Zinc precipitation by heavy-metal tolerant sulfate-reducing bacteria enriched on phosphogypsum as a sulfate source

In the present study, heavy-metal tolerance and precipitation by a mixed culture of sulfate-reducing bacteria (SRB) were evaluated. These bacteria have been enriched during a previous study from a sewage sludge using phosphogypsum as sulfate source. Taking into account that both sulfate and zinc are naturally occurring in phosphogypsum, zinc tolerance of SRB was tested in synthetic media containing 20 mM sulfate and zinc chloride at concentrations ranging from 0 to 200 mg L⁻¹. Zinc tolerance was determined by bacterial growth susceptibility and zinc removal monitoring. Bacterial growth and sulfate reduction were possible between 10 and 150 mg L⁻¹ of initial zinc concentration. Zinc concentrations more than 150 mg L⁻¹ were lethal to SRB. Zinc was removed effectively by SRB to less than 5% from medium containing 150 mg L⁻¹ initial zinc concentrations or less. Energy-dispersive X-ray analysis showed that precipitation of zinc occurred in the form of sulfide. The results presented in this paper have shown that this mixed culture might be of use for bioremediation of sulfate and heavy-metals containing wastewaters.     

Biological Removal of High Loads of Thiosulfate Using a Trickling Filter Under Alkaline Conditions

Uncontrolled release of thiosulfate can cause high oxygen demand, or generate toxic compounds under anaerobic scenarios. Biooxidation of thiosulfate in a biotrickling filter (BTF) colonized by an alkaliphilic sulfide-oxidizing bacterial consortium was studied at pH ≈10. Inlet thiosulfate concentrations were varied from 3.5 to 21.3 g L^?1, with a residence time of 216 s, emulating conditions encountered in wastewater from mining processes. Sulfate production, oxygen concentration, and biomass in both packing and effluent were periodically analyzed to characterize bioreactor performance. Removal efficiencies near 100 % were obtained during the entire experimental period, with a maximum elimination capacity of 242 g thiosulfate m^?3 h^?1. Although the BTF was able to transfer large amounts of oxygen to biooxidize thiosulfate to sulfate, under high initial thiosulfate loads, thiosulfate was not completely oxidized to sulfate, since biooxidation was conditioned to oxygen supply. Respirometric tests performed to investigate biomass adaptation and activity revealed oxygen consumption values of 0.5 mmol O₂ (g protein)^?1 min^?1 for the period with the highest thiosulfate inlet load.     

Tailings Weathering and Arsenic Mobility at the Abandoned Zgounder Silver Mine,Morocco

The abandoned Zgounder Mine (Morocco) was exploited for Ag from 1982 to 1990 and generated nearly 490,000 t of mill tailings before it was closed without being reclaimed. The tailings contain low concentrations of sulfide (mainly as pyrite, sphalerite, and galena) and carbonates (mainly dolomite). Silicates (muscovite, albite, chlorite, labradorite, actinolite, and orthoclase) occur in high concentrations. The most abundant trace elements are As, Ti, Fe, Mn, Zn, and Pb. We studied the geochemical behavior of the mine wastes to identify the main factors controlling drainage water chemistry. Particular emphasis was put on sorption phenomena to explain the low As concentrations in the leachates despite significant As levels in the tailings. Weathering cell tests carried out on various tailings produced two types of contaminated drainage: acidic and neutral. The kinetic test leachates contained high concentrations of some contaminants, including As (0.8 mg L^?1), Co (11 mg L^?1), Cu (34 mg L^?1), Fe (70 mg L^?1), Mn (126 mg L^?1), and Zn (314 mg L^?1). Acidity and contaminants in the leachates were controlled by dissolution of soluble salts and Fe hydrolysis rather than sulfide oxidation. Batch sorption tests quantified the significance of As sorption, and sequential extraction showed that most of the As sorption was associated with the reducible fractions (Fe and Mn oxides and oxyhydroxides).     

Copper Ion Recovery from Mine Water by Ion Flotation

Solutions containing copper ions are produced at copper mines due to its dissolution from ores and dumps. It is important to recover these ions to prevent this toxic element from entering the environment and because it could be economical. We investigated the use of ion flotation for extracting Cu ions from diluted mine water from the Veshnaveh Mine in Qom, Iran. Experiments were conducted using floatation cells at pH 6, 9, and 12 with diluted solutions containing 10 mg L^?1 of Cu. Sodium dodecyl sulfate and hexadecyl trimethyl ammonium bromide (HTAB) were used as collectors and methyl isobutyl carbinol (MIBC) and ethanol were used as frothers. The best result was achieved by maximizing Cu ion recovery and minimizing water recovery at pH 12, using 100 mg L^?1 of HTAB and 0.1 % (v/v) of MIBC. Copper and water recovery were 79 and 24 %, respectively.     

The Impact of Mine Tailings on the Witwatersrand and the Surrounding Water Bodies in Gauteng Province,South Africa

The gross alpha and beta activity in treated water from one of the numerous gold mines in Gauteng province averaged 1.15?±?0.13 and 0.87?±?0.11 Bq L^?1, respectively. The average readings of the fissure water from the same mine were 0.56?±?0.10 and 0.52?±?0.11 Bq L^?1, respectively. Water samples collected at the foot of the Princess gold mine tailings dump in Gauteng province and from downstream, before the drainage joins other water sources, also had high average gross alpha and beta activity and high average concentrations of radionuclides. The hazard quotient value evaluated, based on ²³⁸U of the water sample types in these vicinities, was far above one, indicating that it may pose serious health risks to the inhabitants.     

Geochemical and Mineralogical Characterization of a Pyritic Waste Pile at the Anjir Tangeh Coal Washing Plant, Zirab, Northern Iran

Coal washing at the Anjir Tangeh plant, in Zirab, northern Iran, has produced more than 1.5 Mt of coal wastes. These waste materials were geochemically and mineralogically characterised to guide development of an appropriate remediation scheme. Three vertical trenches up to 4 m deep were excavated from the coal waste pile surface and 25 solid samples were collected at 0.5 m intervals. The samples were analysed for total concentrations of 54 elements, paste pH, SO ₄ ^?2 , CO ₃ ^?2 , and HCO₃ ^?. The lowest pH values were measured at a depth of 0.3 m. The upper portion (1 m) of one profile was moderately oxidised, while oxidation in the other two profiles did not extend more than 0.8 and 0.5 m beneath the pile surface. The waste piles have low acid-producing potential (15–21.87 kg CaCO₃/t) and high values of acid-neutralizing potential (0.06–96.2 kg CaCO₃/t). Fe, Al, S, Na, Mn, Pb, Zn, Cd, and Ag increased with increasing depth, while Mo, Sr, Zr, and Ni decreased with increasing depth. The results show pyrite oxidation at depth and subsequent leaching of the oxidation products. Mn, Zn, Cu, Pb, Ag, and Cd are the most important contaminants of concern at this site.     

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.     

Environmental Geochemistry and a Quality Assessment of Mine Water of the West Bokaro Coalfield,India

Mine water from the West Bokaro coalfield was qualitatively assessed with respect to domestic and irrigation criteria. Thirty water samples from different mines were collected and analyzed for pH, electrical conductivity, total dissolved solids (TDS), total hardness, major cations, anions, and dissolved silica. The pH of the samples ranged from 6.6 to 8.3 in the post-monsoon season and 6.7–8.4 in the pre-monsoon season, indicating its near-neutral to slightly alkaline nature. TDS ranged from 349 to 1029 mg L^?1 in the post-monsoon season and 499–1458 mg L^?1 in the pre-monsoon season. The spatial differences in TDS reflect the local lithology, surface activities, and hydrology. Ca–Mg–SO₄ and Ca–Mg–HCO₃ were the dominant hydrogeochemical facies; SO₄ ^2? and HCO₃ ^? were the dominant anions and Ca²⁺ and Mg²⁺ were the dominant cations during both seasons. High SO₄ ^2? concentrations are attributed to oxidative weathering of pyrite and gypsum dissolution. Computed supersaturation with respect to dolomite and calcite for most samples may result from the dissolution of gypsum after the water is saturated with respect to the carbonate minerals. Despite moderate to high TDS, total hardness, and SO₄ ^2? concentrations, most of the sampled mine water was of good to permissible quality for irrigation; however, locally higher salinity and Mg restrict its suitability for irrigation at some sites.     

Mineralogical and Geochemical Characterization of Mine Tailings and Pb, Zn, and Cd Mobility in a Carbonate Setting (Northern Tunisia)

Millions of tonnes of Pb–Zn ore flotation tailings and waste rock have been discharged at sites in northern Tunisia without concern for environmental issues. The tailings are dominantly fine grained (<125 μm), with high porosity and permeability. The tailings were characterized to assess base metal (Pb, Zn, and Cd) mobility. The relatively low percentage of iron sulphide and the dominance of carbonates in the matrices of the tailings indicated that only neutral mine drainage is likely. Batch sequential testing showed that the calcium and sulphate, which are the major ionic species in solution, are derived mainly from the dissolution of gypsum and not from neutralization of acidity generated by pyrite oxidation. Yet, despite the carbonate setting, the resultant neutral to slightly alkaline pH, and prolonged weathering, the studied flotation tailings maintain their capacity to release contaminants, notably Zn and Cd, into the environment. The amount of Zn that dissolves (2,400 μg L^?1, on average), though significant, is below the background concentrations in the Mejerda River and the environmental norms established for surface waters. Pb concentrations come close to the standards, but only Cd (18 μg L^?1, on average) sometimes exceeds current river water concentrations and environmental standards.     

Comparison of Antimony Sources and Hydrogeochemical Processes in Shallow and Deep Groundwater Near the Xikuangshan Mine,Hunan Province,China

Antimony pollution in the groundwater of the Xikuangshan (XKS) antimony (Sb) mine area in China’s Hunan Province has attracted increasing attention. A total of 43 water samples were collected to help understand the hydrogeochemical characteristics, identify the Sb source, and evaluate the water–rock interactions of the Shetianqiao aquifer (SA). The Sb concentrations in shallow and deep SA water samples were 0.1–47.4 mg L^?1 and 0.3–19.2 mg L^?1, respectively. Stibnite oxidation and leaching from arsenic alkali residue mine wastes were the main Sb sources for the shallow SA water, whereas stibnite oxidation and stronger water–rock interaction were the predominant Sb sources for the deep SA water. The higher Sb concentration (>?10.0 mg L^?1) in shallow SA water was predominantly induced by weathering of Sb-bearing minerals, evaporation/concentration effects, and cation exchange, whereas the higher Sb concentration in deep SA water was largely caused by weathering of Sb-bearing minerals, evaporation/concentration effects, ion exchange, and competitive adsorption. These findings provide a more detailed understanding of the geochemical behavior of Sb in groundwater and can be used to develop suitable Sb pollution management strategies.

     

Survivorship and growth of Typha latifolia L. across a NaCl gradient: a greenhouse study

Oil sands surface mining operations in northeastern Alberta have created a substantial area of land needing to be reclaimed. Historically, these lands were a mosaic of uplands and boreal wetlands, particularly peatlands. While protocols for upland reclamation are well-defined, protocols for peatland reclamation are still in development. Two major concerns for peatland reclamations are (1) the ability of wetland plants to tolerate the increased sodicity present after surface mining and (2) the potential for the invasion of aggressive wetland plants, such as Typha latifolia, that could crowd out peatland plants and hinder the development of a peat layer. This study addresses these concerns by quantifying the response of T. latifolia seedlings to a sodium gradient. In the lowest two concentrations (0 and 300 mg L^?1), there was about 100% survival rate as compared to about 56% at sodium concentration of 2400 mg L^?1. At 300 mg L^?1, T. latifolia leaf health began to decrease, and at 600 mg L^?1, the health, plant height and the biomass aboveground decreased substantially. Our findings suggest that T. latifolia populations might be kept in check by keeping sodium concentrations within a range between 300 and 600 mg L^?1.     

Predicting erosion at valley fills with two reclamation techniques in mountainous terrain

ABSTRACT

Minimising erosion resulting from mining is important to improve of reclamation and management. Geomorphic landform design (GLD) is a reclamation technique that attempts to replicate a long-term erosionally stable condition. Erosion was evaluated using the Revised Universal Soil Loss Equation (RUSLE) comparing two reclamation scenarios (conventional and GLD) to the undisturbed condition. Soil loss rates were highest during the post-mining, pre-vegetation condition (conventional: 123.2 t ha^?1 yr^?1; GLD: 204.3 t ha^?1 yr^?1). Long-term erosion rates showed little difference between valley fills reclaimed with GLD and conventional methods; however, erosion was concentrated along the conventional fill face and distributed over the GLD landform.     

Changes in Efficiency and Hydraulic Parameters During the Passive Treatment of Ferriferous Acid Mine Drainage in Biochemical Reactors

The objective of this study was to evaluate the effects of different reactive mixtures and hydraulic retention times (HRTs) on hydraulic parameters (hydraulic conductivity, k_sat, and porosity) and the efficiency of passive biochemical reactors (PBRs) for treatment of ferriferous acid mine drainage (AMD). Five 10.7 L PBRs were filled with three reactive mixtures, containing either a carbon-rich substrate (60% w/w) or an inert/neutralizing agent (50% w/w). The PBRs were tested over a 450 day period using two qualities of iron-rich AMD (4 and 1 g L^?1 Fe in AMD1 and AMD2, respectively), and two HRTs, of 5 and 7 days. During the last week of the columns’ operation, a tracer test (5 g L^?1 of NaCl) was also performed, in addition to monthly measurements using the falling head method. Changes in HRT and k_sat were evaluated throughout the experiment. The PBRs increased the pH of AMD influents from 3.5 to 6 and efficiently removed Al, Cd, Cr, Ni, Pb, and Zn (>?90%), whereas Fe was only partially and inconsistently treated. No significant differences were observed among the three tested mixtures, regardless of the HRT or the AMD quality. Results from the tracer test and k_sat measurements showed no significant decrease in the initial values of the hydraulic parameters with time except for column 3, where a slight decrease was observed. Although sorption could have been important during the start-up of the PBRs, post-testing characterization of the spent reactive mixtures showed that the Fe was mainly retained as oxy-hydroxides and sulfides. Given the PBRs’ marginal effectiveness for Fe-rich AMD, pre-treatment removal of the iron is recommended.     

Hydrogeochemistry and Contamination of Trace Elements in Cu-Porphyry Mine Tailings: A Case Study from the Sarcheshmeh Mine,SE Iran

Geochemical and hydrochemical investigations were performed to understand the contamination potential of the Sarcheshmeh mine tailings. The geochemical mobility for the tailings is as follows: Cu > Cd > Co > Zn > Ni > Mn > S > Cr > Sn > As > Se > Fe = Bi > Sb = Pb = Mo. Highly mobile and contaminant elements (Cd, Cu, Zn, Mn, Co, Ni, S, and Cr), which significantly correlated with each other, were mainly concentrated in the surface evaporative layer of the old, weathered tailings, due to the high evaporation rate, which causes subsurface water to migrate upward via capillary action. The contamination potential associated with the tailings is controlled by: (1) dissolution of secondary evaporative soluble phases, especially after rainfall on the old weathered tailings, accompanied by low pH and high contamination loads of Al, Cd, Co, Mg, Cr, Cu, Mn, Ni, S, Se, and Zn; (2) processing of the Cu-porphyry ore under alkaline conditions, which is responsible for the high Mo (mean of 2.55 mg/L) and very low values of other contaminants in fresh tailings in the decantation pond; (3) low mobility of As, Fe, Pb, Sb, Mo, and Sn due to natural adsorption and co-precipitation in the tailings oxidizing zone. Speciation modeling showed that sulfate complexes (MSO₄ ⁺, M(SO₄)_(aq), M(SO₄) ₂ ^?2 , and M(SO₄) ₂ ^? ) and free metal species (M⁺² and M⁺³) are the dominant forms of dissolved cations in the acidic waters associated with the weathered tailings. In the alkaline and highly alkaline waters, trace element speciation was controlled by various hydroxide complexes, such as M(OH)⁺, M(OH) ₃ ^? , M₃(OH) ₄ ⁺² , M₂(OH) ₃ ⁺ , M(OH)_2(aq), M(OH) ₄ ^?2 , Me(OH) ₂ ⁺ , Me(OH) ₄ ^? , Me(OH) ₂ ⁺ , Me(OH)_3(aq), and Me(OH) ₄ ^? (where M represents bivalent and Me represents trivalent cations). The speciation pattern of As, Mo, and Se is mainly dominated by oxy-anion forms. The obtained results can be used as a basis for environmental management of the Cu-porphyry mine tailings.     

Extraction of titanium (IV) from acidic media by tri-n-butyl phosphate in kerosene

The extraction of titanium (IV) from sulfate, and nitrate solutions has been studied using tri-n-butyl phosphate (TBP) in kerosene. Extraction of titanium was affected by acid concentration over the range of 0.5–4 mol L^?1. The titanium distribution coefficient reached a minimum between 1 and 2 mol L^?1 acid for both sulfate and nitrate solutions. Third phase formation was observed in the extraction of titanium from acidic media at all condition tested. At the next stage, the stripping of titanium was studied using H₂SO₄, H₂SO₄ + H₂O₂ and Na₂CO₃. The kinetics of the stripping were very slow for H₂SO₄. The use of complex forming stripping agents (H₂SO₄ + H₂O₂) and Na₂CO₃ significantly improved the kinetics of stripping. About 98% recovery was achieved by extracting titanium from an aqueous nitrate solution using TBP and stripping with sodium carbonate.     

Effect of a commercial peat moss-shrimp wastes compost on pucinellia growth in red mud

Abstract

Revegetation of red mud can be difficult without chemical or organic ameliorant for red mud. A greenhouse experiment was conducted to examine the short-term effect of a commercial peat moss-shrimp wastes compost on the growth of pucinellia (Pucinellia distorts L.) in a bauxite residue (red mud) from the Alcan's Vaudreuil alumina refinery at Jonquière (Québec), Canada. Characterization of the red mud revealed that the residue was strongly alkaline (pH_se=11.4) and contained soluble salts (EC_se=10.3 dS m^?1), soluble Na (2743 mg L^?1), soluble Al (275 mg L^?1) and low levels of plant-available nutrients. Red mud components included approximately 40.4% Fe, 18.3% Al, 13.4Percnt; Si, 7.5% Ti, 6.7% Na and 3.5% Ca expressed in oxide. Hematite (∝Fe₂O₃) was the main mineral in the red mud. The results of the revegetation study have shown that compost amendment treatments affected pH values, salinity, organic carbon and DTPA-exlractable Al contents compared to the control. The highest rate (45%) of compost reduced the initial pH to about 9.3. The dry weight yield of pucinellia increased as the percentage of compost in the red mud increased. However, survival and plant growth were very poor when the compost was applied at 18 and 23% rates. The critical substrate pH value for pucinellia growth was between 9.5 and 9.7. In general, the leachates from the compost amended red mud are slightly more concentrated with respect to Al, compared with the unamended red mud (control).     

The removal of sulfate and metals from mine waters using bacterial sulfate reduction: Pilot plant results

A treatment process that bacterially converts sulfate into elemental sulfur via a hydrogen sulfide intermediate was demonstrated at pilot scale for the treatment of three mine waters that contained metals and sulfate. Ethanol served as the bacterial carbon and energy source. The mine waters were treated at rates that ranged from 50–150 L day⁻¹. Contaminant concentrations up to 13 mg L⁻¹ copper, 0.1 mg L⁻¹ mercury, 0.04 mg L⁻¹ cadmium, 3.5 mg L⁻¹ zinc, 0.68 mg L⁻¹ cobalt, 1.3 mg L⁻¹ nickel, 49 mg L⁻¹ iron, and 63 mg L⁻¹ aluminum were removed to meet water quality effluent limits. Manganese removal was about 80% under normal operating conditions but increased to 96% when the process was optimized for manganese removal. The process was shown to be capable of decreasing sulfate concentrations from 1800 mg L⁻¹ to less than 250 mg L⁻¹, nitrate from 100 mg L⁻¹ to less than 1 mg L⁻¹, arsenic from 8 mg L⁻¹ to less than 0.03 mg L⁻¹, and calcium from 310 mg L⁻¹ to less than 100 mg L⁻¹. Acid mine waters were neutralized using bacterially-generated alkalinity; no external alkalinity source was needed.     

Pyrite Weathering in Reclaimed Shale Overburden at an Oil Sands Mine near Fort McMurray,Canada

Saline-sodic shale overburden associated with oil sand mining is a potential source of salt release to surface water and groundwater and can lead to salinization and/or sodification of reclamation covers. Weathering of shale overburden due to oxidation of sulphide minerals within the shale leads to sulphate (SO₄ ^2?) production and increased salinity. The controls on the rates of weathering of a shale overburden dump in the oil sands region of northern Alberta were determined from soil chemistry sampling and in situ monitoring of pore gases (O₂, CO₂, CH₄) in three shallow profiles (1.9–4.45 m deep) and one deep (25 m deep) profile under reclamation covers of varying thickness. Oxidation, defined by the depth over which O₂ concentrations were depleted, reached depths of approximately 1.1 m under the reclamation soil covers over a 6 year period after dump placement. Calculations of SO₄ ^2? production rates and weathering depths were consistent with numerical simulations of the diffusion and subsequent consumption of atmospheric O₂ in the overburden. The rate of SO₄ ^2? production during the 6 year weathering period estimated from direct measurements of solids chemistry ranged from 0.70 to 8.3 g m^?2 day^?1. The rates calculated from the oxygen diffusion models were within that same range, between 1.6 and 4.1 g m^?2 day^?1.     

Evaluation of Hydraulic Conductivity of Itabirites of the Alegria Centro and Alegria Sul Open Pits,Samarco Mineração S.A., Minas Gerais State,Brazil

Itabirites in Samarco Mineração S.A.’s open mine pits in the Quadrilátero Ferrífero region, Minas Gerais State, Brazil, were hydrogeologically characterized. Itabirites, which represent the main aquifer in the region, were divided into four lithotypes based on their mineralogical composition. Statistical analysis of fracture frequency and rock quality designation were evaluated and correlated to hydraulic conductivity results. Preliminary analysis showed a highly fractured rock mass with relatively constant fracturing with depth, regardless of lithology. Field experiments were performed to determine the hydraulic conductivity and provide input data for an analysis of fracture frequency. Infiltration tests showed a median hydraulic conductivity of 1.2 × 10^?7 m/s, while packer tests indicated a median hydraulic conductivity of 9.6 × 10^?7 m/s. Fracture frequency was related to hydraulic conductivity through the cubic law. Median hydraulic conductivity values for the rock types at the mine were found to range from 1.2 × 10^?7 to 1.0 × 10^?6 m/s.     

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.