Acid mine drainage formation and arsenic mobility under strongly acidic conditions: Importance of soluble phases, iron oxyhydroxides/oxides and nature of oxidation layer on pyrite

Changes in chemical speciation and mobility of arsenic during the mixing of arsenic-bearing "snow-melting" system effluent and river water in the Ishikari Plain, Japan

An effective and ingenious method called "snow-melting" system was widely implemented for snow management in the Ishikari Plain, Japan. In this system, groundwater is pumped up, mixed with snow, and discharged into a nearby river. Since the groundwater in the Ishikari Plain is contaminated with arsenic (As), the impacts of directly discharging As-bearing groundwater into the river were assessed and monitored. In-situ monitoring data collected between 2013 and 2015 showed that As concentrations were higher in the groundwater (23-95 μg/L) than in the river water (2-71 μg/L). The major As speciation in the groundwater and river water were dissolved arsenite (As(III)) and As in suspended iron (Fe)-bearing solids, respectively. Precipitation of dissolved Fe when "snow-melting" system effluent mixes with the river water could be attributed to more oxic and oxidizing conditions of the resulting fluid mixture. Dissolved iron (Fe), mainly as ferrous ion (Fe2+), coexisted with dissolved As(III) in groundwater, so after mixing with the river water, Fe2+ was oxidized to ferric ion (Fe3+) and then precipitated as amorphous Fe oxyhydroxide phases that also sequestered dissolved arsenate (As(V)) via adsorption and coprecipitation. A strong correlation between As and Fe contents in river sediments was also observed, suggesting that Fe-bearing phases play an essential role in As immobilization. The results also showed a strong interaction between groundwater and river water that affected the chemical speciation and mobility of As and Fe. In addition, it was found that discharging As-bearing groundwater did not have profound impact on river water quality. Based on the results, dissolved Fe, Fe-bearing solid phases, and geochemical conditions strongly influenced how As speciates and migrates in a system where two fluids are mixed. This study could provide significant insights concerning the impacts of As on surrounding environments where As-bearing groundwaters are used and discharged without treatment.

Compositional heterogeneity of secondary minerals in mine waste rock: Origins and implications for water quality

Secondary minerals in mine waste materials impose strong controls on water quality by scavenging solutes of concern. This study investigates the mineralogical and compositional characteristics of secondary Fe(oxy)hydroxides and Ca-sulfates, two globally ubiquitous secondary precipitates, in weathered mine waste rock. Bulk analyses show that Si, Ca, Fe, Al, and S-bearing primary phases were the most abundant in the entire samples, but up to a few wt% of secondary Fe(oxy)hydroxides and Ca-sulfates were present as well. In these secondary phases, trace metal impurities like V (37 mg/kg in Ca-sulfates), Cr (23 mg/kg in Fe-oxides and 21 mg/kg in Ca-sulfates), and Cd (up to 15 mg/kg in Fe-oxides and Ca-sulfates) could not be detected by bulk techniques (XRF and XRD), but their deportment to some extent characterized by automated mineralogy, and their spatial distribution assessed at high-resolution through microscale LA-ICP-MS analysis. Element mapping revealed that metal(loid)s were generally enriched at grain rims, reflective of peripheral sequestration through surface adsorption. An exception was V, which was uniformly distributed in the studied secondary Fe-oxides, suggestive of isomorphic substitution during co-precipitation. Factor analysis revealed distinct groups of elements co-associated within each secondary mineral (e.g., divalent transition metal cations versus oxyanionic metalloids), likely caused by similar primary mineral sourcing or a comparable sequestration mechanism. Our results demonstrate the importance of secondary mineral precipitates for scavenging (trace) elements and the insights that can be gained from complementary mineralogical and element analyses for the interpretation of trace element dynamics in waste rock.

Biogenic iron mineral formation and the fate of arsenic driven by its coupling with ferrous iron in acid mine drainage environment

Acid mine drainage (AMD) containing arsenic produced during coal mining is a global environmental problem. However, the coupled driving process of the key element Fe and the associated element As in the AMD environment has received little attention. Therefore, in this study, we investigated the A. ferrooxidans-mediated ferrous iron-arsenic interaction in a simulated AMD system. We reveal that in As-rich AMD the co-existing element As can regulate the metabolic activity of A. ferrooxidans to accelerate the oxidation of Fe2 + and the subsequent formation of Fe3+ minerals, thereby altering the pH and ORP of the system. XRD, SEM, and XPS analyses showed that the synthesized Fe mineral mainly consisted of As-containing schwertmannite (Sch). As in an AMD system could be efficiently removed (98.7 % after 72 h) through the formation of Fe minerals, thereby reducing its own environmental risk. SO42- plays an important role in As precipitation on the surface and in crystal tunnels of Sch. As-containing Sch is not only beneficial for the precipitation of As, but also for long-term reduction in As toxicity in AMD systems. Our results provide new insight for evaluating the fates of Fe and As, and the environmental and ecological risks of As in AMD produced from natural coal mines.

Lithology as a factor for the distribution of metals in stream sediments associated with sediment-hosted Cu deposits: a case study from the Alta-Kvænangen tectonic window, northern Norway

The Kåfjord area in northern Norway hosts numerous Cu deposits that were subjected to mining activities back in the nineteenth century. Relicts of the historical mining activity are still visible at several abandoned mines and associated mine waste disposal sites that may represent an environmental threat. The area was subjected to mining activities during the nineteenth century and abandoned mines and associated mine waste disposal sites still may represent a significant environmental threat. The Cu mineralization, found within the Paleoproterozoic Alta-Kvænangen Tectonic Window, primarily occurs as epigenetic sulfide-quartz-carbonate hydrothermal veins that crosscut the Kvenvik volcano-sedimentary complex and the overlying Storviknes sedimentary sequence. This study aims to determine the geochemical composition of stream sediments associated with the sediment-hosted Cu deposits and examine the role of host lithologies in the dispersion of elements associated with the deposits. Sediments from two streams and a river in the Kåfjord area were analyzed using phase and element analyses (aqua regia chemistry), complemented by a seven-step sequential extraction procedure. Results from Annaselva stream, draining Cu occurrences in the carbonate sediments of the Storviknes sequence, showed a significant positive correlation of Cu with mobile chalcophile elements (Pb, Zn, Ni, Tl, Hg, Ag, Sb, Bi) and lithophile elements (Sr, Ca, Ba, Al, K). In contrast, Brakkelva stream, draining the mafic volcanics of the Kvenvik complex, exhibited no statistically significant correlations between Cu and any of the analyzed elements. Møllneselva River, draining both lithologies, showed a strong Cu-Sc correlation, with principal component analysis indicating limited distinction between lithology-derived elements. These results did not completely align with statistical analysis outcomes highlighting the challenges of statistical data interpretation using a limited number of samples.

Integrated 3D geo-environmental assessment of acid-forming materials in historic coal waste piles for sustainable management

Coal mining produces coal mine waste rock (CMWR), posing significant environmental risks, including acid mine drainage (AMD) if unmanaged. The Jerada Mine in eastern Morocco has accumulated CMWR since it began operations in 1936, with no rehabilitation efforts until 2001. This study assessed the stability of the T08 pile, which has been deposited over five decades across various oxidation zones. More than 400 samples from 13 drill holes were thoroughly analyzed, including particle size distribution, X-ray fluorescence (XRF), and other advanced techniques, culminating in a 3D model to identify potentially acid-forming (PAF) zones. Particle sizes (D30 and D90) ranged from 16.3 to 16.5 μm in low-oxidation zones to 353.3-409 μm in highly oxidized areas, respectively. Sulfur content varied from 0.32 to 2.05 wt% for sulfide and from 0.0013 to 0.17 wt% for sulfate, with an acidification potential ranging from 14.42 to 29.2 kg CaCO₃/t and negative net neutralization potential (NNP) from -35.12 to -11.14 kg CaCO₃/t. NAG tests revealed a low pH of approximately 4 and acidity levels exceeding safety thresholds, with low neutralizing minerals content. Pyrite was the dominant sulfide, alongside ankerite, hematite, and goethite. Highly oxidized zones exhibited larger particle size distributions, increasing porosity and airflow. Thereby, enhancing oxidation and converting iron into different oxidation states. This process affects sulfur speciation, leading to sulfate formation. The 3D model estimated 3.8 Mt of PAF material in the upper pile, highlighting a heterogeneous distribution linked to porosity and oxidation levels, underscoring the necessity for further kinetic testing to evaluate long-term AMD risks.

Pyrite in recirculating stacking hybrid constructed wetland: Electron transfer for nitrate reduction and phosphorus immobilization

Pyrite is considered as an effective and environmentally friendly substrate in constructed wetlands (CW) for wastewater treatment, but its application in recirculation stacking hybrid constructed wetlands (RSHCW) has been scarcely studied. This study uses varying amounts of pyrite as the substrate in RSHCW, leveraging the recirculation of wastewater to alter microenvironments such as dissolved oxygen (DO) and pH, to explore the potential mechanisms of nitrogen (N) and phosphorus (P) removal in pyrite-based RSHCW. The results show that as the proportion of pyrite increases, the removal rate of total phosphorus (TP) in the effluent also increases (25%→58%), significantly enhancing the deposition of iron-bound phosphorus (Fe-P) on the substrate, thereby turning CW into a P reservoir. Even in the absence of a carbon source, the total nitrogen (TN) removal rate in the CW still increases by 20%, which can be attributed to the enrichment of sulfur autotrophic denitrifying bacteria driving autotrophic denitrification by pyrite. Additionally, the addition of pyrite significantly increases the electron transfer system activity (ETSA) in the CW system by approximately 6.14 times and facilitates a "charging and discharging" function through the sulfur-iron electron cycle. Selective enrichment of microbes in moderated pH environment due to RSHCW recirculation in the pyrite-CW (PCW) enhances the coordination among microbial communities and the interaction among functional genes. This study provides new insights into the mechanisms of N and P removal in CWs under the influence of pyrite.

Different fates of Sb(III) and Sb(V) during the formation of jarosite mediated by Acidithiobacillus ferrooxidans

Secondary iron-sulfate minerals such as jarosite, which are easily formed in acid mine drainage, play an important role in controlling metal mobility. In this work, the typical iron-oxidizing bacterium Acidithiobacillus ferrooxidans ATCC 23270 was selected to synthesize jarosite in the presence of antimony ions, during which the solution behavior, synthetic product composition, and bacterial metabolism were studied. The results show that in the presence of Sb(V), Fe2+ was rapidly oxidized to Fe3+ by A. ferrooxidans and Sb(V) had no obvious effect on the biooxidation of Fe2+ under the current experimental conditions. The presence of Sb(III) inhibited bacterial growth and Fe2+ oxidation. For the group with Sb(III), products with amorphous phases were formed 72 hr later, which were mainly ferrous sulfate and pentavalent antimony oxide, and the amorphous precursor was finally transformed into a more stable crystal phase. For the group with Sb(V), the morphology and structure of jarosite were changed in comparison with those without Sb. The biomineralization process was accompanied by the removal of 94% Sb(V) to form jarosite containing the Fe-Sb-O complex. Comparative transcriptome analysis shows differential effects of Sb(III) and Sb(V) on bacterial metabolism. The expression levels of functional genes related to cell components were much more downregulated for the group with Sb(III) but much more regulated for that with Sb(V). Notably, cytochrome c and nitrogen fixation-relevant genes for the A.f_Fe2+_Sb(III) group were enhanced significantly, indicating their role in Sb(III) resistance. This study is of great value for the development of antimony pollution control and remediation technology.

A meta-analysis of influencing factors on soil pollution around copper smelting sites

Non-ferrous smelting activities have caused serious heavy metal(loid) pollution in soil which seriously threatens human health globally. A number of studies have been conducted to assess the characteristics and risks of soil heavy metal(loid) pollution around copper (Cu) smelting sites. However, the current research mainly focuses on soil pollution around a single smelter, and the global impact of Cu smelting on soil and its quantitative relationship with related factors need to be further studied. Meta-analysis can integrate a large amount of data and quantitatively analyze the relationship between multiple factors. To investigate the extent to which Cu smelting sites have contributed to heavy metal(loid) pollution in soils, a meta-analysis was conducted on 189 research publications from 1993 to 2023. Furthermore, a single meta regression was used to analyze the relationship between the soil heavy metal(loid)s (HMs) and influencing factors on a global scale. The results of meta-regression analysis showed that compared with the soil background value, Cu smelting significantly increased the concentration of HMs in soil (315%), with the concentration increase for each heavy metal(loid) being: Cu (1012%) > Cd (622%) > As (315%) > Pb (277%) > Zn (188%) > Cr (96%) > Ni (95%) > Mn (45%). Among these, Cu, Cd, and As were the major pollutants in soils around Cu smelting sites. Land use type was a key factor affecting HMs concentrations in surrounding soils, and the influence of non-agricultural land (381%) was greater than that of agricultural land (203%). In addition, the influence of Cu smelting on HMs were negatively correlated with distance (QM=9.86) and positively correlated with latitude (QM=10.7). There was no significant correlation between heavy metal(loid) pollution and soil chemical properties, average annual rainfall and temperature, longitude, or other factors. Our work may be meaningful to the risk control and remediation for Cu smelting sites.

Response of bacterial communities in desert grassland soil profiles to acid mine drainage pollution

Acid mine drainage (AMD) causes serious environmental pollution, which imposes stresses on soil ecosystems. Therefore, it is critical to study the responses of soil bacterial communities to AMD pollution in ecologically fragile desert grasslands. Here, the bacterial community composition, structure, and assembly processes in vertical soil profiles of an AMD contaminated desert grassland were explored using 16S rRNA high-throughput sequencing. The results showed that the surface layers of the profiles exhibited lower pH and higher heavy metals (HMs) content due to AMD influence. The AMD contamination led to reduced bacterial diversity in the surface soil layer of the profiles and significantly changed the bacterial community composition and structure. Gradients in pH, TK, TN, and HMs were the main factors driving bacterial community variability. In contrast to the uncontaminated profile, deterministic processes were important in shaping soil bacterial community in the AMD contaminated profiles. These findings will enhance understanding about the responses of soil bacteria in desert grassland soil to the environmental changes caused by AMD contamination and will improve the remediation of AMD contaminated soil.

A novelty strategy for AMD prevention by biogas slurry: Acetate acid inhibition effect on chalcopyrite biooxidation and leachate

With the widespread application of anaerobic digestion technology, biogas slurry become the main source of organic amendments in practice. Comprehensive studies into the inhibitory effects of low molecular weight (LMW) organic acids, essential components in biogas slurry, on the sulfide minerals biooxidation and its bioleaching (AMD) have been lacking. In this study, acetic acid (AA) served as a representative of LMW organic acids in biogas slurry to investigate its impact on the inhibition of chalcopyrite biooxidation by Acidithiobacillus ferrooxidans (A. ferrooxidans). It was shown that AA could slow down the chalcopyrite biooxidation and inhibit the jarosite formation on the mineral surface. Compared with the control group (0 ppm AA), the sulfate increment in the leachate of the 50 ppm, 100 ppm, and 200 ppm AA-treated groups decreased by 36.4%, 66.8%, and 69.0%, respectively. AA treatment (≥50 ppm) could reduce the oxidation of ferrous ions in the leachate by one order of magnitude. At the same time, the bacterial concentration of the leachate in the 50 ppm, 100 ppm, and 200 ppm AA-treated groups decreased by 70%, 93%, and 94%, respectively. These findings provide a scientific basis for new strategies to utilize biogas slurry for mine remediation and contribute to an enhanced comprehension of organic amendments to prevent AMD in situ in mining soil remediation.

Transforming restored heavy metal-contaminated soil into eco-friendly bricks: An insight into heavy metal stabilization and environmental safety

Materialization is currently the primary method for utilizing restored heavy metal-contaminated soil (RHMCS). However, compared to ordinary building materials, the migration and transformation mechanisms of heavy metals (HMs) while preparing these materials remain unclear. To bridge these gaps, this study investigated the migration and transformation mechanisms of As and Pb during the sintering of RHMCS into bricks. This study is the first to conduct a systematic study from the perspectives of both the inner and outer brick layers on the patterns and mechanisms of HM migration and transformation during the sintering process, along with the safety of product utilization. Approximately 90% of As and 36% of Pb migrated out of the RHMCS, with significant transformations observed after sintering. Adjusting the sintering parameters increased migration at long dwell times and high temperatures. These findings indicate different migration behaviors and transformations of HMs within the brick layers, emphasizing the need for cautious application and potential secondary pollution risks. A potential ecological risk index confirmed the safety of the bricks in accordance with construction material standards. Overall, this study provides crucial insights into safe and effective RHMCS utilization, contributing significantly to environmental remediation and sustainable construction practices.

Long-term performance of the adsorption layer system for the recycling and repurposing of arsenic-bearing mudstone as road embankment

The adsorption layer system has shown great potential as a cost-effective and practical strategy for the recycling and management of excavated rocks containing potentially toxic elements (PTEs). Although this system has been employed in various civil engineering projects throughout Japan, its long-term performance to immobilize PTEs has rarely been investigated. This study aims to evaluate the effectiveness of the adsorption layer system applied in an actual road embankment approximately 11 years after construction. The embankment system is comprised of a layer of excavated arsenic (As)-bearing mudstone built on top of a bottom adsorption layer mixed with an iron (Fe)-based adsorbent. Collection of undisturbed sample was carried out by implementing borehole drilling surveys on the embankment. Batch leaching experiments using deionized water and hydrochloric acid were conducted to evaluate the water-soluble and acid-leachable concentrations of As, Fe, and other coexisting ions. The leaching of As from the mudstone layer was likely induced by As desorption from Fe-oxides/oxyhydroxides naturally present under alkaline conditions, including the oxidation of framboidal pyrite, which was identified as a potential source of As. This was supported by electron probe microanalyzer (EPMA) observations showing the presence of trace amounts of As in framboidal pyrite crystals. Arsenic leached from the mudstone layer was then immobilized by Fe oxyhydroxides found in the adsorption layer. Based on geochemical modeling and X-ray photoelectron spectroscopy (XPS) results, leached As predominantly existed as the negatively charged HAsO42- oxyanion, which is readily sequestered by Fe oxyhydroxides. Moreover, the effectiveness of the adsorption layer was assessed and its lifetime was estimated, and the results revealed it still possessed enough capacity to adsorb As released from mudstone in the foreseeable future. This prediction utilized the maximum potential amount of As that could leach from the excavated rock layer with time.

A review of passive acid mine drainage treatment by PRB and LPB: From design, testing, to construction

An extensive volume of acid mine drainage (AMD) generated throughout the mining process has been widely regarded as one of the most catastrophic environmental problems. Surface water and groundwater impacted by pollution exhibit extreme low pH values and elevated sulfate and metal/metalloid concentrations, posing a serious threat to the production efficiency of enterprises, domestic water safety, and the ecological health of the basin. Over the recent years, a plethora of techniques has been developed to address the issue of AMD, encompassing nanofiltration membranes, lime neutralization, and carrier-microencapsulation. Nonetheless, these approaches often come with substantial financial implications and exhibit restricted long-term sustainability. Among the array of choices, the permeable reactive barrier (PRB) system emerges as a noteworthy passive remediation method for AMD. Distinguished by its modest construction expenses and enduring stability, this approach proves particularly well-suited for addressing the environmental challenges posed by abandoned mines. This study undertook a comprehensive evaluation of the PRB systems utilized in the remediation of AMD. Furthermore, it introduced the concept of low permeability barrier, derived from the realm of site-contaminated groundwater management. The strategies pertaining to the selection of materials, the physicochemical aspects influencing long-term efficacy, the intricacies of design and construction, as well as the challenges and prospects inherent in barrier technology, are elaborated upon in this discourse.

Driving factors for distribution and transformation of heavy metals speciation in a zinc smelting site

Heavy metal pollution at an abandoned smelter pose a significant risk to environmental health. However, remediation strategies are constrained by inadequate knowledge of the polymetallic distribution, speciation patterns, and transformation factors at these sites. This study investigates the influence of soil minerals, heavy metal occurrence forms, and environmental factors on heavy metal migration behaviors and speciation transformations. X-ray diffraction analysis revealed that the minerals associated with heavy metals are mainly hematite, franklinite, sphalerite, and galena. Sequential extraction results suggest that lead and zinc are primarily present in the organic-sulfide fractions (F4) and residual form (F5) in the soil, accounting for over 70% of the total heavy metal content. Zinc displayed greater instability in carbonate-bound (16%) and exchangeable (2%) forms. The migration and diffusion patterns of heavy metals in the subsurface environment were visualized through the simulation of labile state heavy metals, demonstrating high congruence with groundwater pollution distribution patterns. The key environmental factors influencing heavy metal stable states (F4 and F5) were assessed by integrating random forest models and redundancy analysis. Primary factors facilitating Pb transformation into stable states were available phosphorus, clay content, depth, and soil organic matter. For Zn, the principal drivers were Mn oxides, soil organic matter, clay content, and inorganic sulfur ions. These findings enhance understanding of the distribution and transformation of heavy metal speciation and can provide valuable insights into controlling heavy metal pollution at non-ferrous smelting sites.

Nickel-doped red mud-based Prussian blue analogues heterogeneous activation of H2O2 for ciprofloxacin degradation: waste control by waste

Red mud (RM) is a typical bulk solid waste with Fe/Al/Si/Ca-rich characteristics that has been used to prepare various heterogeneous catalysts such as iron-based catalysts and supported catalysts. Prussian blue analogues (PBA) is a low-cost, environmentally friendly, and active site rich iron-based metal organic framework, but its catalytic properties are adversely affected by their easy aggregation. In this study, nickel-doped RM-based PBA (RM-Ni PBA) was synthesized by acid dissolution-coprecipitation method for the degradation of ciprofloxacin (CIP). The characterization showed that RM-Ni PBA was a material with excellent dispersibility, large specific surface area, and abundant active sites. The degradation results showed that the removal efficiency of CIP in the RM-Ni PBA/H2O2 system was 16.63, 1.78, and 1.81 times that of RM, RM-PB, and Ni PBA, respectively. It was found that 1O2 was the main reactive oxygen species (ROS) dominated the degradation process, and its formation was accompanied by the mutual conversion of Ni(II)/Fe(II) and Ni(III)/Fe(III). Notably, the degradation process maintained a satisfactory efficiency over a wide pH range (3-9) and exhibited strong anti-interference ability against impurities such as Cl-, SO42-, and NO3-. The components and contents of RM-Ni PBA remained relatively stable during the degradation process. In addition, the degradation intermediates of CIP were identified, and possible degradation pathways were proposed. This study is expected to provide theoretical basis and technical guidance for the application of RM-based heterogeneous catalyst in the treatment of antibiotic wastewater.

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.

Sulfur Vacancies in Pyrite Trigger the Path to Nonradical Singlet Oxygen and Spontaneous Sulfamethoxazole Degradation: Unveiling the Hidden Potential in Sediments

Pharmaceutical residues in sediments are concerning as ubiquitous emerging contaminants. Pyrite is the most abundant sulfide minerals in the estuarine and coastal sediments, making it a major sink for pharmaceutical pollutants such as sulfamethoxazole (SMX). However, research on the adsorption and redox behaviors of SMX on the pyrite surface is limited. Here, we investigated the impact of the nonphotochemical process of pyrite on the fate of coexisting SMX. Remarkably, sulfur vacancies (SVs) on pyrite promoted the generation of nonradical species (hydrogen peroxide, H2O2 and singlet oxygen, 1O2), thereby exhibiting prominent SMX degradation performance under darkness. Nonradical 1O2 contributed approximately 73.1% of the total SMX degradation. The SVs with high surrounding electron density showed an advanced affinity for adsorbing O2 and then initiated redox reactions in the sediment electron-storing geobattery pyrite, resulting in the extensive generation of H2O2 through a two-electron oxygen reduction pathway. Surface Fe(III) (hydro)oxides on pyrite facilitated the decomposition of H2O2 to 1O2 generation. Distinct nonradical products were observed in all investigated estuarine and coastal samples with the concentrations of H2O2 ranging from 1.96 to 2.94 μM, while the concentrations of 1O2 ranged from 4.63 × 10-15 to 8.93 × 10-15 M. This dark-redox pathway outperformed traditional photochemical routes for pollutant degradation, broadening the possibilities for nonradical species use in estuarine and coastal sediments. Our study highlighted the SV-triggered process as a ubiquitous yet previously overlooked source of nonradical species, which offered fresh insights into geochemical processes and the dynamics of pollutants in regions of frequent redox oscillations and sulfur-rich sediments.

Inhibition of pyrite oxidation through forming biogenic K-jarosite coatings to prevent acid mine drainage production

This study proposes a novel method by forming biogenic K-jarosite coatings on pyrite surfaces driven by Acidithiobacillus ferrooxidans (A. ferrooxidans) to reduce heavy metal release and prevent acid mine drainage (AMD) production. Different thicknesses of K-jarosite coatings (0.7 to 1.1 μm) were able to form on pyrite surfaces in the presence of A. ferrooxidans, which positively correlated with the initial addition of Fe2+ and K+ concentrations. The inhibiting effect of K-jarosite coatings on pyrite oxidation was studied by electrochemical measurements, chemical oxidation tests, and bio-oxidation tests. The experimental results showed that the best passivation performance was achieved when 20 mM Fe2+ and 6.7 mM K+ were initially introduced with a bacterial concentration of 4 × 108 cells·mL-1, reducing chemical and biological oxidation by 70 % and 98 %, respectively (based on the concentration of total iron dissolved into the solution by pyrite oxidation). Similarly, bio-oxidation tests of two mine waste samples also showed sound inhibition effects, which offers a preliminary demonstration of the potential applicability of this method to actual waste rock. This study presents a new perspective on passivating the oxidation of metal sulfide tailings or waste and preventing AMD.

Potential mobilization of water-dispersible colloidal thallium and arsenic in contaminated soils and sediments in mining areas of southwest China

Water-dispersible colloids (WDCs) are vital for trace element migration, but there is limited information about the abundance, size distribution and elemental composition of WDC-bound thallium (Tl) and arsenic (As) in mining-contaminated soils and sediments solutions. Here, we investigated the potential mobilization of WDC-bound Tl and As in soils and sediments in a typical Tl/As-contaminated area. Ultrafiltration results revealed on average > 60% of Tl and As in soil solution (< 220 nm) coexisted in colloidal form whereas Tl and As in sediment solution primarily existed in the truly dissolved state (< 10 kDa) due to increased acidity. Using AF4-UV-ICP-MS and STEM-EDS, we identified Fe-bearing WDCs in association with aluminosilicate minerals and organic matter were main carriers of Tl and As. SAED further verified jarosite nanoparticles were important components of soil WDC, directly participating in the migration of Tl and As. Notably, high pollution levels and solution pH promoted the release of Tl/As-containing WDCs. This study provides quantitative and visual insights into the distribution of Tl and As in WDC, highlighting the important roles of Fe-bearing WDC, soil solution pH and pollution level in the potential mobilization of Tl and As in contaminated soils and sediments.

A combined and sustainable approach and a novel mechanism for recovering Bi, Au and Ag from high-chloride leachate of waste printed circuit board smelting ash

High-chloride leachate is a solution rich in precious metals that is produced in chloride hydrometallurgy. It has high levels of both rare and precious metals and hazardous chloride ions, and resource recovery from this solution and its safe disposal have become key objectives in the field of hydrometallurgy. In this study, a sustainable process involving "ultrasound-assisted precipitation-Pb powder cementation" was proposed for the stepwise separation and high-value utilization of Bi, Au and Ag obtained from high-chloride leachate. Targeted separation and conversion of Bi were achieved by precipitation-re-acid hydrolysis-ultrasonication-assisted coprecipitation-centrifugal purification. Under the optimal process conditions, the removal rate of Bi reached 99.52%, while the loss rates of Au and Ag were only 4.63% and 8.72%, respectively. Single-factor experiments of Au and Ag cementation by Pb powder showed that the recovery rates of precious metals could be improved by increasing the temperature, raising the solution pH, and applying mechanical force and ultrasonication. A possible reaction mechanism for Au and Ag cementation with Pb powder was proposed based on macroscopic kinetic analysis and microscopic mineral characterization. This work provides technical support and a theoretical basis for the separation and enrichment of rare and precious metals in chloride hydrometallurgy.

Fe/S oxidation-coupled arsenic speciation transformation mediated by AMD enrichment culture under different pH conditions

Arsenic (As) speciation transformation in acid mine drainage (AMD) is comprehensively affected by biological and abiotic factors, such as microbially mediated Fe/S redox reactions and changes in environmental conditions (pH and oxidation-reduction potential). However, their combined impacts on arsenic speciation transformation remain poorly studied. Therefore, we explored arsenic transformation and immobilization during pyrite dissolution mediated by AMD enrichment culture under different acidic pH conditions. The results for incubation and mineralogical transformation of solid residues show that in the presence of AMD enrichment culture, pH 2.0, 2.5, and 3.0 are more conducive to the formation of jarosites and ferric arsenate, which could immobilize high quantities of dissolved arsenic by adsorption and coprecipitation. The pH conditions significantly affect the initial adsorption of microbial cells to the minerals and the evolution of microbial community structure, further influencing the biodissolution of pyrite and the release and oxidation process of Fe/S. The results of Fe/S/As speciation transformation of the solid residues show that the transformation of Fe, S, and As in solution is mainly regulated by pH and potential values, which imposed significantly different effects on the formation of secondary minerals and thus arsenic oxidation and immobilization. The above results indicated that arsenic transformation is closely related to the Fe/S oxidation associated with pyrite bio-oxidation, and this correlation is critically regulated by the pH conditions of the system.

Shewanella oneidensis MR-1 dissimilatory reduction of ferrihydrite to highly enhance mineral transformation and reactive oxygen species production in redox-fluctuating environments

Diverse paths generated by reactive oxygen species (ROS) can mediate contaminant transformation and fate in the soil/aquatic environments. However, the pathways for ROS production upon the oxygenation of redox-active ferrous iron minerals are underappreciated. Ferrihydrite (Fh) can be reduced to produce Fe(II) by Shewanella oneidensis MR-1, a representative strain of dissimilatory iron-reducing bacteria (DIRB). The microbial reaction formed a spent Fh product named mr-Fh that contained Fe(II). Material properties of mr-Fh were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Magnetite could be observed in all mr-Fh samples produced over 1-day incubation, which might greatly favor the Fe(II) oxygenation process to produce hydroxyl radical (•OH). The maximum amount of dissolved Fe(II) can reach 1.1 mM derived from added 1 g/L Fh together with glucose as a carbon source, much higher than the 0.5 mM generated in the case of the Luria-Bertani carbon source. This may confirm that MR-1 can effectively reduce Fh and produce biogenetic Fe(II). Furthermore, the oxygenation of Fe(II) on the mr-Fh surface can produce abundant ROS, wherein the maximum cumulative •OH content is raised to about 120 μM within 48 h at pH 5, but it is decreased to about 100 μM at pH 7 for the case of MR-1/Fh system after a 7-day incubation. Thus, MR-1-mediated Fh reduction is a critical link to enhance ROS production, and the •OH species is among them the predominant form. XPS analysis proves that a conservable amount of Fe(II) species is subject to adsorption onto mr-Fh. Here, MR-1-mediated ROS production is highly dependent on the redox activity of the form Fe(II), which should be the counterpart presented as the adsorbed Fe(II) on surfaces. Hence, our study provides new insights into understanding the mechanisms that can significantly govern ROS generation in the redox-oscillation environment.

Inputs and transport of acid mine drainage-derived heavy metals in karst areas of Southwestern China

Heavy metal pollution caused by acid mine drainage (AMD) is a global environmental concern. The processes of migration and transformation of heavy metals carried by AMD are more complicated in karst areas where carbonate rocks are widely distributed. Water, suspended particulate matter (SPM), and sediments are the crucial media in which heavy metals migrate and it is important to elucidate the geochemical behavior of AMD heavy metals in these environments. This study tracked AMD heavy metals from release to migration and transformation in a natural river system in a karst mining area. AMD directly impacted the hydrochemical composition of the karst water environment, but the carbonate rock naturally neutralized the acidity of the AMD. AMD heavy metal concentrations decreased gradually after the tributaries from the mining area entered the main river, with the metals tending to accumulate in SPM and sediments. The forms in which heavy metals were present were influenced by pH and their relative concentrations. Raman spectroscopy and transmission electron microscopy of sediments from the mining area suggested that the presence of an iron phase plays an important role in the fate of AMD-derived heavy metals. It is, therefore, necessary to elucidate the mechanisms of iron phase precipitation from sediments in order to control AMD-derived heavy metals in karst mining areas. This study improves our understanding of the geochemical behavior of heavy metals in karst environments and provides direction for the prevention and control of AMD in affected areas.

A highly efficient process to enhance the bioleaching of spent lithium-ion batteries by bifunctional pyrite combined with elemental sulfur

Bioleaching technologies have been shown to be an environmentally friendly and economically beneficial tool for extracting metals from spent lithium-ion batteries (LIBs). However, conventional bioleaching methods have exhibited low efficiency in recovering metals from spent LIBs. Therefore, relied on the sustainability principle of using waste to treat waste, this study employed pyrite (FeS2) as an energy substance with reducing properties and investigated its effects in combination with elemental sulfur (S0) or FeSO4 on metals bioleaching from spent LIBs. Results demonstrated that the bioleaching efficiency was significantly higher in the leaching system constructed with FeS2 + S0, than in the FeS2 + FeSO4 or FeS2 system. When the pulp densities of FeS2, S0 and spent LIBs were 10 g L-1, 5 g L-1 and 10 g L-1, respectively, the leaching efficiency of Li, Ni, Co and Mn all reached 100%. Mechanistic analysis reveals that in the FeS2 + S0 system, the activity and acid-producing capabilities of iron-sulfur oxidizing bacteria were enhanced, promoting the generation of Fe (Ⅱ) and reducible sulfur compounds. Simultaneously, bio-acids were shown to disrupt the structure of the LIBs, thereby increasing the contact area between Fe (Ⅱ) and sulfur compounds containing high-valence metals. This effectively promoted the reduction of high-valence metals, thereby enhancing their leaching efficiency. Overall, the FeS2 + S0 bioleaching process constructed in this study, improved the leaching efficiency of LIBs while also effectively utilizing waste, providing technical support for the comprehensive and sustainable management of solid waste.

Contribution of Mine-Derived Airborne Particulate Matter to Ca, Fe, Mn and S Content and Distribution in the Lichen Punctelia hypoleucites Transplanted to Bajo de la Alumbrera Mine, Catamarca (Argentina)

The aim of this work was to relate the contribution of mine-derived airborne particulate matter to Ca, Fe, Mn and S content and distribution in Punctelia hypoleucites transplanted to Bajo de la Alumbrera, an important open-pit mine in Catamarca, Argentina. Lichen samples were transplanted to four monitoring sites: two sites inside the mine perimeter and two sites outside the mine. After three months, elemental distribution in samples was analyzed by microparticle-induced X-ray emission (microPIXE), and elemental concentration was determined by specific techniques: Ca and Fe by instrumental neutron activation analysis, Mn by inductively coupled plasma atomic emission spectrometry and S by a turbidimetric method. A differential distribution of S and Ca in thalli transplanted in-mine sites was detected compared to that of samples transplanted outside-mine sites. An overlap of Fe and S in the upper cortex of the apothecium section was observed, leading to infer a mineral association of both elements. Similar association was observed for Ca and S. In addition to these results, the significantly higher concentration detected for S and Mn in in-mine site samples suggests a contribution of Fe, S, Ca and Mn of mining origin to the content and distribution of these elements in P. hypoleucites. MicroPIXE complemented with Mössbauer spectroscopy analysis determined the presence of pyrite particles together with other iron-bearing minerals displaying different degrees of oxidation. These results point to a mining origin of the airborne particulate matter trapped by the lichen thalli transplanted to Bajo de la Alumbrera. These findings indicate that P. Hypoleucites acts as an excellent air quality biomonitor in the Bajo de la Alumbrera mine area.

Arsenic species in soil profiles from chemical weapons (CWs) burial sites of China: Contamination characteristics, degradation process and migration mechanism

In this study, soil profiles and pore water from Japanese abandoned arsenic-containing chemical weapons (CWs) burial sites in Dunhua, China were analyzed to understand the distribution of arsenic (As) contamination, degradation, and migration processes. Results of As species analysis showed that the As-containing agents underwent degradation with an average rate of 87.55 ± 0.13%, producing inorganic pentavalent arsenic (As5+) and organic arsenic such as 2-chlorovinylarsonic acid (CVAOA), triphenylarsenic (TPA), and phenylarsine oxide (PAO). Organic arsenic pollutants accounted for 1.27-18.20% of soil As. In the vertical profiles, total As concentrations peaked at about 40-60 cm burial depth, and the surface agricultural soil exhibited moderate to heavy contamination level, whereas the contamination level was insignificant below 1 m, reflecting As migration was relatively limited throughout the soil profile. Sequential extraction showed Fe/Al-bound As was the predominant fraction, and poorly-crystalline Fe minerals adsorbed 33.23-73.13% of soil As. Oxygen-susceptible surface soil formed poorly-crystalline Fe3+ minerals, greatly reducing downward migration of arsenic. However, the reduction of oxidizing conditions below 2 m soil depth may promote As activity and require attention.

Degradation of norfloxacin by red mud-based prussian blue activating H2O2: A strategy for treating waste with waste

The massive accumulation of red mud (RM) and the abuse of antibiotics pose a threat to environment safety and human health. In this study, we synthesized RM-based Prussian blue (RM-PB) by acid solution-coprecipitation method to activate H2O2 to degrade norfloxacin, which reached about 90% degradation efficiency at pH 5 within 60 min and maintained excellent catalytic performance over a wide pH range (3-11). Due to better dispersion and unique pore properties, RM-PB exposed more active sites, thus the RM-PB/H2O2 system produced more reactive oxygen species. As a result, the removal rate of norfloxacin by RM-PB/H2O2 system was 8.58 times and 2.62 times of that by RM/H2O2 system and PB/H2O2 system, respectively. The reactive oxygen species (ROS) produced in the degradation process included ·OH, ·O2- and 1O2, with 1O2 playing a dominant role. The formation and transformation of these ROS was accompanied by the Fe(III)/Fe(II) cycle, which was conducive for the sustained production of ROS. The RM-PB/H2O2 system maintained a higher degradation efficiency after five cycles, and the material exhibited strong stability, with a low iron leaching concentration. Further research showed the degradation process was less affected by Cl-, SO42-, NO3-, and humic acids, but was inhibited by HCO3- and HPO42-. In addition, we also proposed the possible degradation pathway of norfloxacin. This work is expected to improve the resource utilization rate of RM and achieve treating waste with waste.

Acid mine drainage (AMD) treatment using galvanic electrochemical system Al-Cu

Acid mine drainage was evaluated using a galvanic (GV) electrochemical system, Al-Cu (anode/cathode), based on a 32 factorial design. The factors analyzed were anodic area/volume ratios (A/V) of 0.037, 0.072, and 0.112 cm2/cm3, and treatment time from 0.25-8 h, and analyses were performed in duplicate with 11 degrees of freedom. The response variables were the total dissolved solids and concentrations of As, Cu, Co, Cr, Pb, Fe, Ni, and S O 4 2 - . The pH, electrical conductivity, and temperature were monitored during the process. Significant differences between treatments were determined by analysis of variance with Tukey's test (p < 0.05) using Statgraphics Centurion XVI.I software. The results showed that a greater electrode surface, A/V ratio, and treatment time improved pollutant removal. The spontaneous reactions generated by the galvanic cell, through the current that flows owing to the potential difference between the Al and Cu electrodes, allows the removal of heavy metals, arsenic, and S O 4 2 - by coagulation and precipitation mechanisms. The removal efficiencies achieved were Cu (99.1%), As (76.6%), Ni (80.2%), Pb (83.6%), Cr (100%), Fe (93.71%), and 92.9% for sulfates. The X-ray diffraction and Raman analyses of the solid fraction indicated that cuprite was formed with a purity of 96%, and the recovery of Cu by the GV system may be a viable option for mining companies.

Carbonate rocks as natural buffers: Exploring their environmental impact on heavy metals in sulfide deposits

Carbonate rocks are closely related to the genesis and spatial distribution of polymetallic sulfide deposits. The natural buffering of carbonate rocks can reduce the ecological impact of heavy metals produced by mining and smelting. Ignoring the buffering effect of carbonate rocks on the heavy metals in the mine environment leads to inaccurate ecological risk assessment, wasting land resources and funds. This study investigates Cd, Zn, and Pb distribution and speciation in the water and soil-rice system in the polymetallic sulfide deposit at Daxin, Guangxi. The study aims to reveal the effects of the natural buffering of carbonate rocks on the migration and transformation of heavy metals. The results show that the water Zn and Cd concentrations decreased from 1857.0 to 0.9 mg L-1 to 0.16 and 0.001 mg L-1, respectively, from the mining area to 4 km downstream. The natural buffering of carbonate increases the water pH from 2.80 to 7.64, resulting in a tendency for Cd, Zn, and Pb to separate from the aqueous phase and enrich the sediments. Soil Cd content in the mining area reached 110.0 mg kg-1 (mean value 55.88 mg kg-1), and rice Cd seriously exceeded the maximum limit. However, the weathering of carbonate reduces the migration ability and bioavailability of Cd. Soil Cd is mainly in the Fe-Mn bound and carbonate-bound fractions, resulting in lower Cd content in downstream soils (mean value 2.73 mg kg-1). Soil CaO, tFe2O3, and Mn hindered the uptake of soil Cd by rice rendering a lower exceedance of Cd in downstream rice. Therefore, this study recommends a farmland management plan under the premise of rice Cd content and integrated soil Cd content, which ensures food safety and fully utilizes farmland resources. This result provides a scientific basis for ecological risk assessment, mine environmental protection, and management in the carbonatite sulfide mine environment.

The impact of perfluorooctanoic acid shock on hydrogen-driven nitrate and arsenate removal

Perfluorooctanoic acid (PFOA) is a type of toxic per- and poly-fluoroalkyl substance (PFAS) commonly found in groundwater due to its use in firefighting and industrial applications. The main purpose of this study was to investigate the influence of PFOA shock on the biological performance of a hydrogen-driven bioreactor for nitrate and arsenate removal. Four hydrogen-driven removal reactors (HdBRs) used for the simultaneous removal of nitrate and arsenal were operated with concentrations of either 0, 1, 5, and 10 mg/L of PFOA to induce shock on the systems and examine the corresponding bacterial response. Our results showed that PFOA shock inhibited and decreased the maximum hydrogen-driven arsenate removal rate. Principal Component Analysis (PCA) confirmed that this performance decrease occurred due to a bacterial strike triggered by PFOA shock. PFOA toxicity also led to protein secretion and sludge density decreases. Bacterial analyses showed shifts in the community population due to PFOA shock. The dominant bacteria phylum Proteobacteria became more abundant, from 41.24% originally to 48.29% after exposure to 10 mg/L of PFOA. Other phyla, such as Euryarchaeota and Bacteroidetes, were more tolerant to PFOA shock. Although some of the predominant species within the sludge of each HdBR exhibited a decline, other species with similar functions persisted and assumed the functional responsibilities previously held by the dominant species.

Highly active complexes of pyrite and organic matter regulate arsenic fate

Arsenic (As) presents high toxicity and strong carcinogenicity, and its health risks are regulated by its oxidation state and speciation. As can form complexes with the surface of minerals or organic matter through adsorption, affecting its toxicity and bioavailability. However, the regulation effect of the interaction of coexisting minerals and organic matter on As fate remains largely unknown. Here, we discovered that minerals (e.g., pyrite) and organic matter (e.g., alanyl glutamine, AG) can form pyrite-AG complexes, promoting As(III) oxidation under simulated solar irradiation. The formation of pyrite-AG was explored in terms of the interaction of surface oxygen atoms, electron transfer and crystal surface changes. From the perspective of atoms and molecules, pyrite-AG showed more oxygen vacancies, stronger reactive oxygen species (ROS) and a higher electron transport capacity than pyrite alone. Compared with pyrite, pyrite-AG effectively promoted the conversion of highly toxic As(III) to less toxic As(V) due to the enhanced photochemical properties. Moreover, quantification and capture of ROS confirmed that hydroxyl radicals (•OH) played an important role in As(III) oxidation in the pyrite-AG and As(III) system. Our results provide previously unidentified perspectives on the effects and chemical mechanisms of highly active complexes of mineral and organic matter on As fate and provide new insights into the risk assessment and control of As pollution.

Review on arsenic environment behaviors in aqueous solution and soil

Arsenic pollution in environment has always been an important environmental problem that has attracted wide attention in recent years. Adsorption is one of the main methods of treatment for arsenic in the aqueous solution and soil because of the advantages of high efficiency, low cost and wide application. Firstly, this report summarizes the commonly and widely used adsorbent materials such as metal-organic frameworks, layered bimetallic hydroxides, chitosan, biochar and their derivatives. The adsorption effects and mechanisms of these materials are further discussed, and the application prospects of these adsorbents are considered. Meanwhile, the gaps and deficiencies in the study of adsorption mechanism was pointed out. Then, this study comprehensively evaluated the effects of various factors on arsenic transport, including (i) the effects of pH and redox potential on the existing form of As; (ii) complexation mechanism of dissolved organic matter and As; (iii) factors affecting the plant enrichment of As. Finally, the latest scientific researches on microbial remediation of arsenic and the mechanisms were summarized. The review finally enlightens the subsequent development of more efficient and practical adsorption material.

Immobilization of arsenic in different contaminated soils by zero-valent iron-embedded biochar: Effect of soil characteristics and treatment conditions

Although zero-valent iron-embedded biochar (ZVI-BC) has been proposed as an effective amendment for arsenic (As)-contaminated soils, the impacts of soil characteristics and treatment conditions on the remediation process remained poorly understood. Herein, the immobilization of As in four As-contaminated soils (i.e., smelting soil, storage soil, agricultural soil, and mining soil) by ZVI-BC under different amendment dosages, cultivation temperatures, and soil moisture contents were investigated. ZVI-BC showed high As immobilization capacity in all four soils via forming the AsFe co-precipitation, and the liable As was reduced by 82.4-97.0 % with a 2 % (w/w) amendment. The higher temperature could raise the concentration of liable As in all four soils, especially for the storage soil, in which liable As at 35 °C was almost 3 times of that at 25 °C after 50-days treatment, because the elevated temperature enhanced the destruction of the generated AsFe coprecipitation as well as the desorption of As in soils. Too much soil moisture was unfavorable for the As immobilization after 50-days treatment. Flooding tended to inhibit the community diversity of As-detoxicated bacteria, e.g., Halomonas, Bryobacter, and Anaerolinea, thus resulting in the release of liable As. According to the correlation analysis, the crucial influencing factor for As immobilization was different in four soils, which was determined by the soil properties and proportion of liable As. Our study indicates that ZVI-BC is an effective amendment for As immobilization under various conditions, and the biogeochemical processes of As-associated Fe minerals determine the As immobilization during amendment.

Environmental risk of tailings pond leachate pollution: Traceable strategy for leakage channel and influence range of leachate

Identifying the leakage channel and the influencing range is essential for controlling the environmental risks of leachate from the tailings pond. The investigation of leachate pollution in tailings pond has the defect of focusing only on the scope of tailings pond in recent studies. This study innovatively built a comprehensive investigation and accurate verification system for leachate leakage of tailings pond integrated with the aeromagnetic survey, ground penetrating radar, hydrochemistry and isotope coupling methods. Geophysical exploration found that among the four fault zones, and the F1 was the channel for leachate to recharge the groundwater 2.53 km away from the tailings pond. The fissures inside the tailings pond were connected with the natural fissures outside, forming a leachate migration channel. The hydrochemistry and isotope characteristics showed that the groundwater far away from the tailings pond were polluted by arsenic containing leachate, which verified the geophysical exploration results. The significant correlation between arsenic and SO2-4 concentration indicated that arsenic in leachate originated from the oxidation release of sulfide minerals (i.e., arsenopyrite). This study sheds light on the comprehensive investigation of leachate leakage in the tailings pond. This development method also provides guidance for environmental risk identification of other contaminated sites.

Dissolved thiolated arsenic formed by weathering of mine wastes

Aqueous thiolated arsenic (As) species play an important role in the biogeochemical cycling of As in wetlands and hydrothermal systems. Although mine wastes such as tailings ponds and waste rock piles may harbor similarly sub-oxic and neutral to alkaline conditions that favor the formation and mobility of thio-As species, quantitative data on their existence in these systems is lacking. We conducted laboratory column experiments under contrasting redox conditions with waste rock from the Antamina mine, Peru, and processed tailings from Montague, Nova Scotia, Canada. Dissolved As concentrations between 1 and 7000 μg/L were recorded in drainages across these mine waste types, with up to 13 μg/L As present in thiolated form, predominantly monothioarsenate. Higher percentages of thio-As species (up to 5%) were observed in drainages from enargite-rich materials compared to arsenopyrite-bearing materials (<0.5%). The lower abundance of dissolved thio-As in the arsenopyrite-rich mine waste samples is attributed to their partially oxidized nature and reduced mineral reactivity under the experimental circumneutral drainage pH, the difference in S [-II/0]-to-As molar ratios compared to the enargite-rich mine waste samples, as well as the oxidation of di- and tri-thiolated As species by dissolved Fe. Overall, our results demonstrate that aqueous thiolated As species may occur in mine wastes with different As-bearing minerals and could play an important role in governing the mobility and fate of As in these systems.

(Bio)dissolution of arsenopyrite coupled with multiple proportions of pyrite: Emphasis on the mobilization and existential state of arsenic

The formation of arsenic-bearing acid mine drainage (AMD) via the oxidation of arsenopyrite refuse ore has attracted significant attention. Pyrite, as main a concomitant mineral, is a crucial factor that affects the (bio)dissolution of arsenopyrite, but there are still some points on the detailed action mechanism under normal environmental conditions that need further study. In this study, the effect mechanism of pyrite with a systematic pyrite content (0, 10, 25, 50, 75, 90, and 100 wt %) on arsenopyrite oxidation and arsenic release in the presence of Acidithiobacillus ferrooxidans was investigated. The X-ray diffraction (XRD), scanning election microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical analyses were also carried out. Results showed that the existence of pyrite and Acidithiobacillus ferrooxidans significantly accelerated the dissolution of arsenopyrite and the oxidation of As (Ⅲ) to As (Ⅴ), resulting from the galvanic effect, an increase in the Fe³⁺/Fe²⁺ ratio and the oxidation-reduction potential (Eh) value, and a decrease in pH level. As the detected main intermediate products, element sulphur was considered as the dominating obstructive factor during arsenopyrite oxidation, while the added pyrite could accelerate its oxidation. Moreover, a close relationship between different mineral proportions and the galvanic effect was also observed and discussed. Finally, suggestions on AMD governance and source control are proposed.

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.

Source and evolution of sulfate in the multi-layer groundwater system in an abandoned mine-Insight from stable isotopes and Bayesian isotope mixing model

The source and evolution of sulfate (SO₄^2-) in groundwater from abandoned mines are widely concerned environmental issues. Herein, major dissolved ions, multi-isotopes (δ³⁴S, δ¹⁸O_sulfate, δ²H and δ¹⁸O_water), machine learning (Self-organizing maps) and Bayesian isotope mixing model were used to identify the source and evolution of SO₄^2- in an abandoned mine (Fengfeng mine, northern China) with a multi-layer groundwater system. Groundwater in the study area was mainly divided into three clusters (Cluster I, Cluster II and Cluster III), dominated by Na-SO₄, Ca-SO₄ and Ca-HCO₃ types, respectively. According to δ²H and δ¹⁸O_water, groundwater in the study area mainly originated from atmospheric precipitation. δ³⁴S, δ¹⁸O_sulfate and SO₄^2- suggested that bacterial sulfate reduction did not affect the SO₄^2- isotopic composition. Dual SO₄^2- isotopes, and MixSIAR model revealed that the main source of SO₄^2- in the study area was pyrite oxidation/gypsum dissolution, accounting for an average of 57.4 % (gypsum), 71.24 % (pyrite oxidation) and 52.93 % (pyrite oxidation) of SO₄^2- in the samples of Clusters I-III, respectively. Combined with the hydrochemical diagrams, the evolution of SO₄^2- in different clusters of samples was derived. Cluster I was mainly gypsum dissolution; In contrast, Clusters II and III were mainly pyrite oxidation accompanied by carbonate dissolution, and Cluster II was also influenced by cation exchange. These findings will help in developing management strategies for protecting groundwater quality, which will provide a reference for the study of solute sources and S cycling in abandoned mines.

ROS formation driven by pyrite-mediated arsenopyrite oxidation and its potential role on arsenic transformation

Pyrite-mediated arsenopyrite oxidation is an important process affecting arsenic (As) mobility. The iron sulfides-induced reactive oxidation species (ROS) can exert significant influence on As transformation. However, the impact of pyrite-arsenopyrite association on ROS production and its contribution to As transformation were rarely estimated. Here, ROS formation and the redox conversion of As during the interaction between pyrite and arsenopyrite as function of O₂, pH and pyrite surface oxidation were investigated. Pyrite promoted arsenopyrite oxidation and As(III) oxidation due to heterogeneous electron transfer. The electron transfer from arsenopyrite facilitated O₂ reduction on pyrite surface with increasing ROS formation. Hydroxyl radical (HO˙), superoxide (O₂^•)^- and hydrogen peroxide (H₂O₂) were the main reactive species for As(III) oxidation. Iron (hydr)oxides produced from pyrite surface oxidation provided fast electron transfer channels for efficient O₂ reduction as evidenced by electrochemical experiment, further verifying the promoted effect of surface-oxidized pyrite (SOP) on arsenopyrite dissolution. However, total As and As(V) obviously decreased during SOP-mediated arsenopyrite oxidation. Iron (hydr)oxides retained appreciable As through adsorption to limit its mobility, and decreased HO˙ production to inhibit As(III) oxidation via decomposing H₂O₂. This work furthers our understanding of arsenic transformation in the environment which has important implications for mitigating arsenic pollution.

Remediation of Acid Mine Drainage (AMD) Using Steel Slag: Mechanism of the Alkalinity Decayed Process

Steel slag has been proven to be an effective environment remediation media for acid neutralization, and a potential aid to mitigate acid mine drainage (AMD). Yet its acid neutralization capacity (ANC) is frequently inhibited by precipitate after a period of time, while the characteristics of the precipitate formation process are unclear yet. In this study, ANC for basic oxygen steel slag was conducted by neutralization experiments with dilute sulfuric acid (0.1 M) and real AMD. Some partially neutralized steel slag samples were determined by X-ray diffraction (XRD), scanning electron microscopy combined with an energy dispersive spectrometer (SEM-EDS), and N2 adsorption tests to investigate the potential formation process of the precipitate. The results indicated that Ca-bearing constitutes leaching and sulfate formation were two main reactions throughout the neutralization process. A prominent transition turning point from leaching to precipitate was at about 40% of the neutralization process. Tricalcium silicate (Ca3SiO5) played a dominant role in the alkalinity-releasing stage among Ca-bearing components, while the new-formed well crystalline CaSO4 changed the microstructure of steel slag and further hindered alkaline components releasing. For steel slag of 200 mesh size, the ANC value for the steel slag sample was 8.23 mmol H+/g when dilute sulfate acid was used. Neutralization experiments conducted by real AMD confirmed that the steel slag ANC was also influenced by the high contaminants, such as Fe2+, due to the hydroxides precipitate reactions except for sulfate formation reactions.

Immobilization of As(III) by gibbsite and catalytic oxidation to As(V): Profound impacts of doping and unraveling of associated mechanisms

As(III) is highly toxic, and its adsorption and oxidation to As(V) by minerals represent two effective approaches to remediate As(III)-contaminated sites. Gibbsite, one of the most abundant natural minerals, shows decent adsorption for As(III), and in this study, mechanisms of As(III) immobilization and oxidation by gibbsite with different dopants (M = Fe(III), Mn(III), Mn(IV)) are addressed by periodic DFT calculations. Influences of Fe(III) content and Mn oxidation state are also inspected. Although a majority remain structurally similar to those of pristine gibbsite, new adsorption configurations emerge due to doping: Inner-sphere complexes with M - As bonds for all doping, bidentate binuclear complexes for double Fe(III) doping, and physisorption with weak O_Mn-As interactions for Mn(IV) doping. As(III) adsorption affinities are significantly altered by doping and rely on dopants, while inner-sphere complexes with M-O_As bonds are always lowest-energy except doping Mn(III) that prefers trigonal bipyramidal coordination and impedes As(III) chemisorption. Doping causes strong M-3d and O_As-2p orbital interactions that facilitate As(III) adsorption whereas disappear for pristine gibbsite. Double Fe(III)- and Mn(IV)-doped gibbsite materials are effective for As(III) oxidation to As(V), and mechanisms differ significantly although all are characterized by dual electron transfers. Activation barriers for the most favorable reaction paths amount to 1.02 and 1.26-1.31 eV, respectively. Physisorbed and outer-sphere As(III) complexes exhibit comparable reactivities as chemisorbed complexes that become focus of literature reports, and may also be involved during interfacial and environmental reactions. Results rationalize experimental observations available, and provide significantly new insights that conduce to manage As-associated pollution and design efficient As(III) scavengers and oxidation catalysts.

Conventional and recent advances in gravity separation technologies for coal cleaning: A systematic and critical review

"Affordable and clean energy" is enshrined in the UN Sustainable Development Goals (SDGs; #7) because of its importance in supporting the sustainable development of society. As an energy source, coal is widely used because it is abundant and its utilization for electricity and heat generation do not require complex infrastructures and technologies, which makes it ideal for the energy needs of low-income and developing countries. Coal is also essential in steel making (as coke) and cement production and will continue to be on high demand for the foreseeable future. However, coal is naturally found with impurities or gangue minerals like pyrite and quartz that could create by-products (e.g., ash) and various pollutants (e.g., CO₂, NO_X, SO_X). To reduce the environmental impacts of coal during combustion, coal cleaning-a kind of pre-combustion clean coal technology-is essential. Gravity separation, a technique that separates particles based on their differences in density, is widely used in coal cleaning due to the simplicity of its operation, low cost, and high efficiency. In this paper, recent studies (from 2011 to 2020) related to gravity separation for coal cleaning were systematically reviewed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 1864 articles were screened after removing duplicates, and after a thorough evaluation 189 articles were reviewed and summarized. Among of conventional separation techniques, dense medium separator (DMS), particularly dense medium cyclone (DMC), is the most popular technologies studied, which could be attributed to the growing challenges of cleaning/processing fine coal-bearing materials. In recent years, most of works focused on the development of dry-type gravity technologies for coal cleaning. Finally, gravity separation challenges and future applications to address problems in environmental pollution and mitigation, waste recycling and reprocessing, circular economy, and mineral processing are discussed.

Impacts of coexisting mineral on crystallinity and stability of Fe(II) oxidation products: Implications for neutralization treatment of acid mine drainage

The neutralization treatment of acid mine drainage involves the oxidation of Fe(II), but little is known about the effects of co-existing minerals on the oxidation and hydrolysis of Fe(II) to iron oxides. Here we investigated the transformation of fresh and heated Fe(II) oxidation coprecipitates, which were synthesized in the presence and the absence of five co-existing minerals (montmorillonite, kaolin, quartz (SiO₂)_, aluminium oxide (Al₂O₃) and calcium carbonate (CaCO₃)). In the FeSO₄ system with montmorillonite or kaolin, the formation of lepidocrocite was inhibited with the increase of clay mineral contents. In the same system, heated coprecipitates of montmorillonite were mainly comprised of amorphous ferrihydrite and its transformation was retarded by the excess montmorillonite. In the FeCl₂ system with SiO₂, Al₂O₃ or CaCO₃, akaganeite formation was inhibited with the increase in the corresponding mineral contents. In the same system, goethite formation was blocked by either CaCO₃ or Al₂O₃ and the growth of lepidocrocite was inhibited by CaCO₃ or SiO₂. However, magnetite formation was enhanced by addition of CaCO₃. These findings are important for predicting products of abiotic Fe(II) oxidation during the neutralization of acid mine drainage and for better understanding the transformation of amorphous iron oxides in the complicated environmental matrix.

Impact of H2O on the Microscopic Oxidation Mechanism of Lollingite: Experimental and Theoretical Analyses

Lollingite (FeAs2) is considered an arsenic-bearing mineral that is oxidized faster than arsenopyrite. The geometric configuration, chemical valence bond, and microscopic reaction of the oxidation on the surface of lollingite were systematically studied, which are of great significance for understanding the mechanism of oxidative dissolution. X-ray photoelectron spectroscopy (XPS) measurements and density functional theory (DFT) calculations were carried out to characterize the (101) surface oxidation process of lollingite under the O2/O2 + H2O conditions. XPS results confirmed that the participation of water molecules can promote the formation of abundant OH structures on the surface of lollingite, while the relative concentration of O, As(III), and Fe(III) increased. Moreover, the DFT results demonstrated that the (101) As-terminal plane of FeAs2 was the most stable surface with the lowest surface energy. H2O molecules were physically adsorbed onto the Fe atoms of the lollingite surface, while oxygen molecules can readily be adsorbed on the Fe-As2 site by chemical adsorption processes. The oxidation process of the lollingite surface with water includes the following mechanisms: adsorption, dissociation, formation of the hydrogen bond, and desorption. The dissociation of the H2O molecule into OH and H led to the hydroxylation of both Fe and As atoms and the formation of hydrogen bonding. The participation of H2O molecules can also reduce the reaction energy barrier and accelerate the oxidation reaction of the lollingite surface, especially as far as the water dissociation and formation of hydrogen bonds are concerned. According to PDOS data, there is considerable hybridization between the d orbitals of bonded Fe atoms and the p orbitals of O atoms, as well as between the p orbitals of bonded As atoms and the p orbitals of O atoms. Due to a strong propensity for orbital hybridization and bonding between the s orbitals of the H atoms in H2O molecules and the p orbitals of the O atoms on the (101) surface, water molecules have the ability to speed up the oxidation on the surface.

Remediation technologies for acid mine drainage: Recent trends and future perspectives

Acid mine drainage (AMD) is a highly acidic solution rich in heavy metals and produced by mining activities. It can severely inhibit the growth of plants, and microbial communities and disturb the surrounding ecosystem. In recent years, the use of different bioremediation technologies to treat AMD pollution has received widespread attention due to its environment-friendly and low-cost nature. Various active and passive remediation technologies have been developed for the treatment of AMD. The active treatment involves the use of different chemical compounds while passive treatments utilize natural and biological processes like constructed wetlands, anaerobic sulfate-reducing bioreactors, anoxic limestone drains, vertical flow wetlands, limestone leach beds, open limestone channels, and various organic materials. Moreover, different nanomaterials have also been successfully employed in AMD treatment. There are also reports on certain plant growth-promoting rhizobacteria (PGPR) which have the potential to enhance the growth and productivity of plants under AMD-contaminated soil conditions. PGPR applied to plants with phytoremediation potential called PGPR-assisted phytoremediation has emerged as an economical and environment-friendly approach. Nevertheless, various approaches have been tested and employed, all the approaches have certain limitations in terms of efficiency, secondary pollution of chemicals used for the remediation of AMD, and disposal of materials used as sorbents or as phytoextractants as in the case of PGPR-assisted phytoremediation. In the future, more research work is needed to enhance the efficiency of various approaches employed with special attention to alleviating secondary pollutants production and safe disposal of materials used or biomass produced during PGPR-assisted phytoremediation.

Leaching Characteristics of Potentially Toxic Metals from Tailings at Lujiang Alum Mine, China

To investigate the leaching characteristics and potential environmental effects of potentially toxic metals (PTMs) from alum mine tailings in Lujiang, Anhui Province, soaking tests and simulated rainfall leaching experiments were conducted for two types of slag. PTMs comprising Cd, Cr, Cu, Mn, and Ni were detected in the slag. Cu and Cd contents exceeded the national soil risk screening values (GB 15618-2018). pH values of the two slag soaking solutions were negatively correlated with the solid:liquid ratio. pH values of the sintered slag soaking solutions with different solid:liquid ratios finally stabilized between 4.4 and 4.59, and those of the waste slag soaking solutions finally stabilized between 2.7 and 3.4. The concentrations of Cd, Cr, Cu, Mn, and Ni leached from waste slag were higher than those from sintered slag, and the dissolved concentrations of these PTMs in sintered slag were higher under rainfall leaching conditions than soaking conditions (the difference in Cr concentration was the smallest, 5.6%). The cumulative release of Cd, Cr, Cu, Mn, and Ni increased as the leaching liquid volume increased. The kinetic characteristics of the cumulative release of the five PTMs were best fitted by a double constant equation (R² > 0.98 for all fits). Single factor index evaluations showed that Mn and Ni were the PTMs with high pollution degrees (P_i for Mn and Ni exceed 1) in the leaching solutions. However, considering the biotoxicity of PTMs, the water quality index evaluations showed that the water quality of the sintered slag soaking solution, the waste slag soaking solution, and the sintered slag leachate was good, poor, and undrinkable, respectively. The health risk assessment showed that the total non-carcinogenic risk (HI) values in adults for both the sintered slag leachate and waste slag soaking solution exceeded the safe level of 1, with HI values of 3.965 and 2.342, respectively. The hazard quotient (HQ) for Cd was 1.994 for the sintered slag leachate, and Cd and Cr make up 50.29% and 15.93% of the total risk, respectively. Cr makes up 28.38% of the total risk for the waste slag soaking solution. These results indicate a high non-carcinogenic risk of exposure to Cd and Cr in the leaching solution used for drinking purposes. These findings may provide a reference for the evaluation and ecological control of PTM pollution in alum mining areas.

Passive co-treatment of phosphorus-depleted municipal wastewater with acid mine drainage: Towards sustainable wastewater management systems

Industrial processes typically produce large wastewater volumes, which, if left untreated, greatly affect receiving ecosystems. However, wastewater treatment can be costly and energy-intensive, with the developing world particularly struggling with wastewater management. As such, simple and cost-effective solutions are urgently required with the passive (no energy or reagents) co-treatment of different wastewater matrices holding great promise. Here, wastewater from a phosphorus recovery system (chemical precipitation) was co-treated with acid mine drainage (AMD). Specifically, phosphorus-rich municipal wastewater was treated with hydrated lime, as to synthesize a wastewater-derived phosphorus product, i.e., calcium phosphate (Ca₃(PO₄)₂), also producing a phosphorous-depleted alkaline effluent. The feasibility of valorising this effluent is examined here by using it for the passive co-treatment of real AMD. Different liquid-to-liquid (v/v) ratios were considered, with the optimum ratio (AMD to phosphate-depleted wastewater) being 1:9. The pH of the co-treated effluent was adjusted to 8.4 (from an initial value of 11.5 in the phosphorus-depleted wastewater and 2.2 in AMD), while metals (∼100% reduction of Fe, Mn, Ni, Cu, Pb, ≥99.5 for Al, Zn, and Mg, 80% for Cr, and 75% for As) and sulphate (89.26% reduction) contained in AMD were greatly removed. This was also the case for the remaining orthophosphate that was contained in the phosphorus-depleted wastewater (93.75% reduction). The electrical conductivity was also reduced in both the AMD (88.75%) and the phosphorus-depleted wastewater (69.21%), suggesting the removal of contaminants from both matrices. Results were underpinned by state-of-the-art analytical techniques, including FE-SEM/FIB/EDX, FTIR, and XRD, along with geochemical modelling (PHREEQC). Contaminants were removed through complexation, (co)adsorption, crystallization, and (co)precipitation. Overall, results suggest that the co-treatment of these wastewater matrices is feasible and could be directly scaled up (e.g., using waste stabilization ponds), while opportunities for the beneficiation of the produced sludge and for water reclamation (e.g., through membrane filtration) could also arise, further promoting the sustainably of this passive co-treatment method.

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.

Sulfur defect and Fe(III) (hydr)oxides on pyrite surface mediate tylosin adsorption in lake water: effect of solution chemistry and dissolved organic matter

Pyrite affects the adsorption of tylosin (TYL) due to their coexistence in the lake system. As well as the reactivity groups of S-S-H, S-OH, and Fe-OH, defects also have the possibilities to influence the adsorption of organic contaminants. However, the role of these active sites in antibiotic adsorption on pyrite has not been deeply studied. Besides, pH, N, P, dissolved oxygen, and dissolved organic matter (DOM) fluctuate greatly in lake at different seasons, which may change the surface characteristics of pyrite. Hence, the adsorption of TYL on natural pyrite considered solution chemistry and DOM in lake water was explored in this study. The fitting results of the kinetic and isotherm models showed that the adsorption included physical and chemical interactions. The neutral initial solution pH was conductive to TYL adsorption owing to the combined result of electrostatic and cover of Fe-oxyhydroxide. NO₃^- and NH₄⁺ had no effect on TYL adsorption, whereas H₂PO₄^- promoted adsorption by forming flocculent Fe(H₂PO₄)₃ precipitates. The dissolved oxygen increased adsorption. This is due to the co-promotion of the pyrite oxidation by oxygen and sulfur defects. The Fe(II)-DOM complex caused by pyrite surface oxidation reduced the concentration of TYL in solution by gathering. Except for the surface charge, reactivity groups on pyrite significantly influenced the adsorption of TYL. The bond fracture of S-S resulted in sulfur defects that contributed to pyrite oxidation. As a result, Fe(III)/Fe(II) on the surface of pyrite or in solution produced a complex Fe(III)/Fe(II) with anions and DOM. In addition, Fe(III)-S on sulfur defects interacted with the O-H of TYL through hydrogen bonding. Furthermore, the Fe-O-C bond is formed by the interaction of C-OH on TYL and Fe(III) (hydr)oxides on the surface of pyrite. The study provides a deep insight into the effect of pyrite surface active sites on amphoteric antibiotic adsorption. It helps to understand antibiotic migration and interactions with widespread pyrite in the real environment.

Enhanced generation of reactive oxygen species by pyrite for As(III) oxidation and immobilization: The vital role of Fe(II)

The migration and conversion of arsenic in the environment usually accompany by the redox of iron-bearing minerals. For instance, the oxidation of pyrite can generate reactive oxygen species (ROS) affecting the species of arsenic, but the types and roles of ROS have been unclear. This paper demonstrated the vital role of Fe(II) in the pyrite for the formation of ROS. Results showed that exogenous addition of Fe(II) significantly enhanced the removal rate of As(III) by pyrite. 2,2'-bipyridine (BPY) decreased the oxidation of As(III) by complexing with Fe²⁺ in solution, whilst EDTA enhanced the oxidation of As(III) by boosting the autoxidation of Fe²⁺. In addition, neutral pH is superior for the oxidation of As(III) and removal of total arsenic. Importantly, Methanol, SOD enzyme and PMOS inhibited 54%, 28% and 17.5% of As(III) oxidation, respectively, which indicated O₂^•- and •OH were the main contributors to As(III) oxidation, and Fe(IV) contributed a small part of As(III) oxidation. The content of As(V) in the FeS₂-Fe²⁺-As(III) system was higher than that in the FeS₂-As(III) system, further confirming the vital role of Fe(II) for As(III) oxidation. Lepidocrocite was produced in a single Fe²⁺ system, which was not detected in the FeS₂-As(III) system. Thus, the presence of mineral surfaces changed the oxidation products of Fe²⁺ and accelerated the oxidation and immobilization of As(III). FA (Fulvic Acid) and HA (Humic Acid) accelerated the oxidation of As(III), but the oxidation of As(III) by pyrite was inhibited to a certain extent, with increasing phenolic hydroxyl groups in phenolic acid. Our findings provide new insight into the oxidative species in the pyrite-Fe(II) system and will help guide the remediation of arsenic pollution in complex environmental systems.