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).     

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.     

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.     

Enhancement of Sludge Sedimentation Properties in a Concentrated Acid Mine Drainage Using Nano- and Micro-magnetite Particles

Conventional treatment of AMD involves neutralization with consequent precipitation of metals as hydroxides. In AMD with a high concentration of metals, the settling rate of the sludge/water interface is low. We investigated the use of nano- and micro-magnetite particles to assist the settling and thickening of floc particles. The magnetite was produced from ferrous sulphate crystals (melanterite, Fe₂SO₄·7H₂O) obtained by leaching pyrite from a coal mine. AMD was obtained from the treatment plant at the same mine and the water was neutralized with Ca(OH)₂ at pH 8.7?±?0.1. Laboratory studies were conducted in 1 L test tubes with and without the addition of magnetite particles and a flocculant. Sedimentation curves (interface settling) were generated to evaluate the rate of sedimentation. For the studied effluent, the best option was 4 g L^?1 of magnetite particles and 5 mg L^?1 of high molecular weight anionic polyacrylamide. The magnetite particles were recovered magnetically from the sludge with ≈ 90% efficiency. Thus, the combined use of magnetite and a flocculant increased the sludge settling rate and, consequently, reduced the area needed for settling basins.

     

Using Multiple Methods to Predict Mine Water Inflow in the Pingdingshan No. 10 Coal Mine,China

To ensure safe mining of the no. 2 coal seam in the Pingdingshan No. 10 coal mine, three methods (analogue, big well, and numerical simulation) were used to forecast mine water inflow and their performance. The big well method predicted the largest water inflow: 233.8 m³/h in the ?230 m level and 281.1 m³/h in the ?300 m level. The numerical simulation predicted the least inflow, 205.7 and 228.6 m³/h respectively for the 230 and ?300 m levels; this was closest to the measured values. Based on this work, it appears that combining numerical simulations with other methods are a good way to accurately forecast mine water inflow.     

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.     

Using Numerical Modeling to Understand the Discharge from a Flooded Abandoned Underground Mine

The Rosice-Oslavany coal-mining district, which spans 22 km², is a typical example of a historical mining site where mine works flooded after closure. Mining lasted for 240 years, with shafts reaching depths of 1500 m. A single drainage adit dewatered the mine workings, which were all hydraulically connected. Mine water discharges have stabilized at an average value of 50?60 L/s, significantly exceeding the projected discharge value of 30 L/s. Groundwater flow was modeled to understand the discrepancy between the expected and observed discharges. Comparison of modeling scenarios have confirmed the importance of the hydraulic connection of the mine workings to overlying streams; stream seepage was identified as the key source of the influent mine water. The measured and simulated mine water discharges correlated well with the seepage characteristics of the surface streams.     

Hydrochemical Prediction of Mine Water Inrush at the Xinli Mine,China

Seawater poses a great threat to the Xinli Mine, an undersea gold mine in China. A hydrochemical method was used to assess the risk of sea water inrush into the mine. A detailed hydrochemical survey and sampling were carried out and the concentrations of conservative ions in the mine water were analyzed. Principal component analysis indicated that the potential water inrush channels were located in the hanging wall of the ore-controlling fault. A composite principal component was calculated from the Na⁺, Cl^?, Mg²⁺, SO₄ ^2?, and K⁺ concentrations, which reflected the effects of potash feldspathization and cation exchange, to assess the risk of seawater inrush.     

Impact of a Saline Mine Water Discharge on the Development of a Meromictic Pond,the Rontok Wielki Reservoir,Poland

A characteristic feature of the mines in the Upper Silesian Coal Basin in southern Poland is their highly saline mine water. In the past, this water was often discharged into anthropogenic reservoirs located a short distance from the mines, which completely changed the physicochemical properties of the water. In some cases, it also led to stratification of the reservoir waters, i.e. to the formation of meromictic water bodies. The Rontok Wielki reservoir, a former fish breeding pond, was converted into a settling tank for the highly saline (Cl^? = 38,000 mg/L) water discharging from the Silesia Mine. The water in the tank stratified in three distinct zones: a mixolimnion, chemocline, and monolimnion. The saline mine water input ceased in 2003 and since then, there has been a gradual decrease in the electrical conductivity and [Cl^?] in the reservoir waters. Moreover, meromixis has been entirely eliminated and freshwater breeding species have reappeared. A control, the Rontok reservoir, which was also a breeding pond, but was never used to settle saline mine water, was also studied for comparison.     

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.     

Assessing Pilot-Scale Treatment Facilities with Steel Slag-Limestone Reactors to Remove Mn from Mine Drainage

Pilot-scale mine water treatment facilities were operated for over four years at the Ilwol mine, South Korea. A steel slag-limestone reactor (referred to as the slag reactor) was tested and a successive alkalinity producing system (SAPS) and a SAPS incorporating slag from a basic oxygen steelmaking furnace were compared. The SAPS decreased Mn from 23.3 to 7.4 mg L^?1 on average because the alkalinity generated led to saturation with rhodochrosite. Adding a slag reactor removed Mn down to levels of 0.002–1.8 mg L^?1 from influent Mn as high as 17.1 mg L^?1 with a residence time of 5–25 h. Mn-containing carbonates and oxides were precipitated, which was supported by the geochemical modelling and observed with scanning electron microscopy with energy dispersive spectroscopy. The increased alkalinity in the SAPS before the slag reactor helped remove Mn at a pH range of 8.0–8.3. Mn removal rates and Mn-standardized Mn removal rates in the slag reactor were 0.76 mg L^?1 h^?1 and 0.105 h^?1 in average, respectively. The passive treatment of Mn using an Fe-pretreatment and alkalinity-generation system, a slag-limestone reactor, and a wetland rather than a SAPS including slag, an oxidation-settling pond, and a wetland is suggested to consistently meet the effluent standards for Mn and pH.

     

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.     

Groundwater Source Discrimination and Proportion Determination of Mine Inflow Using Ion Analyses: A Case Study from the Longmen Coal Mine,Henan Province,China

Complex hydrogeological conditions in China’s coal mines have contributed to frequent mine water disasters. A simple and effective method to determine water inflow sources and paths is therefore essential. The Longmen Mine, located in Henan Province, in central China was used as a case study. A Piper diagram and cluster analysis were used to screen the characteristic values of 18 water samples from potential aquifers. A comprehensive fuzzy evaluation of the groundwater ions was carried out to determine the main source of the total mine inflow. Then, based on conservation of ionic masses, a matrix function was established to calculate the groundwater recharge composition. Finally, using measured water inflows for the Cambrian limestone aquifer, the calculated and observed results were compared. The results showed that the Carboniferous Taiyuan Formation limestone aquifer (the L₇ limestone aquifer) accounts for 60.8% of the total mine inflow, while the Cambrian limestone and roof sandstone aquifers account for 34.8 and 4.4% of the inflow, respectively. The normal mine inflow totals about 19,200 m³/day, of which 6,840 m³/day is from the Cambrian limestone aquifer. This agrees well with the calculated value of 6,720 m³/day. Thus, the method is feasible and reliable.     

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.

     

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.     

Source Discrimination of Mine Water Inrush Based on Spectral Data and EGA–PNN Model: A Case Study of Huangyuchuan mine

Methods currently used to identify water sources and predict mine water inrush points are mostly based on water temperatures, water levels, or hydrochemical data. However, these methods are relatively complex. Therefore, to rapidly and effectively identify the source of mine water inrush, an elite strategy was used to optimize a genetic algorithm. The optimized elitist genetic algorithm (EGA) was applied to parameter selection of a probabilistic neural network (PNN) using spectral data to construct an EGA–PNN discriminant model. Water samples were collected from four different sources in the Huangyuchuan Mine in north China, including Permian sandstone fissure water, Carboniferous coal seam roof water, Ordovician limestone water, and Permian mined-out water. Full spectral data of the water samples were obtained, and 80% of the sample data were randomly selected as the training set for the EGA–PNN model. Theoretical analysis and experimental results showed that after 100 iterations, the average recognition rate was ≈ 95.69% with a mean square error average of only ≈ 8.21?×?10^?3. This study provides a novel methodology that can be used to rapidly identify mine water inrush sources in similar geological coalfields elsewhere in northern China.

     

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.     

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.     

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.     

Soil Infiltration,Permeability, and Rock Fracturing Assessment to Establish Water Flow Patterns in a Mine with Acid Mine Drainage

The flow of acid mine drainage (AMD) and neutral water were assessed inside an underground mine using a volumetric capacity technique, while water infiltration through the ground was assessed by performing three double ring constant load infiltrometer tests. Measured infiltration velocities were slow to moderate, between 0.036 and 2.07 cm/h. Total rainwater infiltration for the sub-basin was 0.031 hm³/yr. Tests performed on representative rock cores of the stratigraphical column of the area indicated that the permeabilities of the altered schist was 4.73E?10 cm/s, the tuff was 1.47E?09, and the graphitic phyllite was 2.47E?06. A structural analysis was performed inside the mine to assess fractures and faults using the mine plans for three different levels. Three major discontinuity paths were identified. Since the ground and rock permeabilities were low, the large water volumes inside the mine were attributed to these fractures. The results of this study are being used to understand flow patterns in the mine and to optimally locate a water treatment system to control the AMD.