Simultaneous Removal of Copper, Zinc, and Sulfate from Coal Mine Waste in a Laboratory SRB Bioreactor Using Lactate or Ethanol as Carbon Sources

The feasibility of inoculating coal mine waste piles with sulfate-reducing bacteria (SRB) to prevent the production of acidic leachates containing sulfate and metal contaminants was evaluated in batch and column bioreactors. The results showed that SRB growth and activity could be attained in the presence of acidic (pH 4.5) coal mine waste using lactate or ethanol as a carbon source, while no obvious growth was found at pH <3.5. Inoculation of coal mine waste in batch reactors with lactate or ethanol as a carbon source resulted in efficient neutralization and high removal of sulfate and metals. Similar results were attained in dynamic-flow columns inoculated with SRB. SEM-EDS analysis of the precipitates showed iron sulfide to be the main component. This study indicates that SRB could possibly be used to prevent or limit acidic drainage from coal mine waste piles.     

Development of the Sleeper Pit Lake

Abstract.  The Sleeper open pit gold mine operated from the mid-1980s through the mid-1990s. Operations were mostly sub-water table and extensive dewatering was required to lower groundwater levels by 180 m. Dewatering flows peaked at 930 L/s, with most flow contributed from an alluvial aquifer. After completion of mining, the pit was rapidly filled with water pumped from the alluvial aquifer to reduce the exposure time of sulfide wall rocks and waste rocks in the ultimate pit. The pumped alluvial groundwater provided a large volume of low total dissolved solids (TDS), high alkalinity water that controlled the early chemistry. The rising lake waters were amended with lime to buffer excess acidity contributed to the lake from reactive pit wall rocks during submergence. The pore water contained in submerged waste rock at the base of the pit was elevated in TDS and subsequently of higher density that the lake water. The density contrast and waste rock location limited contributions of waste rock pore water to the main body of the lake. Some stratification of the early lake occurred, with shallow water characterized by higher pH, low dissolved metals, and sulfate; deeper water had lower pH and higher dissolved metals and sulfate. The reservoir of alkalinity in the shallow layer mixed with the deeper waters and created a stabilized lake with a homogenized column that exceeded water quality expectations. Current water quality meets all Nevada primary drinking water standards with the exception of sulfate, TDS, and manganese, which are slightly elevated, as predicted. Chemistry has remained stable since development of the initial lake.     

Distribution of Organic Carbon in the Berkeley Pit Lake, Butte, Montana

Abstract.  The concentration of dissolved organic carbon (DOC) in the Berkeley pit lake water ranges from 2 to 4 mg/L, and is comparable to that of its inflow waters. On the dates sampled, the DOC concentrations decreased towards the surface of the lake, in a manner similar to the concentration of dissolved Fe. This may reflect adsorption of DOC onto newly formed ferric precipitates in the epilimnion of the lake. The total organic carbon (TOC) content of the lake sediment is 0.20 to 0.33%, and is on the low end of TOC in natural aquatic sediments. In contrast, the DOC concentrations of sediment pore waters are unusually high, ranging from 50 to 380 mg/L, and are much higher than DOC values of pore waters from typical marine or lacustrine sediments. The high DOC concentrations are explained by release of adsorbed organic carbon from ferric precipitates as they age and recrystallize, coupled with the relative scarcity of heterotrophic bacteria in the acidic and heavy metal-rich waters that would otherwise consume DOC through reduction of sulfate.     

Organic wastes as carbon sources to promote sulfate reducing bacterial activity for biological remediation of acid mine drainage

Chicken manure, dairy manure and sawdust were evaluated as carbon sources in promoting sulfate reduction, and the mechanism of heavy metals removal in sulfidogenic bioreactor was revealed. The sulfate reduction reached 79.04% for chicken manure, 64.78% for dairy manure, and 50.27% for sawdust on 35th day, which showed that chicken manure could promote sulfate reducing bacteria (SRB) activity, followed by dairy manure and sawdust. In batch experiment, although chicken and dairy manure bioreactors showed sulfidogenic activity, it demonstrated less than 5% contribution from sulfide precipitation and over 95% from other removal mechanisms (sorption to manure particles and hydroxides precipitation, etc.). Column bioreactor showed satisfactory performance in biological remediation of acid mine drainage, evidenced by effluent Eh and pH, high removal efficiencies of sulfate and metals, and a considerable SRB counts. SEM–EDS analysis of the formed precipitate showed metal sulfides were formed. The results indicated that organic waste played an important role in sulfidogenic activity, which could not only provide reducing condition and carbon source for sulfate reduction process, but also reduce the adverse effect of heavy metal and strong acidity on SRB activity owning to metals sorption and acidity buffer of organic waste.     

A Kinetic Analysis of Microbial Sulfate Reduction in an Upflow Packed-Bed Anaerobic Bioreactor

The effects of initial sulfate concentration on anaerobic sulfate reduction and sulfide generation kinetics were investigated in an up-flow bioreactor, using a consortium of sulfate-reducing bacteria (SRB) from water produced from a Brazilian oil reservoir. Redox potential and sulfate concentration were measured to indicate the growth and activity of the SRB throughout the experimental runs. The results of the batch regime indicate that sulfate conversion and sulfide generation are both first-order processes for initial sulfate concentrations of 1,000 and 3,500?mg/L. The kinetic constants for the sulfate conversion indicate that the enhanced initial sulfate content was initially inhibiting, but that the sulfide generation reaction is almost independent of the initial sulfate concentration, likely due to the presence of at least two in-series processes that are faster than the microbial conversion of the sulfate.     

Effects of a Barite Mine on Ground Water Quality in Andhra Pradesh,India

Abstract.  An investigation was undertaken to determine the effects of a large barite mining operation on local ground water quality near Mangampeta,Andhra Pradesh, India.Water samples were collected from drinking water wells in the mining and adjacent regions. The drinking water in the mining region had sulphate concentrations that ranged from 211 to 589 mg/L, compared to sulphate concentrations of 25 mg/L or less in the non-mined areas. The natural existence of barite and the widespread mine waste dumps at Mangampeta are believed to be responsible for the higher levels of sulphate in the ground water.     

Microbial Alkalinity Production to Prevent Reacidification of Neutralized Mining Lakes

Abstract.  Microbial alkalinity production was evaluated as a method to prevent reacidification of neutralized mining lakes by acidic ground and seepage water. We used 60 L mesocosms to represent the sediment and water column of a shallow acidic mine lake. To enhance alkalinity production, acidic and neutralized lake waters were treated with either phosphorus (controlled eutrophication) or organic matter (controlled saprobization). Controlled eutrophication could not produce enough autochthonous biomass as substrate for microbial alkalinity production to change the acidity of the water. Chemical pre-neutralization of the acidic water caused the inorganic carbon concentration to increase, but at the same time, hindered algae growth by reducing the availability of phosphate by sorption to the freshly precipitated iron hydroxide. This effect was so strong that even high phosphorus additions could not increase the algae biomass production. In contrast to controlled eutrophication, controlled saprobization produced significant alkalinity. Despite inhibition of the most important alkalinity producing process, namely microbial sulfate reduction, by low pH values, the microbial alkalinity production rate was not affected by pre-neutralization of the water column. Other alkalinity producing processes raised the pH in the reactive zone until sulfate reduction was no longer inhibited.     

Geochemistry and Isotopic Composition of H2S-rich Water in Flooded Underground Mine Workings,Butte, Montana,USA

Abstract.   Groundwater being pumped from the flooded West Camp mine workings of Butte, Montana, is elevated in hydrogen sulfide (H₂S), has a circum-neutral pH, and has high arsenic but otherwise low metal concentrations. The daily flux of H₂S and As pumped from the extraction well are each estimated at roughly 0.1 kg. Isotopic analysis of coexisting aqueous sulfide and sulfate confirms that the H₂S was produced by bacterial sulfate reduction. the mine waters are close to equilibrium saturation with amorphous FeS, amorphous ZnS, siderite, rhodochrosite, calcite, and goethite, but are undersaturated with orpiment (As₂S₃). The higher solubility of orpiment relative to other mental sulfides allows concentrations of dissolved arsenic (~ 100 g/L) that are well above human health standards. The West Camp waters differ markedly from the acidic and heavy metal-rich mine waters of the nearby Berkeley pit-lake. These differences are partly attributed to geology, and partly to mining history.     

Contaminated Alluvial Ground Water in the Butte Summit Valley

Abstract.  Ground water in alluvial sediments of upper Silver Bow Creek is chronically contaminated with heavy metals, including Cd, Cu, Fe, Mn, and Zn. Most of this contamination stems from slag, mill tailings, and waste rock from the Butte mining district that had been deposited along the ancestral Silver Bow Creek floodplain. Much of this mine waste is now buried by fill, topsoil, buildings, or parking lots. Although the pH values of most wells in the region are in the 5.5 to 7.0 range, a cluster of monitoring wells near the site of a former mill and smelter contain water that is strongly acidic (pH < 4.5), with extremely high dissolved metal concentrations (Cu up to 750 mg/L; Zn up to 490 mg/L). Ground water discharging from the area is currently collected by a subsurface French drain and conveyed to a treatment facility where lime is added to precipitate metals from solution.     

Neutralizing Coal Mine Effluent with Limestone to Decrease Metals and Sulphate Concentrations

Abstract.   This paper describes pilot scale tests of a novel process for the neutralisation of acidic mine water. Leachate from a waste coal dump was neutralised with limestone, and iron, aluminium, and sulphate were removed. Specific aspects studied were: the process configuration; the rates of iron oxidation, limestone neutralisation, and gypsum crystallisation; the chemical composition of the effluents before and after treatment; the efficiency of limestone utilisation; and the sludge solids content. The acidity was decreased from 12,000 to 300 mg/L (as CaCO₃), sulphate from 15,000 to 2,600 mg/L, iron from 5,000 to 10 mg/L, aluminium from 100 to 5 mg/L, while the pH increased from 2.2 to 7.0. Reaction times of 2.0 and 4.5 h were required under continuous and batch operations respectively for the removal of 4 g/L Fe (II). The iron oxidation rate was found to be a function of the Fe (II), hydroxide, oxygen, and suspended solids (SS) concentrations. The optimum SS concentration for iron oxidation in a fluidised-bed reactor was 190 g/L. Up-flow velocity had no influence on the rate of iron oxidation in the range 5 to 45 m/h. Sludge with a high solids content of 55% (m/v) was produced. This is high compared to the typical 20% achieved with the high density sludge process using lime. It was determined that neutralisation costs could be reduced significantly with an integrated iron oxidation and limestone neutralisation process because limestone is less expensive than lime, and a high-solids-content sludge is produced. Full scale implementation followed this study.     

Year-Round Performance of a Passive Sulfate-Reducing Bioreactor that Uses Rice Bran as an Organic Carbon Source to Treat Acid Mine Drainage

The development of compact and cost-effective passive treatment systems is of critical importance for acid mine drainage (AMD) remediation in Japan. The purpose of this study was to construct an AMD treatment system comprising a sulfate-reducing bioreactor using rice bran as a carbon source for sulfate-reducing bacteria (SRB) and to demonstrate its stable operation for at least a year in terms of continuous sulfate reduction and metal removal. Our 35 L bioreactor comprised a packed inoculum layer of a mixture of rice husks, limestone, and field soil, which was covered with rice bran. During operation, the AMD input flow rate was adjusted to 11.7 mL/min (hydraulic retention time, HRT; 50 h). Throughout the year, physicochemical analyses of system input and output AMD samples revealed that both pH and oxidation–reduction potential values were consistent with the process of sulfate reduction by SRB, although this reduction was observed to be stronger in summer than in winter. Efficient metal removal was observed, with concentrations at the outlet port of <0.33 mg/L Zn, <0.08 mg/L Cu, and <0.005 mg/L Cd, more than meeting Japan’s national effluent standards. Illumina sequencing of 16S rRNA genes revealed that Desulfatirhabdium butyrativorans-related species, which belong to a lineage within Deltaproteobacteria, were dominant (39–48% of the total SRB population) within the bioreactor.     

Performance of a SAPS-Based Chemo-Bioreactor Treating Acid Mine Drainage Using Low-DOC Spent Mushroom Compost, and Limestone as Substrate

Static and continuous experiments were carried out in a down flow chemo-bioreactor, modeled on successive alkalinity producing systems, for acid mine drainage treatment. Spent mushroom compost (SMC) was used as the immobilizing substrate and nutrient source for sulfate reducing bacteria (SRB). Operational success was assessed using effluent to influent ratios during continuous flow; these averaged: 0.0175, 0.12, and 0.071 for Fe, Cu, and Mn, respectively, and 0.11 for sulfate. In contrast, Mg was released by the SMC, increasing its concentration in the effluent. Acidity was consistently less than 1 mg/L. The pH of the effluent was higher than 7 for most of the experiment. SMC was shown to release sufficient organic carbon during the experiment to establish and maintain anaerobic conditions and sustain the SRB.     

Sequential precipitation of Cu and Fe using a three-stage sulfidogenic fluidized-bed reactor system

The exposure of sulfides, such as pyrite (FeS₂) to water and air leads to the formation of acidic metal and sulfate containing waters, generally referred to as acid mine drainage (AMD). Under anaerobic conditions and in the presence of a suitable electron and carbon source, sulfate-reducing bacteria (SRB) can reduce sulfate to hydrogen sulfide which can precipitate metals as low-solubility sulfides. In the present study, a three-stage fluidized-bed reactor (FBR) system was operated at 35 °C with ethanol as an electron and carbon source for SRB to sequentially precipitate Cu and Fe from synthetic AMD. The system consisted of two pre-settling tanks before a sulfidogenic FBR for the sequential precipitation of Cu and Fe with biogenic H₂S gas and HS⁻ containing effluent, respectively. Cu and Fe precipitation efficiencies were over 99% and sulfate and COD removals 60-90%. Biologically produced alkalinity increased the initial pH of the AMD from 3.0 to neutral values.     

Treatment of Mine Water for Sulphate and Metal Removal Using Barium Sulphide

Abstract.   The integrated barium sulphide process consists of: preliminary treatment with lime, sulphate precipitation as barium sulphate, H₂S-stripping, crystallization of CaCO₃, and recovery of barium sulphide. Our tests showed that during lime pre-treatment, sulphate was lowered from 2 800 mg/L to 1 250 mg/L by gypsum crystallization; metals were precipitated as hydroxides. The BaS treatment then lowered sulphate to less than 200 mg/L. Sulphide was lowered from 333 to less than 10 mg/L (as S) in the stripping stage, using CO₂ gas for stripping. The stripped H₂S-gas was contacted with Fe (III)-solution and converted quantitatively to elemental sulphur. The alkalinity of the calcium bicarbonate-rich water was reduced from 1 000 to 110 mg/L (as CaCO₃) after CO₂-stripping with air due to CaCO₃ precipitation. Fe (II), after sulphur production, was re-oxidized to Fe (III) using an electrolytic step. The running cost of the BaS process is R2.12/m³ (US$1 = SAR6.5) for the removal of 2 g/L of sulphate.     

Geochemistry of Perched Water in an Abandoned Underground Mine, Butte, Montana

Abstract.  The Lexington tunnel is the last accessible underground mine working in the Butte, Montana mining district. Used as recently as 1993, the tunnel and adjacent workings have been abandoned for over 10 years. Although the Lexington tunnel is over 200 m above the regional water table, perched water is present over much of its extent. Mine water near the portal is moderately acidic (pH 4 to 5), with extremely high concentrations of metals, including Cu (up to 1000 mg/L) and Zn (up to 1400 mg/L). In the middle reaches of the tunnel, the quality of the water is much better, with near-neutral pH, high bicarbonate alkalinity, and lower concentrations of heavy metals. The low acidity and metal content is attributed to a lack of pyrite and other sulfides in this portion of the mine, as well as the presence of carbonate minerals, such as rhodochrosite (MnCO₃), in exposed veins. Sulfide minerals are more widespread further back in the tunnel, and are now oxidizing rapidly, leading to pockets of severe acid drainage (pH< 3, dissolved Zn up to 5000 mg/L). Geochemical modeling suggests that the near-neutral waters—the most voluminous type encountered in the Lexington tunnel—are close to equilibrium saturation with rhodochrosite and hydrous Zn-carbonate (ZnCO₃•H₂O). The Eh of these waters is most likely controlled by redox reactions involving dissolved Mn²⁺ and secondary, Zn-rich, hydrous Mn-oxides. In contrast, the Eh of the acidic waters appears to be controlled by reactions involving Fe²⁺ and Fe³⁺. Most of the acidic waters are saturated with K-jarosite, which forms delicate, straw-like dripstones at several localities. Decaying mine timbers could be an important renewable source of organic carbon for heterotrophic microorganisms, such as iron- and sulfate-reducing bacteria, especially deeper in the mine workings where the ground is saturated with anoxic ground water.     

A Screening-Level Laboratory Method to Estimate Pit Lake Chemistry

Abstract.  An analog pit lake (APL) test has been developed to predict pit lake water quality following closure of an equatorial copper-gold mine. The juvenile (0-9 years after closure) pit lake (JPL) water budget will comprise 10% rainfall; 26% surface runoff; 40% wallrock runoff, and 24% deep groundwater inflow. The mature (>65 years after closure) pit lake (MPL) will consist of 39% rainfall; 29% surface runoff; 15% wallrock runoff; 3% deep groundwater inflow, and 1% shallow groundwater inflow, with the balance (13%) contributed by the JPL. Wallrock runoff due to incident precipitation was replicated in humidity columns, subaqueous wallrock leachate by leaching columns of each rock type with groundwater, rainwater by addition of sea salt to deionized water, and surface runoff by a sample from a local creek. The solutions were combined in aquaria and the appropriate fraction evaporated, 7% for the JPL and 36% for the MPL. Electron microprobe analysis of precipitates identified clays and Al, Cu, and Zn adsorbed to ferrihydrite surfaces. A preliminary pit design resulted in an acidic (pH 3.3) JPL containing 7 mg/L Cu. However, by modifying the design to exclude a potentially acidgenerating andesite unit, the JPL water quality improves (e. g., pH 6.7; Cu 0.002 mg/L). The MPL pH with the andesite would be 6.1 (Cu = 2.2 mg/L), while the final design results in a pH of 7.1 and 0.22 mg/L Cu. The APL test can also be used to corroborate numerical models predictions and assess the efficacy of mitigation alternatives.     

Removal of Sulphate, Metals, and Acidity from a Nickel and Copper Mine Effluent in a Laboratory Scale Bioreactor

Abstract  Mine effluents should be treated so that they can either be re-used (e. g. for mining activities or irrigation purposes) or discharged into a river system. The results of this study showed that applying laboratory scale biological sulphate removal technology to a nickel/copper mine effluent (BCL mine, Botswana) consistently lowered sulphate concentrations from an average of 2000 to 450 mg/L, and increased the pH from 5.8 to 6.5. During this period, the hydraulic retention time varied from 24 to 12 h. The Ni and Zn concentrations were reduced from a maximum of 5.86 to 0.15 mg/L and from a maximum of 38 mg/L to 0.03 mg/L, respectively, presumably precipitated as metal sulphides.     

Anaerobic Bioremediation of Acid Mine Drainage using Emulsified Soybean Oil

Abstract  Batch incubation and flow-through column experiments were conducted to evaluate the use of emulsified soybean oil for in situ treatment of acid mine drainage. Addition of soybean oil, soluble substrates, and a microbial inoculum to the batch incubations resulted in complete depletion of SO₄, 50% reduction in Fe, and an increase in pH to >6. A one time injection of emulsified soybean oil, lactate, yeast extract, and a microbial inoculum stimulated SO₄ and metal ion reduction for ≈300 days in laboratory columns packed with mine tailings receiving influent solutions with a pH≈3 and≈5. In all emulsion treated columns, SO₄ and Fe were reduced, pH increased to >6, and Al, Cu and Zn removal efficiency was 99% or greater. Cu, Fe, Mn and Zn were removed as metal sulfides and/or carbonates with removal efficiency decreasing with increasing metal sulfide solubility. The low pH and high heavy metals concentrations did not significantly inhibit biological activity. However, SO₄ removal with associated precipitation of metal sulfides may have been limited by the short hydraulic retention time (6-7 days) of the columns. There was a significant hydraulic conductivity loss in one of the four treated columns, indicating that hydraulic conductivity loss may be an issue under certain conditions.     

Treatment of Acid Leachate from Coal Discard using Calcium Carbonate and Biological Sulphate Removal

Abstract.   An integrated approach is proposed for treating acidic coal discard leachate, consisting of CaCO₃ handling and dosing, CaCO₃-neutralization, and biological sulphate removal. It was found that: powdered CaCO₃ can be slurried to a constant density and used to neutralize the acid water, remove Fe (II), Fe (III), and Al, and partially remove the sulphate (to saturation level); biological sulphate removal can be used to lower the sulphate to less than 200 mg/L using ethanol as the carbon and energy source; CO₂ produced during calcium carbonate treatment can be used for H₂S-stripping and; H₂S gas recovered in the sulphate removal stage can be used for iron removal.     

硫酸盐还原菌利用不同生物质碳源对酸性矿山废水的处理

针对多组分酸性矿山废水(Acid Mine Drainage,AMD)污染严重,治理费用高的特点,基于硫酸盐还原菌(Sulfate-Reducing Bacteria,SRB)处理AMD具有成本低、适用性强、环境友好等诸多优点,从长期受煤矸石淋溶水污染的土壤中纯化培养一株SRB,并采用廉价易得的玉米芯、甘蔗渣和花生壳作为SRB生长碳源分别构造1号,2号,3号组动态柱,进行处理AMD的模拟实验,以探讨SRB利用生物质碳源处理AMD的有效性和规律性。各动态柱分别按照正交试验最优配比进行装填,其中,1号柱中SRB生物量和60目玉米芯按固液比分别为106. 8∶100(mg∶m L)和3. 5∶100(g∶m L)装填,2号柱中SRB生物量和100目甘蔗渣按固液比分别为71. 2∶100(mg∶m L)和4. 5∶100(g∶m L)装填,3号柱中SRB生物量和100目花生壳按固液比分别为106. 8∶100(mg∶m L)和4. 5∶100(g∶m L)装填。实验结果显示,以100目甘蔗渣为碳源的2号柱处理AMD的效果较好,对SO_4~(2-),Fe~(3+),Mn~(2+),Cr~(6+),Cr~(3+)平均去除率分别为61. 63%,99. 81%,72. 35%,96. 8%,100%,而体系出水的p H值和ORP值分别为6. 38～7. 30,-246 m V,表明SRB以甘蔗渣为碳源时的生长代谢活性优于玉米芯和花生壳,甘蔗渣可实现较持久的碳源供应。通过反应前后生物质材料的SEM和XRD分析表明,大量的Fe元素主要通过生物质材料的化学吸附方式被去除,而Mn和Cr元素主要通过与硫酸盐还原菌的代谢产物反应生成金属硫化物沉淀除去,少部分金属元素通过生物质材料的物理吸附被去除。同时,反应前生物质材料表面结构完整,反应后的生物质材料结构被破坏并附着纳米级金属硫化物沉淀。