Reduction of acid mine drainage by passivation of pyrite surfaces: A review

Inhibition of acid rock drainage with iron-silicate or phosphate film: in rainy and submerged environments

Iron phosphate-based coating and iron silicate-based coating were used to inhibit the oxidation of sulfide minerals in rainy and submerged environments. The inhibiting effectiveness of coating agents on the oxidation of iron sulfide minerals was investigated using pyrite and rock samples resulting from acid drainage. The film formed with both surface-coating agents was identified by pyrite surface analysis. It was also confirmed that the formation of coatings varies depending on the crystallographic orientation. The inhibitory effects under rainy and submerged conditions were investigated using column experiments. Submerged conditions accelerated deterioration compared to that under rainy conditions. Iron phosphate coating had a significantly better oxidation-inhibitory effect (84.86-98.70%) than iron silicate coating (56.80-92.36%), and at a concentration of 300 mM, H+ elution was inhibited by more than 90% throughout the experiment. Furthermore, methods for effective film formation were investigated in terms of producing Fe3+; (1) application of coating agents mixed with oxidant (H2O2), (2) application of coating agent after the use of the oxidant. In a rainy environment, applying iron phosphate-based coating using the sequential method showed oxidation inhibition effects for cycles 1-9, whereas applying the mixed material showed effects for cycles 9-13. The use of a surface-coating agent after applying an oxidant did not inhibit oxidation. The surface coating agent and the oxidizing agent should be applied as a mixture to form a film.

Treating waste with waste: Lignin acting as both an effective bactericide and passivator to prevent acid mine drainage formation at the source

Acid mine drainage (AMD) induced by pyrite oxidation is a notorious and serious environmental problem, but the management of AMD in an economical and environmentally friendly way remains challenging. Here, lignin, a natural polymer and abundant waste, was employed as both a bactericide and passivator to prevent AMD formation. The addition of lignin to a mimic AMD formation system inoculated with Acidithiobacillus ferrooxidans at a lignin-to-pyrite weight ratio of 2.5: 10 reduced the combined abiotic and biotic oxidation of pyrite by 68.4 % (based on released SO42-). Morphological characterization of Acidithiobacillus ferrooxidans revealed that lignin could act on the cell surface and impair the cell integrity, disrupting its normal growth and preventing biotic oxidation of pyrite accordingly. Moreover, lignin can be used alone as a passivator to form a coating on the pyrite surface, reducing abiotic oxidation by 71.7 % (based on released SO42-). Through multiple technique analysis, it was proposed that the functional groups on lignin may coordinate with iron ions on pyrite, promoting its deposition on the surface. In addition, the inherent antioxidant activity of lignin may also be actively involved in the abatement of pyrite oxidation via the reduction of iron. Overall, this study offered a "treating waste with waste" strategy for preventing AMD formation at the source and opened a new avenue for the management of AMD.

Inhibition photooxidation of pyrite under illumination via altering photogenerated carrier migration pathways: Role of DTC-TETA surface passivation

The oxidation of pyrite is the main cause of acidic mine drainage (AMD), which is a very serious environmental problem in numerous mining areas around the world. Previous studies have shown that passivation agents create a hydrophobic film on the surface of pyrite, effectively isolating oxygen and water. However, the presence of abundant sulfide minerals in tailings ponds may exacerbate AMD when exposed to solar radiation, due to the semiconductor properties of pyrite. It remains uncertain whether the current surface passivation coating can effectively prevent the oxidation of pyrite under light conditions. This paper is the first to investigate the passivation effect as well as the mechanism of surface passivation coating on pyrite under illumination from the perspective of materials science. The results demonstrated that the triethylenetetramine-bisdithiocarbamate (DTC-TETA) passivation coating on pyrite almost completely suppressed the photooxidation of pyrite under illumination by changing the migration path of photogenerated charge carriers. The formation of NC(S)2-Fe chelating groups provides atomic-level interface channels for DTC-TETA to transfer electrons to pyrite and creates a favorable reduction environment for pyrite. Besides, DTC-TETA coating greatly improves the electron-hole pairs recombination efficiency of pyrite, which significantly inhibits the photogenerated electron reduction of oxygen to generate reactive oxygen species (ROS). Moreover, DTC-TETA coating captures the photogenerated holes, avoiding direct oxidation of pyrite by holes. Density functional theory (DFT) calculations revealed that the DTC-TETA coating increases the adsorption energy barrier for oxygen and water. The results extend the existing knowledge on passivation mechanisms on pyrite and hold significant implications for the future screening, evaluation, and practical application of surface passivating agents.

Enhanced efficiencies on purifying acid mine drainage in constructed wetlands based on synergistic adsorption of attapulgite-soda residue composites and microbial sulfate reduction

Constructed wetlands (CWs) are a promising approach for treating acid mine drainage (AMD). However, the extreme acidity and high loads of heavy metals in AMD can easily lead to the collapse of CWs without proper pre-treatment. Therefore, it is considered essential to maintain efficient and stable performance for AMD treatment in CWs. In this study, pre-prepared attapulgite-soda residue (ASR) composites were used to improve the substrate of CWs. Compared with CWs filled with gravel (CWs-G), the removal efficiencies of sulfate and Fe, Mn, Cu, Zn Cd and Pb in CWs filled with ASR composites (CWs-ASR) were increased by 30% and 10-70%, respectively. These metals were mainly retained in the substrate in stable forms, such as carbonate-, Fe/Mn (oxide)hydroxide-, and sulfide-bound forms. Additionally, higher levels of photosynthetic pigments and antioxidant enzyme activities in plants, along with a richer microbial community, were observed in CWs-ASR than in CWs-G. The application of ASR composites alleviated the adverse effects of AMD stresses on wetland plants and microorganisms. In return, the increased bacteria abundance, particularly SRB genera (e.g., Thermodesulfovibrionia and Desulfobacca), promoted the formation of metal sulfides, enabling the saturated ASR adsorbed with metals to regenerate and continuously capture heavy metals. The synergistic adsorption of ASR composites and microbial sulfate reduction maintained the stable and efficient operation of CWs. This study contributes to the resource utilization of industrial alkaline by-products and promotes the breakthrough of new techniques for low-cost and passive treatment systems such as CWs.

Bioindicator responses to extreme conditions: Insights into pH and bioavailable metals under acidic metal environments

Acid mine drainage (AMD) caused environmental risks from heavy metal pollution, requiring treatment methods such as chemical precipitation and biological treatment. Monitoring and adapting treatment processes was crucial for success, but cost-effective pollution monitoring methods were lacking. Using bioindicators measured through 16S rRNA was a promising method to assess environmental pollution. This study evaluated the effects of AMD on ecological health using the ecological risk index (RI) and the Risk Assessment Code (RAC) indices. Additionally, we also examined how acidic metal stress affected the diversity of bacteria and fungi, as well as their networks. Bioindicators were identified using linear discriminant analysis effect size (LEfSe), Partial least squares regression (PLS-R), and Spearman analyses. The study found that Cd, Cu, Pb, and As pose potential ecological risks in that order. Fungal diversity decreased by 44.88% in AMD-affected areas, more than the 33.61% decrease in bacterial diversity. Microbial diversity was positively correlated with pH (r = 0.88, p = 0.04) and negatively correlated with bioavailable metal concentrations (r = -0.59, p = 0.05). Similarly, microbial diversity was negatively correlated with bioavailable metal concentrations (bio_Cu, bio_Pb, bio_Cd) (r = 0.79, p = 0.03). Acidiferrobacter and Thermoplasmataceae were prevalent in acidic metal environments, while Puia and Chitinophagaceae were identified as biomarker species in the control area (LDA>4). Acidiferrobacter and Thermoplasmataceae were found to be pH-tolerant bioindicators with high reliability (r = 1, P < 0.05, BW > 0.1) through PLS-R and Spearman analysis. Conversely, Puia and Chitinophagaceae were pH-sensitive bioindicators, while Teratosphaeriaceae was a potential bioindicator for Cu-Zn-Cd metal pollution. This study identified bioindicator species for acid and metal pollution in AMD habitats. This study outlined the focus of biological monitoring in AMD acidic stress environments, including extreme pH, heavy metal pollutants, and indicator species. It also provided essential information for heavy metal bioremediation, such as the role of omics and the effects of organic matter on metal bioavailability.

Alumina inhibits pyrite oxidative dissolution by regulating solid film passivation layer and S, Fe, and Al speciation transformation

The oxidation of pyrite results in the formation of a solid film passivation layer on its surface. This layer effectively hinders the direct interaction between H2O, O2, and the pyrite surface, thereby impeding the oxidation dissolution of pyrite. There are few studies on whether alumina (Al2O3), a common aluminum-containing oxide, affects the formation of a solid film passivation layer on the surface of pyrite and inhibits the oxidation dissolution of pyrite. This research investigates the impact of Al2O3 incorporation on the speciation transformation of S, Fe, and Al on the surface of pyrite during oxygen pyrite process. The oxidation of pyrite followed the "polysulfide-thiosulfate" complex oxidation pathway. When <1.5 g/L Al2O3 was introduced, it increase pyrite oxidation, whereas ≥1.5 g/L Al2O3 prevented pyrite oxidation. The process of Al2O3 dissolution results in the consumption of H+ and the subsequent release of Al3+. This, in turn, facilitates the hydrolysis of Fe3+ and Al3+ to generate a secondary mineral layer on the pyrite surface. As a result of the accumulation of S promotes the formation of polysulfide chemical (FeSn) or iron deficiency sulfide (Fe1-xS), resulting in the formation of a solid film passivation layer composed of sulfur film and secondary mineral layer. The results demonstrated that Al2O3 can promote the formation of a solid film passivation layer on the surface of pyrite, which has significant implications for controlling the oxidation dissolution process of pyrite and offers a new perspective for the source control of acid mine drainage.

Construction and application of a composite model for acid mine drainage quality evaluation based on analytic hierarchy process, factor analysis and fuzzy comprehensive evaluation: Guizhou Province, China, as a case

The process of mining activities often causes the formation of acid mine drainage (AMD). Through rock fractures and underground rivers, AMD can easily enter the groundwater environment near mines and cause serious pollution to water quality. In order to effectively evaluate the quality of polluted mine water and to understand its threat to the ecosystem around the mine. In this study, four AMD pollution distribution areas, Guiyang City, Bijie City, Qianxinan Prefecture, and Qiandongnan Prefecture in Guizhou Province, were used as the study area. A composite model for mine water quality evaluation was constructed using factor analysis (FA), analytic hierarchy process (AHP), and fuzzy comprehensive evaluation (FCE). Furthermore, by introducing the weighted average method and the level characteristic value (J), the water quality type and the water body environmental quality were evaluated comprehensively, respectively. Compared with the traditional evaluation model, the AHP-FA-FCE model has obvious advantages in the selection of evaluation indicators, the determination of indicator weights, and the comprehensive evaluation of water quality types, and the evaluation results obtained are more reasonable and accurate. Three common factors mainly controlled by mineral oxidation factor, human activity factor, and mineral dissolution factor were extracted by dimension reduction of the original hydrochemical data by FA. The water quality of the mine water samples was evaluated using SO4 2- , Fe, Al, Mn, Na, and F- as evaluation indicators, and the results showed that the mine water samples in the study area as a whole were dominated by class V water, which accounted for 77.78% of the total. Based on the statistical analysis of the original data, it was found that influenced by the water-rock interactions in the study area and the AMD pollution components, the hydrochemical type of the mine water is mainly SO4 2- -Ca-Mg type. The water body environmental quality of mine water in four areas, Guiyang City, Qianxinan Prefecture, Bijie City, and Qiandongnan Prefecture, is from excellent to poor. The average level characteristic value of all the areas is more than 3, and the overall environmental quality of the water body is poor. The strong water-rock interaction and mining activities in the study area may be the main cause of AMD pollution. The results of this study may provide some theoretical reference for the water quality evaluation of AMD-polluted areas. PRACTITIONER POINTS: A composite model for mine water quality evaluation was constructed. A factor analysis-based evaluation indicator selection method is proposed. This study improved the weighting process of the traditional fuzzy comprehensive evaluation. A water quality discriminant based on the weighted average method is proposed. The water environmental quality of various types of mine water was evaluated.

Identifying sources of acid mine drainage and major hydrogeochemical processes in abandoned mine adits (Southeast Shaanxi, China)

Acid mine drainage (AMD) has resulted in significant risks to both human health and the environment of the Han River watershed. In this study, water and sediment samples from typical mine adits were selected to investigate the hydrogeochemical characteristics and assess the environmental impacts of AMD. The interactions between coexisting chemical factors, geochemical processes in the mine adit, and the causes of AMD formation are discussed based on statistical analysis, mineralogical analysis, and geochemical modeling. The results showed that the hydrochemical types of AMD consisted of SO4-Ca-Mg, SO4-Ca, and SO4-Mg, with low pH and extremely high concentrations of Fe and SO42-. The release behaviors of most heavy metals are controlled by the oxidation of sulfide minerals (mainly pyrite) and the dissolution/precipitation of secondary minerals. Along the AMD pathway in the adit, the species of Fe-hydroxy secondary minerals tend to initially increase and later decrease. The inverse model results indicated that (1) oxidative dissolution of sulfide minerals, (2) interconversion of Fe-hydroxy secondary minerals, (3) precipitation of gypsum, and (4) neutralization by calcite are the main geochemical reactions in the adit, and chlorite might be the major neutralizing mineral of AMD with calcite. Furthermore, there were two sources of AMD in abandoned mine adits: oxidation of pyrite within the adits and infiltration of AMD from the overlying waste rock dumps. The findings can provide deeper insight into hydrogeochemical processes and the formation of AMD contamination produced in abandoned mine adits under similar mining and hydrogeological conditions.

Dynamic coupling of ferrihydrite transformation and associated arsenic desorption/redistribution mediated by sulfate-reducing bacteria

Sulfate-reducing bacteria play an important role in the geochemistry of iron (oxyhydr)oxide and arsenic (As) in natural environments; however, the associated reaction processes are yet to be fully understood. In this study, batch experiments coupled with geochemical, spectroscopic, microscopic, and thermodynamic analyses were conducted to investigate the dynamic coupling of ferrihydrite transformation and the associated As desorption/redistribution mediated by Desulfovibrio vulgaris (D. vulgaris). The results indicated that D. vulgaris could induce ferrihydrite transformation via S2--driven and direct reduction processes. In the absence of SO42-, D. vulgaris directly reduced ferrihydrite, and As desorption and re-sorption occurred simultaneously during the partial transformation of ferrihydrite to magnetite. The increase in SO42- loading promoted the S2--driven reduction of ferrihydrite and accelerated the subsequent mineralogical transformation. In the low and medium SO42- treatments, ferrihydrite was completely transformed to a mixture of magnetite and mackinawite, which increased the fraction of As in the residual phase and stabilized As. In the high SO42- treatment, although the replacement of ferrihydrite by only mackinawite also increased the fraction of As in the residual phase, 22.1% of the total As was released into the solution due to the poor adsorption affinity of As to mackinawite and the conversion of As5+ to As3+. The mechanisms of ferrihydrite reduction, mineralogy transformation, and As mobilization and redistribution mediated by sulfate-reducing bacteria are closely related to the surrounding SO42- loadings. These results advance our understanding of the biogeochemical behavior of Fe, S, and As, and are helpful for the risk assessment and remediation of As contamination.

A review: The formation, prevention, and remediation of acid mine drainage

In abandoned open-pit coal mines, surface water and groundwater form acidic waters with high concentrations of metal ions due to chemical interactions with ores such as pyrite, and the formation of acid mine drainage (AMD) is one of the major sources of pollution of world concern. For this reason, this paper reviews the formation mechanisms and influencing factors of AMD. It also describes the prediction, prevention, and remediation techniques for AMD, identifying key research gaps. It also discusses the current challenges and shortcomings faced globally in the management of AMD. The formation of AMD is mainly caused by the oxidation of pyrite in mines, but it is mainly influenced by history, climate, topography, and hydrogeology, making the formation mechanism of AMD extremely complex. Currently, the remediation technologies for AMD mainly include active treatment and passive treatment, which can effectively neutralize acidic wastewater. However, the prediction technology for AMD is blank, and the source treatment technology such as passivation and microencapsulation only stays in the experimental stage. This leads to the high cost of treatment technologies at this stage and the inability to identify potential risks in mines. Overall, this review provides remediation tools for AMD from predicting root causes to treatment. Geophysical technology is an effective method for predicting the motion path and pollution surface of AMD in the future, and resource recovery for AMD is a key point that must be paid attention to in the future. Finally, integrated treatment technologies that deserve further exploration need to be emphasized.

Experimental and modeling investigation of dual-source iron release in water-solid-gas interaction of abandoned coal mine drainage

After mine closure and flooding, abandoned iron-prone devices and equipment (e.g., steel bolts and ground support meshes) and iron-bearing minerals (e.g., pyrite) form a dual-source iron pollution system in mine groundwater. Dual-source iron contributes to the water-solid-gas interaction in abandoned coal mines and the release of iron at different periods after mine closure, posing environmental risks in groundwater and discharging acid mine drainage, which contains large amounts of iron. In this study, a series of hydrochemical experiments were conducted to simulate the iron release process of the dual-source system, and electrochemical experiments were carried out to reveal the reaction mechanism, characterize the dual-source iron pollution release mode and quantify the release rate ratio. PHREEQC package was used to simulate the long-term hydrogeochemistry reactions of the water-solid-gas interaction to determine the key factors and suitable conditions that inhibit dual-source iron release. The results show that the dual-source system of iron-bearing minerals (pyrite) and steel bolts promote iron release from each other. The resulting calculated annual iron release indicated that the overall iron release rate ratio is: dual-source > bolt > pyrite, indicating that mine water would remain acidic for a long time due to the continuous release of iron from the system. Numerical modeling results show that maintaining the environment temperature below 25 °C and the pH above 3.5 is an effective way to reduce the iron release rate.

Beneficial use of dredged sediments as a resource for mine reclamation: A case study of Lake Dianchi's management in China

Dredging is one of the most effective methods for inhibiting the endogenous contamination of natural lakes. However, both the amount and the scope of dredging will be restricted if the disposal of the dredged sediment incurs considerable environmental and economic costs. The use of dredged sediments as a post-mining soil amendment for mine reclamation benefits both sustainable dredging and ecological restoration. This study incorporates a field planting experiment with a life cycle assessment to confirm the practical effectiveness of sediment disposal via mine reclamation, as well as its environmental and economic superiority over other alternative scenarios. The results show that the sediment offered plentiful organic matter and nitrogen for mine substrate, stimulating plant growth and increasing photosynthetic carbon fixation density, followed by enhanced plant root absorption and an improved soil immobilization effect on heavy metals. A 2:1 ratio of mine substrate to sediment is recommended to significantly promote the yield of ryegrass while reducing levels of groundwater pollution and soil contaminant accumulation. Due to the significant reduction in electricity and fuel, mine reclamation had minimal environmental impacts on global warming (2.63 × 10^-2 kg CO₂ eq./kg DS), fossil depletion (6.81 × 10^-3 kg oil eq./DS), human toxicity (2.29 × 10^-5 kg 1,4-DB eq/kg DS), photochemical oxidant formation (7.62 × 10^-5 kg NO_x eq./kg DS), and terrestrial acidification (6.69 × 10^-5 kg SO₂ eq./kg DS). Mine reclamation also had a lower cost (CNY 0.260/ kg DS) than cement production (CNY 0.965/kg DS) and unfired brick production (CNY 0.268/kg DS). The use of freshwater for irrigation and electricity for dehydration were the key factors in mine reclamation. Through this comprehensive evaluation, the disposal of dredged sediment for mine reclamation was verified to be both environmentally and economically feasible.

Suppression of pyrite oxidation by co-depositing bio-inspired PropS-SH-tannic acid coatings for the source control acid mine drainage

In previous works, both tannic acid (TA) and organosilane-based passivators have been proven to possess good inhibition effects on pyrite oxidation, which could effectively prevent acid mine drainage (AMD) generation at the source. However, the hydrophilicity of TA passivation film and the complex coating process of organosilane-based passivators (high temperature conditions were required during the process carried out) may limit their further practical use. Therefore, to achieve the purpose of better coating treatment of pyrite under mild conditions, TA and γ-mercaptopropyltrimethoxysilane (PropS-SH) were introduced to synergistically passivate pyrite in this work. Electrochemistry tests and chemical leaching experiments both confirmed that PropS-SH-TA coated pyrite had better oxidation resistance than raw pyrite and single PropS-SH or TA coated pyrite. Additionally, the analyses of scanning electron microscopy (SEM) measurements and static water contact angle tests demonstrated that a scaly coating was formed on PropS-SH-TA coated pyrite surface, which may be the reason for the significant improvement of its surface hydrophobicity. Finally, the study on the film-forming mechanism of PropS-SH-TA composite passivator displayed that the benzoquinone derivatives formed by TA could copolymerize with PropS-SH through Michael addition or Schiff base reaction, which constructed a dense hydrophobic film on pyrite surface. The newly formed composite film could provide a better oxidation barrier for pyrite based on TA passivation film.

Synergistic mechanism and application of microbially induced carbonate precipitation (MICP) and inorganic additives for passivation of heavy metals in copper-nickel tailings

Tailings are one of the largest quantities of hazardous waste in the world, and their treatment is difficult and expensive. In this work, a new, low-cost technique coupling microbially induced carbonate precipitation (MICP) and inorganic additives was proposed, optimized, and applied. The results showed that CaO was the best additive among the six tested, with an optimum dosage of 5%. A 90-day experiment indicated that the MICP-CaO coupled technique was highly effective for all the concerned heavy metals (Cu, Ni, Pb, and Cr) in the Cu-Ni tailings. During the stabilization period (20-90 days), the passivation rates were stable at 78.8 ± 2.9% (Cu), 78.1 ± 1.0% (Ni), 89.2 ± 1.0% (Pb), and 97.8 ± 0.5% (Cr), 2%-866% higher than the single technique of either MICP or CaO. Multiple analyses demonstrated that the synergistic effect of MICP and CaO produced a large amount of calcite (1.5% of the tailings). This calcite cemented the tailings particles, sequestrated heavy metal ions into the lattices, and played a key role in heavy metal passivation. Moreover, CaO and MICP improved the strength and compactness of solidified body, respectively. This work demonstrates the feasibility of the MICP-CaO coupled technique in tailings solidification, which can be applied in practical projects.

Inhibition of humic acid on copper pollution caused by chalcopyrite biooxidation

Humic acid has the advantages of wide source, easy availability and environmental friendliness, which may be a good choice for inhibiting chalcopyrite biooxidation and alleviating copper pollution. However, there are few researches on the inhibitory effect and mechanism of humic acid on the biooxidation of chalcopyrite. In order to fill this knowledge gap, this study proposed and validated a novel method for inhibiting chalcopyrite biooxidation by means of humic acid. The results showed that the biooxidation of chalcopyrite could be effectively inhibited by humic acid, which consequently decreased the release of copper ions. Humic acid with a concentration of 120 ppm had the best inhibitory effect, which reduced the biooxidation efficiency of chalcopyrite from 40.7 ± 0.5 % to 29.3 ± 0.8 %. This in turn suggested that humic acid could effectively suppress the pollution of copper under these conditions. The analysis results of solution parameters, mineral surface morphology, mineral phases and element composition showed that humic acid inhibited the growth of Acidithiobacillus ferrooxidans, promoted the formation of jarosite and intensified the passivation of chalcopyrite, which effectively hindered the biooxidation of chalcopyrite, and would help to alleviate the pollution of copper.

A new organosilane passivation agent prepared at ambient temperatures to inhibit pyrite oxidation for acid mine drainage control

Acid mine drainage (AMD) is a significant environmental problem caused by the oxidation of pyrite and other metal sulfide ores. Organosilane passivation is an effective strategy to inhibit pyrite oxidation. However, synthetic organic silane passivation agents generally require temperatures of 50-80 °C, resulting in high energy consumption and high synthesis cost. In this study, a 3-aminopropyltrimethoxysilane -methyltrimethoxysilane (APS-MTMS) coatings was successfully prepared at ambient temperatures of 15-40 °C as a passivation agent to inhibit pyrite oxidation. Chemical leaching tests were used to study the inhibition performance of APS-MTMS for pyrite oxidation. The experimental results showed that the release of the total Fe from APS-MTMS-coated pyrite was 11.31 mg/L after chemical oxidation for 7 hours, and the passivation rate can reach 77.78%. The contact angle of the APS-MTMS-coated pyrite was significantly larger (140.4°) than that of the bare pyrite (58.8°), indicating that APS-MTMS prompted the formation of a superhydrophobic surface of pyrite, improving the oxidation resistance. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were applied to probe the interaction mechanism of APS-MTMS with pyrite. The results indicated that APS accelerated the Si-O-Si formation by amino protonation and enriched a crosslinked network of Si-O-Si and Fe-O-Si on the pyrite surface to prevent pyrite oxidation. This study provides a novel method for preparing organosilane passivation materials at ambient temperatures for AMD control.

Resource Utilization of Acid Mine Drainage (AMD): A Review

Acid mine drainage (AMD) is a typical type of pollution originating from complex oxidation interactions that occur under ambient conditions in abandoned and active mines. AMD has high acidity and contains a high concentration of heavy metals and metalloids, posing a serious threat to ecological systems and human health. Over the years, great progress has been made in the prevention and treatment of AMD. Remediation approaches like chemical neutralization precipitation, ion exchange, membrane separation processes, and bioremediation have been extensively reported. Nevertheless, some limitations, such as low efficacy, excessive consumption of chemical reagents, and secondary contamination restrict the application of these technologies. The aim of this review was to provide updated information on the sustainable treatments that have been engaged in the published literature on the resource utilization of AMD. The recovery and reuse of valuable resources (e.g., clean water, sulfuric acid, and metal ions) from AMD can offset the cost of AMD remediation. Iron oxide particles recovered from AMD can be applied as adsorbents for the removal of pollutants from wastewater and for the fabrication of effective catalysts for heterogeneous Fenton reactions. The application of AMD in beneficiation fields, such as activating pyrite and chalcopyrite flotation, regulating pulp pH, and leaching copper-bearing waste rock, provides easy access to the innovative utilization of AMD. A review such as this will help researchers understand the progress in research, and identify the strengths and weaknesses of each treatment technology, which can help shape the direction of future research in this area.

Evolution of Sulfidic Legacy Mine Tailings: A Review of the Wheal Maid Site, UK

Historic tailings dams and their associated mine waste can pose a significant risk to human and environmental health. The Wheal Maid mine site, Cornwall, UK, serves as an example of the temporal evolution of a tailings storage facility after mining has ceased and the acid-generating waste subjected to surficial processes. This paper discusses its designation as a contaminated land site and reviews our current understanding of the geochemistry, mineralogy, and microbiology of the Wheal Maid tailings, from both peer-reviewed journal articles and unpublished literature. We also present new data on waste characterisation and detailed mineral chemistry and data from laboratory oxidation experiments. Particularly of interest at Wheal Maid is the presence of pyrite-bearing “Grey Tailings”, which, under typical environmental conditions at the Earth’s surface, would be expected to have undergone oxidation and subsequently formed acidic and metalliferous mine drainage (AMD). The results identified a number of mechanisms that could explain the lack of pyrite oxidation in the Grey Tailings, including a lack of nutrients inhibiting microbial Fe(II) oxidation, passivation of pyrite mineral surfaces with tailings processing chemicals, and an abundance of euhedral pyrite grains. Such research areas need further scrutiny in order to inform the design of future tailings facilities and associated AMD management protocols.