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Purpose Tailings are generally characterized by severe physicochemical conditions that limit the establishment of vegetation. The present study aimed to select suitable combinations of organo-mineral amendments to improve the physicochemical, biochemical, and biological properties of spolic technosols, highly contaminated with metals. Materials and methods Several substrates were prepared by mixing mine tailings (MT) of an abandoned mining area with non-contaminated agricultural soil (anthrosol), green waste compost, lime, and rock phosphate at different rates: S1 - 50% of MT + 50% of agricultural soil; S2 - S1 + 3% of lime (CaCO3); S3 - S1 + 6% of rock phosphate; S4 - S1 + 10% of compost; S5 - S1 + 10% of compost + 3% of lime; S6 - S1 + 10% of compost + 6% of rock phosphate. Untreated MT and agricultural soil were analyzed immediately, and 8 months after incorporating the amendments. Results and discussion Heterotrophic microorganisms were not recovered from untreated MT due to the highly acidic pH and available metal concentrations. However, the addition of organo-mineral amendments ameliorated the tailings' characteristics by increasing pH, conductivity, total organic carbon, and available P levels. Moreover, after 8 months, heterotrophic microorganisms were recovered from those substrates and dehydrogenase activity was enhanced. The incorporation of agricultural soil and green waste compost mixed either with lime (S5) or rock phosphate (S6) was the most effective treatment. Conclusions Both S5 and S6 mixtures successfully reduced the environmental risk posed by tailings, suggesting the potential use of these amendments for the remediation of pyrite mines.

Acid mine drainage can pollute the environment because it is acidic and contains toxic heavy metals. The purpose of this research was the application of a bacterial consortium to remove sulfate and reduce heavy metal lead (Pb) in acid mine drainage. The application was done in the bioreactor for acid mine drainage treatment that was treated with compost. Observations were made every five days and included observation of total bacterial growth using the Standard Plate Count (SPC) method, determination of sulfate content by gravimetry, determination of pH by use of pH meter, and determination of the concentration of heavy metal Pb using the AAS method. As a result, it was obtained that the treatment of non-sterile compost in acid mine drainage was able to reduce the initial heavy metal concentration of Pb of 84% and reduce the sulfate content by 72%, along with increasing pH and an increase in total bacterial growth. Meanwhile, sterile compost treatment was only able to reduce the Pb content by 63% and sulfate by 54%. This result indicates that the addition of compost is more effective than the treatment of sterile compost.

Globally, the major source of environmental pollution as a result of mineral exploitation and processing is acid mine drainage (AMD). AMD refers to outflowing streams of acidic constituents from pyrite-bearing ore mines. The exposure of pyrite (FeS2) in coal waste dumps to atmospheric oxygen and water in the presence of microbial communities promotes the formation of sulphuric acid which leaches out the inherent heavy metals into the mine discharge, a phenomenon called pyrite oxidation. AMDs are usually characterized by a convoy of toxic heavy metals, most of which are transition elements (copper, nickel, zinc, etc.) and arsenic at concentrations higher than the limits permitted by environmental regulations. The impact of this acidic discharge from coal mines on downstream/underground waters and farm lands within the corresponding mining zones have been severally reported by previous researchers, but not so much have been discussed on extensive prediction and remediation. It is in view of this that the current paper reviews the need for extensive prediction and remediation approach for coal mines under the following subheadings; General introduction, AMD sources identification, representative sampling, adoption of a prediction model, determination of AMD potential and quality via static and kinetic tests and the development of an economically sustainable remediation strategy. It is thought that this article would be useful to academia as well as policy makers that are responsible for the development and implementation of environmental regulations in coal mines.

Sulfide-containing mine waste was oxidized to produce acid mine drainage, which lead to acidification of surrounding soil and downstream rivers and posed a threat to the surrounding environment. Quartz often coexists with sulfide minerals and affects the oxidation of sulfide minerals. In order to explore the role of quartz in the bio-oxidation of sulfide minerals in mine solid waste, the mixed minerals of quartz and sulfide minerals were bio-oxidized by Acidithiobacillus ferrooxidans. The results showed that quartz could improve the microbial activity and increase the acid production of sulfide minerals. The larger the proportion of quartz in bio-oxidation of sulfide minerals, the less the production of secondary minerals such as jarosite, and the larger the leaching amount of iron and sulfate. This research provides new ideas for speeding up the bio-oxidation of sulfide mineral to remove iron and sulfate. It provides a new way to solve acid pollution caused by oxidation of sulfide minerals.

In this study, the arsenic (As) removal characteristics of a Mn-Fe binary coating formed on waste sand filter of an acid mine drainage treatment facility are investigated. Owing to the Mn-Fe binary coating forming on the surfaces of the sand grains, its potential for arsenic removal, particularly As(III), was evaluated and characterized through batch experiments and x-ray absorption spectroscopy. Sorption isotherms reveal that the Mn-Fe binary coating exhibits comparable removal efficiencies for As(III) and As(V) under low initial As concentrations. However, at higher initial As(III) and As(V) concentrations, the As(III) removal efficiency increases because of newly formed active adsorption sites from reductive dissolution of Mn. The oxidation of the As(III) and reduction of the Mn oxide phases are verified through As K-edge and Mn K-edge X-ray absorption near edge fine structure analysis. The outstanding As(III) removal efficiency of the Mn-Fe binary coating suggests synergy of Fe- and Mn-oxides, highlighting a potential application for this coating system. The natural formation of binary coating through acid mine drainage treatment reported in this study indicates that similar coating can form naturally in other environments, thus, providing plausible natural attenuation processes for arsenic immobilization.

The prevention of acid generation from sulfidic mine wastes is a problem that challenges the global scientific community for decades. A promising strategy is related to the formation of coating layer around sulfides for inhibiting surface oxidation. In the current research, the conditions favoring the formation of an efficient silicate-based coating around pyrite and arsenopyrite were studied, using batch tests. The coating solutions contained silicate-oxyanions, an oxidant (H2O2) and buffered at pH 6. The effect of Si concentration (0.1–50 mM), liquid/solid ratio (5–100 mL/g) and contact time (up to 24 h) was investigated. Pyrite tailings treated with a solution of 1 mM Si/0.1 M H2O2 at L/S:100 mL/g for 24 h resulted in the optimum formation of a coating, which reduced the amount of SO4−2-released by 72%, compared to the sample treated in the absence of Si. However, silicate treatment had a negative effect on arsenopyrite tailings inducing As mobilization.

In this study, the treatment of acid mine drainage (AMD) and immobilization of heavy metals released from CFT (copper flotation tailings) were investigated using strongly alkaline demolition waste (DW), collected from the urban renewal areas. Shake flask batch tests were conducted to assess the influence of time and different ratios of CFT/DW on the acidity and heavy metal release characteristics of the drainage water. During the tests, samples were collected from filtered leachates at regular intervals to monitor pH, SO42- and release of heavy metals. The results indicated that the pH increased from 2.21 (t=0) to 10.37 after 120 minutes of shaking in an orbital shaker. The highest SO42- release ([SO42-]=4558 mg L-1, t=0) was measured at 1:3 dose of CFT:DW application with 257 mg L-1 (pH=10.37) at the end of 120 minutes. The addition of DW almost completely reduced the release of heavy metals from CFT due to its high alkaline content. As a result, it was suggested that DW could effectively be used for the treatment of AMD and immobilization of heavy metals released from CFT.

The Iberian Pyrite Belt in southwest Spain hosts some of the largest and diverse extreme acidic environments with textural variation across rapidly changing biogeochemical gradients at multiple scales. After almost three decades of studies, mostly focused on molecular evolution and metagenomics, there is an increasing awareness of the multidisciplinary potential of these types of settings, especially for astrobiology. Since modern automatized exploration on extraterrestrial surfaces is essentially based on the morphological recognition of biosignatures, a macroscopic characterization of such sedimentary extreme environments and how they look is crucial to identify life properties, but it is a perspective that most molecular approaches frequently miss. Although acid mine drainage (AMD) systems are toxic and contaminated, they offer at the same time the bioengineering tools for natural remediation strategies. This work presents a biosedimentological characterization of the clastic iron stromatolites in the Tintillo river. They occur as laminated terraced iron formations that are the most distinctive sedimentary facies at the Tintillo river, which is polluted by AMD. Iron stromatolites originate from fluvial abiotic factors that interact with biological zonation. The authigenic precipitation of schwertmannite and jarosite results from microbial-mineral interactions between mineral and organic matrices. The Tintillo iron stromatolites are composed of bacterial filaments and diatoms as Nitzschia aurariae, Pinnularia aljustrelica, Stauroneis kriegeri, and Fragilaria sp. Furthermore, the active biosorption and bioleaching of sulfur are suggested by the black and white coloration of microbial filaments inside stromatolites. AMD systems are hazardous due to physical, chemical, and biological agents, but they also provide biogeochemical sources with which to infer past geochemical conditions on Earth and inform exploration efforts on extraterrestrial surfaces in the future.

Hydrogeochemical processes responsible for groundwater composition within the Asutifi-North district were assessed. The aim was to delineate the factors influencing groundwater within the district. Results show that the pH values of groundwater within the district are moderately acidic to neutral and ranged from 4.4 to 7.5 with a mean value and standard deviation of 6.1 ± 0.7 pH units. 67.4% of groundwater is acidic (pH 4–6.5) due principally to the influence of aquifer materials on the chemistry of groundwater. Acid mine drainage investigations in groundwater within the district shows that, when exposed, sulphides such as pyrites (FeS2) and arsenopyrite (FeAsS) react with water and oxygen to principally produce Fe(OH)3. The major ion concentrations are within the WHO (2004) Guideline values for drinking water. The relative abundance of cations and anions in groundwater within the district is in the order of: Ca2+ > Na+ > Mg2+ > K+ and HCO3− > Cl− > SO42−, respectively. The study further shows that, albite/anorthite-(plagioclase) and calcite/dolomite(carbonates) dissolution as well as ion-exchange reactions may have contributed significantly to major ion concentrations in groundwater within the district. Hydrochemical facies using Piper trillinear diagrams delineated two major water types, the Ca–Mg–HCO3 and Na–Cl water types, with Ca–Mg–Cl, Ca–Mg–SO4–Cl and Na–K–HCO3 as minor water types. Using principal component analysis (PCA), three (3) main principal components accounting for 73.1% of the total variance with eigenvalues > 1 were extracted. PCA delineated the main natural processes through which groundwater within the district acquires its chemical characteristics, the incongruent dissolution of silicate/aluminosilicates and the prevalence of pollution principally from the application of inorganic fertilizers such as nitrates and ammonia via agricultural activities within the district.

Abstract This overview presents the updated physicochemical characteristics of thallium and its stable isotopes (205Tl/203Tl) in the context of their occurrence and fate in abiotic and biotic systems. This also deals with the thallium behavior in geochemical interactions in and between different environmental compartments and describes its natural (geogenic) and industrial sources. The particular emphasis is placed on some extreme environments, including acid mine drainage areas where oxidation processes of Tl-bearing pyrite and other sulfides lead to very high concentrations of this metal in reactive acidic waters. Many geochemical studies have also employed stable thallium isotopes to reconstruct redox conditions in different environmental systems, to fingerprint relative pollution source strengths and to evaluate mobility of this element and its geochemical interactions in the mineral-water and soil–plant systems. This is the reason why this overview also highlights the growing potential of stable Tl isotopes in solving different geologic and environmental issues. Graphic abstract

Herein, basic oxygen furnace (BOF) and submerged arc furnace (SAF) slags were used for the treatment of acid mine drainage (AMD). Their composition, complexity, and heterogeneity permits their application in AMD remediation. To fulfil the goals of this study, batch experimental approach was adopted. This was done using a 3.5 kl reactor equipped with a propeller. Characterization of feed and product minerals were done using X-ray fluorescence (XRF), X-ray diffraction (XRD), and High resolution scanning electron microscopy coupled with energy dispersive spectroscopy (HRSEM-EDS). The obtained results showed an increase in pH, which was proportionally linked to the interaction of AMD with the slags. The pH was observed to increase from 2 to 9.4, and 9.2 for BOF and SAF slags, respectively. Furthermore, the acquired pH was conducive for the removal of chemical species from the aquasphere. This was also confirmed by PH REdox EQuilibrium (in C language) (PHREEQC). Moreover, close to 99%-removal efficacy for Fe, Al, and Mn, and ≥50% removal efficacy for sulphate were noted for individual material. This confirms that these materials have the potential to give comparative outputs and effects. PH REdox EQuilibrium (in C language) (PHREEQC) confirmed the formation of metals hydroxide and gypsum from the interaction of slags and AMD. This corroborated the XRD, XRF, and HR-SEM-EDS results. In light of the obtained results, this comparative study proved that the steel slags from different industrial operations could potentially be used for the treatment of AMD. This initiative will go a long way in unpacking viable routes for valorization and beneficiation of steel slags hence minimizing their environmental footprints.

Pyrite, as one of the most abundant sulfide minerals, can be easily oxidized to generate acid mine drainage (AMD). In the present study, a new composite passivator named PropS-SH/sepiolite (PSPT) using γ-mercaptopropyltrimethoxysilane (PropS-SH) as the main passivator and natural sepiolite particles as filler was fabricated and used to suppress the oxidation of pyrite. Electrochemical tests and chemical leaching experiments were carried out to evaluate the passivation performance of PSPT coatings with different amount of sepiolite particles on pyrite oxidation. The results showed that the addition of appropriate sepiolite could significantly improve the inhibition ability of PropS-SH against pyrite oxidation. However, excessive addition of sepiolite particles weakened the inhibition ability of the PSPT coatings owing to aggregations of sepiolite. Additionally, the coating mechanism of PSPT on pyrite was also proposed based on the characterization of FTIR, XPS, and 29SiNMR measurements, which indicated that sepiolite particles could be embedded in PropS-SH network through oxygen bridges, thus improving the stability of the composite coatings.

The control of pyrite (FeS2) oxidation from a source is a problem of great concern on treatment of acid mine drainage (AMD). Compared with air and water, the effect of light on pyrite oxidation has not attracted enough attention. However, we found that pyrite photocorrosion in the light promoted the oxidation of pyrite. Herein, we introduce a method of coating pyrite with graphene oxide (GO), which can inhibit the oxidation and photocorrosion of pyrite while it can also degrade organic pollutants. The characterization results show that a covalent bond forms between the GO and pyrite. The stable and uniform GO coating prevents the permeation of O2 and H2O and promotes the transfer of photogenerated electrons. Moreover, it changes the conduction band (CB) and valence band (VB) levels of GO–pyrite. All of these are vital for preventing the corrosion of pyrite and promoting its photocatalytic ability. More importantly, the effect of CB and VB levels on the oxidized species was discussed. The inhibition of photocorrosion is achieved by the reaction of GO with the photoinduced h+, •OH, and •O2–. The study provides insights for source treatment of AMD under light and the reuse of massive abandoned pyrite.

The elevated concentrations of rare earth elements (REE) and yttrium (REE+Y) in acid mine drainage (AMD) constitute an opportunity for REE+Y recovery. However, the source and control of REE+Y signatures in AMD remains uncertain. Water, rock, sediment and sludge samples were collected from an ion-adsorption rare earth mining area to investigate REE+Y concentration and fractionation patterns in AMD. High concentrations of REE+Y occur in the pristine mine water (MW), and decrease progressively with MW passing through nitrification-denitrification (NDT) and coagulating-precipitation (CPT) treatment procedures in a water treatment plant. Concentrations of REE+Y are 1 to 3 orders of magnitude higher in MW, NDT and CPT samples than those in well water (WW), and are negatively correlated (R2 0.72) with pH (3.8 to 8.7), suggesting that an enhanced acidic dissolution of minerals contributes REE+Y to AMD from the source area. Speciation calculation indicates that REE+Y are mainly free ions and sulfate complexes in MW and NDT samples, while carbonato and dicarbonato complexes in CPT samples. Normalized REE+Y patterns of water samples show a coherent enrichment of heavy REE (HREE) over light REE (LREE) and negative Ce anomalies. HREE-enriched patterns and Ce anomalies are kept relatively constant in MW, NDT and CPT samples, despite their huge disparity in REE+Y concentrations, indicating a limited impact of preferential precipitation of LREE over HREE on REE+Y fractionations. The HREE-enriched patterns possessed by AMD are similar to those of sediment samples, while are distinct from whole rocks. These behaviors suggest a major role of sediment source in controlling REE+Y concentrations and patterns in AMD. Results of XRD show abundance of muscovite, kaolinite and feldspar in sediments. Combining to SEM-EDS examinations, minerals such as kaolinite, schwertmannite (Fe16O16(SO4)3(OH)6(H2O)10·10H2O) and ferrihydrite are suggested to be the main hosts of REE+Y in sediments. Hence, HREE-enriched patterns of AMD result from preferential leaching of HREE from sediments which accumulate REE+Y after being initially mobilized from rocks under the conditions prevailing in mine site. The free form and sulfate complexation preserves REE+Y patterns and facilitates REE+Y mobility in the AMD system. Based on the plant treatment capacity, the potentially recoverable LREE and HREE are calculated to range between 1116 g/day and 3373 g/day, and between 1288 g/day and 3764 g/day, respectively.

Substrate amendments composed of crab shell (CS) waste materials have been shown to significantly improve the longevity and performance of acid mine drainage (AMD) treatment systems containing spent mushroom compost (SMC), yet the development of key microbial populations within these systems has not been investigated. To better understand the effects of CS on microbial dynamics in these systems, clone libraries and real-time quantitative PCR (qPCR) were performed on materials from a laboratory-scale AMD treatment system containing SMC and 0 to 100% CS substrate after receiving a continuous flow of AMD for 148 days (428 pore volumes). The proportion of CS in the substrate positively correlated with the diversity of sulfate-reducing bacteria (SRB) and archaeal clones, but negatively correlated with fungal diversity. CS also impacted microbial community structure, as revealed in Unifrac significance and principal coordinate analysis tests. The column containing 100% CS substrate supported 7 different genera of SRB-the most ever observed in an AMD treatment system. Moreover, the copy numbers of functional genes representing fermenters, sulfate reducers, and chitin degraders increased with increasing proportions of CS. These observations agree well with the chemical performance data, further validating that by supporting more abundant key microbial groups, chitinous substrates may provide benefits for improving both the longevity and performance of AMD treatment systems, and may provide similar benefits for the treatment of other environmental contaminants that are amenable to anaerobic bioremediation.Key points• Crab shell improves the longevity and performance of acid mine drainage treatment.• The diversity of sulfate-reducing bacteria is enhanced with crab shell amendments.• Crab shell supports more abundant key microbial groups than spent mushroom compost.

In the Karoo coalfields, mining operations that release acid mine drainage (AMD) are threatening groundwater resources. An important parameter controlling the extent and severity of AMD impact is the natural attenuation of rocks in response to AMD. Very little is known about such response of Karoo rocks in saturated and unsaturated conditions, a research gap filled by this paper. Laboratory column leach experiments were used to study the responses of different rock types from the Witbank, Ermelo and Highveld coalfields of South Africa. The results of the experiments show that rock samples with high quartz mineral content offered little attenuation of AMD and those consisting of plagioclase and clays offered some attenuation, while those with high carbonate mineral content, neutralized and reduced the concentration of heavy metals from AMD. The presence of oxygen increased the rate of heavy metal removal from AMD. For all rock samples under saturated and unsaturated conditions, the sulfate and chloride concentrations of AMD remained unchanged after the leaching process, showing that these parameters are conservative and can be used as potential natural tracers of AMD movement in the subsurface. The research shows that laboratory leach tests may be used to rank the various rock types in the Karoo coalfields in terms of their capacity to buffer the impacts of AMD. Such a ranking could inform policy and decision makers in regard to handling and storage of AMD-generating wastes, as well as to location and design of AMD waste storage facilities.

The Sao Domingos area (Corte do Pinto, Portugal) represents a large sulfide ore deposit in the Iberian Pyrite Belt that was mined primarily for copper and sulfur in the past. Currently, the deserted mine and mine wastes are the reason for the production of acid mining drainage releasing potentially harmful elements. Because metastable secondary sulfates may temporary sink toxic pollutants, the in situ monitoring of their distribution is required. In this work, we tested a handheld Raman spectrometer equipped with a 532 nm laser excitation for this task. Twelve selected samples of complex composition were analyzed directly in the field using the handheld Raman spectrometer. For comparison, the collected samples were additionally analyzed through laboratory-based Raman spectroscopy and X-ray diffraction. Based on the in situ measurements, rozenite, melanterite, coquimbite, jarosite, metavoltine, chalcanthite, bonattite, antlerite, halotrichite-group minerals, gypsum, and sulfur were detected. The results show that handheld Raman spectrometer is comparable with other laboratory techniques and such handheld systems can be deployed successfully for monitoring of sulfate distribution directly on site.

Coal mine spoil is a long-lasting legacy of historic coal mining operations that continues to impact water quality across Appalachia. Metal(loid) release from abandoned coal mine spoil, which can be a significant source of acid mine drainage (AMD), is dependent on speciation and distribution within the parent coal shale. This work aimed to determine how the micron- and sub-micron scale mineralogy, morphology, and texture of metal(loid)-bearing phases in a coal-shale control the rate and release of metal(loid)s during subsequent weathering through two primary objectives: (1) determine the microscale speciation and distribution of Fe and other metal(loid)s in a parent coal shale, and (2) determine the amount of metal(loid)s released during simulated weathering of shale physically crushed into silt- to sand-sized particles. This work was accomplished through a combination of electron microscopy and synchrotron-based X-ray microprobe analyses. This suite of techniques also provides insight into the geochemical history of the coal shale that could not be determined by bulk techniques. Trace elements were associated with either Fe-sulfides or with other phases that included metal(loid)-sulfides, aluminosilicates, and organic matter. Three distinct pools of Fe-sulfides were present: (i) larger mm-scale grains, with minimal internal fractures; (ii) μm- to mm-scale aggregates of μm-scale crystals forming secondary coatings on the larger mm-scale grains, and (iii) μm- to mm-scale aggregates forming framboidal grains. Fe-sulfide mineralogy was dominated by pyrite with minor contributions of marcasite and a S(-II)-bearing phase. Larger pyrite grains and their secondary coatings contained homogeneous distributions of Fe and Mn as well as other trace metal(loids) including V, Ti, Cr, As, Se, Cu, and Zn. The fine-grained pyrite aggregates were strongly enriched in As and Se and contained discrete Cu- and Zn-bearing particles. Clays and organic matter surrounding the sulfide minerals were identified by micro-XRD and FT-IR spectroscopy. Simulated batch weathering of the physically crushed shale resulted in metal(loid) release that varied as function of size fraction and time. Metal(loid) release increased with decreasing particle size from sand-sized to silt-sized fractions. Although small amounts of Fe were released into solution after two days, the bulk of Fe release occurred after 10 days and continued for six months, after which Fe was gradually removed from solution. The weathering trends for Mn, Cu, Zn, and Ni were similar to Fe. In contrast, As and Se were characterized by rapid release into solution followed by removal prior to 10 days. These results indicate that micrometer-scale metal(loid) distribution within Fe sulfides controlled metal(loid) release into solution during simulated weathering of a coal shale. Specifically, elements concentrated in mineral coatings (As, Se) were rapidly mobilized in a short-lived pulse whereas elements associated with the larger grains (Fe, Mn, Cu, Zn, and Ni) exhibited a delayed but prolonged release into solution. The non-concomitant contaminant release indicates that an understanding of the textural relationships in the source material is required to understand weathering trends. This work highlights the importance of non-point sources of AMD, and addressing these sources is a critical step in improving water quality in the region.

Acid mine drainage (AMD) has been proposed as a potential source of strategic rare earth elements (REEs) due to its high concentrations (>1000 µg/L) of dissolved REEs, as well as the middle rare earth element (MREE) enriched pattern exhibited by both coal mine- and metal mine-derived AMD, in which some of the most energy-critical REEs are significantly concentrated. However, the source of REEs and the origin of the MREE enrichment observed in AMD discharges is poorly understood; suggestions include dissolution of MREE-enriched surface coatings, fractionation by colloids, solid-liquid exchange reactions, incongruent dissolution of pyrite, and selective leaching of MREE-enriched phases. Filtration experiments on acidic to circumneutral AMD (unfiltered to

Discharge of acidic water associated with sulfide, pyrite with other metals from abandoned or active mines is the major cause of acid mine drainage in mining regions. The liquid discharged from mining sectors often contains harmful, toxic heavy metals such as copper, iron, sulfur, nickel and zinc. The production of acidic pH and presence of metals have adverse effect upon aquatic habitats, environment pollution that further indirectly leads to health related concern in humans and animals. So recent research work focuses on investigation of different types of microalgal species which have capacities to remove heavy metals and toxic pollutants from acid mine drainage. Currently phycoremediation is an ideal substitute method over any other conventional techniques. They made the acidic environment alkaline and also act as bioaccumulators which is required for heavy metal precipitation. Application of microorganisms like bacteria, fungus along with algae can also be an effective approach for bioremediation of acid water drainage.

Mine acid water is acidic water and contains iron and sulfate, which is formed under natural conditions when geological strata containing pyrites are exposed to an oxidizing atmosphere or environment. One of the impacts of the mineralization zone where there is a mining process is the potential for the formation of acid mine drainage, especially in the Cibaliung gold mineralization area and its surroundings, Pandeglang Regency, Banten Province. Acid-forming sulfide minerals include pyrite (FeS2), headquarters (FeS2), picoliters (FexSx), calcocytes (CuS), covellite (CuS), chalcopyrite (CuFeS2), molybdenite (MoS), mulenite (NiS), chalocytes (CuS), covellite (CuS), chalcopyrite (CuFeS2), molybdenite (MoS), mulenite (NiS), chalocytes (CuS), covellite (CuS), chalcopyrite (CuFeS2), molybdenite (MoS), mulenite (NiS), galena (PbS) ) and sphalerite (ZnS). Of all these minerals, pyrite is the most dominant sulfide in acid formation. Alkaline mine water (alkaline mine drainage) is mine water that has an acidity level (pH) of 6 or more, containing alkalinity but still containing dissolved metals that can produce acids. The quality of mine water, acid or alkali, depends on the presence or absence of acid mineral content (sulfides) and alkaline materials in the geological strata. Acid water formation tends to be more intensive in mining areas. This can be prevented by avoiding exposure to sulfide-containing materials in the free air. Acid-forming sulfide minerals include pyrite (FeS2), headquarters (FeS2), picoliters (FexSx), calcocytes (CuS), covellite (CuS), chalcopyrite (CuFeS2), molybdenite (MoS), mulenite (NiS), chalocytes (CuS), covellite (CuS), chalcopyrite (CuFeS2), molybdenite (MoS), mulenite (NiS), chalocytes (CuS), covellite (CuS), chalcopyrite (CuFeS2), molybdenite (MoS), mulenite (NiS), galena (PbS) ) and sphalerite (ZnS). Of all these minerals, pyrite is the most dominant sulfide in acid formation. Formation of potential acidic water also occurs in tailings which are residues/processing residues containing sulfide minerals. The formation of acid mine drainage does not always develop in every sulfide-ore mining. In certain types of ore deposits, there are neutralizing agents which prevent the formation of acid mine drainage.

During coal mining activities, a lot of coal gangue is produced, which usually contains high mercury (Hg) concentrations as well as the acid mine drainage (AMD) generator of pyrite. In the present study, the total mercury (THg) and methylmercury (MeHg) in gangue, water, sediment, paddy soil, and rice samples, collected from abandoned coal mining areas, were analyzed. Results showed that the THg concentrations ranged from 0.37 to 35 mg/kg (11 ± 8.4 mg/kg) and 0.15 to 19 mg/kg (2.0 ± 3.9 mg/kg) in gangue and sediments, respectively. For paddy soils, the THg concentrations and MeHg varied from 0.16 to 0.91 mg/kg and 0.71 to 11 ng/g, respectively. Rice samples exhibited wide concentration ranges of THg (3.0-22 ng/g) and MeHg (0.71-8.9 ng/g). Sequential extraction of Hg revealed that the nitric acid-extractable state Hg (F4) was the dominant Hg species in gangue and sediment, while humic acids state Hg (F3) was the dominant form in paddy soil. Compared with gangue, higher percentages of F3 and the residual state Hg (F5) in both sediment and soil samples implied the transformation of F4 to F3 and F5 during transportation. Soil n-HAs (the difference between the total organic carbon and humic acids) were positively correlated with both THg and MeHg in soil and rice, indicating that n-HAs enhance Hg bioavailability under acidic conditions. Further studies should be conducted to reveal the factors influencing the transformation of different Hg fractions, providing ideas on decreasing the bioavailability of Hg in coal mining areas.

Acid and metalliferous drainage (AMD) oxidation reaction rates were determined using oxygen consumption rates in a high sulfur overburden rock from the Australian Latrobe Valley coal provinces, and a mid to low range sulfur waste rock from a porphyry copper deposit in Papua, New Guinea. Nine grain sizes were tested, ranging from material retained by a 0.038 mm sieve through to a 40 mm sieve. Oxygen consumption rates in sealed cells were measured to establish pyrite oxidation rates (POR) in each sample. The oxygen consumption rates displayed a strong exponential reaction correlation with particle size for the material. The POR was found to range from 0.28 to 10.90 wt%/year FeS2 for the materials tested. A relationship between particle size and POR was established for comparative purposes. The smaller grind sizes included in this study extend the AMD/POR particle size data set available in the literature and will assist with geochemical engineering for designing tailings storage facilities. The potential economic and mine design ramifications of additional reactivity of fine mine materials is assessed and discussed using a unit cost framework for applying neutralizing materials.

The influence of acid mine drainage (AMD) on heavy minerals (FeTiO3, ZrSiO4) was investigated at DanChon coast (Pb–Zn mining district in northeastern region of Korea), where mine tailings have been...

We characterized carbide lime, a by-product of acetylene manufacturing, and compared it to commercial calcium oxide (CaO), which is typically used to treat AMD. Chemical and X-ray diffraction data revealed that the carbide lime was a calcium-rich lime. Morphological analysis indicated that it differed from commercial CaO in its morphology, having a layered structure. The presence of functional groups among the samples was confirmed by a Fourier transform infrared spectral study. Physical characterization, including nitrogen adsorption–desorption isotherm and particle size distribution demonstrated that the carbide lime had greater surface area and finer particle size than the commercial CaO. Jar tests were used to evaluate the effect of the carbide lime and CaO loading on actual AMD. The optimum quantity of carbide lime for treating the AMD was 0.4 g/l, which increased the pH and reduced the metal and sulphate concentrations to acceptable levels. The carbide lime showed superior acid-neutralizing and contaminant diminution at all studied loadings. Additionally, an Imhoff cone test confirmed that the sludge produced using carbide lime settled better that that produced using CaO powder.

Acid mine drainage is one of the main environmental hazards to ecosystems worldwide and it is directly related to mining activities. In Ecuador, such acidic-metallic waters are drained to rivers without treatment. In this research, we tested a laboratory combined (Ca-Mg) Dispersed Alkaline Substrate (DAS) system as an alternative to remediate acid drainage from the Zaruma-Portovelo gold mining site, at El Oro, Ecuador. The system worked at low and high flow hydraulic rates during a period of 8 months, without signs of saturation.. Analysis of physico-chemical parameters and water composition (ICP-OES, ICP-MS) demonstrated that treatment effectively increased water pH and promoted the retention of about 80% of Fe, Al, Mn and Cu. Under acid conditions As, Cr and Pb concentrations decreased with Fe and possible precipitation of jarosite and schwertmannite. However, the homogeneous depletion of Cr at pH above 6 could be related to ferrihydrite or directly with Cr (OH)(3) precipitation. After DAS-Ca, sulphate, phosphate and rare earth elements (REE) concentrations decreased to 1912, 0.85 and 0.07 mg/L respectively, while DAS-Mg contributed to form a complex model of minor carbonate and phosphate phases as main sink of REE. DAS-Mg also promoted the retention of most divalent metals at pH values over seven. Thus, this low cost treatment could avoid environmental pollution and international conflicts. Anyway, further investigations are needed to obtain higher Zn retention values. PROMETEO Ecuadorian program (Secretary of Superior Education, Science, Technology and Innovation) info:eu-repo/semantics/publishedVersion

If the excavated underground veins are not backfilled, they may be a factor in the continued outflow of acid mine drainage (AMD). The flow rate of AMD can be reduced by backfilling underground drifts from abandoned mines. In addition, the quality of AMD may be improved as the flow rate of AMD reduces. In this paper, the quality of the AMD after backfilling was evaluated by a three-dimensional geochemical analysis model when the groundwater level was recovered after backfilling. The measured dissolved iron (Fe) and sulfate ion (SO42−) concentrations and pH before backfilling the drift were reproduced by the calibration of the simulation. Using the calibrated model, the pH at the outlet of the drift was changed from about pH 3 before backfilling to about pH 4 to 5 after backfilling. When calcite was contained in the filling materials of the drift, the pH approached neutral. However, when gypsum was formed, the neutralization was inhibited. The Fe concentration discharged from the drift was calculated at approximately 0.002 mol/L before backfilling. The total Fe concentration was calculated at 0.0004 mol/L or less after backfilling, and the dissolved Fe concentration decreased by several orders of magnitude after backfilling. A geochemical model quantitatively evaluated the improvement in water quality after backfilling the drifts. This method can be applied to the other abandoned mines with similar hydrogeological conditions.

Acid mine drainage (AMD) is a common environmental problem in many sulphide mines worldwide, and it is widely accepted that the microbial community plays a major role in keeping the process of acid generation active. The aim of this work is to describe, for the first time, the microbial community thriving in goethite and jarosite Fe precipitates from the AMD of the Libiola mine. The observed association is dominated by Proteobacteria (&gt, 50%), followed by Bacteroidetes (22.75%), Actinobacteria (7.13%), Acidobacteria (5.79%), Firmicutes (2.56%), and Nitrospirae (1.88%). Primary producers seem to be limited to macroalgae, with chemiolithotrophic strains being almost absent. A phylogenetic analysis of bacterial sequences highlighted the presence of heterotrophic bacteria, including genera actively involved in the AMD Fe cycle and genera (such as Cytophaga and Flavobacterium) that are able to reduce cellulose. The Fe precipitates constitute a microaerobic and complex environment in which many ecological niches are present, as proved by the wide range of bacterial species observed. This study is the first attempt to quantitatively characterize the microbial community of the studied area and constitutes a starting point to learn more about the microorganisms thriving in the AMD of the Libiola mine, as well as their potential applications.

The flotation tailings obtained from Bor Copper Mine contain pyrite (FeS2) and chalcopyrite (CuFeS2), these sulfide minerals are known to promote acid mine drainage (AMD) which poses a serious threat to the environment and human health. This study focuses on the treatment of mine tailings to convert the AMD supporting minerals to more stable forms, while simultaneously valorizing the mine tailings. A combination of hydrometallurgical processes of high-pressure oxidative leaching (HPOL), solvent extraction (SX), and electrowinning (EW) were utilized to recover copper from mine tailings which contain about 0.3% Cu content. The HPOL process yielded a high copper leaching rate of 94.4% when water was used as a leaching medium. The copper leaching kinetics were promoted by the generation of sulfuric acid due to pyrite oxidation. It was also confirmed that a low iron concentration (1.4 g/L) and a high copper concentration (44.8 g/L) obtained in the stripped solution resulted in an improved copper electrodeposition current efficiency during copper electrowinning. Moreover, pyrite, which is primarily in the mine tailings, was converted into hematite after HPOL. A stability evaluation of the solid residue confirmed almost no elution of metal ions, confirming the reduced environmental loading of mine tailings through re-processing.

Mine tailings exposed to water and oxygen generate acid mine drainage (AMD) when the neutralizing minerals are insufficient to buffer the acid produced by sulfide oxidation. Mineral reactivity, such as sulfide oxidation and carbonate dissolution, leads to several changes within mine tailings in terms of their physical, mineralogical, and geochemical properties, which may lead to the release of metal(oid)s (e.g., As, Cu, Zn, Fe, S) into the environment. Fresh and oxidized tailings were sampled at two vertical profiles in a tailings storage facility (TSF). The TSF contains tailings from gold ore processing at a mine that has been closed for more than 25 years. Oxidized tailings have formed by in-situ oxidation of fresh tailings over more than 20 years. The collected samples were analyzed for: i) chemical composition by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence (XRF), and total S/C; and ii) mineralogical composition by X-ray diffraction (XRD), Mineral Liberation Analyzer (MLA), Mossbauer spectroscopy, and Fe L-edge X-ray absorption near-edge spectroscopy (XANES). Mineralogically, the fresh tailings included more than 22 wt% carbonates and more than 10 wt% sulfides. In contrast, the oxidized tailings were composed mainly of secondary minerals such as iron oxy-hydroxides and gypsum. Geochemically, the fresh tailings exhibited a circumneutral behavior during weathering cell experiments and contaminants such as As were negligibly released (

The reclamation of mine waste deposits is imperative but often hindered by the scarcity of natural topsoil. Studies have used various materials to reconstruct topsoil but mainly in coal mines, with scant information for metalliferous mines. Acid mine drainage sludge (AMDS), as a mass-produced waste in metalliferous mines, is a potential topsoil substitute because of its capacity to buffer acidification and support plant growth. In this study, a pot experiment with three plant species was conducted to evaluate the environmental safety and sustainable fertility of AMDS with the amelioration of fertilizers. Results showed that all the plants could survive in the AMDS even without fertilizers. The contents of heavy metal(loid)s were high but remained stable over the experimental period. Improving the AMDS with fertilizers enhanced its nutrient supply by increasing macronutrient contents and activities of soil enzymes, leading to significant increases in plant biomass. The AMDS also sustained its nutrient status throughout the experiment. Nevertheless, the extremely low NH4+-N and bioavailable phosphorus contents made these nutrients hardly accessible to plants, owing to the composting of the organic manure and the low richness and diversity of the bacterial community in the AMDS. Present results suggest that AMDS can be used as a viable and safe substitute for natural soil in reclaiming mine solid wastes but also needs proper improvement, especially for enhancing the microbial richness and diversity.

Acid mine drainage (AMD) is a serious environmental issue associated with mining due to its acidic pH and potentially toxic elements (PTE) content. This study investigated the performance of the Fe-Al bimetallic particles for the treatment of combined AMD-gold processing effluents. Batch experiments were conducted in order to eliminate potentially toxic elements (including Hg, As, Cu, Pb, Ni, Zn, and Mn) from a simulated waste solution at various bimetal dosages (5, 10, and 20 g/L) and time intervals (0 to 90 min). The findings show that metal ions with greater electrode potentials than Fe and Al have higher affinities for electrons released from the bimetal. Therefore, a high removal (&gt, 95%) was obtained for Hg, As, Cu, and Pb using 20 g/L bimetal in 90 min. Higher uptakes of Hg, As, Cu, and Pb than Ni, Zn, and Mn also suggest that electrochemical reduction and adsorption by Fe-Al (oxy) hydroxides as the primary and secondary removal mechanisms, respectively. The total Al3+ dissolution in the experiments with a higher bimetal content (10 and 20 g/L) were insignificant, while a high release of Fe ions was recorded for various bimetal dosages. Although the secondary Fe pollution can be considered as a drawback of using the Fe-Al bimetal, this issue can be tackled by a simple neutralization and Fe precipitation process. A rapid increase in the solution pH (initial pH 2 to &gt, 5 in 90 min) was also observed, which means that bimetallic particles can act as a neutralizing agent in AMD treatment system and promote the precipitation of the dissolved metals. The presence of chloride ions in the system may cause akaganeite formation, which has shown a high removal capacity for PTE. Moreover, nitrate ions may affect the process by competing for the released electrons from the bimetal owing to their higher electrode potential than the metals. Finally, the Fe-Al bimetallic material showed promising results for AMD remediation by electrochemical reduction of PTE content, as well as acid-neutralization/metal precipitation.

Acid mine drainage (AMD) formation is mainly caused by the oxidation of pyrite. Carrier-microencapsulation (CME) using metal-catecholate complexes has been proposed to passivate sulfide minerals by forming surfaceprotective coatings on their surfaces. Among the various metal-catecholate complexes, Ti-catecholate formed stable coatings having superior acid-resistance, but a thick enough passivating film required considerable time (ca. 14 days) to grow. Meanwhile, Fe-catecholates can form Fe-oxyhydroxide coatings within 2 days, however, they are less stable than Ti-based coating. To address these drawbacks of using a single metal-complex, this study investigated the concurrent use of Fe-catechol and Ti-catechol complexes for accelerating the formation of stable passivating coating on pyrite & nbsp;Compared with a single metal-complex system, the coating formation was significantly accelerated in mixed system. Linear sweep voltammetry showed the simultaneous decomposition of [Fe(cat)]+ and [Ti(cat)3]2 & ndash; as the main reason for improved coating formation. Electrochemical properties of coatings formed by single and mixed complex systems, confirmed by electrochemical impedance spectroscopy and cyclic voltammetry, indicated the coating formed in the mixed system had higher resistance and more electrochemically inert than the other cases. The simultaneous use of Fe-catechol and Ti-catechol complexes enhanced pyrite passivation by accelerating metal-complex decomposition and forming more stable coating composed of Fe2TiO5.

Secondary iron minerals associated with acid mine drainage (AMD) such as copiapite, jarosite, schwertmannite, goethite, ferrihydrite, and hematite can be generated from pyrite oxidation. This study was an effort to determine the AMD potential of the Darrehzar mine, a porphyry copper mine in the Kerman Cenozoic magmatic arc, using remote sensing and field data. The spectral angle mapper method was applied on Sentinel 2a images to identify AMD minerals and classify the study area. The produced map was verified by field surveys and laboratory analysis of rocks and sediments as well as pH and electrical conductivity measurements of water samples. Jarosite–clay group minerals were detected in the mine pit and in an active waste dump, and jarosite–goethite and goethite–hematite group minerals were identified in inactive waste dumps. Moreover, acidic water was observed in the pit, while the neutral water was where it arrives and discharges from the mine.

An environmental concern at coal preparation operations is the release of elements resulting from the oxidation or dissolution of certain minerals contained in the process waste streams. Using a standard conductivity test, the electrical conductivity (EC) of water samples obtained from mixing with various particle size and density fractions of a given plant waste material were measured as an indicator of total dissolved solids. The net neutralization potential (NNP) of the fractions were also measured to predict the pH of the supernatant upon disposal. As a result, the particle size and density fractions contributing to high EC levels were identified with the objective of potentially extracting and isolating these fractions which can significantly reduce the negative environmental impacts. The results showed that the EC generated from coarse refuse streams were significantly higher than the values obtained from fine refuse streams. Based on the NNP values, the coarse refuse stream generates highly acidic pH, while the fine refuse in contact with water produces circumneutral pH. Furthermore, the high specific gravity (>2.68) fractions which comprised less than 10% of the coal waste streams were found to be the primary source of elevated EC levels. The remaining fractions were found to be of minimal environmental concern. Based on the obtained results, modifications to the coal preparation plants were proposed to minimize the environmental concerns of coal waste disposal. Modifications include pyrite removal from the spiral refuse and desulfurization of flotation feed and sieve bend underflow streams using low-cost mineral spiral circuitry. After the segregation, the pyrite (high density) fraction, which encompasses around 1% of the coarse and fine refuse streams, will be isolated/encapsulated and the fine refuse stream dewatered and co-disposed with the coarse refuse stream. The proposed modifications to the processing and disposal practices not only minimize the generation of acid mine drainage thereby reducing the release of trace elements and EC of the discharged water, but also enhances the recovery and quality of the final clean coal product.

Acid mine drainage treatments using limestones have been widely reported in the literature; however, additional studies are needed to select the most effective limestone type based on an adequate characterization and in consideration of the kinetics of the rock's reaction upon exposure to high iron concentrations. In this study, with the aim to select the most appropriate limestone to use in a passive treatment system, the regular characterization (calcium carbonate analysis, determination of specific superficial area, and porosity) was complemented with a heterogeneous kinetic analysis of limestone dissolution. The physico-chemical conditions of high acidity and a high Fe concentration were similar to those measured in leachates from the "Compañía Minera Zimapán" (CMZ) tailings impoundment located in a historical Mexican mining zone. Column experiments were carried out with the selected limestone to treat leachates from two tailing deposits; one highly weathered and un-active (CMZ) and the other still active (San Miguel Nuevo). Removal efficiencies close to 100% were reached for arsenic, iron, cadmium, and aluminum. There was also a partial removal of zinc and silica, and the pH increased close to neutrality. Electrical conductivity, sulfate levels, and oxidation reduction potential were also measured during the experiments. Concentration profiles for some elements were established. Chemical results, stoichiometric relationships between elements obtained by scanning electron microscopy-energy dispersive spectroscopy, and scanning electron microscopy-wavelength dispersive spectroscopy allowed for determining the chemical associations of the elements at the surface. The results indicated that the methodology for limestone selection to treat AMD from San Miguel Nuevo tailings was adequate; however, additional studies are required to improve the permeability and the lifetime of the system used to treat CMZ leachates.

Coal fly ash can be used in in various configurations (e.g. as cap, bottom liner, or blending) at a mine site, but comparative studies investigating their capacity to control acid mine drainage are limited. Batch and column leaching experiments were conducted to investigate the effects of fly ash-mine tailings mix ratios and system configurations on leachate chemistry. Acidic mine tailings (pH 2.72) were obtained from waste piles at a former gold and pyrite mine. Mixing the fly ash with the tailings in a 1:1 (w/w) ratio decreased Zn, Ni, Fe, Mn, Pb, and Cu leaching by 90 ± 6%, increased the pH from extremely acidic (2.9) to alkaline (8.0), and decreased electrical conductivity from 4 to 2.5 mS cm−1 due to solute precipitation. Using the fly ash as a ‘chemical liner’ beneath the tailings, applying the fly ash as both a cap and bottom liner, or blending the fly ash with tailings produced significantly less acidity, salinity, and metal leaching than using the fly ash as a cap. The capacity of fly ash to control acid generation is attributed to its acid neutralizing capacity and high pH (11.1).

We investigated the feasibility of using alkaline basic oxygen furnace (BOF) steel slag to treat acid mine drainage (AMD). Simulated AMD was treated with different doses of slag (10, 20, 30, 40, 50, and 60 g/L) for 24 h in batch reactors. A dose of 30 g/L was considered optimal because it raised the pH to 8.6 and resulted in 99% removal of trace metals in 24 h. The pH increased to 6.36 from the initial pH of 1.5 within 0.5 h of reaction time. Approximately 95% of all trace metals were removed. Of the major cations and anions, Mg showed the highest percentage removal (72%), followed by SO4 (30%), K (8%), and Na (2.1%) at the 30 g/L dose and 0.5 h reaction time. However, Ca concentrations increased by 28% due to leaching from the slag. PHREEQC was used to predict the possible mineral phases precipitating during treatment. Calculated saturation indices indicated that Fe was removed mainly as goethite, hematite, and amorphous Fe(OH)3; Al was removed as gibbsite and amorphous Al(OH)3; Mn was removed as manganite, hausmannite, and pyrolusite; Mg was removed as Mg(OH)2; and Ca and SO4 were only minimally controlled by gypsum precipitation. Moreover, sulfate removal was increased by the precipitation of alunite, an Al-oxy hydroxysulfate mineral. Other trace elements were either co-precipitated with or adsorbed onto the Fe, Al, and Mn precipitates. Field emission scanning electron microscope analysis of the slag after interaction with the AMD revealed that metals and SO4 precipitated on the slag surface.

The tailings produce acid mine drainage (AMD) due to sulfide minerals, especially pyrite oxidation. AMD has caused serious pollution to the surrounding aquatic and terrestrial ecosystems because of its famous low pH value and high metal and sulfate concentration, which is an urgent environmental problem faced by the world's ore mining industry. Here, we show that silicic protective surface films can suppress the oxidation of pyrite-bearing tailings for AMD control at-source without pre-oxidation of pyrite and solution pH adjuster and buffer. We found that the silicic protective surface films formed by calcium silicate can inhibit the oxidation of pyrite-bearing tailings and reduce the production of AMD through chemical leaching tests. Fourier transform infrared (FTIR) analyses and scanning electron microscopy with energy-dispersive spectrometry (SEM/EDS) confirmed the presence of silicic protective surface films of calcium silicate on the surface of pyrite-bearing tailings.

The impact of coal mining on the environment has been reviewed. The environmental problem generated by this activity is due to the outflow of highly acidic and heavy metals-laden water from a mine generally called Acid Mine Drainage (AMD). AMD is usually generated when a naturally occurring sulphide mineral (e.g. pyrite) is exposed to air and water during the process of mining. Upon oxidation, the sulphide decomposes to sulphuric acid which leaches out soluble metals in concentrations higher than the permissible environmental limits. Heavy metals herein refer to those with densities greater than 5g/cm 3 and can be injurious to aquatic life of downstream waters and food crops planted on soils around the mine which when consumed leads to severe health cases like cancer, high blood pressure and a host of others. This article brings to bear an introduction to the AMD problem, the chemistry behind it, factors that influence its formation, its severity, cost of treatment/mine reclamation, selected impacted areas, a conclusion and an array of recommendations for action. The authors are persuaded that this article would further contribute to the knowledge base of this global environmental phenomenon not just for the purpose of learning but also as a contribution to the realisation of the United Nations Sustainable Development Goals (SDGs-6) of “clean water and sanitation”.

Coal mining is an activity to exploit land to get coal stored underground. Environmental problems in coal mining activities are generally associated with Acid Mine Drainage (AMD). The purpose of this study was to find out the best combination of organic matter and incubation time in remediating acid mine drainage on wetlands with water hyacinth plants. This research was conducted at PT Berau Coal in Tanjung Redeb, Berau, East Kalimantan. This study used a split-plot design. The main plot was the treatment of a combination of organic matter which consisted of 4 levels: A0 as a control (without organic matter), A1 with a combination of compost + sawdust (1:2), A2 with a combination of compost + sawdust (1:1), A3 with a combination of compost + sawdust (2:1). The subplot was treatment incubation time consisting of 2 levels, namely for 15 days and 33 days. Data analysis used variance analysis at the 5% level followed by the Duncan Multiple Range Test with a level of 5% when there were significant differences. The results showed that the addition of organic matter had a significant effect on the increase in pH and a decrease in the concentration of Mn in water, but it did not significantly affect the decrease in Fe concentration in water. The best combination of organic matter in acid mine remediation in this study was compost + sawdust (2:1) during the incubation time of 33 days

The conventional rare earth element (REE) industry has historically sought to develop ore deposits where geologic processes have produced mineralized zones with commercially attractive REE concentrations. These deposits are extremely uncommon, particularly in the USA. Given the criticality of these materials and the need for sustainable domestic supply, the current research seeks to leverage other autogenous processes that lead to concentrated REE resources. One such process is the generation of acid mine drainage (AMD). AMD is very common in many coal mining districts and results from the exposure and oxidation of pyrite during mining. During the generation and migration of AMD, liberated sulfuric acid mobilizes several metal ions including REEs. Treatment of AMD is required under U.S.C §1251, the Clean Water Act, and often consists of neutralization, oxidation, and metal hydroxide precipitation. To investigate the deportment of REEs during this process, a field sampling campaign was undertaken, whereby the concentration of REEs in AMD and AMD precipitates was measured directly. In the nine sites evaluated in this study, the REE concentrations of the precipitates varied from 29 to 1286 ppm with an average of 517 ppm among the sampled sites. The individual elements were enriched compared with the associated bulk Northern Appalachian (NAPP) coal material by factors ranging from 3 to 15. Furthermore, the distribution of REEs in all precipitate samples favored the heavy REEs (HREEs) when compared with traditional REE ores. This research represents the first part of multi-part research endeavor to characterize, classify, and determine the practicality of refining REEs from AMD and its by-products.

The mining wastes coming from Sidi Kamber mine stored at the surface are exposed to weathering conditions, which favour the leaching of toxic metals into the environment. This situation presents serious risks for humans and ecosystems. To better understand this problem, eight representative samples of Sidi Kamber mine tailing were taken from the surface along two vertical trenches and tested using static and dynamic leaching tests. The studied samples present a wide diversity in terms of particle size distribution, mineralogical and chemical compositions. These parameters may greatly affect the reaction rates. The mineralogical investigations show the presence of various sulphide minerals, such as pyrite, galena, sphalerite and chalcopyrite which are present in either free and/or associated with gangue minerals (i.e. quartz, albite, chlorite and muscovite). Moreover, the presence of only minerals with low neutralizing potential such as silicates, promotes the acid mine drainage generation, which is characterized by high concentrations of metals and sulphates. Leaching tests showed an acidic pH and the release of some toxic contaminants (i.e., Pb, Zn and Cu), which exceed the recommended limits (Algerian regulation law for industrial wastewater and US EPA thresholds).

Thallium (Tl) is a well-recognized hazardous heavy metal with very high toxicity. It is usually concentrated in sulfide minerals, such as pyrite (FeS2), sphalerite (ZnS), chalcopyrite (CuS) and galena (PbS). Here, this study was carried out to investigate the indigenous microbial communities via 16S rRNA gene sequence analysis in typical surface sediments with various levels of Tl pollution (1.8–16.1 mg/kg) due to acid mine drainage from an active Tl-containing pyrite mining site in South China. It was found with more than 50 phyla from the domain Bacteria and 1 phyla from the domain Archaea. Sequences assigned to the genera Ferroplasma, Leptospirillum, Ferrovum, Metallibacterium, Acidithiobacillus, and Sulfuriferula manifested high relative abundances in all sequencing libraries from the relatively high Tl contamination. Canonical correspondence analysis further uncovered that the overall microbial community in this area was dominantly structured by the geochemical fractionation of Tl and geochemical parameters such as pH and Eh. Spearman's rank correlation analysis indicated a strong positive correlation between acidophilic Fe-metabolizing species and Tltotal, Tloxi, and Tlres. The findings clarify potential roles of such phylotypes in the biogeochemical cycling of Tl, which may facilitate the development of in-situ bioremediation technology for Tl-contaminated sediments.

Acid mine drainage (AMD) formed from pyrite (iron disulfide) weathering contributes to ecosystem degradation in impacted waters. Solar irradiation has been shown to be an important factor in the biogeochemical cycling of iron in AMD-impacted waters, but its impact on dissolved organic matter (DOM) is unknown. With a typical AMD-impacted water (pH 2.7-3) collected from the Perry State Forest watershed in Ohio, we observed highly efficient (>80%) photochemical mineralization of DOM within hours in a solar simulator resembling twice summer sunlight at 40°N. We confirmed that the mineralization was initially induced by •OH formed from FeOH2+ photodissociation and was inhibited 2-fold by dissolved oxygen removal, suggesting the importance of both the photochemical reaction and oxygen involvement. Size exclusion chromatography and Fourier transform ion cyclotron resonance mass spectrometry elucidated that any remaining organic matter was comprised of smaller and highly aliphatic compounds. The quantitative and qualitative changes in DOM are likely to constitute an important component in regional carbon cycling and nutrient release and to influence downstream aquatic ecosystems in AMD-affected watersheds.

Portland cement is an effective but expensive option for source control of acid mine drainage (AMD); the cost could be reduced by blending the cement with cheap waste materials such as fly ash from coal combustion and sludge produced from neutralization of acid mine drainage with lime. To test how these two additives affect cement performance in reducing AMD generation, blended cement slurries were applied to sulfidic waste rocks from Brukunga, South Australia, in leaching columns monitored for around 1 year. Acidity, metal and sulfate loads decreased greatly (by 80–95%) for all cement applications but the effect varied, depending mostly on the depth of penetration of the cement in the column (a function of slurry viscosity). The fly ash-blended cements penetrated further into the columns than the more viscous surface-capping sludge-blended cements, causing a greater decrease of leachate acidity loads and sulfide oxidation due to better coverage of the waste rocks and more acidity neutralization by cement dissolution. The AMD sludge showed no evidence of releasing its adsorbed heavy metals, but the fly ash released some Si, indicating that it is not chemically stable in the cement. There was little secondary mineral growth in the blended cements; the ettringite in the AMD sludge-blended cement formed from bassanite present in the sludge rather than exposure to acid mine drainage. Overall analysis of the long-term effectiveness of the blended cement applications shows that cement placed as a surface cap on top of the waste rock provides more value, because the slower cement dissolution rates ensure continued effectiveness for many years. Scaling up the results from the laboratory study to the field scale at the Brukunga mine site suggests that benefit/cost ratios in the order of 20–30 might be achieved compared to the present use of lime neutralization for AMD treatment.

The Sarcheshmeh porphyry copper deposit (1.7 Gt @ 0.65% Cu, 0.02% Mo, 1.22 ppm Ag, 0.06 ppm Au) is one of the giant Miocene continental arc porphyry ore systems in the Tethyan metallogenic copper belt. The supergene sulfide ore zone (6 Mt. @ 2.43% Cu, 0.022% Mo, 1.55 ppm Ag and 0.114 ppm Au) is mainly capped by a hematitic gossan. This hematitic gossan is a possible surficial exploration target for unexposed porphyry copper ores. The total tonnage of waste rocks is about 2.6 G tonnes of gossanized as well as sulfide-bearing waste rocks with an average modal content of 10% pyrite-chalcopyrite. The gossanized waste rocks show boxwork texture and are composed of hematite, goethite, jarosite, malachite, chalcanthite, brochantite and delafossite. In order to assess the exploration, economic and environmental aspects of chalcophile and precious elements in the waste rocks, a total of 86 waste rocks and 10 residual gossan samples were collected by a systematic random sampling method, analysed by XRF and ICP-MS methods for major oxides and 50 minor and trace elements at ALS Minerals Lab, Ireland. The highly anomalous elements in immature residual gossans are Au (0.775 ppm), Ag (13.4 ppm) and Mo (122 ppm). The gossanized waste rocks are also enriched in Au (0.608 ppm), Ag (87 ppm) and Mo (2960 ppm). These geochemical signatures could be used as possible exploration guides for concealed porphyry copper deposits. The enrichment of Au, Ag and Mo is caused by the lower mobility of these elements in the immature gossans and gossanized waste rocks. The elemental enrichment factors normalized to the Sarcheshmeh ore zone are Au (2.50), Pd (1.05), Ag (4.67), Pb (4.6), Zn (17.34), Sn (2.64), W (1.47), Re (22.22), Se (5.38), Te (5.75), Tl (4.1), Bi (3.29), Ga (1.15), In (11.5), La (1.2), Ce (1.2) and Y (4.1), respectively. The mean contents of the most valuable by-product elements in the gossanized waste rocks include Cu (3168.2 ppm), Mo (180.22 ppm), Au (0.085 ppm), Ag (5.7 ppm), W (42.76 ppm), Re (0.01 ppm), Bi (10.87 ppm) and Se (13.45 ppm). The S-NNP diagram highlights that the sulfide-bearing waste rocks have also a negative impact on the environment, are prone to generate acid mine drainage (AMD) and release the potentially harmful metal (loids): Pb (107 ppm), Zn (365.3 ppm), As (83.53 ppm), Sb (10.24 ppm), In (0.44 ppm), and Se (13.45 ppm) into the surrounding area. These elemental values occurred at concentrations about 4–269 times greater than the crustal abundances and natural background of fresh granodiorite. As such, the heavy metal-rich gossans and sulfide-bearing waste rocks around the Sarcheshmeh mining areas may be considered as an exploration guide for valuable by-product elements as well as environmental concern.

This paper describes a mixed flow reactor experiment and associated data analysis scheme that are well suited for studying the chemical and physical processes that occur in limestone drains used to treat acid mine drainage (AMD). The experiment simulates the slowly evolving, near steady state, reactions that form coatings on limestone. The resulting coatings can be recovered for analysis of their structure and composition. Analysis of the time evolution of the composition of the effluent solutions is used to isolate and understand key factors that affect limestone drain performance. The experiment investigated reactions between acidic aluminum sulfate solutions and calcite. The aluminum sulfate feed solutions contained 0.002-0.01 molal (32-329 mg/kg) Al and had pH values ranging from 3.7 to 4.2. At the beginning each experiment, the rate of H+ consumption by reaction with the calcite was fast causing a distinct increase of the effluent pH. The pH increase caused some of the dissolved Al to precipitate as a coating on the calcite surfaces. The coating blocked the transfer of ions to and from the calcite causing the reaction rates to be limited by ion diffusion through the coating. The continued growth of the coating caused it to become an increasingly effective barrier to ion transport, which caused the neutralization rate to slow and the effluent solution pH to decline toward that of the feed solution. Powder X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) suggested that the coatings were mostly poorly crystalline gibbsite. Effluent solutions were analyzed to determine pH along with Al, Ca and S concentrations. The coating thickness at each sample time was estimated from the amount of Al lost from the solution since the beginning of the experiment. This thickness and the Ca and H+ fluxes were used to find the apparent H+ diffusion coefficient in the coatings. Department of Geosciences at Virginia Tech; College of Science at Virginia Tech; Graduate School at Virginia Tech Palomino-Ore thanks the Fulbright program for the opportunity to study in the USA and the Department of Geosciences, the College of Science and the Graduate School at Virginia Tech for financial support. We thank F. Marc Michel for manufacturing the reactor used in this study. We thank Neil Johnson for help with the XRD, Qing Tang for help with the SEM, and Athena Tilley for ICP OES analyses. We greatly appreciate helpful reviews by Charles Cravotta, Kate Campbell, and Jane Hammarstrom. Public domain – authored by a U.S. government employee