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.     

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.     

Pilot-scale Studies of Different Covers on Unoxidised Sulphide-rich Tailings in Northern Sweden: the Geochemistry of Leachate Waters

Abstract.  Leachate water quality from covered and uncovered unoxidised sulphide-rich tailings in six pilot-scale (5x5x3 m³) test cells was monitored during 2004 and 2005. The covers consisted of a layer of clayey till, sewage sludge, apatite or Trisoplast (a commercial mixture of tailings, bentonite, and a polymer). All layers were protected by an unspecified till except in one reference cell, where the tailings were left open. All leachate waters showed near-neutral pH as a result of neutralization by calcite in the tailings and by Ca(OH)₂ added prior to deposition. Average dissolved sulphur concentrations in the leachates were ≈ 600 mg L^-1, except in the cell with sewage sludge (300 mg L^-1). The source of sulphur was mainly pyrite oxidation, but residual sulphur probably remained from the enrichment process. The near-neutral pH favoured precipitation of metal-(oxy)hydroxides with subsequent removal of trace elements such as Cd, Cu and Pb (< 15 μg L^-1) from the solutions. High concentrations of Co, Mn, Ni, and Zn were found in leachates from the apatite, Trisoplast, and uncovered tailings cells. High As concentrations were found in the leachates in the sewage sludge and clayey till cells. The lowest metal concentrations, redox potential, and highest pH were found in the sewage sludge cell. Decreased elemental metal concentrations during 2004 suggest improved performance over time.     

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.     

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.     

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.     

Use of Marine Waste Extract as a Nitrogen Source for Biological Sulfate Reduction: Development of a Suitable Alternative

Marine wastes extract (MWE), prepared from marine organic wastes, was used to develop an alternative nitrogen source for sulfate-reducing bacteria (SRB) in environments like acid mine drainage that are acidic in nature and contain high levels of sulfate and dissolved metals. The MWE contains 13.95 g L^?1 of nitrogen, and other micronutrients like K, Na, P, S, Ca, Fe, Mg, Mn, Zn, Co, Cu and Ni, and has a C/N ratio of 0.107. A modified SRB medium (MSRB) was developed by replacing the commercial nitrogen source of standard SRB growth medium with MWE. MSRB was compared with modified Postgate B, Postgate B, and Widdel and Pfennig media, which contained bactopeptone and NH₄Cl, as nitrogen sources. Results showed that the growth media could support a total microbial population of 2.8 × 10¹²–6.2 × 10¹² cells mL^?1 with 96, 80, 92.5, and 65 % SRB in MSRB, Postgate B, modified Postgate B, and Widdel and Pfennig media, respectively. The sulfate reduction efficiency was 97, 87, 72, and 68 % at reduction rates of 12.41, 11.10, 4.35, and 8.8 mg L^?1 h^?1, respectively, for the same media. We conclude that MWE could be a cost-effective substitute for commercially available nitrogen sources for SRB for large-scale treatment of sulfate-rich wastewater.     

Effect of Ore Mineralogy and Bedrock Lithology on Metal Loading Rates and Acid-Mine Drainage: Bayhorse Creek,Idaho and the North Fork of the American Fork River,Utah

Metal contamination of the water in two streams was investigated at the Ramshorn Mine along Bayhorse Creek in Idaho, and the Pacific Mine along the North Fork of the American Fork River in Utah. The studies were conducted to determine what remediation measures should be implemented at each site to reduce metal loads in the streams. Discharge measurements and chemical analyses of filtered and unfiltered water samples allowed dissolved and total metal loads to be calculated. Copper, Fe, Mn, Pb, Zn, and As were found at both sites, and Cd also was present at the Utah site. Of these, Fe had the highest dissolved and total loading rates at the Ramshorn Mine, with Mn and Zn having intermediate rates; Fe and Zn had the highest loading rates at the Pacific Mine. Hydrous ferric oxides, particularly ferrihydrite, are abundant at both sites. Pyrite is the iron source at the Pacific Mine, while it is siderite at the Ramshorn Mine. The lack of sulfide at the latter site inhibits acid mine drainage (AMD) formation, and the presence of dolomite provides abundant alkalinity to neutralize any AMD that might be generated. PHREEQC was used to gain insight into the metal phases and oxidation states, to calculate saturation indices, and to perform surface sorption modeling. The results suggest that most of the metals at both sites are transported in the suspended rather than dissolved state, As occurs exclusively in the less toxic As⁵⁺ form, and several metals are likely sorbed to ferrihydrite. Based in part on the results of these studies, the US Forest Service removed the tailings at the Pacific Mine site, but only capped and regraded the tailings pile at the Ramshorn Mine.

     

Soil pollution related to the mercury mining legacy at Asturias (Northern Spain)

Asturias (NW Spain) is regarded as an important metallogenic province with particular emphasis on mercury (Hg) and arsenic (As). Different Hg mineral species, as well as As-rich minerals, are found in the ore deposits in this part of Spain. Metallurgical activity to extract Hg from these ores was also carried out at many sites. Consequently, the combination of emissions during mining of the ore and additional releases during the inefficient roasting operation gave rise to significant releases of Hg and As to the surrounding soils. All the Hg mines of the district were abandoned before the introduction of any environmental regulations; consequently, the environment is globally affected. Mean Hg contents in soils range from 42 to 155 mg kg^?1, whereas average As concentrations range from 17 to 831 mg kg^?1.     

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.     

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.     

Rotifer Diversity in the Acidic Pyrite Mine Pit Lakes in the Sudety Mountains (Poland)

The diversity of rotifers was studied in three artificial water bodies (Azure Lake, Yellow Lake, and Purple Lake), which were once pyrite mines. The physicochemical parameters and the zooplankton composition of the water were determined. Azure Lake had a pH of 3.4–6.9, conductivity values of 165–194 µS cm^??1, and low concentrations of sulphate, calcium, magnesium, copper, and iron, while the other lakes had a pH of 2.6–2.9, a conductivity of 1636–3400 µS cm^??1, and high concentrations of sulphate (up to 2863 mg dm^??3), Cu (up to 2650 µg dm^??3), and Fe (up to 178.3 mg dm^??3). The rotifer community in the lakes comprised 27 taxa (15 in Azure Lake, 13 in Purple Lake and 14 in Yellow Lake). We also found two species that are rarely observed in Poland (Aspelta cincinator and Elosa spinifera), and three species commonly found in acidic water (E. worallii, Cephalodella delicata, and C. hoodi). The types of rotifers in Azure Lake differed from those in the other two lakes. The Shannon–Weaver biodiversity index (H′) was the highest in Purple Lake (H′?=?1.255) and lowest in Azure Lake (H′?=?0.455). The effect of some of the physicochemical parameters on rotifer diversity is discussed.     

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.     

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.     

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.     

Stream bottom sediments as a means to assess metal contamination in the historic mining district of Almadén (Spain)

Located in the southern half of Spain, Almadén is the world’s largest Hg district and mercury has been mined there for over 2000 years. Its slag heaps and old metallurgy plants represent a risk to watercourses that flow through the district and receive the run-off from the mines. This study collected sediment samples along the length of the main watercourses in the mining district. High levels of heavy metals were detected, with Hg levels varying between 1.77 and 255.88 mg kg^?1, Pb levels between 20.59 and 131.07 mg kg^?1 and Zn levels between 59.06 and 131.07 mg kg^?1. The dispersion of these heavy metals in rivers as a result of mining activities has caused sediment quality degradation. As such, when measured using reference indexes such as the SeQI and the EF, sediment quality for the entire district is practically poor, due to anthropogenic contributions, with the concomitant threat to the surrounding environment.     

Alkalinity generation and metals retention in a successive alkalinity producing system

Alkalinity generation and metals retention were evaluated during the initial year of operation of a treatment wetland, consisting of four 185 m² inseries cells comprised of alternating vertical-flow anaerobic substrate wetlands (VFs) and surface-flow aerobic settling ponds (SFs). The substrate in the VFs consists of spent mushroom substrate (SMS) and limestone gravel, supplemented with hydrated fly ash in a 20∶10∶1 ratio by volume. Approximately 15±4 L/min of acid mine drainage (AMD) from an abandoned underground coal mine in southeastern Oklahoma, USA, was directed to the system in October 1998 (mean influent water quality: 660 mg L⁻¹ net acidity as CaCO₃ eq., pH 3.4, 215 mg L⁻¹ total Fe, 36 mg L⁻¹ Al, 14 mg L⁻¹ Mn, and 1000 mg L⁻¹ SO₄ ⁻²). Flow through the first VF resulted in substantial increases in alkalinity, decreased metal concentrations and circumneutral pH. 258±84 mg L⁻¹ of alkalinity was produced in the first VF by a combination of processes. Final discharge waters were net alkaline on all sampling dates (mean net alkalinity=136 mg L⁻¹). Total Fe and Al concentrations decreased significantly from 216±45 to 44±28 mg L⁻¹ and 36±6.9 to 1.29±4.4 mg L⁻¹, respectively. Manganese concentrations did not change significantly in the first two cells, but decreased significantly in the second two cells. Mean acidity removal rates in the first VF (51 g m⁻² day⁻¹) were similar to those previously reported.     

Factors Controlling the Migration of Tailings-Derived Arsenic: A Case Study at the Yara Siilinjärvi Site

The behaviour of arsenic (As) derived from tailings was investigated at the Yara Siilinjärvi apatite mine and industrial site in eastern Finland. The study assessed factors influencing the migration and fate of As and compared the anthropogenic As load to the natural geogenic background. Environmental risks related to As were assessed by examining the As concentrations in humus, glacial till, aquatic sediments, groundwater, and surface water. The occurrence and fractionation of As and the presence of secondary precipitates and geochemical transformations in the tailings and in the ambient soil and sediment were evaluated by selective extraction. The water-derived emissions were evaluated by field measurements, hydrogeochemical analysis, and modelling. Results indicate elevated environmental risks due to dust and seepage emissions from the tailings since the concentrations and mobility of As and other potentially harmful elements (PHEs) such as Co, Ni, and Zn were elevated relative to the geogenic background. These elements were mainly associated with Fe (oxy)hydroxides in the soil and their mobility was closely linked to Fe biogeochemistry. Additionally, although the concentrations of As and PHEs were high in the tailings pond and seepage water, they decreased in ambient groundwater and surface water, indicating Fe (oxy)hydroxide stability. This was supported by hydrogeochemical modelling, which indicated precipitation of Fe oxides and hydroxides. According to speciation modelling, As was present mainly as toxic trivalent arsenious acid (H₃AsO₃) in groundwater and as the less toxic pentavalent As acid (H₂AsO₄ ^? and HAsO₄ ^2?) in surface water.     

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.     

Assessment of contaminants transport in a watershed affected by acid mine drainage,by coupling hydrological and geochemical modeling tools

Erini Stream (Thrace, northeastern Greece) is adversely affected by the presence of an abandoned mixed sulfide mine located in the upper watershed. The GIS based model SWAT (Soil Water and Assessment Tool) was applied to characterize hydrologic processes in the watershed. Model performance was evaluated by comparing the simulation results with field data including flow and concentration measurements from 12 monitoring points, for the time period from June 2005 to July 2006. Flow rate results indicated good agreement between simulated and measured data, with coefficient correlations R² in the range of 0.74–0.89. Simulation was focused on the dispersion of three pollutants, Zn, Cd and Mn. Using SWAT alone, simulation results systematically overestimated pollutants levels in Erini Stream.Geochemical model PHREEQC was used in combination with SWAT to obtain more accurate predictions regarding contaminants concentrations along the course of Erini Stream. The profiles of main metal contaminants, i.e. Zn, Cd and Mn, under wet conditions, were described with satisfactory precision assuming equilibrium with the carbonate minerals ZnCO₃·H₂O and otavite and partial supersaturation with respect to rhodochrosite. However, precipitation of discrete carbonate phases does not seem to be the predominant attenuation mechanism under dry conditions. Coprecipitation or sorption on the surface of precipitating calcite is another potential removal mechanism under these conditions.The methodology presented allows the reliable assessment of acid mine drainage impacts in the downstream aquatic environment and the design of effective measures for its mitigation based on an optimized number of monitoring data.