A Numerical Multi-Component Reactive Model for Pyrite Oxidation and Pollutant Transportation in a Pyritic,Carbonate-Rich Coal Waste Pile in Northern Iran

A one-dimensional numerical finite volume model is presented to simulate pyrite oxidation and reactive transportation of the oxidation products in a pyritic, carbonate-rich, coal waste pile. The proposed model incorporates the shrinking core concept for describing pyrite oxidation, pyrite surface area reduction, oxygen diffusion, and transport of the oxidation products through the waste pile. The model governing equations were solved using the PHOENICS computational fluid dynamics model. The accuracy of the model was verified with field data. Pyrite oxidation was more intense at shallower depths where oxygen decreased almost linearly from the pile surface to an approximate depth of 2 m. The lowest pH, 3.5, was predicted at a depth of 0.5 m. The waste pile has high neutralisation potential due to buffering by carbonate minerals. The maximum concentration of SO₄ ^2?, 31.6 mol/m³, was predicted at an approximate depth of 4 m and to remain constant throughout the rest of waste profile. Simulation of a scenario with a cap shows that iron and sulphate was removed from the upper parts of the pile; their peak concentrations shifted downward due to dilution. Oxygen source removal limited iron and sulphate production. These results will be useful for developing an appropriate remediation scheme.     

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.     

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).     

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.     

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.     

Heavy metal pollution diagnosis and ecological risk assessment of the surrounding soils of coal waste pile at Naluo Coal Mine,Liupanshui, Guizhou

In accordance with the National Soil Environmental Quality Standards of China, Grade I and Grade II (GB15618-1995), this study adopted single pollution index (SPI) and Nemeiow synthetical pollution index (NSPI) methods to analyse and assess the ecological risk of the seven heavy metals, namely Cd, Hg, As, Cu, Pb, Cr and Zn, contained in the surrounding soils of one coal waste pile at Naluo Coal Mine, Liupanshui, Guizhou, China. The results revealed that (1) Cd had higher SPI than any other heavy metal and the maximum Cd SPI, indicative of serious pollution, was found in the soil sample collected from the 150 m distant from the centre along possible coal gangue alluvial flow; (2) synthetical pollution assessment of heavy metals per Grade I found that soil sample collected from sites 150 m from the centre along possible coal gangue alluvial flow had the maximum NSPI, which suggests that the soil is seriously polluted, and that there is a link between heavy metal pollution level in the surrounding soils of the coal waste pile and the sampling direction; (3) synthetical pollution assessment of heavy metals per Grade II revealed that sampling distance had a bearing on the pollution level in the surrounding soils of the coal waste pile, and the soil samples collected from 100 or 150 m distant in all the sampling paths had minor pollution.     

Chemical Fractionation and Contamination Intensity of Trace Elements in Stream Sediments at the Sarcheshmeh Porphyry Copper Mine, SE Iran

This paper presents chemical fractionation and contamination intensities of trace elements in stream sediments at the Sarcheshmeh mine, southeastern Iran, which is one of the world’s largest Oligo-Miocene porphyry copper deposits. Evaluation of environmental pollution indices and maximum probable background concentrations revealed that As, Cu, Cd, Mo, Pb, Sb, Se, S, and Zn are highly concentrated in the contaminated sediments, while Cr, Co, Ni, Fe, and Mn show lower enrichment values. Discharges of industrial effluents (especially those contaminated by tailings), reject waste from the semi-autogenous mill, and rock waste drainages are the main anthropogenic contaminant sources. High values of As, Cu, Fe, Mo, Pb, and Zn were associated with the oxidizable, primary sulfide, and residual sediment fractions. Relatively high percentages of Co (>92?%), Cr (>58?%), Cu (>79?%), Fe (>40?%), Mn (>97?%), Ni (>87?%), and Zn (>83?%) in the sediments associated with the rock waste drainages were readily released during the extraction of water-soluble, exchangeable, and carbonate fractions. Sediments that received reject waste drainages were also polluted by As (>351.7?mg?kg^?1), Cu (>1.58?%), Mo (>91.8?mg?kg^?1), Pb (>291.8?mg?kg^?1), and Zn (>762.4?mg?kg^?1). A large percentage of these contaminants were found to be adsorbed and co-precipitated with amorphous Fe-oxides and carbonate phases. The chemical fractionation pattern of the potentially hazardous trace elements corresponded well with the mineralogical composition of the contaminated sediments.     

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.     

Geochemical Behavior of Mine Tailings and Waste Rock at the Abandoned Cu–Mo–W Azegour Mine (Occidental High Atlas, Morocco)

The abandoned Azegour mine is located in the High Atlas Mountains of Marrakesh (Morocco), and was mined for Cu, Mo, and W. About 850,000 t of waste rocks and tailings were deposited on the surface and have been exposed to weathering for 40 years. The remaining acid-producing potential (AP), acid-neutralizing potential, and geochemical behavior of the Azegour Cu-and Mo-rich tailings were investigated. The tailings were found to contain 9.6–19 wt% sulfur, mostly as sulfate (gypsum, anhydrite, and jarosite) while the waste rocks contain less (1.25–6.58 wt%) sulfur. The waste rocks and tailings contain 0.21–9.24 wt% Mo and 0.003–2.78 wt% Cu. The gangue is mostly composed of quartz, talc, chlorite, pyrophyllite, actonolite, clinoptilolite, and alusite. Lead, zinc, cobalt, arsenic, titanium, and nickel are also present. The calcium, which is mainly expressed as calcite, gypsum, scheelite, and powellite, is present at higher concentrations in the waste rocks (18–22 wt% Ca) than in the tailings (4.7–8.6 wt% Ca). Static ABA determinations showed that the Azegour mine wastes still have high AP, 38–205 kg CaCO₃/t in the waste rocks and 46–387.7 kg CaCO₃/t in the tailings. This was confirmed in weathering cell tests, where the Azegour tailings leachate had a pH range of 1.98–3.19 and high concentrations of SO₄ (468–45,400 mg/L), Ca (230–675 mg/L), Fe (3–55,900 mg/L), Mn (0.1–1,430 mg/L), and Cu (2.3–9,000 mg/L). The Mo concentrations were high (35 mg/L) during the two first weeks of kinetics tests; W concentrations were below the 0.005 mg/L detection limit.     

Heavy metal leaching of contaminated soils from a metallurgical plant

Laboratory tests were carried out to determine the primary parameters affecting the efficiency of the process of leaching heavy metals from natural soil collected inside a metallurgical plant in Italy. The soil samples tested consisted primarily of medium density, fine silica sand that had been contaminated with lead and zinc metallurgical wastes by percolating rainwater. Samples were obtained 1–2 m below ground level in an area where the surface consists of artificial strata composed of soil mixed with metallurgical solid waste. The soil layer tested hosts a low-permeability aquifer (at depths generally greater than 10 m below ground level) that is also contaminated by heavy metals. Batch leaching experiments were conducted using acid solutions (acetic, nitric, hydrochloric and sulphuric) as extracting agents. During leaching tests, concentrations of Zn, Pb, Cd, Cu, Mn and Al were monitored. The results indicate that the best leaching solution varies for all analytes and soil samples examined. Statistical analysis was used to identify correlations between efficiency and leaching rate.     

煤矸石对铜尾矿中重金属(Zn,Pb,Cd,Cr和Cu)形态及生物有效性的影响

铜尾砂堆积在地表会随着淋溶和风化作用溶出重金属元素,对环境产生一定危害,其生态修复的关键是进行基质改良,进行植物修复。通过黑麦草盆栽实验,将淮南煤矸石添加入铜尾砂,探讨矸石对铜尾砂中重金属行为的影响。结果表明:矸石添加能显著提高铜尾砂p H、有机质和养分水平(总氮、总磷和总钾),缓解尾矿砂贫瘠环境。矸石添加后,铜尾砂中Zn,Pb,Cd和Cu的交换态和碳酸盐结合态重金属逐步向铁锰结合态、有机结合态和残渣态转化(除个别处理Pb和Cu残渣态),铜尾砂中有效态Zn,Pb,Cd和Cu浓度不断降低,从而降低了黑麦草中相应重金属浓度,总体表现为铜尾砂-黑麦草系统内Zn,Pb,Cd和Cu生物活性降低效应。然而,由于矸石中Cr浓度相对铜尾砂偏高,其添加会引起尾矿砂中有效态Cr浓度及Cr迁移性增加而增大黑麦草对Cr的吸收。因此,煤矸石可对尾矿砂中Zn,Pb,Cd和Cu产生一定稳定化作用,而虽然矸石内源性Cr会释放到铜尾砂,其也可被黑麦草富集,由此,煤矸石可视为一种潜在的废弃物改良剂,对铜尾砂具有一定生态改良潜力。     

Assessment of Metals Pollution from Tailing Sites in the North Caucuses Region,Russia

The concentrations of metals were determined in the water and bottom sediments of both the Urup and Kuban Rivers near tailings sites in the North Caucasus region of southern Russia. The average concentrations in the Urup followed the order Fe?>?Mn?>?Pb?>?Cu?>?Zn?>?Cd?>?Ni?>?Co, while in the Kuban, the order was Fe?>?Pb?>?Zn?>?Ni?>?Mn?>?Cd, with copper and cobalt not detected. The levels of Zn, Cu, Pb, Cd, and Ni were above Russia’s maximum permissible concentration in both rivers. The water pollution index (WPI) values in Urup ranged from 12.97 to 28.17, indicating that the river is extremely polluted (Class VII), while the WPI value for Kuban ranged from 2.34 to 4.33 downstream of the tailings site, which corresponds to Class IV (contaminated). Calculating the coefficient of accumulation in sediments (CAS) revealed that in Urup, the CAS values for Ni and Cu were 3046 and 11638, respectively, which indicates an emergency environmental situation, while for Co, Fe, and Mn, the situation is high level chronic pollution (CAS?>?10⁴). The Kuban CAS values of Fe and Mn were also >?10⁴, again highly and chronically polluted. Most of the metals in both rivers are bound to the sediments, with minimal mobility. The potential ecological risk is moderate to considerable in Urup, and low in the Kuban River.     

贵州都匀牛角塘铅锌矿区选矿尾矿中重金属元素分布特征研究

在检测贵州都匀牛角塘铅锌矿区尾矿中铅、锌、砷、锑、铊、铬、铜、锰、镍、镉和汞含量的基础上,以贵州省A层土壤背景值为参比,利用单因子污染指数法、内梅罗综合污染评价法、地累积指数法、潜在生态危害指数法对矿区尾矿中重金属污染状况进行综合评价。结果表明,矿区6个堆场尾矿突出污染元素为镉、锌,永胜堆场尾矿中突出污染元素为汞、砷、锑。矿区6个堆场尾矿原矿石主要来源于矿区铅锌矿,永胜堆场尾矿的原矿石主要来源于丹寨、独山、榕江一带的汞矿和锑矿。相关性分析说明了尾矿中重金属元素的来源,尾矿金属元素资源再利用意义不大,且潜在环境问题突出。四种方法评价结果一致,均反映矿区尾矿突出污染元素为镉、锌,永胜堆场尾矿突出污染元素为汞、砷、锑。各堆场的综合生态危害指数大小顺序为永胜>陈工>垠垠>山佳>水牛石>狮子洞>振霖,永胜堆场重金属潜在环境污染问题最严重,应当引起环保部门的重视。     

Water quality variation of mining-subsidence lake during the initial stage: cases study of Zhangji and Guqiao Mines

Four quarters?? water collecting and monitoring samples were done in the mining subsidence lakes of different water storing periods (2 to 7 years), considering the water storing time and pollution sources state of the subsidence lakes. The following indexes were discussed such as organic indexes (TOC, COD_Mn, BOD, COD), nutrient salts (TN, NH ₄ ⁺ , NO ₃ ^? , NO ₂ ^? , Kjeldahl Nitrogen, TP, PO ₄ ^3? ), etc. It is shown that water quality of the mining subsidence lake during the initial stage (2 years to 7 years) can stay relatively stable with a fluctuation during different quarters in a year, which can reach class III or IV of the Surface Water Environmental Quality Standard.     

Assessment of Trace Elements in Soils and Mine Water Surrounding a Closed Manganese Mine (Anti Atlas,Morocco)

Five mine water samples, 23 topsoil samples, and four mine waste (tailings) samples were collected to assess the effects of a closed Moroccan Mn mine. Based on the pH, electrical conductivity, and concentrations of sulphate, Cu, Zn, As, Cd, Pb, and Mn, mining has not adversely influenced mine water quality. Soil samples were analyzed for 23 chemical elements and the results were interpreted by univariate and multivariate statistical techniques. Based on an enrichment factor (EF) calculation, only Cd, As, V, and Mn were selected for further study. Geochemical background (GB) and geoaccumulation index (I_geo) were determined for these elements to differentiate between geogenic and anthropogenic enrichment. The GB values showed that the Tiwiyyine soils contained a high geogenic content of Cd, As, V, and Mn that reflected the geochemistry of the parental rocks in this mineralized region. The I_geo calculation revealed that these soils were moderately influenced by anthropogenic activity, which had increased the concentrations of those elements. Finally, geochemical maps revealed that mining was likely responsible for the anthropogenic soil pollution.     

Evaluation of Metal Attenuation from Mine Tailings in SE Spain (Sierra Almagrera): A Soil-Leaching Column Study

A laboratory study was undertaken using mine tailings and soil columns to evaluate some of the natural processes that can control the mobility of metals at Pb–Ag mine tailings impoundments. The effects of buffering, pH, and salinity were examined with tailings from the El Arteal deposit. Al, Ba, Cd, Cu, Fe, Mn, Ni, Pb, Sr, and Zn were mobilized when the tailings were leached. However, when the mine tailings were placed above alluvial soils, Al, Ba, Cd, Cu, Mn, Pb, and Zn were retained, although Fe and Sr clearly remained mobile. Most of the metal retention appears to be associated with the increase in pH caused by calcite dissolution. The sorption of some metals (Cu, Pb, and Zn) onto oxyhydroxides of Fe and Mn, sulphates, clay materials, and organic matter may also explain the removal of these metals from the leachate.     

Column Kinetic Tests Assessing Geochemical Behavior of Mine Wastes in the Jerada Coal District (Morocco)

The Jerada anthracite mine in Morocco was abandoned in 2001 after producing approximately 20 million tonnes of solid waste. The acid generating potential of these wastes was determined by performing tests on five samples collected from relatively older and more recent waste deposits. No carbonate minerals were identified. Pyrite was the only sulphide mineral observed and much of it had been completely transformed into Fe-oxides. Analysis of the waste indicated low levels (<1 %) of Ca and Mg, while Fe and Al concentrations generally exceeded 5 %. Modified Sobek static tests and column kinetic tests were conducted for 24 months. The static test results were not conclusive (20 <net neutralising potential <20 Kg CaCO₃/t). Leachates from the kinetic tests for three of the five samples showed an initially acidic pH, while those of the remaining two became acidic by the end of the tests. Sulfate concentrations (SO₄ ^2?) decreased over time from 5000 to 200 mg/L.     

Removal of Metals and Acidity from Acid Mine Drainage Using Liquid and Dried Digested Sewage Sludge and Cattle Slurry

The metal removal and neutralization capacities of digested sewage sludges from municipal wastewater treatment plants, cattle slurry (liquid manure), and Biofert granules (dried granular anaerobic sludge) were compared under batch conditions using synthetic AMD (pH 2.8) containing high concentrations of Al, Cu, Fe, Mn, Pb, and Zn (100, 15, 270, 15, 2, and 30 mg/L, respectively). The effects of contact time and solids concentration were examined. Metal removal was variable for all materials. Contact time had a significant effect, with total removal often increasing over the experimental time interval (i.e. 30 min to 24 h). Removal efficiency (%) was generally highest for Cu, Pb, and Al, while Mn and Zn were the least removed. Cattle slurry was the best material for metal removal, with the following maximum removals at a solids concentration of 12.9 g/L: Cu >98 %, Al >98 %, Fe >60 %, Mn >18 %, Pb >96 %, and Zn >60 %. Metal removal using digested sewage sludge reached 88 % for Al, 98 % for Cu, 94 % for Pb, and 30 % for Zn. Neutralization was complete within 30 min after AMD was mixed with digested sludges or cattle slurry, with the pH reaching a maximum of 5.5 with the slurry. In contrast, neutralization by the Biofert granules only reached equilibrium after 300 min, and pH remained <4.0 except at high solids concentrations. It appears that recycled waste-derived organic materials can neutralize AMD and remove dissolved metals by adsorption and precipitation, creating a more treatable waste stream or one that could be discharged directly to surface water. Potential methods of safe disposal of metal-enriched organic materials are discussed.     

Carbothermal Reduction of Barium Sulfate-Rich Sludge from Acid Mine Drainage Treatment

The alkali–barium–calcium (ABC) desalination process is basically an integrated lime/limestone neutralisation process combined with a sulfate removal stage using barium carbonate (BaCO₃), and a sludge processing stage. The BaSO₄/CaCO₃ sludge generated during the desalination stage is treated to recover BaS and CaO by dewatering and thermal processes, with the ultimate goal of producing sulfur and recovering BaCO₃. BaCO₃ is the main raw material used for sulfate removal and its recovery ensures that the ABC process is environmentally and financially sustainable. South Africa is also a large importer of sulfur. We evaluated the optimum conditions for the thermal treatment of BaSO₄/CaCO₃ sludge to recover by-products. A high temperature tube furnace was used to reduce BaSO₄/CaCO₃ sludge obtained from a pilot plant test conducted at a gold mine shaft. We used response surface methodology to investigate the combined effects of relevant process variables (time, temperature, and the carbon/barium sulfate (C/BaSO₄) molar ratio to maximize the reduction of BaSO₄/CaCO₃ sludge. At optimal process conditions (T = 1,028 °C; molar ratio of C/BaSO₄ = 2.8 mol/mol), the tube furnace yield of BaS from waste sludge was over 78.5 % after 35 min. Furthermore, the results were similar to those generated by roasting a laboratory-grade mixture of barite and calcite concentrates.     

The Oxidative Precipitation of Thallium at Alkaline pH for Treatment of Mining Influenced Water

Thallium (Tl) may exceed regulatory limits in mining-influenced water (MIW) associated with processing cadmium, copper, gold, lead, and zinc ores. It is a toxic metal that is soluble over a wide pH range, resulting in both persistence in the environment and poor removal by conventional lime precipitation. This study evaluated the effect of potassium permanganate (KMnO₄) at alkaline pH on Tl removal from MIW in batch experiments. The oxidation of Tl⁺ to Tl³⁺ by KMnO₄ and subsequent Tl removal was explored at Tl concentrations of ≤1 mg/L in synthetic and actual MIW. In addition to Tl, the synthetic MIW contained ≈5 mg/L of Mn, while the actual MIW contained >10 mg/L of Al, Cu, Fe, Mn, and Zn and had a pH ≈ 2.5. Dissolved Tl <2 μg/L in synthetic MIW was achieved at a pH ≈ 9 (CaO addition) and ≥5 mg/L of KMnO₄. In the actual MIW, dissolved Tl <2 μg/L was achieved at pH ≈ 9 and ≥12 mg/L of KMnO₄. The Tl removal mechanism is complicated due to the presence of reduced Mn in the synthetic MIW and multiple metals in the actual MIW. However, effective Tl removal was achieved by adding KMnO₄ to synthetic and actual MIW at alkaline pH.