Search Results (282)

Acidic mine drainage (AMD) rich in heavy metals and sulfates causes severe environmental hazards. SRB and SOB are ideal remediation strains, yet their microaerophilic symbiotic metabolism and metabolite characteristics remain ambiguous. This study explores their symbiotic metabolic mechanisms, optimizing culture parameters via response surface methodology and multi-objective genetic neural network algorithms. The optimal conditions are 32.60 °C, pH = 7.20, strain ratio at 1:1 and DO = 0.3–0.5 mg/L, achieving 80.27% sulfate removal and 60.60% elemental sulfur production. Under optimized microaerobic symbiosis, Cu²⁺, Zn²⁺ and sulfate removal rates reach 90.16%, 80.59% and 63.97%, with a S⁰ yield of 64.67%. SEM-EDS, XRD, XPS, and microbial diversity analysis verify that heavy metals are eliminated as metal sulfide precipitates, and most of the sulfate transforms into recyclable elemental sulfur. Full article

Shanxi Province in China is one of the world’s major bauxite producers. The co-existence of coal and bauxite mining makes this province particularly prone to acid mine drainage (AMD) and, thus, a significant area for investigating heavy metal mobility in an aluminum-rich geological environment. In this study, heavy metal leaching from bauxite under simulated AMD conditions and the geochemical mechanisms controlling their mobility were examined in this study. XRF analysis demonstrated that the bauxite is predominantly composed of Al₂O₃, Fe₂O₃ and SiO₂, while XRD, FTIR, and SEM-EDS revealed that diaspore and kaolinite dominate bauxite, together with accessory Fe- and Ti-bearing phases, providing reactive surfaces for adsorption and precipitation. After batch leaching with synthetic acidic sulphate solutions (pH = 3), Ca(OH)₂ neutralization was regulated. The data reveal that pH is the key factor controlling heavy metal mobility. Acidic conditions enhanced metal release while alkaline conditions favored hydroxide precipitation, surface complexation and co-precipitation. The removal efficiency was 91%–99% for Cd and Zn, 100% for Cd and Zn, 69%–90% for Cr, 35%–100% for Cu, 92%–100% for Ni and up to 100% for Pb. The chemical and mineralogical composition played an indirect role by providing adsorption sites but did not prevent the release of metals under acidic conditions. These results reveal that pH adjustment is the major mechanism controlling heavy metal immobilization in AMD-impacted bauxite systems and contributes to the knowledge of geochemical processes controlling metal mobility in acidic mine drainage. Full article

Ecological restoration of abandoned mountainous mines remains challenging because of complex geological conditions, severe substrate degradation, and long-term environmental impacts. Conventional restoration strategies primarily emphasize vegetation establishment and slope stabilization, while the potential contribution of carbon sequestration is often insufficiently considered. Enhanced Rock Weathering (ERW) has recently emerged as a promising negative-emission technology that accelerates the natural weathering of silicate minerals to remove atmospheric CO₂ while improving soil quality. This paper synthesizes current knowledge on ERW and proposes a conceptual framework for integrating this technology into the ecological restoration of abandoned mountainous mines. The framework comprises four complementary dimensions: (1) Physical Restoration, utilizing fragmented rock materials to improve slope stability and substrate structure; (2) Acid–Base Neutralization, exploiting alkaline silicate minerals to alleviate acid mine drainage (AMD) and regulate geochemical conditions; (3) Pedogenic Optimization, promoting soil formation, improving soil physicochemical properties, and facilitating CO₂ infiltration and mineral carbonation; and (4) Biological Synergy, enhancing plant–microbe–mineral interactions to accelerate weathering processes and support long-term ecosystem development. Drawing on existing evidence, we discuss how the use of on-site waste rock as reactive substrates may simultaneously reduce restoration-related carbon emissions, provide essential mineral nutrients (e.g., Ca, Mg, and K), and enhance carbon sequestration potential. Overall, this synthesis suggests that integrating ERW into abandoned mine restoration has the potential to simultaneously advance ecological rehabilitation and climate-change mitigation. The proposed framework provides a theoretical basis for future experimental validation, field-scale implementation, and the development of low-carbon strategies for sustainable mine restoration. Full article

Mining of sulfide-rich deposits enhances the oxidation of sulfide minerals, generating acid mine drainage (AMD) characterized by high sulphate and dissolved metal concentrations and the formation of secondary iron minerals (hematite, goethite, and jarosite). As these minerals display diagnostic features in the visible–near-infrared (VNIR) region, multispectral satellite data provide a cost-effective means of monitoring. Here, the performances of Sentinel-2 and the VNIR bands from WorldView-3 are assessed and compared for the mapping and discrimination of secondary iron minerals in Sierra Minera de Cartagena–La Unión (SE Spain). Both datasets were analyzed using a band ratio and a parabola fitting technique focused on reflectance maxima. Band ratio results were interpreted as broad spectral patterns rather than definitive mineral identifications. Mineral maps were validated by applying X-ray diffraction on 74 surface soil samples. Although both sensors were able to reproduce the main spatial patterns of iron mineral distribution, Sentinel-2 data better discriminated hematite, goethite, and jarosite, especially when using the parabola fitting approach, whereas WorldView-3 VNIR data distinguished mainly hematite from the combined goethite–jarosite group. The better performance of Sentinel-2 is attributed to its red-edge and near-infrared band configuration. These findings indicate that freely available Sentinel-2 imagery can support systematic monitoring of oxidation processes in mining environments and contribute to environmental risk assessment in degraded landscapes. Full article

Accurate identification of acid-producing layers is key to controlling acid mine drainage (AMD) in abandoned coal mines. This study collected 337 core samples from 34 boreholes in the Modigou mining area, Shanxi, China, and established a combined static–mineralogical–kinetic approach to evaluate the acid-generating and neutralization potentials of sulfur-bearing rocks. Three-stage net acid generation (NAG) tests identified the pyrite-bearing layer of the Benxi Formation and the No. 10 coal seam of the Taiyuan Formation as the main acid producers, with NAG values of 360.41 and 97.87 kg H₂SO₄/t, respectively, while the Taiyuan limestone showed a high neutralization capacity (ANC = 490 kg H₂SO₄/t). NAG pH was strongly negatively correlated with sulfur content (Pearson r = −0.75, p < 0.01). Sulfide oxidation acid production showed staged attenuation, with average decreases of 64.81% and 47.65% in the second and third stages. Humidity cell experiments demonstrated continuous acid production over 63 days under dry–wet cycles, with increased acid generation rates at higher flow velocities (Darcy flux: 3.54 × 10⁻³ cm/s for accelerated vs. 8.84 × 10⁻⁴ cm/s for standard conditions). Multi-dimensional flow-through simulations confirmed the AMD formation mechanism of “acid supply, buffer, and fracture conduction”. The identified acid-producing layers matched well with field discharge points. This multi-method coupling system provides a theoretical basis for source control of AMD in abandoned high-sulfur coal mines in the Yellow River Basin. This study did not account for microbial catalysis, which is a key limitation of the static chemical oxidation method used. Full article

Acid mine drainage (AMD) pollution from closed coal mines in karst regions represents a major environmental challenge in the global mining industry. The complexity of hydrogeological conditions in such regions leads to significant challenges in both predictability and controllability of pollution. Taking the Yudong River Basin in Guizhou Province, Southwest China, as the study area, and based on six years (2017–2023) of systematic remediation practices and monitoring data, this study systematically evaluates the effectiveness and applicable conditions of three types of treatment technologies: centralized treatment stations, source control combined with end-of-pipe treatment, and water-sealing ecological plugging. On this basis, governance models applicable to karst regions are distilled. The results show that after six years of remediation, the number of pollution points in the Yudong River Basin decreased from 27 to 12. At the outflow section, the total Fe reduction rate reached 88.3%, the total Mn reduction rate reached 62.3%, and the proportion of contaminated river length was reduced by 78.5%. Each of the three technologies has its own applicable conditions. Centralized treatment stations, characterized by mature technology but high operational costs, are suitable for emergency transition periods. Source control combined with end-of-pipe treatment addresses both symptoms and root causes, making it applicable to complex pollution points. Water-sealing ecological plugging, although cost-controllable, carries a risk of secondary pollution in karst-developed areas. The failure of water-sealing ecological plugging technology is mainly attributed to two mechanisms: bypass flow through karst conduits and overflow induced by water level rise. Based on the six-year remediation practice, this study proposes a source control model for karst conduits centered on the core concepts of “filling, isolating, plugging, intercepting, draining, and controlling”. The implementation process consists of four stages: detailed investigation, graded optimization, stepwise implementation, and long-term monitoring. The core innovation lies in the cross-disciplinary application of coal mine water control techniques to environmental remediation, achieving a shift from passive end-of-pipe treatment to active source control. This model can provide theoretical reference and practical guidance for karst mining areas in Southwest China and other regions with similar geological conditions. Full article

Acid mine drainage (AMD) is enriched with arsenite (As(III)), arsenate (As(V)), and jarosite. While jarosite can immobilize arsenic (As) through adsorption and other mechanisms, it dissolves and transforms into other minerals under near-neutral and reducing conditions via microbial mediation, thereby altering As fate. Fulvic acid (FA), a ubiquitous natural organic matter in the environment, has been proven to exhibit complex interactions with various iron minerals, Fe/S-metabolizing microorganisms, and As. However, the role of FA in the bioreduction and transformation of jarosite, as well as its subsequent impact on As mobility and fate, remains unclear. This study aims to elucidate the regulatory effect of FA on the biodissolution and transformation of jarosite, and the corresponding changes in As speciation. The results showed that FA exerted contrasting effects depending on arsenic speciation. In the As(III) treatments, FA intensified the inhibition of microbial dissimilatory sulfate reduction, suppressed sulfide production, and consequently limited orpiment formation. In contrast, in the As(V) treatments, FA enhanced the association of As(V) with jarosite surfaces, reduced aqueous As stress, and supported the persistence of As-tolerant sulfate-reducing populations. This promoted jarosite transformation toward mackinawite and facilitated As immobilization through orpiment precipitation. This study reveals the critical role of FA in the migration and transformation of As in mining areas, providing novel insights for optimizing AMD remediation strategies such as soil capping. Full article

Oil sands tailings from tailings solvent recovery units (TSRU) contain elevated sulfide minerals and can generate acid mine drainage (AMD) upon atmospheric exposure. This study investigated how prior weathering influences acidity and solute release under controlled laboratory conditions. A six-month column leaching experiment was conducted using TSRU tailings with distinct exposure histories: weathered and semi-weathered tailings from a previous greenhouse-scale reclamation capping experiment, along with weakly weathered tailings stored in sealed barrels. Columns were subjected to repeated wet–dry cycles, analyzing the geochemistry of the leachate and solid-phase changes using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). All treatments produced highly acidic leachates (pH < 2), indicating that TSRU tailings retain the capacity to generate acidity regardless of prior exposure. However, the dominant geochemical mechanisms differed by weathering history. Weakly weathered tailings generated progressive increases in acidity and solute release, consistent with active sulfide oxidation. Semi-weathered tailings had more stable responses, suggesting partial sulfide depletion and secondary phase formation. Weathered tailings produced leachates showing evidence of rapid flushing with limited new solute generation. After leaching, residual pyrite remained in all materials, with shifts in surface sulfur speciation providing evidence of progressive surface sulfur oxidation, transformation, and the redistribution of sulfate phases. These results demonstrate the mechanisms involved in AMD generation in TSRU tailings, highlighting the importance of the weathering history and the need for field-scale validation. Full article

Schwertmannite (Sch) is a widespread iron oxyhydroxysulfate mineral in acid mine drainage (AMD) systems, and its transformation strongly influences the environmental fate of chromium (Cr). However, the role of Ca(II), which is commonly introduced during alkaline neutralization of AMD, in regulating the transformation of Cr(VI)-adsorbed schwertmannite (Cr-Sch) and subsequent Cr redistribution remains insufficiently understood. In this study, transformation experiments were conducted under various pH conditions (3.0, 7.0, and 10.0) to investigate the effects of Ca(II) speciation on mineral transformation and Cr behavior. The results demonstrated that the transformation of Cr-Sch was predominantly pH-dependent. Under acidic conditions, Cr-Sch transformed into goethite via dissolution–recrystallization, resulting in transient Cr release followed by partial refixation. The presence of Ca(II) exerted only a minor influence due to weak interactions between Ca²⁺ and positively charged mineral surfaces. Under alkaline conditions, Cr-Sch preferentially transformed into hematite through dehydroxylation and cation rearrangement, leading to the sustained release of adsorbed Cr(VI). In contrast, Ca(II) predominantly precipitated as CaCO₃ precipitate (calcite, aragonite, and vaterite) under alkaline conditions, which coated mineral surfaces and inhibited phase transformation and Cr release. These findings reveal that Ca(II) regulates Cr redistribution primarily through pH-dependent speciation and mineral–surface interactions, highlighting coupled geochemical processes governing iron mineral transformation and contaminant mobility in AMD environments. This study provides mechanistic insights for predicting Cr behavior and optimizing alkaline remediation strategies in mining-impacted systems. Full article

Acidic mine drainage (AMD) poses a severe global environmental threat due to its high acidity and elevated levels of toxic hexavalent chromium (Cr(VI)), for which biogenic iron sulfide (FeS) nanoparticles have emerged as a promising remediation agent; however, their practical application is hindered by aggregation and oxidative deactivation. This research synthesized biogenic FeS nanoparticles via sulfate-reducing bacteria (SRB) and employed humic acid (HA) as a stabilizing agent to enhance Cr(VI) removal performance in simulated AMD conditions. Single-factor experiments combined with response surface methodology identified the optimal biosynthetic conditions for FeS: yeast extract powder dosage of 2.2 g/L, Fe/S molar ratio of 0.8, and NH₄Cl dosage of 3.1 g/L. Under these conditions, the material achieved 84.25% Cr(VI) removal, with the Fe/S molar ratio identified as the most influential parameter governing synthesis and performance. Introducing HA at an optimal dosage of 2 mg/L drove marked improvements in both nanoparticle yield and reactivity: FeS yield increased to 1096.26 mg/L, Cr(VI) removal efficiency reached 99.62%, and residual Cr(VI) dropped from 15.75 mg/L to just 0.38 mg/L. Kinetic and isotherm analyses, paired with SEM/TEM imaging and zeta potential measurements, revealed that HA stabilization improved particle dispersion and reduced lamellar stacking, resulting in a surface-controlled Cr(VI) removal process. FTIR and 2D-COS analyses demonstrated that HA-derived oxygen-containing functional groups, including O–H/N–H, C=O, and C–O moieties, played a central role in interfacial interactions during Cr(VI) sequestration. XRD results confirmed that Cr(VI) was reduced to Cr(III) and primarily immobilized as low-solubility CrOOH and Cr₂S₃, while the formation of Fe–Cr spinel-like phases remains tentative without X-ray Photoelectron Spectroscopy (XPS) validation. Further investigation via surface-sensitive spectroscopy and dynamic leaching tests is needed to fully assess the long-term stability of the reaction products. Full article

Low-saturated hydraulic conductivity covers (LSHCC) or hydraulic barriers are one of the reclamation techniques used to control the acid mine drainage generation (AMD). These covers are intended to limit the infiltration of water into reactive tailings. Compacted clays are among the materials used as LSHCC. The performance of clay-based hydraulic barriers can be affected by their geotechnical and hydrogeological properties. Freeze–thaw cycles can increase their saturated hydraulic conductivity (k_sat). However, these effects can be minimized by adding amendments. To evaluate the performance of these clay-based covers, four field experimental cells were built. The first one simulates a cover composed entirely of clay, the second a clay–silt mixture, the third a clay–sand mixture and the last two layers of clay with an intermediate layer of silt. Each cell has been equipped with a monitoring station with continuous measurements of volumetric water content, suction and temperature. In situ permeability tests were also conducted to assess field hydraulic conductivity. Numerical simulations were also conducted to evaluate the water balance for each cover scenario. The laboratory results showed low-saturated hydraulic conductivity values meeting waterproofing criteria, whereas field measurements and calibrated model values were consistently higher and exceeded the waterproofing criteria. Infiltration monitoring indicated that 15 to 40% of precipitation infiltrated the covers, with possible overestimation due to preferential flow. Discrepancies between laboratory and field-saturated hydraulic conductivity values were mainly attributed to inadequate compaction, unfavorable weather conditions, and excessive water content during cover installation. Variations in saturated hydraulic conductivity over time were generally within statistical variability, although differences among cells and responses to wetting–drying cycles highlight the influence of construction conditions on field performance. Full article

Gold mining in South Africa’s Witwatersrand Basin represents a critical case study of mining-induced environmental degradation affecting interconnected ecological and human systems. While the cascading effects of acid mine drainage (AMD), originating from a legacy of approximately 270 tailings dams containing 6 billion tons of FeS₂ waste and 600,000 tons of residual uranium, are widely documented, this evidence often remains fragmented. This study applies a systematic, framework-based analytical approach that integrates multidisciplinary evidence from geochemical, ecological, agricultural, and public health research within a One Health/EcoHealth perspective. Qualitative field observations are used to contextualize and validate the analytical synthesis along the water–soil–food–human continuum. A four-pathway conceptual model, including environmental dispersion, biotic uptake, trophic transfer, and direct human exposure, is developed to structure and interpret the integrated findings. The results demonstrate that mining-derived contaminants propagate through interconnected pathways, leading to persistent contamination of water resources, agricultural systems, and human communities, particularly within the Wonderfonteinspruit watershed. Evidence synthesized across pathways reveals extreme bioaccumulation and exposure levels and elevated uranium levels in the hair of local children. The study concludes that the impacts of acid mine drainage constitute a systemic socio-ecological failure driven by cumulative and interacting exposure pathways that cannot be effectively addressed through sectoral or single-medium interventions. The principal contribution of this research is the development of an operational, transferable framework that enables integrated risk assessment and supports evidence-based management and remediation strategies in post-mining landscapes. Full article

Acid mine drainage (AMD) and acid-generating mine wastes exhibit low pH, high sulfate levels, and complex multi-metal loads that strain conventional treatment. Thermoacidophilic red algae of the order Cyanidiales, particularly Galdieria sulphuraria (G. sulphuraria), have attracted interest as a biological option because they tolerate extreme acidity and elevated temperatures, grow under low light in mixotrophic or heterotrophic modes, and display rapid metal binding at the cell surface. This review synthesizes about two decades of peer-reviewed work to clarify how G. sulphuraria can be deployed as a practical module within mine water treatment trains. We examine the mechanisms of biosorption and bioaccumulation and show how they map onto two distinct configurations. Processed freeze-dried biomass functions as a regenerable sorbent for rare earth elements (REEs) and selected transition metals in packed beds with acid elution for recovery. Living cultures serve as polishing units for divalent metals and, when present, nutrients or dissolved organics under low light. We define realistic operating windows centered on pH 2–5 and temperatures of approximately 25–45 °C, and we identify matrix effects that govern success, including competition from ferric iron and aluminum, turbidity and fouling risks, ionic strength from sulfate, and suppression of REE uptake by phosphate in living systems. Building on laboratory studies, industrial leachate tests, and ecosystem observations, we propose placing G. sulphuraria upstream of bulk neutralization and outline reporting practices that enable cross-site comparison. The goal is an actionable framework that reduces reagent use and sludge generation while enabling metal capture and potential recovery of valuable metals from mine-influenced waters. Full article

Acid mine drainages (AMDs) enriched with toxic metals pose a significant environmental risk. Microbial bioremediation offers a sustainable and cost-effective approach for metal removal from AMD. In this study, a wild yeast isolated from the Kavart abandoned mine, identified as Rhodotorula sp., was evaluated for its copper (Cu²⁺) and zinc (Zn²⁺) biosorption ability. Biosorption was strongly pH-dependent. Cu²⁺ and Zn²⁺ removal was most efficient (48.1% or 10.07 mg/g and 35.7% or 6.07 mg/g, respectively) at pH 6. Increasing the biomass to 3 g/L at the same pH enhanced Cu²⁺ removal to 71.5% (26 mg/g). Biosorption kinetic analysis showed an excellent fit to the pseudo-second-order model (R² > 0.99), indicating that the mechanism is chemisorption-dominated. Equilibrium data followed the Langmuir isotherm (R² = 0.93), consistent with monolayer adsorption on homogeneous binding sites. SEM-EDS analysis confirmed Cu²⁺ association with the yeast surface, supporting the ICP-OES results. The results demonstrate the isolate as a promising biosorbent, particularly for Cu²⁺, and highlight its potential application in the remediation of AMD-contaminated waters. Full article

The microbial ecology of acid mine drainage (AMD) systems in Armenia, with a long mining history, remains unexplored. This study aimed to characterize the microbial diversity and functional potential of AMD in the Syunik region and to isolate novel microorganisms with biotechnological value. A comprehensive analysis of the microbial communities’ structure of Kavart abandoned, Kapan exploring mines effluent, and Artsvanik tailing was conducted. Metagenomics revealed bacterial-dominated communities, comprising Pseudomonadota (previously “Proteobacteria”) (68–72%), with site-specific variations in genus abundance. A high abundance and diversity of metal resistance genes (MRGs), particularly for copper and arsenic, were identified. Carbohydrate-active enzyme (CAZy) analysis showed a dominance of GT2 and GT4 genes, suggesting a high potential for extracellular polymeric substances (EPS) production and biofilm formation. A novel strain of iron-oxidizing bacteria Arm-12 was isolated that shares only ~90% similarity with known Leptospirillum type species, indicating it may represent a new genus without culturable representatives. The strain exhibits enhanced copper extraction from concentrate. This study provides the first metagenomic insights into Armenian AMD systems and tailing, revealing a unique community rich in metal resistance and biofilm-forming genes. The isolation of a novel highly effective iron-oxidizer Arm-12 highlights the potential of AMD environments as a source of novel taxa with significant applications in biomining and bioremediation processes. Full article