Geochemical characteristics of acid mine drainage and sediments from coal mines, Shanxi Province, China

In this study, geochemical characteristics of acid mine drainage （AMD） and its sediments from the Malan and Sitai coalmines, Shanxi Province, China, were investigated. Many analytical approaches such as IC, ICP-MS, XRD, XRF, and modeling calculation of hydrogeochemistry using PHREEQCI software were employed. The AMD is characterized by higher concentrations of iron and sulfate, a low pH, and elevated concentrations of a wide variety of heavy metals. The results of modeling calculation by PHREEQCI software demonstrate the metals in AMD are present mainly as Me^n＋ and MeSO4^n-2 species. The sediments of AMD are composed mainly of iron-beating minerals such as goethite and schwertmannite, which are controlled by pH, Fe and SO4^2- concentrations. The schwertmannite mineral has been found for the first time in China.     

Spatial variability of arsenic in some iron-rich deposits generated by acid mine drainage

Potential contamination of rivers by trace elements can be controlled, among others, by the precipitation of oxyhydroxides. The streambed of the studied area, located in “La Châtaigneraie” district (Lot River Basin, France), is characterised by iron-rich ochreous deposits, acidic pH (2.7–4.8) and SO₄–Mg waters. Beyond the acid mine drainage, the presence of As both in the dissolved fraction and in the deposits is also a problem. Upstream, at the gallery outlet, As concentrations are high (As_max = 2.6 μmol/l and up to 5 wt% locally, respectively, in the dissolved and in the solid fractions). Downstream, As concentrations decrease below 0.1 μmol/l in the dissolved fraction and to 1327 mg/kg in the solid fraction. This natural attenuation is related to the As retention within ochreous precipitates (amorphous to poorly crystalline Fe oxyhydroxides, schwertmannite and goethite), which have great affinities for this metalloid. Upstream, schwertmannite is dominant while downstream, goethite becomes the main mineral. The transformation of schwertmannite into goethite is observed in the upstream deposits as schwertmannite is unstable relative to goethite. Furthermore, thermodynamic calculations indicate that the downstream goethite is not able to precipitate in situ according to the water chemistry. Goethite mainly results from the transformation of schwertmannite and its solid transport downstream.Moreover, as highlighted by leaching experiments carried out on the ochreous precipitates, this transformation does not seem to affect the As-retention in solids as no release of As was observed in the solution. Arsenic may either be strongly trapped by co-precipitation in the present minerals or it may be quickly released and re-adsorbed on the precipitate surface.     

Sampling riverine sediments impacted by acid mine drainage: problems and solutions

 Sampling acid mine drainage (AMD) or natural acid rock drainage (ARD)-impacted sediments is complex, requiring appropriate field sampling techniques to ensure representative samples that are both repeatable and reproducible. The important factors affecting sampling of riverine sediments are examined. These include sample site location, field observations, representative sampling, sample collection techniques, and sample preservation. A recommended sampling and processing protocol is presented for AMD- and ARD-impacted riverine sediments, which includes sediment sampling, Fe hydroxide floc sampling, chemical analysis, interstitial (pore) water collection, sediment elutriates, sediment fractionation, and physical analysis. The importance of bioassay testing is discussed, as is quality assurance and assessment approaches to define sediment quality criteria. Received: 18 September 1995 · Accepted: 23 October 1995     

Speciation of arsenic in sulfidic waters

Formation constants for thioarsenite species have been determined in dilute solutions at 25°C, ΣH₂S from 10^-7.5 to 10^-3.0 M, ΣAs from 10^-5.6 to 10^-4.8 M, and pH 7 and 10. The principal inorganic arsenic species in anoxic aquatic systems are arsenite, As(OH)₃ ⁰, and a mononuclear thioarsenite with an S/As ratio of 3:1. Thioarsenic species with S/As ratios of 1 : 1,2 : 1, and 4 : 1 are lesser components in sulfidic solutions that might be encountered in natural aquatic environments. Thioarsenites dominate arsenic speciation at sulfide concentrations > 10^-4.3 M at neutral pH. Conversion from neutral As(OH)₃ ⁰ to anionic thioarsenite species may regulate the transport and fate of arsenic in sulfate-reducing environments by governing sorption and mineral precipitation reactions.     

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, SO₄²⁻, 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 ³⁵SSO₄²⁻ showed that AVS and S⁰ are the major short-term (48 h) products of SR in these sediments. Inorganic forms of S(AVS, S⁰, and FeS₂) 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.     

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.     

A natural attenuation of arsenic in drainage from an abandoned arsenic mine dump

At the abandoned As mine in Nishinomaki, Japan, discharged water from the mining and waste dump area is acidic and rich in As. However, the As concentration in the drainage has been decreased to below the maximum contaminant level (0.01 mg/l for drinking water, Japan) without any artificial treatments before mixing with a tributary to populated areas. This implies that the As concentration in water from the waste dump area has been naturally attenuated. To elucidate the reaction mechanisms of the natural attenuation, analysis of water quality and characterization of the precipitates from the stream floor were performed by measuring pH, ORP and electric conductivity on-site, as well as X-ray diffraction, ICP-mass spectrometry and ion-chromatography. Selective extractions and mineral alteration experiments were also conducted to estimate the distribution of As in constituent phases of the precipitates and to understand the stability of As-bearing phases, respectively. The water contamination resulted from oxidation of sulfide minerals in the waste rocks, i.e., the oxidation of pyrite and realgar and subsequent release of Fe, SO₄, As(V) and proton. The released Fe(II) transformed to Fe(III) by bacterial oxidation; schwertmannite then formed immediately. While the As concentrations in the stream were lowered nearly to background level downstream, those in the ochreous precipitates were up to several tens of mg/g. The As(V) was effectively removed by the formed schwertmannite and had been naturally attenuated. Although schwertmannite is metastable with respect to goethite, the experiments show that the transformation of schwertmannite to goethite may be retarded by the presence of absorbed As(V) in the structure. Therefore, the attenuation of As in the drainage and the retention of As by schwertmannite are expected to be maintained for the long term.     

Geochemical effects of oxidation products and framboidal pyrite oxidation in acid mine drainage prediction techniques

Acid mine drainage predictive testwork associated with the Australian Mineral Industries Research Association (AMIRA) P387A Project: Prediction and Kinetic Control of Acid Mine Drainage (AMD) has critically examined static acid assessment and kinetic information from acid–base accounting techniques, including net acid production potential (NAPP), net acid generation (NAG) and column leach tests. This paper compares results on two waste rock samples that were obtained from the Kaltim Prima Coal mine (KPC) containing significant quantities of fine-grained framboidal pyrite. In agreement with other research, the authors' results indicated that framboidal pyrite is more reactive than euhedral forms due to the greater specific surface area of framboidal pyrite. This is evidenced by optical microscopy of reacted samples. Importantly, the results showed that NAPP testing is biased by the rapid acid generating oxidation of framboidal pyrite prior to, and during the acid neutralisation capacity (ANC) test. This can result in negative ANC values for samples containing significant framboidal pyrite (often “corrected” to zero kg H₂SO₄/t) when significant ANC is actually present in the sample. NAG testing using H₂O₂ indicated that samples containing a significant quantity of framboidal pyrite can result in the catalytic decomposition of the H₂O₂ prior to complete oxidation of the sulfide minerals present, requiring sequential addition of H₂O₂ for completion. A benefit of the NAG test, however, is that it assesses the net acid generation capacity of the sample without bias towards acid generation as is observed using NAPP methods. The kinetic NAG test also gives information on the reaction sequence of framboidal and euhedral pyrite. Periodic (kinetic) analysis of sub-samples from column leach tests indicated rapid oxidation of the framboidal pyrite compared to the euhedral pyrite, which was correlated with the greater framboidal pyrite surface area.Calculations to determine the sulfide/sulfate acidity derived from the oxidation of framboidal pyrite prior to; and during the ANC test have been developed to provide a better indication of the actual ANC (ANC_Actual) of the sample. Paste pH values of <pH 4–5 may be one suitable trigger mechanism for the implementation of this new method. This has led to an improved NAPP estimation of total acid production. Together with NAG and column leach testing this improved methodology has resulted in accurate AMD characterisation of samples containing acidic oxidation products and framboidal pyrite.     

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.     

生物纳米FeS强化灰岩去除酸矿废水中砷的研究

通过两种还原型微生物铁还原菌JF-5和硫酸盐还原菌SRB对模拟酸矿废水中Fe~(3+)和SO~(2-)_4的还原作用合成纳米FeS,并将该生物纳米FeS包覆在灰岩表面,以提高灰岩可渗透反应墙(PRBs)对酸矿废水中砷的去除能力。通过批吸附实验研究As(Ⅴ)的静态吸附机理,柱实验研究As(Ⅴ)在包覆灰岩柱中的动态吸附和迁移,结果表明,包覆层生物FeS粒径为纳米级,并呈现一定晶形,能有效提高灰岩表面的比表面积和对As(Ⅴ)的吸附能力,红外光谱分析表明化学吸附为主要吸附机制;生物纳米FeS包覆灰岩静态吸附实验最大吸附量为187.46μg/g,达到纯灰岩吸附量(6.64μg/g)的30倍;JF-5和SRB形成的生物包覆吸附性质优于SRB和Fe(Ⅱ),二者对As(Ⅴ)的吸附能力都远大于纯灰岩对As(Ⅴ)的滞留能力。     

Geochemical assessment of an arsenic mine adjacent to a water reservoir (León, Spain)

A water reservoir constructed for production of hydraulic energy and drinking water in the Riaño valley (León, northern Spain) receives leachates from polluted soils and spoil heaps from a site where small-scale As mining and smelting operations have been developed in the first half of the twentieth century. Water of the upper catchments of the Esla, Yuso and Orza Rivers is stored in this reservoir. The location of these abandoned mine works within the reservoir drainage basin suggested that the stored water could contain high As concentrations. In order to evaluate possible environmental risks, a preliminary soil and surface water geochemical survey has been carried out downstream of the Santa Águeda Mine. Total As concentrations in soils reach 23,800 mg kg^?1 in soils and increase with depth, at least up to a depth of 80 cm. Total As concentrations in surface waters reach 890 μg l^?1. Despite the fact that there is an important As input to the water reservoir, the water flow from the mine catchment is a negligible contribution when compared with the total volume of water inside the dam (0.07%). This fact considerably decreases the environmental risk associated with the presence of untreated spoil heaps containing As-rich minerals at Santa Águeda mine site.     

Geochemical changes during neutralisation of acid mine drainage in a dynamic mountain stream, New Zealand

The Mangatini Stream drains a coal mining area in the mountains of northwestern South Island of New Zealand. Abundant rainfall on pyritic rocks yields acid mine drainage (AMD) to the stream, which flows through a steep gorge at discharges that rapidly increase from <1 to >100 m³/s during frequent rain events. The AMD is treated with finely ground limestone, which is discharged as a slurry at a point in the middle of the gorge. The limestone slurry mixes and reacts with the AMD during flow ∼4 km downstream over ∼12 h. Neutralisation reactions increase stream pH from near 3 (untreated Mangatini Stream water impacted by AMD) to 5–6 in the first 250 m downstream, although mixing is commonly incomplete in this zone. Large stream discharge volumes in rain events dilute the neutralising material input, thus driving the pH back towards 4 downstream of treatment. More complete neutralisation is achieved 4 km downstream, even in major rain events, and pH can rise to >7. Partial neutralisation is sufficient to remove most of the dissolved Fe(III) (typically ∼30 mg/L) from the Mangatini Stream in the first 10 m, and remaining dissolved Fe is essentially all Fe(II), which decreases over time as it oxidises and precipitates. Dissolved Al in the Mangatini Stream (typically ∼50 mg/L) decreases steadily downstream over ∼100 m in the limestone mixing zone. Precipitated Fe and Al form amorphous oxyhydroxides that are transported as suspended solids and deposited on the stream bed with excess limestone in zones of low flow velocity. Dissolved Zn is removed from solution by adsorption to Fe oxyhydroxide when pH reaches ∼5, but dissolved Ni remains in solution despite the neutralisation process. Gypsum precipitation occurs throughout the limestone mixing zone, resulting in at least 30% decrease in dissolved . Minor ettringite forms in the first 100 m, but then probably redissolves. The limestone dosing system is an effective method of neutralising the effects of AMD and removing most dissolved metals in a steep mountain stream with frequent rain events where this dynamic environment places many constraints on treatment options.     

Origin of acid mine drainage in Enugu

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

Geochemical investigations on fluvial sediments contaminated by tin-mine tailings,Cornwall, England

Tin-mine tailings containing high concentrations of Sn, Cu, Zn, Fe, Mn, As, and W are discharged into the Red River of cornwall, England and are then transported into St. Ives Bay under normal flow conditions. Most of the tin-bearing particles in the fluvial sediments are smaller than 170 μm, but tin-bearing composite grains or mineral grains with tin interspersed in the crystal lattices also occur in coarser size fractions. Tin distribution in the sediments is controlledby: (1) the distance from the source of the tailings, and (2) the concentration processes operating on the river bed. Suspended sediment and sediment transported by saltation filtered from river water samples also showed high concentrations of metals although, in contrast to the bottom sediments, they vary within a narrow range. Distributions of Cu, Zn, Fe, As, and Pb in the filtered sediments probably are related to the physical and chemical behavior of their sulphide minerals during fluvial transportation. A regional stream-sediment geochemical reconnaissance survey for tin did not show the highest concentration in the Red River; this indicated that in other rivers and streams tin reconcentration by selective removal of light minerals had taken place in the bottom sediments after mining operations had ceased. These rivers and streams also can transport large quantitiies of land-derived sediment including tin-mine tailings discharged into them when mines were operating. The minimum distance of tin transported by the Red River is at least 10 km; however, most of the tin was derived from mine tailings and is considered to be unnatural.     

Metal contamination and solid phase partitioning of metals in the stream and bottom sediments in a reservoir receiving mine drainage

This study was conducted to assess the anthropogenic impact on metal concentrations in the bottom sediments of the Juam reservoir, Korea, and in stream sediments in its catchment, and to estimate the potential mobility of selected metals (Fe, Mn, Cu, Ni, Pb and Zn) using sequential extraction. A comparison of the metal concentrations in the stream sediments with mean background values in sediments collected from first- or second-order creeks shows that Pb, Cu and Ni are the most affected by anthropogenic inputs. The ²⁰⁶Pb/²⁰⁷Pb ratios of the bottom and core sediments (means: 1.2320 ± 0.0502 and 1.2212 ± 0.0040, respectively) suggest that Pb contamination is mainly due to the waste discharge of abandoned coal and metal mines rather than industrial and airborne sources. Considering the proportion of metals bound to the exchangeable, carbonate and reducible fractions, the comparative mobility of metals is suggested to decrease in the order Mn > Pb > Zn > Ni > Fe ≫ Cu.     

Copper isotope fractionation in acid mine drainage

We measured the Cu isotopic composition of primary minerals and stream water affected by acid mine drainage in a mineralized watershed (Colorado, USA). The δ⁶⁵Cu values (based on ⁶⁵Cu/⁶³Cu) of enargite (δ⁶⁵Cu = −0.01 ± 0.10‰; 2σ) and chalcopyrite (δ⁶⁵Cu = 0.16 ± 0.10‰) are within the range of reported values for terrestrial primary Cu sulfides (−1‰ < δ⁶⁵Cu < 1‰). These mineral samples show lower δ⁶⁵Cu values than stream waters (1.38‰ ? δ⁶⁵Cu ? 1.69‰). The average isotopic fractionation (Δ_aq-min = δ⁶⁵Cu_aq − δ⁶⁵Cu_min, where the latter is measured on mineral samples from the field system), equals 1.43 ± 0.14‰ and 1.60 ± 0.14‰ for chalcopyrite and enargite, respectively. To interpret this field survey, we leached chalcopyrite and enargite in batch experiments and found that, as in the field, the leachate is enriched in ⁶⁵Cu relative to chalcopyrite (1.37 ± 0.14‰) and enargite (0.98 ± 0.14‰) when microorganisms are absent. Leaching of minerals in the presence of Acidithiobacillus ferrooxidans results in smaller average fractionation in the opposite direction for chalcopyrite (Δ_aq-min^o=-0.57±0.14‰, where min^o refers to the starting mineral) and no apparent fractionation for enargite (Δ_aq-min^o=0.14±0.14‰). Abiotic fractionation is attributed to preferential oxidation of ⁶⁵Cu⁺ at the interface of the isotopically homogeneous mineral and the surface oxidized layer, followed by solubilization. When microorganisms are present, the abiotic fractionation is most likely not seen due to preferential association of ⁶⁵Cu_aq with A. ferrooxidans cells and related precipitates. In the biotic experiments, Cu was observed under TEM to occur in precipitates around bacteria and in intracellular polyphosphate granules. Thus, the values of δ⁶⁵Cu in the field and laboratory systems are presumably determined by the balance of Cu released abiotically and Cu that interacts with cells and related precipitates. Such isotopic signatures resulting from Cu sulfide dissolution should be useful for acid mine drainage remediation and ore prospecting purposes.     

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.     

Geochemical modeling approach to predicting arsenic concentrations in a mine pit lake

Between 1968 and 1983, the North pit at the Getchell Mine, Humboldt County, NV, filled with water to form a lake. In 1983, water quality data were collected with the following results: As concentrations of 0.29 to 0.59 mg/L, pH of 7.1 to 7.9, SO₄ concentrations of 1490 to 1640 mg/L, and TDS of 2394 to 2500 mg/L. Using geochemical modeling techniques presented here, pit lake waters have been theoretically allowed to react for 8.5 a, the approximate time that the North pit had been completely full by 1983. Modeling results predict pH of 7.9 to 8.2, SO₄ concentrations of 1503 to 1644 mg/L, TDS of 2054 to 2366 mg/L, and As concentrations ranging from 0.57 in the hypolimnion to 96 mg/L in the epilimnion. In the epilimnion, model results do not match observed As concentrations, suggesting that mechanisms, such as precipitation of arsenate salts or adsorption to mineral surfaces, may control As levels in an actual pit lake system. Adsorption to Fe oxyhydroxide surfaces is questioned by the authors because of the low Fe content in the Getchell system, but adsorption to Al(OH)₃ (gibbsite) and clay mineral surfaces may be important in controlling natural As concentrations.     

Microbial effects on geochemical behavior of arsenic in As-contaminated sediments

The purpose of this study is to investigate the contamination level and chemical speciation of As in sediments from the Hwachon Au mine area, and to study the effects of indigenous bacteria on geochemical behavior of As in As-contaminated sediments from the mine. Concentrations of heavy metal and metalloids in one composite sample of 9 Hwachon sediments were 24.9 As mg/kg, 16.6 Cd mg/kg, 230 Pb mg/kg and 1080 Zn mg/kg. This indicates that this area was seriously contaminated with As, Cd and Zn. From the result of sequential extraction analysis, most of As (87.9%) existed as a phase of As which coprecipitated with Fe oxyhydroxides. Under aerobic condition, As concentration leached from sediments were 4 times higher in non-sterile than in sterile condition. This enrichment of As leaching could be caused by increase of pH and exudation secreted during microbial metabolism. On the other hand, under anaerobic condition, As concentration has dramatically increased in non-sterile solution with time. This As leaching has begun on 4–5th days of incubation and the highest concentration of 511 As μg/l was recorded on about 11th day. Arsenic leaching under anaerobic condition was caused by microbial enhancement of Fe leaching. Total Fe concentration increased from the 4th day, and this Fe leaching might cause lixiviation of As which had been coprecipitated with Fe oxyhydroxide.