Acid Mine Drainage Sources Research Articles

Influence of Natural Sources on Mercury in Water, Sediment and Aquatic Biota in Seven Tributary Streams of the East Fork of the Upper Carson River, California

The East Fork of the Upper Carson River (EFUCR) drainagebasin contains the Leviathan mine site, a known source of acidmine drainage, and numerous small prospects and mineralizedareas, some of which are enriched in mercury. In 1999 aninvestigation was undertaken to characterize total mercuryconcentrations in water, sediment, and whole aquaticmacroinvertebrates from seven tributaries of the EFUCR watershedon a seasonal time step. In the fall, methyl mercury in water,sediment and Stoneflys was determined for three sites. Both total and dissolved mercury in water at all sites, notimpacted by acid mine drainage, exhibited a seasonal trend withthe lowest concentrations occurring in the winter, higherconcentrations in the summer, and the highest concentrationsrecorded in the fall. Winter samples were taken during a periodof ice melt. It is hypothesized that the high fall concentrations were due to elevated mercury concentrations ingroundwater, which was recharging the stream under baseflow conditions and had interacted with substrate naturally enrichedin mercury. Mercury concentrations in Leviathan Creek wereelevated when acid mine drainage was being discharged directlyinto the Creek. Mercury concentrations in individual stoneflyscollected from specific stream reaches were similar, and methylmercury and total mercury concentrations in macroinvertebratetissue were roughly equivalent. Comparison of mercury bodyburden of macroinvertebrates between tributaries showed thatmacroinvertebrates in the Cottonwood Creek watershed had highermercury concentrations relative to the other sites. Thistributary had higher sediment mercury concentrations than allsimilar tributaries not impacted by acid mine drainage.

Use of flue gas desulfurization by-product for mine sealing and abatement of acid mine drainage

Broken Aro mine is an abandoned underground mine complex last mined in 1910. Acid mine drainage (AMD) from the mine has negatively impacted the water quality in Simmons Run. Re-mining of Broken Aro allowed for recovery of an energy reserve, exposure of the AMD source, de-watering of the mine complex, and simple placement of a continuous mine seal. The fixated FGD scrubber by-product was chosen as the material for mine seal construction due to its low hydraulic conductivity and high alkalinity. The final seal was approximately 2600 ft long, 15 ft wide and was installed in two 4–6 ft compacted lifts for a total height of 8–12 ft. The seal was constructed concurrent with mining activities to maintain a continuous hydraulic barrier. The seal has retained water inside the mine complex and has decreased the contaminant loads to Simmons Run.

Chemical and physical controls on waters discharged from abandoned underground coal mines

Abandoned up-dip drift mines in high-sulphur coal are a major source of acid mine drainage (AMD) in Appalachia. Studies of mines in the Monday Creek watershed of southeastern Ohio show that mines are recharged by surface runoff into subsidence features that dilate the natural stress-relief fracture system. The direct connection between the ground surface and the mines leads to a rapid response in the hydrograph, with a one- to four-day lag between precipitation and corresponding peak mine discharge. Subsidence occurs in topographic depressions where overburden is presumably relatively thin. Subsidence features drain 20–36% of the surface area. Unsaturated storage appears to be volumetrically insignificant, so that far more recharge occurs than the 5% often assumed for this region. Mine storage can change rapidly due to subsidence recharge. Hydrologically, mines with subsidence features behave like karst systems, with meteoric ‘quickflow’ representing more than 50% of the total flow. Mine discharge concentrations are relatively uniform through time, suggesting either equilibrium controls on chemistry or drainage of a well-mixed pool, or both. Evidence of dilution by high flows is slight. The first high flows after a baseflow period show only a slight increase in concentrations, attributed to flushing of stored reaction products. Loadings (concentrations x flow) depend on volumetric discharge and as a consequence are highly variable. The Eh/pH environment in up-dip drift mines indicates that mine waters are in contact with the atmosphere at least part of the time, unlike a true groundwater. Iron buffering partly controls pH, which clusters around values of 3.6–5.0.

Effects of acid mine drainage from an abandoned copper mine, Britannia Mines, Howe Sound, British Columbia, Canada, on transplanted blue mussels ( Mytilus edulis)

Juvenile mussels ( Mytilus edulis) were transplanted to Howe Sound, British Columbia, Canada, along an apparent pollution gradient of acid mine drainage (AMD) from an abandoned copper (Cu) mine. Cages containing 75 mussels each were placed at a total of 15 stations and were exposed to concentrations of dissolved Cu in surface waters ranging from 5 to 1009 μg/l for a period of 41 days. Mussels located at stations closer to the source of AMD at the mouth of Britannia Creek bioaccumulated higher concentrations of Cu and zinc (Zn) in their tissues. Mussel growth was adversely affected by Cu tissue concentrations above 20 μg/g dry wt., while declines in survival and condition index occurred in mussels that bioaccumulated greater than 40 μg/g dry wt. Cu. Tissue Zn concentrations (117–192 μg/g dry wt.) were likely not high enough to have a direct impact on mussel health. Reduced survival of transplanted mussels was supported by an absence of natural mussels in contaminated areas. Phytoplankton was also severely reduced in areas contaminated by mine waters. Based on the weight of evidence, AMD from the Britannia mine had a deleterious impact on mussel survival in a zone extending at least 2.1 km to the north and 1.7 km to the south of Britannia Creek on the east shore of Howe Sound.

Metal exposure in a benthic macroinvertebrate, Hydropsyche californica, related to mine drainage in the Sacramento River

A biomonitoring technique was employed to complement studies of metal transport in the upper Sacramento River affected by acid mine drainage. Metals (Al, Cd, Cu, Fe, Hg, Pb, and Zn) were determined in a resident invertebrate, Hydropsyche californica (Insecta: Trichoptera), and streambed sediments (<62 µm) to assess metal contamination within a 111-km section of the river downstream of the mining area. Metals in H. californica also were interpreted to be broadly indicative of metal exposure in fish. Total Hg was determined in the whole body of the insect, whereas Al, Cd, Cu, Fe, Pb, and Zn were additionally separated into operationally defined cytosolic (used as an indicator of exposure to bioavailable metal) and particulate fractions. Total concentrations of Cd, Cu, Hg, Pb, and Zn in sediments were consistent with documented upstream sources of acid mine drainage. Metal distribution patterns in H. californica and sediments were generally consistent for Cd, Cu, and Pb but inconsistent for Hg and Zn. Concentrations in H. californica indicated that bioavailable Cd, Cu, Pb, and Zn was transported at least 120 km downstream of the mine sources. Zinc in H. californica was elevated, but unlike sediments, did not decrease downstream. Mercury in H. californica was not elevated.

Hydrochemical characterization of acute acid mine drainage at Iron Duke mine, Mazowe, Zimbabwe

Acid mine drainage (AMD) with a minimum pH of 0.52 was recorded at Iron Duke mine near Mazowe, Zimbabwe during an investigation of the environmental geochemistry of mine waters in the Greenstone Belts of Zimbabwe. Hydrochemical data for waters emanating from the Iron Duke waste-rock pile indicate their super-saturation with respect to Fe and SO42–. Extremely high dissolved concentrations of Al, Zn, Cu, Co, Ni, V, Cr, Cd and As also prevail. Substantial losses of metals from solution occur within 400 m of the AMD source through the precipitation of crystalline sulphates, principally melanterite. Further downstream, hydrous oxide precipitation forms the dominant mechanism of metal attenuation in waters characteristically under-saturated with respect to Fe sulphates. Speciation and saturation index data generated using the equilibrium model WATEQ4F, suggest that such codes have broad utility for generic prediction of the mineralogical contraints on metal mobility in acute AMD systems. Major discrepancies between modelled and empirical hydrochemistries are, however, evident for super-saturated waters in which the kinetics of Fe precipitation are slow, and in which total ionic strengths markedly exceed their theoretical maximum.

Renovation of a failed constructed wetland treating acid mine drainage

Acid mine drainage (AMD) from abandoned underground mines significantly impairs water quality in the Jones Branch watershed in McCreary Co., Kentucky, USA. A 1022-m2 surface-flow wetland was constructed in 1989 to reduce the AMD effects, however, the system failed after six months due to insufficient utilization of the treatment area, inadequate alkalinity production and metal overloading. In an attempt to improve treatment efficiencies, a renovation project was designed incorporating two anoxic limestone drains (ALDs) and a series of anaerobic subsurface drains that promote vertical flow of mine water through a successive alkalinity producing system (SAPS) of limestone beds overlain by organic compost. Analytical results from the 19-month post-renovation period are very encouraging. Mean iron concentrations have decreased from 787 to 39 mg l–1, pH increased from 3.38 to 6.46 and acidity has been reduced from 2244 to 199 mg l–1 (CaCO3 equivalent). Mass removal rates averaged 98% for Al, 95% for Fe, 94% for acidity, 55% for sulfate and 49% for Mn during the study period. The results indicate that increased alkalinity production from limestone dissolution and longer residence time have contributed to sufficient buffering and metal retention. The combination of ALDs and SAPS technologies used in the renovation and the sequence in which they were implemented within the wetland system proved to be an adequate and very promising design for the treatment of this and other sources of high metal load AMD.

A mass balance approach to estimate the dilution and removal of the pollutants in stream water polluted by acid mine drainage

A few simple mass balance equations were developed to simultaneously estimate how much the pollutants from acid mine drainage (AMD) in stream water are diluted and removed during their migration. The application of the equations requires knowledge of the variations in the concentrations of the dissolved pollutants and the stoichiometry of the precipitation reaction of the pollutants when none of the pollutant shows a conservative behavior along the stream path. The calculation should be restricted to the pollutants showing much higher concentrations in the polluted main stream water than in the combining or diluting water of the same target area. The mass balance equations were applied to estimate the dilution factor and precipitation fractions of pollutants in Imgok Creek such as Fe, SO4 and Al from the AMD of Yeongdong mine. The results show that the estimation, especially for SO4 and Al, significantly depends on the kinds of the precipitates. When FeOHSO4 and AlOHSO4 are assumed to precipitate, the maximum removal fractions of SO4 and Al by precipitation are respectively 34% and 46% of the original input, which is much higher than the values estimated when SO4 is considered to be perfectly conservative. It indicates that the stoichiometry of precipitation reaction is very important in the interpretation of the pollutant dilution and migration and assessment of environmental impacts of AMD. The applicability of the mass balance equations may still need to be verified. However, examining the calculated dilution factor and precipitation fractions with the equations can provide invaluable information on not only the behavior but also unexpected input of the pollutants in the stream water polluted by AMD and other point sources.

Comparative testing between conventional and microencapsulation approaches in controlling pyrite oxidation

Oxidation of pyrite in mining waste or overburden is the main source of acid mine drainage (AMD) production, which causes major environmental pollution. Presently, the most common method of controlling AMD is through the mixing of alkaline substances, such as limestone, with the AMD producing materials. However, the effectiveness of this method is still questionable due to the potential for iron armoring. Pyrite microencapsulation, utilizing either phosphate or silica coatings, is a novel approach for controlling AMD that is under development in our laboratory. Although under laboratory conditions these approaches have been shown to be very effective in controlling pyrite oxidation, testing under natural conditions for possible field application is necessary. We are monitoring an outdoor leaching column experiment to evaluate the performance of both conventional and microencapsulation approaches for controlling AMD. The experiment consists of control, limestone, phosphate, and silica treatments on mine spoil and tailing samples contained in leaching columns and set up in the field. Preliminary results indicate that, after a period of nineteen months in the field, application of microencapsulation and conventional approaches significantly reduced pyrite oxidation. Among the microencapsulation approaches used with the mine spoil, the silica coatings seemed to be superior. The average leachate sample pH was 1.9 from the control, 2.1 from the limestone, 4.6 from the phosphate and 5.9 from the silica coatings. The results of these outdoor leaching experiments have shown that the application of silica coatings could offer an improved solution for the abatement of AMD. However, long-term monitoring and evaluation are still needed.

Minewater remediation at a French zinc mine: sources of acid mine drainage and contaminant flushing characteristics

Abstract Recent closure of a zinc mine in southwestern France has resulted in flooding of workings and discharge of contaminated minewater from the workings, polluting a small stream. The minewater discharge is of near neutral pH and is contaminated with high levels of zinc, cadmium, manganese, iron and sulphate. With the exception of iron, concentrations of these contaminants have fallen dramatically since the discharge arose. The main source of recharge to the mine is likely to be overlying aquifers associated with near-surface weathering. A classification is proposed to explain the hydrogeochemical sources of contaminants and the changes in discharge water quality with time. Primary sources related to active sulphide oxidation dominate the minewater chemistry in the unflooded workings, whilst secondary sources related to remobilization of secondary minerals dominate in the flooded workings. Prediction of contaminant flushing rates has been carried out on the basis of this classification. Zinc and cadmium levels are expected to reach stable medium-term levels within 2–5 years of the discharge first occurring. Potential remediation strategies include plugging of the discharging mine portal and flooding of upper workings, coupled with conventional chemical and wetland treatment.

The Problem of Acid Mine Drainage, with an Illustrative Case History

Acid mine drainage refers to the oxidation of sulphide minerals, notably pyrite, which occurs when they are exposed to air and water in a mine or are present in spoil or mineral stockpiles. The primary oxidation products of pyrite are ferric and ferrous sulphates, and sulphuric acid. Nonetheless certain conditions have to be fulfilled if acid mine drainage is to develop. If acid mine drainage is to be controlled, then its accurate prediction is necessary. As far as control is concerned, this can be brought about by preventing or inhibiting acid generation, by control of acid migration or by treatment of acid mine drainage. The case history provided deals with the problem of acid mine drainage at a tin mine in the Transvaal, South Africa. As the mine was due to close, the problem of possible ground-water pollution due to acid mine drainage had to be investigated as part of an environmental management program. Waste dumps occur around the tin mine and it was suspected that water draining from these dumps might be a source of pollution. Samples were taken from the dumps for analysis and ground-water samples were collected from boreholes, trenches and pits. Surface water samples were taken from reservoirs and streams. Soil samples were taken from trenches and a stream bed. Analysis of the surface water showed that some samples had low pH values and high concentrations of sulphate. High concentrations of sulphate were also found in ground-water samples. These high concentrations were primarily associated with acid mine drainage. The principal source of acid mine drainage proved to be the pyrite dumps. Water samples taken from the mine workings were not acidic. This was attributed to the presence of an-kerite and calcite in the host rocks which would tend to neutralize acidic waters. However, this water did contain high sulphate concentrations, high electrical conductivity and total dissolved solids. Fortunately ground-water gradients in the area around the dumps are low. This together with the compartmentalization of ground water by dykes suggests that it is unlikely that ground water will be affected beyond the mine lease area.

Field assessment of acid mine drainage contamination in surface and ground water

Both sulfate and conductivity are useful indicators of acid mine drainage (AMD) contamination. Unlike pH, they are both extremely sensitive to AMD even where large dilutions have occurred. The advantage of using sulfate to trace AMD is that unlike other ions it is not removed to any great extent by sorption or precipitation processes, being unaffected by fluctuations in pH. These two parameters are also closely associated as would be expected, as conductivity is especially sensitive to sulfate ions. Therefore, as sulfate analysis is difficult in the field, conductivity can be used to predict sulfate concentration in both AMD and contaminated surface waters using regression analysis. Most accurate predictions are achieved by using equations given for specific conductivity ranges or AMD sources. There is also potential to use conductivity to predict approximate concentrations of key metals when the pH of the water is within their respective solubility ranges.

Fluvial metal transport near sources of acid mine-drainage: Relationships of soluble, suspended and deposited metal

AbstractThe Afon Goch (Anglesey, UK) is a short (12 km source to estuary) stream highly contaminated by acid mine drainage (AMD) throughout its length, due to past-mining at the head of the stream. Metal distribution is strongly controlled by the pH, which increases downstream particularly at confluences with two unpolluted tributaries. A pH increase causes precipitation of metals, primarily Fe as hydroxide, thus altering the transport of the metal load, potentially allowing storage of metal within the river as deposited material. However, further work suggests that the controls on whether metal can behave non-conservatively, and therefore the controls on metal distribution, are more complicated than being purely pH dependent. This is because much of the Fe load, even at the low pH at the head of the stream, is not soluble Fe3+ but colloidal Fe hydroxide. Consequently, coagulation is a requisite intermediate step between precipitation and potential for settling. It is possible that in reaches of the stream away from tributary confluences, the process of coagulation is the predominant influence on metal distribution. Furthermore, because much of the metal load in the water column is very fine, its deposition results in a sediment in which the metals can be intimately associated with a biofilm at the sediment/water interface. Such associations change both deposition and erosion characteristics of the sediment and have implications for subsequent diagenesis and mineral morphology.

PYRITE MICROENCAPSULATION: POTENTIAL FOR ABATEMENT OF ACID MINE DRAINAGE1

Oxidation of pyrite in mining waste or overburden is the main source of acid mine drainage (AMD) production which causes major environmental pollution. Presently, the most common method of controlling AMD problems is through the mixing alkaline substances, such as limestone, with the AMD producing materials. However, the effectiveness of this method is still questionable. The main reason for this is that the surface of pyrite particles in mining waste are still exposed to the atmospheric O{sub 2} after treatment. Experimental evidence on novel pyrite microencapsulation technologies currently under development in our laboratory are presented. It was demonstrated that these technologies, which include ferric hydroxide-phosphate-coatings and ferric-hydroxide-silica coatings, could effectively protect pyrite from oxidation.

Supergene processes on ore deposits?a source of heavy metals

The study of supergene processes (i.e., secondary processes running in ore deposits and driven by thermodynamic nonequilibrium between ore-and rock-forming minerals and natural waters, gasses, etc.) is important in order to understand the migration of heavy metals from ore into their adjacent surroundings. The contamination of the local environment can be characterized by the composition of pore waters. The Pb-Zn-Cu ore deposits of Zlate Hory (Czech Republic) have been chosen for a detailed study of pore solutions. A simple model has been created to describe the evolution of supergene processes in the ore deposits. This model is based on the determination of chemical composition of pore solutions. The dilution of pore solutions of such mineral deposits results in acid mine drainage. Pore solutions can have, during specific stages of their evolution, relatively high concentrations of Cu (0.09 mol/kg), Zn (0.1 mol/kg), SO4 (0.8 mol/kg) and an extremely low pH (1.38). The supergene alteration of pyrite is the most important process determining the character of pore water. This reaction causes significant acidification and is a leading source of acid mine drainage. The leached zone originates from the interaction of pyrite and limonite. Increased concentrations of heavy metals and sulfates occur in pore waters. The dynamic composition of pore waters within ore deposits undergoing the supergene process can be used to distinguish: (1) three main zoneslimonite, transition, and primary zone and (2) two areas—an area with the highest intensity of weathering processes and an area of weathering initiation. In these areas the rate of sulfide oxidation is higher as a result of low pH. From the study of these zones and areas we can further our knowledge of ore body, pore solution, acid mine drainage, and contamination of the local environment.

The potential use of coal mine refuse as feedstock for gasification or combustion and concurrent elimination as a source of acid mine drainage

The mining and processing of high sulfur coals produce millions of tons of waste rock yearly; mostly shales that are both organic-rich and potentially toxic. The toxicity results from the oxidization of the iron disulfide minerals when exposed to the atmosphere with the subsequent production of acid mine drainage. These rock materials are specially handled and chemically treated in an attempt to prevent the production of acid and the resultant impact upon the quality of surface- and groundwater. Many such reclamation attempts are not successful. As a result, acid mine drainage is the single most serious environmental problem facing the high-sulfur coal industry. The burial and isolation of these materials which attempt to eliminate their toxic potential at the same time, precludes the utilization of the potential energy source represented by their organic content. Many of these materials have organic contents sufficiently high to provide the heat potential of lignite. It is proposed that these waste materials be utilized as feedstock for gasification or combustion. This would allow to take advantage of their energy potential while at the same time rendering the materials environmentally inert due to the thermal decomposition and subsequent oxidation of the iron disulfide minerals. The resultant thermally altered shales could then be used in reclamation as synthetic minesoils. The data presented here evaluate the properties of these materials as conversion feedstock.

Distribution of reduced inorganic sulfur compounds in lake sediments receiving acid mine drainage

The sediments of Lake Anna, Virginia, act as a major sink for incoming acid mine drainage (AMD) pollutants (Fe, SO 4 2−, H +) due to bacterial sulfate reduction (SR). Acid-volatile sulfide (AVS), elemental S, and pyrite concentrations in the sediments of the polluted arm of the lake are significantly greater than those in unpolluted sections of the lake. Measurements of SR using 35S SO 4 2− showed that AVS and S 0 are the major short-term (48 h) products of SR in these sediments. Inorganic forms of S(AVS, S 0, and FeS 2) made up from 60 to 100% of the total sediment S concentration. Pyrite concentrations in the sediment were high but decreased exponentially with distance from the AMD source, suggesting that the pyrite was deposited as stream detritus from the abandoned mines. Iron monosulfide and elemental S concentrations were highest at a station 1 km away from the AMD inflow, indicating formation in situ. There was no evidence for the formation of organic S species. The results suggest that in Fe- and S-rich locations such as those contaminated with acid mine drainage, the distribution of end products of SR may vary substantially from those reported for more moderate environments.

Leaf Litter Decomposition in a Reservoir Affected by Acid Mine Drainage

The effects of acid mine drainage on the decomposition of vascular plant material in a reservoir were compared at three sites: (1) a control site with no acid mine drainage (average pH = 6.3), (2) an experimental site with dilute acid mine drainage (average pH = 5.7) and (3) an experimental site near the acid mine drainage source (average pH = 3.7). The decomposition rate (loss of ash free dry weight from litter bags) of leaves from three types of trees and a rush differed significantly between leaf species and between sites. For all leaf species, the decay rate coefficients (k) for the control site were at least twice those for the most severely affected experimental site. Heterotrophic activity, measured with 14C glucose, was depressed at both experimental sites as compared to the control site. Numbers of bacteria were about 1010 cells per gram dry detritus, and did not differ significantly between control and experimental sites. It was concluded that: (1) both microbial activity and the process of leaf decomposition were inhibited in a region close to the source of contamination although (2) the degree of inhibition decreased as the acid mine drainage was diluted within the reservoir.

Changes in water and sediment bacterial community structure in a lake receiving acid mine drainage

Water and sediment bacterial communities in a freshwater impoundment were studied over a 13-month period for stress-related responses to a point source of acid mine drainage (AMD). Comparisons of community structure were made on collections taken at the mouth of the acid stream, at a point 2 km downstream, and at the mouth of an uncontaminated stream. Monthly measurements of pH and specific conductance indicated the expected decrease in the AMD pollution with increasing distance from the source. Acridine orange direct counts did not differ significantly among the sites; however significantly fewer viable heterotrophs were observed by plate counts at the acid impacted station relative to the uncontaminated site. The diversity of the communities was significantly lower at the sites receiving mine drainage as compared with the unaffected station, and comparisons of community similarity showed that collections from the impacted sites were more like each other than like the control site. The assemblage at the latter site contained many bacterial guilds not found at the contaminated sites. The guilds unique to the control site showed a reduced in vitro ability to tolerate heavy metals as compared with the general community.

Evaluation of acid production potential of mining waste materials

The formation of acidic effluents from mining waste materials is discussed and the chemisry involved explained. The bacteriumThiobacillus ferrooxidans plays an important role in acid production due to its ability to rapidly oxidize reduced forms of iron and sulphur which can result in the generation of H2SO4. The sulphide mineral pyrite (FeS2), often present in waste materials, is generally recognized as the chief source of acid mine drainage.