe colloids had already formed in the mildly acidic conditions in Mineral Creek (pH 6.6) upstream of the confluence with the Animas River. Colloidal Fe continued to form downstream of both mixing zones. The Fe- and Al-rich colloids were important for transport of Cu, Pb, and Zn, which appeared to have sorbed to them. Partitioning of Zn between dissolved and colloidal phases was dependent on pH and colloid concentration. Mass balances showed conservative transports for Ca, Mg, Mn, SO₄, and dissolved silica through the two mixing zones and small losses (<10%) of colloidal Al, Fe and Zn from the water column.     

Characterization of Kolar gold field mine tailings for cyanide and acid drainage

The gold mining process at Kolar gold field (KGF) mines has generated about 32 million tons of tailings. Gold was extracted from the mined ores using cyanidation technique that involved dissolution of gold in the ore by water soluble alkali metal cyanides (example, sodium cyanide or potassium cyanide). Of the several dumps that received the mine tailings only the Kennedy’s Line dump was active prior to closure of the KGF mines in the year 2000. The Kennedy’s Line dump received sulfide bearing tailings in slurry form that comprised of spent ore and process water bearing soluble alkali metal cyanide. Depending on the pH of the tailing slurry, the free cyanides may exist as aqueous hydrogen cyanide that can escape to the atmosphere as hydrogen cyanide gas or occur as soluble cyanide (CN⁻) ions that can be leached by infiltrating water to the sub-surface environment. Additionally, the presence of pyrite minerals in the Kennedy’s Line dump makes them susceptible to acid drainage. This study examines the potential of gold tailings of Kennedy’s Line dump to release cyanide ions (CN⁻) and acid drainage to the sub-surface environment by performing physico-chemical and leaching tests with tailing samples collected from various depths of the dump, sub-surface soil samples beneath the dump and groundwater samples from vicinity of Kennedy’s Line dump. The chemical mechanisms responsible for the ambient cyanide and pH levels of the tailing dump, sub-surface soil samples and groundwater are also inferred from the laboratory results.     

Fuzzy modelling of acid mine drainage environments using geochemical,ecological and mineralogical indicators

Fuzzy logic was applied to model acid mine drainage (AMD) and to obtain a classification index of the environmental impact in a contaminated riverine system. The data set used to develop this fuzzy model (a fuzzy classifier) concerns an abandoned mine in Northern Portugal—Valdarcas mining site. Here, distinctive drainage environments (spatial patterns) can be observed based on the AMD formed in the sulphide-rich waste-dumps. Such environments were established, as the effluent flows through the mining area, using several kinds of indicators. These are physical–chemical, ecological and mineralogical parameters, being expressed in a quantitative or qualitative basis. The fuzzy classifier proposed in this paper is a min–max fuzzy inference system, representing the spatial behaviour of those indicators, using the AMD environments as patterns. As they represent different levels (classes) of contamination, the fuzzy classifier can be used as a tool, allowing a more reasonable approach, compared with classical models, to characterize the environmental impact caused by AMD. In a general way it can be applied to other sites where sulphide-rich waste-dumps are promoting the pollution of superficial water through the generation of AMD. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Geochemical transport modelling of drainage from experimental mine tailings cells covered by capillary barriers

The use of covers with capillary barrier effects (CCBEs) for reducing acid mine drainage (AMD) from sulphidic mine tailings is simulated using the MIN3P finite volume model for coupled groundwater flow, O₂ diffusion and multi-component reactive transport. The model is applied to simulate five pilot-scale in situ test cells containing reactive tailings from the Manitou mine site, Val d’Or, Que., Canada. Four of the cells were constructed with CCBEs over the tailings, while the fifth tailings cell was left uncovered. Observed and simulated discharge from the base of each cell showed that the capillary barrier covers significantly reduced sulphide oxidation and AMD. Compared to acidic discharge from the uncovered cell, discharge from the four CCBE-covered cells had neutral pH levels and 1–7 orders of magnitude lower concentrations of SO₄, Fe, Zn, Cu and Al. The simulations showed that the moisture retaining layer of the CCBEs reduced AMD by inhibiting O₂ diffusion into the underlying reactive wastes. Provided the moisture-retention layer of the CCBE remains close to saturation, its thickness had a relatively minor effect. Under such near-saturated conditions, O₂ availability is limited by its diffusion rate through the bulk porous medium and not by the diffusion rate through the oxidized grain shells. The model is providing important new insights for comparing design alternatives for reducing or controlling AMD.     

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。     

A laboratory study of covers made of low-sulphide tailings to prevent acid mine drainage

Covers with capillary barrier effects (CCBE) are considered to be one of the most effective ways to control acid mine drainage (AMD) production from mine wastes. The use of low-sulphide tailings in CCBE has been proposed recently for cases where other types of material may be unavailable near the mining site. This paper presents leaching column test results showing that CCBEs with a moisture-retaining layer made of slightly reactive tailings, with three different sulphide contents, can effectively limit the production of AMD from the acid-generating tailings placed underneath. With these layered covers, the leachate pH was maintained near neutrality throughout the testing period. When compared to uncovered tailings, the efficiency of the cover systems for reducing the amount of contaminants in the percolated water was determined to be greater than 99% for zinc, copper and iron. This study shows that the use of low-sulphide tailings can improve the ability of a CCBE to limit gas diffusion by consuming a fraction of the migrating oxygen.     

Assessment of metal loads in watersheds affected by acid mine drainage by using tracer injection and synoptic sampling: Cement Creek,Colorado, USA

Watersheds in mineralized zones may contain many mines, each of which can contribute to acidity and the metal load of a stream. In this study the authors delineate hydrogeologic characteristics determining the transport of metals from the watershed to the stream in the watershed of Cement Creek, Colorado. Combining the injection of a chemical tracer, to determine a discharge, with synoptic sampling, to obtain chemistry of major ions and metals, spatially detailed load profiles are quantified. Using the discharge and load profiles, the authors (1) identified sampled inflow sources which emanate from undisturbed as well as previously mined areas; (2) demonstrate, based on simple hydrologic balance, that unsampled, likely dispersed subsurface, inflows are significant; and (3) estimate attenuation. For example, along the 12-km study reach, 108 kg per day of Zn were added to Cement Creek. Almost half of this load came from 10 well-defined areas that included both mined and non-mined parts of the watershed. However, the combined effect of many smaller inflows also contributed a substantial load that could limit the effectiveness of remediation. Of the total Zn load, 58.3 kg/day came from stream segments with no visible inflow, indicating the importance of contributions from dispersed subsurface inflow. The subsurface inflow mostly occurred in areas with substantial fracturing of the bedrock or in areas downstream from tributaries with large alluvial fans. Despite a pH generally less than 4.5, there was 58.4 kg/day of Zn attenuation that occurred in mixing zones downstream from inflows with high pH. Mixing zones can have local areas of pH that are high enough for sorption and precipitation reactions to have an effect. Principal component analysis classified inflows into 7 groups with distinct chemical signatures that represent water-rock interaction with different mineral-alteration suites in the watershed. The present approach provides a detailed snapshot of metal load for the watershed to support remediation decisions, and quantifies processes affecting metal transport.     

Heavy metal geochemistry of the acid mine drainage discharged from the Hejiacun uranium mine in central Hunan,China

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 Fe_Total, 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.     

Arsenic mobility in two mine tailings drainage systems and its removal from solution by natural geochemical barriers

Sulfide-mineral-bearing mill wastes are sources of high concentrations of acid, soluble metals, and As. These are serious problems for ore mining areas such as the Kemerovo and Cheljabinsk regions in Russia. This study evaluated the distribution of the mill wastes, the mobility of As from the wastes, and the potential of natural materials to attenuate As dispersion in the broader environment. Arsenic contents in wastes of the Belovo Zn-processing (Kemerovo) and the Karabash Cu-smelting plants (Cheljabinsk) are 2–3 orders of magnitude higher than the content of continental crust. Main mineral forms of As in these wastes are arsenopyrite (FeAsS) and scorodite (FeAsO₄·2H₂O). High dissolved As concentrations are found in water draining the wastes and in rivers adjacent to the mill sites. The water concentrations commonly exceed drinking water standards. High As concentrations in bottom sediments of the affected rivers extend a 100 m downstream of the waste drainage input. These sediments are also a source of river water contamination. Experiments were conducted to evaluate the ability of natural water to mobilize As from the wastes. The Belovo tailings released 86% of their contained As to the infiltrating water, whereas the less reactive Karabash tailings released only 22% of total As. The experimental leachates were used as influent to columns that tested the ability of limestone and natural clay to reduce the concentration of dissolved As and associated metals. Some dissolved As was precipitated with Fe, Pb and Sb initially in the limestone column. The decrease in dissolved As is consistent with the accumulation of As in yellow ferriferous sediments in the Belovo settling pond. In the pond and wetland sediments, As mobility is also decreased by the formation of sulfides and arsenides. Cubanite (CuFe₂S₃), klaprothite (Cu₃BiS₃)_, rammelsbergite (NiAs₂), maucherite (Ni₁₁As₈), semseyite (Cu₉Sb₈S₂₁), and skutterudite (CoAs₃) were found in the chemically reducing lower sediments of the Belovo settling pond.     

Modeling and predicting of drainage quality for sulfide mine tailings impoundments

Effluent from tailings impoundments of sulfide mine is an important environmental problem. The oxidation of sulfide minerals in tailings impoundments and consequent release of acid and contaminants, including heavy metals and arsenic, to tailings pore-water can last for decades to centuries. Pollution of water bodies including surface water and groundwater occurs when infiltration of precipitation is unhindered, bottom liners are absent and no drainage collection is installed. So there is a great need to develop reliable modeling techniques for characterizing geochemical interactions taking place within the tailings and predicting potential future environmental hazard which favor further prevention and remediation of the acidic mine drainage （AMD）. In this paper, a comprehensive dynamic model for tailings-water interaction was established on the basis of considering the coupling and feedback among many factors and processes such as sulfide oxidation, gangue dissolution, oxygen diffusion, water flow and mass transport,     

Chemical availability of arsenic and heavy metals in sediments from abandoned cinnabar mine tailings

The understanding of the solid-phase speciation of arsenic in soils and sediments is important in the evaluations of its potential mobility and availability in the environment. The spoil heaps of abandoned mercury mines contain waste materials with high arsenic and heavy metals concentrations. The weathering of these tailings can cause their mobilization to the surroundings. In this work, the mobility and availability of arsenic and some heavy metals were evaluated in sediments from two heavily polluted mercury mining districts in Asturias (NW Spain). For this purpose, a slightly modified version of the Bureau Community of Reference sequential extraction scheme was applied to sediments. The total contents in the operationally defined fractions were analysed by inductively coupled plasma-atomic emission spectrometry. Extremely high total arsenic concentrations were found in all sediments ranging from 4,000 to 24,800 mg kg^?1. High easily mobilizable arsenic contents were found in the first mining area, related to the solubilization of Ca-bearing phases, supported by extracts analyses, X-ray diffraction results and the positive correlation found among the As and Ca fractionations. Ni and Zn were the most mobile among heavy metals, being Cr the least mobile, suggesting an anthropogenic origin due to the metallurgical processes, transport or dispersion generated from neighbour spoil heaps. In the second mining area, the bulk of As was concentrated in the residual phase, as well as Cr, Cu, Fe, Pb, Ti, indicating a mineralogical origin and the low availability of these elements. The strong correlations established between As and Fe and Ti distributions support the hypothesis that As is mainly associated to structural mineral phases in these sediments.     

Distribution and behavior of heavy metals in a river polluted by acid mine drainage in the Dabaoshan mine area, China

Acid mine drainage （AMD） has been recognized as a major environmental pollution problem over past decades. This pollutant effluent is complex and is characterized by elevated concentrations of iron and sulfate, low pH, and high concentrations of a wide variety of metals depending on the host rock geology. Massive inadvertent discharges from acid mines have given rise to dramatic cases of ecological damage. These events indicate an improved understanding of the mechanism controlling metal transport to the river is important, since the aquatic ecology will be affected, to some degree, dependent on the phase （dissolved or particulate） in which the metal is transported. In this study, polluted water samples were collected along the Hengshi River near the Dabaoshan mine, Guangdong, China, in April 2005. The concentrations of dissolved Cu, Zn, Cd and Pb have been determined using ICP-MS and the chemical speciation of those metals in suspended particles was examined using BCR methods and SEM/EDX mineralogical analysis. Combining these two sets of data, the intention was to develop geochemical concepts, which explain the behavior of Cu, Zn, Cd and Pb in particle-water interactions of heavy metals in AMD. The results show that the dissolved heavy metals exhibited non-conservative behavior in the Hengshi River. The dissolved and particulate Cu, Zn, Cd and Pb have the similar spatial distribution, which decreased gradually along the river except in the lower reaches because of the absorption-desorption between dissolved and particulate phases. Although the metal concentrations in both phases were elevated, dissolved metals were dominant and had the maximum concentrations in the low pH region.     

粤北大宝山矿酸性排水中铅元素环境地球化学

粤北大宝山铁多金属矿床的开发给环境带来了严重的危害。采选冶产生的酸性排水及固体废弃物堆积的淋滤酸水,携带浸滤出的大量重金属离子流入下游河道,严重影响矿区及酸水流域的生态环境。结果表明,河流水中高Pb含量直接源于尾砂,并受水体pH值的显著影响。河流底泥能够大量聚集水体中的Pb,在水体pH值降低时,相对稳定存在的Pb会被再次从河流底泥中释放出来,形成河流二次污染。土壤中Pb含量受土壤pH值和土壤粒度的影响,食用蔬菜中Pb的高含量由土壤Pb高含量决定,并受土壤pH值的影响,通过改善农业灌溉水质,提高土壤pH值,可以降低蔬菜重金属Pb含量。     

The physical, chemical and mineralogical properties of three cemented layers within sulfide-bearing mine tailings

The oxidation and subsequent dissolution of sulfide minerals within mine tailings impoundments releases H⁺, Fe(II), SO₄ and trace elements to the tailings pore water. Subsequent pH-buffering and hydrolysis reactions result in the precipitation of secondary phases such as gypsum, goethite and jarosite. In areas of intense precipitation, cemented layers or “hardpans” often form within the shallow tailings. Three cemented layers within pyrrhotite-bearing mine tailings at the Fault Lake, Nickel Rim and East Mine impoundments located near Sudbury, Canada, were examined. The location of the three cemented layers within the tailings stratigraphy varies as does their location relative to the water table. The morphology, mineralogy and chemical composition of the cemented layers also vary between sites. The bulk density within the three cemented layers all showed an increase relative to the surrounding uncemented tailings ranging from 9% to 29%. The porosity of each cemented layer decreased relative to the surrounding uncemented tailings ranging from an 8% to 18% decrease. The cemented layers also showed relative enrichment of total sulfur, carbon and trace elements relative to the surrounding uncemented tailings. Arsenic concentrations showed an enrichment in the cemented layers of up to 132%, Cd up to 99%, Co up to 84%, Cu up to 144%, Ni up to 693% and Zn up to 145% relative to the surrounding uncemented tailings. All the cemented layers studied show an evolution of the secondary phases with time from a gypsum–jarosite-based cement to a goethite-rich cement. The formation of these layers could potentially have a significant effect on the environmental impacts of sulfide-bearing mine waste.     

Removal of metal from acid mine drainage (AMD) by using natural zeolite of Nizarneshwar Hills of Western India

The mining industry faces stringent effluent discharge regulations and has acknowledged that it is necessary to look into innovative technologies to recycle considerable amount of effluent rather than discharging into surface water. Effluents from mines give rise to aesthetic unpleasantness. The focus of the investigations was to cope with more stringent effluent discharge regulations and to protect the ecosystem from harmful pollutants in the mine effluents. Copper is one of the heavy metal in the mine systems, which are known to be a harmful element. The present study has been undertaken to investigate a process that might remove Cu(II) from mine waste water by using natural zeolite, such as stilbite, and compared with synthetic resins like CSA-9 and CSA-609D. In this study, natural zeolite was used as a low-cost adsorbent to evaluate its ability to remove heavy metals from acid mine drainage. The zeolite used in this study is the natural clay mineral from the Nizarneshwar Hills of Western India. Three resins tested are CSA-9, natural zeolite–stilbite, and CSA-609D. Batch testing has been conducted to select effective ion-exchange resins for copper removal and to determine effective regenerants for regeneration of exhausted resins. All tests were conducted at bench scale and in batch mode. Three strong acid cation exchangers were evaluated to compare their metal removal capacities. The metal concentration in the effluent was reduced with all resins tested. It was found that, among all the three types of natural zeolite, stilbite shows the highest removal efficiency of copper in every parameter that is considered for evaluating the performance of resins.     

Comparison of color, chemical and mineralogical compositions of mine drainage sediments to pigment

 Forty-three untreated and actively and passively (wetland) treated coal mine drainage sediments and five yellow-red pigments were characterized using X-ray fluorescence, fusion-inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, and tristimulus colorimeter. Primary crystalline iron-bearing phases were goethite and lepidocrocite, and iron phases converted to hematite upon heating. Quartz was nearly ubiquitous except for synthetic pigments. Gypsum, bassinite, calcite, and ettringite were found in active treatment sediments. Iron concentrations from highest to lowest were synthetic pigment>wetland sediment>natural pigment>active treatment (untreated sediments varied more widely), and manganese was highest in actively treated sediments. Loss on ignition was highest for passively treated sediments. No clear trends were observed between quantified color parameters (L*, a*, b*, and Redness Index) and chemical compositions. Because sediments from passive treatment are similar in chemistry, mineralogy, and color to natural pigments, the mine drainage sediments may be an untapped resource for pigment. Received: 29 December 1997 · Accepted: 11 May 1998     

Heavy metal partitioning in river sediments severely polluted by acid mine drainage in the Iberian Pyrite Belt

This study provides a geochemical partitioning pattern of Fe, Mn and potentially toxic trace elements (As, Cd, Cr, Cu, Ni, Pb, Zn) in sediments historically contaminated with acid mine drainage, as determined by using a 4-step sequential extraction scheme. At the upperstream, the sediments occur as ochreous precipitates consisting of amorphous or poorly crystalline oxy-hydroxides of Fe, and locally jarosite, whereas the estuarine sediments are composed mainly of detrital quartz, illite, kaolinite, feldspars, carbonates and heavy minerals, with minor authigenic phases (gypsum, vivianite, halite, pyrite). The sediments are severely contaminated with As, Cd, Cu, Pb and Zn, especially in the vicinity of the mining pollution sources and some sites of the estuary, where the metal concentrations are several orders of magnitude above background levels. Although a significant proportion of Zn, Cd and Cu is present in a readily soluble form, the majority of heavy metals are bonded to reducible phases, suggesting that Fe oxy-hydroxides have a dominant role in the metal accumulation. In the estuary, the sediments are potentially less reactive than in the riverine environment, because relevant concentrations of heavy metals are immobilised in the crystalline structure of minerals.     

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