Removal of Metals and Acidity from Acid Mine Drainage Using Municipal Wastewater and Activated Sludge

Co-treatment of acid mine drainage (AMD) and municipal wastewater (MWW) using the activated sludge process is an innovative approach to AMD remediation that utilizes the alkalinity of MWW and the adsorptive properties of the wastewater particulates and activated sludge biomass to buffer acidity and remove metals. The capacity of these materials to treat AMD was investigated in batch mode metal removal tests using high-strength synthetic AMD (pH 2.8, Al 120–200 mg/L, Cu 18–30 mg/L, Fe 324–540 mg/L, Mn 18–30 mg/L, and Zn 36–60 mg/L). Using material from a range of MWW treatment plants, the performance of screened and settled MWW, activated sludges with mixed liquor suspended solids (MLSS) concentrations of 2.0 and 4.0 g/L, and return activated sludges with 6.0 and 7.4 g/L MLSS were compared. Similar trends were observed for the MWW and activated sludges, with removal efficiency generally decreasing in the order Al = Cu > Mn > Zn > Fe. Trends in Fe removal using settled MWW and activated sludges were highly variable, with removal <30 %. Using activated sludges, average removal efficiencies for Al, Cu, Mn, and Zn were 10–65 %, 20–60 %, 10–25 %, and 0–20 %, respectively. Sludge solids concentration was an important controlling factor in metal removal, with removal of Al, Cu, Mn, and Zn increasing significantly with solids concentration. Municipal wastewaters had greater neutralization capacities than activated sludges at high AMD loading ratios. Mixing AMD with screened MWW gave the highest removal efficiency for all metals, achieving average removal of 90–100 % for Al, Cu, and Fe, 65–100 % for Zn, and 60–75 % for Mn. These empirical findings are useful for developing process design parameters in co-treatment systems. Utilizing MWW and activated sludge to remediate AMD can potentially reduce materials and energy requirements and associated costs.     

Assessment of Soil and Water Contamination at the Tab-Simco Coal Mine: A Case Study

In 1996, the Tab-Simco site, an abandoned coal mine 10 km southeast of Carbondale, Illinois, was listed as one of the most highly contaminated AMD sites in the mid-continent region. A suite of impacted soil and water samples were collected from various locations to characterize the current extent of AMD pollution, following standard U.S. EPA protocols. The mean pH of soil and water samples were found to be 2.69 and 2.07, respectively. The mean sulfur content of the soil samples was 0.5 %. The AMD-impacted soils contained high concentrations of Fe, Zn, Ni, Cr, Cu, Pb, and As. The AMD also contained high concentrations of Fe, As, Zn, Pb, Cr, Al, Cd, Cu, and Ni, as well as \({\text{SO}}_{4}^{2 - }\), all of which were significantly above their U.S. EPA permissible limits for surface water.     

Treatment of Acid Mine Drainage Using a Fly Ash Zeolite Column

Acid mine drainage (AMD) and fly ash from thermal power plants both pose substantial environmental problems in India. Fly ash from the Talcher super thermal power plant was converted into zeolite and used in a column to treat AMD from the abandoned Gorbi opencast mines (Singrauli coalfields, NCL). The pH of the mine water increased, and 100 % of the total hardness, Ca hardness, Mg hardness, Mn, Zn, Pb, Cd, Ni, and acidity were removed, along with 99 % of the Fe and 90 % of the Cu.     

Thallium and Other Potentially Toxic Elements in the Baccatoio Stream Catchment (Northern Tuscany,Italy) Receiving Drainages from Abandoned Mines

Acid mine drainages (AMD) have adversely affected the southern Apuan Alps (northern Tuscany, Italy). The study particularly focuses on the Baccatoio stream, which receives AMD from the abandoned Pollone and M. Arsiccio mines. The mine waters have an average pH of 2.2 and contain potentially toxic elements (PTE) at concentrations that exceed the Italian regulatory threshold for Al, Fe, Mn, Cu, Zn, As, Ni, Co, Cd, Sb, Pb, and Tl. The AMD flow directly into the stream, severely contaminating it. Downstream of the mined areas, the pH increases and most PTE (especially Fe, Al, As, and Pb) are readily scavenged from the stream waters by precipitation and/or adsorption. However, Tl, which peak at 1000 µg/L in the AMD, behaves almost conservatively along the stream flow path, undergoing only dilution, and remains at or above the concentration of concern of 4 µg/L almost to the coastline, before sharply decreasing to 0.5 µg/L where seawater is encountered. Since the stream water was locally used for irrigation, these observations may have important environmental and public health consequences in such a densely populated area.     

Assessment of Metals Loading in an Acid Mine Drainage Watershed

Watershed-scale modeling can be useful in identifying the main environmental factors and the physical mechanisms responsible for acid mine drainage (AMD) formation, attenuation, and impacts. Since flow rates and water quality of the AMD and receiving streams are related to the rainfall-runoff relationship and associated contaminant dissolution, we thought that hydrologic analysis of the mined area and surrounding drainage basin should be the starting point in documenting the source and fate of AMD contaminants. Further modeling of AMD pollutants could then be performed in terms of metal concentrations and loading at the watershed scale. In this study, monitoring was conducted in the Geopung mine watershed; the watershed analysis risk management framework (WARMF) model was used to evaluate the effect of AMD contributions to downstream metal concentrations. The hydrologic model of the basin was calibrated and verified with rainfall and streamflow data, and the water quality model was calibrated for the dissolved concentrations of metals (Cd, Cu, Zn, and Pb), using discharge data gathered in 2009. There was a strong correlation (r = 0.93) between the observed and simulated runoff values plus high Nash–Sutcliffe model efficiency (NSE = 0.89) and low average percent difference between predicted and measured values (%Diff = 0.46). Subsequent model validation using data gathered in 2010 also showed good agreement (%Diff = 9.76; NSE = 0.77; r = 0.91) between the observed and simulated values. For the metals, the model was calibrated using data from 2010; the correlation between the observed and simulated values was quite good (r = 0.80–0.41).     

The Potential Use of Phosphatic Limestone Wastes in the Passive Treatment of AMD: A Laboratory Study

In Morocco, there are many sedimentary phosphate mines that produce large quantities of phosphatic limestone wastes (PLW) that contain calcite (46 wt%) and dolomite (16 wt%). These mines are located near contaminated sites, such as the abandoned Kettara pyrrhotite mine. The surface drainage water at the Kettara mine site has a pH of 2.9–4.2 and elevated concentrations of SO₄ (from 47 to 5,000 mg/L) and Fe (from 1 to 1,200 mg/L). The efficiency of PLW was assessed in the laboratory as an alternative alkaline material for passive acidic mine drainage (AMD) treatment. A series of experiments were carried out using a synthetic AMD (pH 3) containing Fe (500 mg/L), SO₄ (3.4 g/L), Ca (220 mg/L), Al (160 mg/L), Mn (20 mg/L), Zn (15 mg/L), Cu (23 mg/L), and trace amounts of Co, Cr, and Ni. Experiments were done in both anoxic and oxic conditions, in batch and column tests, with hydraulic retention times of 24 and 15 h, respectively. The PLW efficiently increased the alkalinity and pH, inducing precipitation of most metals. The neutralizing capacity of PLW prepared at different particle sizes (0.8 mm–0.5 cm, 0.5–1, 1–2, and 2–3 cm) was found to be similar in batch tests. The initial AMD value increased from 3 to 5–6.5 during the batch tests and 6.5–8 in the columns. In batch tests under anoxic and oxic conditions, there was a significant decrease in concentrations of Fe (500–120 mg/L), Al (160–1.7 mg/L), and Cu (23–0.002 mg/L). In the column tests, Al and Cu decreased (177–2.5 and 26–0.002 mg/L, respectively), while Fe decreased less significantly (618–300 mg/L). The availability and low cost of the PLW make its use in passive AMD treatment potentially feasible.     

改性煤矸石吸附Cr（VI）的研究

以改性煤矸石对模拟含Cr(VI)废水进行吸附实验。结果表明,在pH值为1.0、吸附时间60min、改性煤矸石用量5g/L时,对进水Cr(VI)为50mg/L的废水进行处理,Cr(VI)的去除率达到99.98%,处理后水样中Cr(VI)含量小于0.50mg/L,达到国家排放标准。利用Freundlich等温式和Langmuir等温式对其吸附进行描述,表明改性煤矸石易于吸附Cr(VI),吸附属于化学吸附。     

Lime Treatment of Mine Drainage at the Sarcheshmeh Porphyry Copper Mine,Iran

Laboratory and field treatment tests were performed to evaluate the effectiveness of lime treatment for mitigation of environmental effects of acid mine drainage (AMD) at the Sarcheshmeh porphyry copper mine. AMD associated with the rock waste dumps is contaminated with Al (>36,215 μg/L), Cd (>105 μg/L), Co (>522 μg/L), Cu (>53,250 μg/L), Mn (>42,365 μg/L), Ni (>629 μg/L), and Zn (>12,470 μg/L). The concentrations of other metals (Fe, Mo, Pb, and Se) are low or below detection limits (As, Cr, and Sb). Due to the very high Al and Mn content and the low concentration of Fe, a two-stage lime treatment method was chosen for the laboratory tests. In the first stage, the AMD was treated at four pH set points: 7.5, 8.9, 9, and 10. In the second stage, after removing the sludge at pH 9, treatment was continued at pH 10 and 11. The results indicated that a two-stage treatment method was not necessary because elements such as Al, Cu, Co, and Zn were easily treated at pH 7.5, while complete removal of Cd, Mn, and Ni only required a pH of 10. Increasing pH during the treatment process only caused a slight increase in Al. Field treatment tests support the laboratory results. Lime treatment of highly contaminated AMD from dump 11, using simple low density sludge pilot scale equipment, show that contaminant metals are treatable using this method. The mean treatment efficiency for contaminant metals was 99.4% for Al, % for Cd, 99.6% for Co, 99.7% for Cu, 98.5% for Mn, 99.7% for Ni, 99% for U, and 99.5% for Zn. The optimum pH for AMD treatment by lime was in the range of 9–10. The produced sludge in the treatment process was highly enriched in the contaminant metals, especially Cu (>7.34%), Al (>4.76%), Mn (>2.94%), and Zn (>1.25%). A correlation coefficient matrix indicates that the distribution pattern of the contaminant metals between soluble and precipitated phases is consistent with the hydrochemical behavior of the metals during the lime treatment process.     

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.     

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 Mineralogy and Geochemistry at the Abandoned Haveri Au–Cu Mine,SW Finland

Fourteen samples from the Haveri Au–Cu mine tailings were studied by reflected-light microcopy, scanning electron microscopy, X-ray powder-diffraction, and sequential extraction methods, and 12 water samples were analyzed for total and dissolved elements to delineate the extent of sulfide oxidation and its impact on nearby surface waters. Water-soluble, adsorbed-exchangeable-carbonate (AEC), Fe (oxy)hydroxides, Fe oxide, and Fe sulfide fractions were extracted sequentially. The oxidation layer was found to vary from 50 to 140 cm: the upper part was nearly depleted in primary sulfides, especially pyrrhotite [Fe_(1?x)S] and pyrite (FeS₂); in the lower part, discontinuous cemented layers were detected. Secondary Fe (oxy)hydroxides and Fe oxyhydroxysulfates were abundant in the oxidation layer and were slightly enriched in trace elements, including As (up to 80 mg/kg), Cu (300 mg/kg), and Zn (150 mg/kg). Almost half of the As (average 25 mg/kg) were present as secondary minerals susceptible to redissolution. The pH of the vadose tailings varied from 2.46 to neutral, and the total sulfur content varied from 1 to 6.5% (average 2.9%). Aqua regia extraction showed that the Haveri tailings are characterized by low concentrations of the elements Cd, Cr, Pd, and slightly elevated concentrations of As, which are present at very low concentrations in the surface water (<6 μg/L). However, runoff that flows on top of the tailings and discharges into the nearby lake carries Co, Cu, Ni, and Zn (concentrations of each range from 500 to 1,800 μg/L). Additionally, dissolution of sulfides and Fe precipitates may mobilize trace metals in the ground water. Thus, overall, there is a small continuous release of AMD into Lake Kirkkojärvi, but the environmental impacts to the lake are presently small.     

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.     

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.     

某工业废渣堆放场地重金属污染特征与健康风险评估

以某工业废渣堆积场为例,探讨了该场地废渣、土壤和地下水中重金属污染特征,着重评估了重金属污染对人体的致癌风险和危害商值。结果表明:1)场地废渣中8种重金属(As、Cu、Ni、Zn、Cd、Pb、Cr、Hg)均有不同程度超标,其中As污染范围最大(超标率达91%),Cr存在高污染集中区,土壤中Cu、Ni、Zn和Cd浓度超出当地背景值,地下水中As和Ni也存在超标现象;2)废渣和土壤中的As、Ni和Cr三种重金属的致癌风险水平均超过了致癌风险可接受水平(1.0×10^-6),其中Cr的致癌风险最高,高达5.3×10^-3,相同金属元素废渣的致癌风险值大于其在土壤中的风险值;3)废渣中As、Cr和Cd的危害商值大于其可接受水平(1),其中Cr的危害商值最大(高达7.5),土壤中重金属的危害商值基本在可接受范围(除As外);4)三种暴露途径按贡献率从大到小依次为:经口摄入>吸入土壤颗粒物>皮肤接触。     

Removal of Trace Metals from Acid Mine Drainage Using a Sequential Combination of Coal Ash-Based Adsorbents and Phytoremediation by Bunchgrass (Vetiver [<Emphasis Type="Italic">Vetiveria zizanioides</Emphasis> L])

Potentially scalable low-cost treatment methods for acid mine drainage (AMD) are very limited. We used a sequential combination of adsorption and phytoremediation by bunchgrass (Vetiver [Vetiveria zizanioides L]) in a semi-batch system to remove Zn, Mn, Ni, and Cu from AMD. The objectives were: (1) to compare the removal of these metals by raw and NaOH-activated coal ash (NaOH-CA); and (2) to determine the effect of sequencing adsorption and phytoextraction on metal removal. The NaOH-CA adsorbed significantly more metals than raw coal ash (RCA) in both batch and semi-batch fixed column experiments, demonstrating the effectiveness of NaOH hydrothermal activation, which forms zeolites. Adsorption by NaOH-CA removed 59.1, 95.7, 67.6, and 77.9% of the Zn, Mn, Ni, and Cu, respectively, compared to 50.6, 95.1, 30.2, and 60.5% for the RCA. Metal removal by phytoremediation was generally less than that by adsorption, accounting for between 3.4 and 54.6% for both adsorbents. Phytoremediation following adsorption by NaOH-CA removed 89.2–99.9% of the metals compared to 70.8–98.5% when phytoremediation followed adsorption by RCA. Overall, relatively high metal removal efficiencies were attained, considering the acidic conditions (pH?<4), at hydraulic residence times of 1 to 5 days. Using coal ash to treat AMD is potentially a low-cost and environmentally friendly option for minimizing the adverse public health and environmental risks associated with both wastes.     

氢氧化镁对重金属离子铜锌的吸附特性研究

研究氢氧化镁对水中Cu(Ⅱ)和Zn(Ⅱ)的吸附热力学和动力学特性,并对氢氧化镁处理重金属离子废水的效果做了总结。结果表明:氢氧化镁用量为0.35 g/L和0.60 g/L时,处理后Cu(Ⅱ)（12 mg/L）和Zn(Ⅱ)（20 mg/L）浓度均低于国家二类污染物一级排放标准;氢氧化镁对Cu(Ⅱ)和Zn(Ⅱ)具有较强的吸附能力,吸附等温线符合Langmuir模型,饱和吸附量分别为76.92 mg/g和37.04 mg/g,计算得到吸附过程的热力学参数ΔG的值分别为-29.32 kJ/mol和-32.20 kJ/mol;二级动力学方程较好地表征了氢氧化镁吸附Cu(Ⅱ)和Zn(Ⅱ)的动力学特性,相关系数均为1.000;从目前研究结果看,氢氧化镁吸附Ni(Ⅱ),Cd(Ⅱ)和Cr(Ⅲ)等均符合Langmuir模型,且吸附效果明显。     

Ca-基膨润土制备重金属废水吸附剂的研究

膨润土因其特殊的晶体结构而具有良好的吸附能力、阳离子交换能力和吸水膨胀能力等性能。近年来，随着人们对其结构和理化性能的进一步了解，膨润土的高层次开发已成为非金属矿物材料的研究热点。文中对钙基膨润土进行了改性处理，并着重探讨了Ca-基膨润土对重金属废水的吸附，并对含Cr^6 和Cu^2 的模拟废水进行了吸附试验，同时比较了钠基土和有机土的吸附效果。进一步探讨了吸附时间及吸附液pH值对改性膨润土吸附Cr^6 的影响。     

淮南矿区煤矸石中微量元素的研究

通过对淮南矿区按煤层和岩性特征系统采样,运用INNA,ICP－MS分析煤矸石中微量元素、冷原子吸收法分析Hg、选择性电极法分析F、化学法分析常量元素,并研究经过科学筛选出的11种重金属元素:Cd,Cu,Ni,Sn,Hg,Mn,As,Cr,Pb,Zn和非金属元素F,初步探讨了这些元素对矿区环境的危害,其中Cd,Cu,Ni,Sn,Hg超过淮南土壤背景值、中国土壤背景值、世界土壤背景值等.Cd 含量是淮南土壤的40倍、世界土壤的7倍;Cu含量是淮南土壤的约2倍、世界土壤约1.5倍;Ni含量是淮南土壤的8倍、世界土壤的4倍;Sn含量是淮南土壤的3倍、世界土壤约2倍;样品中Hg含量是淮南土壤的3 602倍、世界土壤的1 381倍,并指出这种危害是具累积性的.     

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.     

Use of Steel Slag Leach Beds for the Treatment of Acid Mine Drainage

Steel slag from the Waylite steel-making plant in Bethlehem, Pennsylvania was leached with acidic mine drainage (AMD) of a known quality using an established laboratory procedure. Leaching continued for 60 cycles and leachates were collected after each cycle. Results indicated that the slag was very effective at neutralizing acidity. The AMD/slag leachates contained higher average concentrations of Ba, V, Mn, Cr, As, Ag, and Se and lower average concentrations of Sb, Fe, Zn, Be, Cd, Tl, Ni, Al, Cu, and Pb than the untreated AMD. Based on these tests, slag leach beds were constructed at the abandoned McCarty mine site in Preston County, West Virginia. The leach beds were constructed as slag check dams below limestone-lined settling basins. Acid water was captured in limestone channels and directed into basins to leach through the slag dams and discharge into a tributary of Beaver Creek. Since installation in October 2000, the system has been consistently producing net alkaline, pH 9 water. The treated water is still net alkaline and has a neutral pH after it encounters several other acidic seeps downstream.