Treatment Of Acid Mine Drainage Research Articles

Bioelectrochemical treatment of acid mine drainage: Microbiome synergy influences sulfidogenesis and acetogenesis

Bioelectrochemical systems (BES) are emerging as potential technologies that can remediate acid mine drainage (AMD) by cathodic reduction of sulfates to metal sulfides. This study evaluated bioelectrochemical remediation of sulfate rich AMD at two applied cathode potentials; BES-1: −1.0 V and BES-2: −0.8 V. Sulfate reducing bacteria were selectively enriched to be used as biocatalyst in BES. Initially, lactate was fed as carbon source and switched to chemolithoautotrophy with only CO2-fed conditions. Both BESs were operated at 3±0.2 g/l of sulfate with synthetic AMD (SAMD) fed first, and gradually changed to 50% AMD from mining site with 50% SAMD. Sulfate reduction was relatively higher with BES-1: 82% than BES-2: 76% coupled with sulfidogenesis. Interestingly, acetogenesis (BES-1: 2.12±0.2 g/l, BES-2: 1.9±0.2 g/l) was also noticed with high reduction currents (BES-1&2: >-70 mA). Microbiome community analysis revealed the dominant presence of sulfate reducers, acetogens, syntrophic bacteria and Methanobacterium, probing microbial synergy aiding sulfate reduction. An added advantage was the iron-sulfide (FeS) particles formation on cathode, which might have contributed to increased reduction currents. This study reveals insights into microbial synergy for autotrophic sulfate reduction within mixed microbiome communities along with the impact of FeS particles as conducive facilitator for electron transfer in BES, thereby enhancing electrosynthetic acetate production.

Cultivation of Microalgae (Scenedesmus sp.) Using Coal Mining Wastewater and Separation via Coagulation/Flocculation and Dissolved Air Flotation (DAF)

Algae growth can be carried out in treated mine waters, providing biomass and helping to achieve the standards for water discharge. However, efficient separation of algae from the aqueous medium is crucial. The present work investigated the stability of Scenedesmus sp. in treated acid drainage from coal mining and assessed the harvesting of microalgae via coagulation/flocculation and dissolved air flotation (DAF). Successful algae growth was achieved, with cells remaining suspended in the water at a wide range of pH values, requiring the use of reagents for destabilization/aggregation. Algae coagulation/flocculation was attained with the use of tannin or ferric chloride associated with an anionic polymer flocculant at a pH of 8.0 ± 0.1. When combined with the flocculant, both tannin and the inorganic coagulant proved effective in enhancing floc stability and hydrophobicity for the DAF process. In summary, this operational approach facilitated algae biomass recovery and significantly reduced turbidity in the treated water. Finally, a schematic diagram illustrating the algae cultivation and harvesting process is presented, offering a practical alternative to acid mine drainage (AMD) treatment refinement associated with algae biomass production.

A DFT study of the adsorption of fouling molecules (metal sulfides and hydroxides) onto TiZrO4 ceramic membranes

Ceramic membrane fouling is a constraint in the treatment of acid mine drainage (AMD), leading to a decrease in efficiency over time. Here, it is described via first-principles calculations the physical and chemical phenomena occurring on the surface of TiZrO4 filtration membranes due to the adsorption of eight potential fouling compounds [CuS, FeS, Fe2S3, CaS, Al(OH)3, Fe(OH)3, Fe(OH)2, and Cu(OH)2]. The interaction of these fouling molecules was performed onto nanostructured TiZrO4 surfaces with several pores representing the filtration membranes employed in the treatment of AMD. The adsorption energies reveal that the adsorption is feasible with all the fouling molecules studied, and it is strongly related to the molecular polarity of the adsorbate. Consequently, the adsorption of metal sulfides is more feasible than hydroxides with adsorption orders of CaS>FeS>CuS>Fe2S3, and Al(OH)3>Fe-hydroxides>Cu(OH)2. The outcomes suggest that the metal sulfide adsorption depends on the adsorbate intrinsic polarity, solvent effects, adsorbate van der Waals radius, and membrane surface topology, while the adsorption of hydroxides is less influenced by the last two factors. Density-based binding and energy decomposition analyses indicate strong electrostatic attractions and covalent bonds at the adsorbate-membrane interface supporting the chemical fouling onto ceramic filtration membranes. According to our theoretical results and the elevated concentration of Cu and Fe in AMD, we propose that FeS and CuS are mainly responsible for the fouling onto TiZrO4 membrane surfaces. These results offer valuable information on the adsorption phenomena at TiZrO4 membrane surfaces, which can be useful for metallurgy, industrial water treatment, food industry, biotechnology, and pharmaceutical applications.

The treatment of acid mine drainage using a combination of selective precipitation and bio-sorption techniques: A hybrid and step-wise approach for AMD valorization and environmental pollution control

In this study, selective precipitation using magnesium oxide (MgO) and bio-sorption with banana peels (BPs) were explored for the treatment and valorization of acid mine drainage (AMD). The treatment chain comprised two distinct stages of which selective precipitation of chemical species using MgO (step1) and polishing of pre-treated AMD using BPs (step 2). In stage 1, 2.0 L of AMD from coal mine were used for selective precipitation and recovery of chemical species using MgO. The results revealed that chemical species of concern were precipitated and recovered at different pH gradients with Fe(III) precipitated at pH ≤ 4, Al at pH ≥ 4-5, Fe(II), Mn and Zn at pH ≥ 8 while Ca and SO42─ were precipitated throughout the pH range. In stage 2, the pre-treated AMD water was polished using BPs. The results revealed an overall increase of pH from 1.7 to 10, and substantial removal of chemical species in the following removal efficiency: Al, Cu and Zn (100% each), ≥ Fe and Mn (99.99% each), ≥ Ni (99.93%), and ≥ SO42─ (90%). The chemical treatment step removed pollutants partially, whereas the bio-sorption step acted as a polishing stage by removing residual pollutants.

Production of activated carbon from coal with H3PO4 activation for adsorption of Fe(II) and Mn(II) in acid mine drainage

Acid Mine Drainage (AMD) contains Fe(II) and Mn(II) metals, which can cause environmental pollution. This research aimed to investigate the potency of activated carbon made from coal as an adsorbent in AMD treatment. The carbon was made of coal and activated with H3PO4 in a weight ratio of 40%, 800 °C for 120 minutes while supplying 1.5 L/min of nitrogen during the carbonization process. The result shows that BET surface area, total pore volume, and iodine number were 296.4 m2/g, 0.156 cc/g, and 1205 mg/g, respectively. The surface contained many fractures, channels, and big holes, as evidenced by the FT-IR and SEM investigations, and it also had acidic surface functional groups. The optimum contact time adsorption for AMD treatment was 30 minutes, and the first concentration of Fe(II) and Mn(II) metals affected the adsorption. The optimum removal of Fe(II) in AMD treatment was 95.27% at an initial concentration of 3.51 ppm, while the optimum removal of Mn(II) was 99.82% at an initial concentration of 5.71 ppm. This activated carbon has a considerable potency to be used as the adsorbent in AMD treatment to reduce Fe(II) and Mn(II) levels.

Cleaner flotation separation of chalcopyrite from pyrite at low alkalinity: Based on calcium hypochlorite oxidative modification in acid mine drainage system

Efficient and clean flotation separation of copper-sulfur has attracted soaring interest in the beneficiation of sulfide ore. The objective of this work was to examine the influence of calcium hypochlorite (Ca(ClO)2) oxidative modification on the flotation separation of chalcopyrite from pyrite in acid mine drainage (AMD) system. A maximum recovery difference of 69.70 % between both minerals was observed under the recommended conditions (initial pH = 8.5 ± 0.2, [Ca(ClO)2] = 100 mg/L, [EX] = 32 mg/L, and the volume ratio of AMD to pure water = 1:1). A high-grade concentrate with 77.35 % Cu recovery and 29.01 % Cu grade was obtained, demonstrated by mixed-mineral micro-flotation experiments. Analysis of Cu and Fe ions influence indicated that low concentrations of Fe3+ and Cu2+ favored the selective separation of pyrite and chalcopyrite. Moreover, analysis of the pulp ion concentrations showed that Ca(ClO)2 promoted the dissolution of iron ions on the pyrite surface compared to chalcopyrite, thereby enhancing pyrite oxidation. The Ca(ClO)2 interacted more intensively with the pyrite surface, forming a passivated layer that impeded the adsorption of collector, as demonstrated by Zeta potential and contact angle results. The generation of hydrophilic products caused by oxidation on the pyrite surface, such as CaSO4, CaOH+, Fe(Ⅲ)–OOH, and/or Fe2(SO4)3 was confirmed by XPS analysis, further reducing the floatability of pyrite. Furthermore, local electrochemical impedance spectroscopy and scanning electron microscopy analyses further afforded favorable evidence for selective inhibition of pyrite by Ca(ClO)2 in the AMD system. This study provides a new approach to achieve cleaner separation of pyrite and chalcopyrite and offers new perspectives for AMD treatment solutions.

Efficient removal of heavy metals from acid mine drainage by ε-MnO2 adsorption

The clean-up of acid mine drainage (AMD) is challenging, as classical treatment including a pH neutralization step produces large amounts of toxic sludge. Here we demonstrated that removal of heavy metals through adsorption at low pH was achievable with the use of ε-MnO2 adsorbent, which could be produced in a simple one-step process. The material, which was negatively charged even at pH 2, exhibited outstanding potential for the removal of heavy metals at strongly acidic pH. At pH 2, adsorption capacities were achieved of 172.14 mg/g towards Pb2+ (at an initial concentration of 400 mg/L), 65.64 mg/g for Fe3+ (at 300 mg/L) and 8.5 mg/g for Cd2+ (at 10 mg/L). Mechanistic studies revealed that ion exchange was the main adsorption mechanism for removal of Pb2+, while electrostatic interaction was dominant for Fe3+ and Cd2+ removal. In the case of Pb2+ adsorption, double corner sharing (DCS) complexes were formed at the edges, which promoted the dissolution of structural Mn(III), thereby generating Mn2+ and vacancies which promoted Pb2+ adsorption via an ion exchange process. In the case of Fe3+ and Cd2+ adsorption, along with electrostatic adsorption, triangle corner sharing (TCS) dominated complex formation at the intermediate vacancies, and less Mn2+ was released. Note that the Mn2+ was in dynamic equilibrium with structural Mn(Ⅲ) and Mn(Ⅳ). The actual AMD was retreated in 5 cycles by ε-MnO2, the removal rates of 100% were achieved for Pb2+, Fe(total) and Mn2+, together with 98% for Cu2+ and 95.1% for Cd2+, all of which reached the national emission standards. This approach is a highly suitable option for AMD treatment that avoids toxic sludge formation.

Turning harmful Mn2+ to treasure: In-situ formed ε-MnO2 for removing heavy metals from acid mine drainage

Acid mine drainage (AMD) contains high concentrations of heavy metals, causing serious environmental pollution. Current neutralization techniques fail to recover and utilize valuable heavy metals, and generate large quantities of hazardous sludge. Manganese (Mn) is generally present at high levels in AMD. Therefore, this paper proposed a technology to recover Mn from AMD, by adding KMnO4 to converting Mn into ε-MnO2. Ultra-Violet C (UVC) was used to photolyze the residual KMnO4. The study then evaluated the processes and mechanisms involved in the technology. The photolysis of KMnO4 in strong acidic conditions was determined, and new mechanisms were proposed. MnO2 produced by the photolysis process was formed through the reaction between Mn(III) and KMnO4. In the absence of KMnO4, Mn(III) underwent further photolysis and was reduced to Mn2+. The maximum adsorption capacities of in-situ formed ε-MnO2 for Pb2+, Cd2+, and Fe3+ were 449.80, 122.05, and 779.88 mg/g, respectively. Higher Mn-OH levels and MnO2 regeneration were crucial in improving adsorption performance. Proton exchange and inner-circle complexation were the main pathways for Pb2+ and Cd2+ adsorption by in-situ formed ε-MnO2. A phase transformation occurred when a substantial amount of Fe3+ was adsorbed, leading to the gradual transformation to MnFe binary oxides. When applying in-situ formed ε-MnO2 technology for actual AMD treatment, 98.62 % of Mn in AMD was recovered within 24 h in the presence of ε-MnO2 for possible further reuse in industries, with a final recovery of 0.76 kg/m3. Further, this technique removed other heavy metals and reduced the sludge volume by 20.99 % when used as a pre-treatment step for neutralization. These results demonstrated the broad potential of this treatment technology.

Alkaline Chemical Neutralization to Treat Acid Mine Drainage with High Concentrations of Iron and Manganese

Due to its high acidity and toxic metal content, acid mine drainage (AMD) needs to be properly treated before being discharged into the environment. This study took the AMD collected from one specific mine in China as a sample and investigated the treatment methodology for AMD. The water quality of the AMD was measured, and the sample was treated with caustic soda (NaOH) and shell powder (one kind of conventional neutralizer, mainly composed of CaCO3) by the neutralization method. The results show that the AMD has a relatively low pH (2.16) and contains high concentrations of Fe (77.54 g/L), Mn (621.29 mg/L), Cu (6.54 mg/L), Ca (12.39 mg/L), and Mg (55.04 mg/L). NaOH was an effective neutralizer to treat the AMD and performed much better than shell powder. Various metals were precipitated, in the order of Fe(III), Cu, Fe(II), Mn, Ca, and Mg. The metal removal mechanisms included precipitation, adsorption, and co-precipitation. The optimal reaction conditions were the reaction duration was selected as 5 min and the mass ratio of NaOH to AMD was 0.16:1 (w:v). By this stage, the pH rapidly increased from 2.16 to 8.53 during AMD-NaOH interactions and various metals were efficiently removed (from 86.71% to 99.99%) by NaOH. The residual mass concentrations of Fe, Mn, Cu, Ca, and Mg after the treatment were 1.52, 1.77, 0.10, 1.65, and 2.17 mg/L, respectively. These data revealed that NaOH was a good treatment regent for this kind of AMD, based on the discharge criteria of China (GB28661 2012). Also, the shell powder was a helpful neutralizer for pH adjustment and copper removal. This neutralization method has the advantages of convenient operation, high speed, good effect, simple equipment, and low infrastructure cost. In addition, the resulting neutralized residue is a valuable and high-quality raw material, which can be used in metal smelting and separation.

Acid mine drainage treatment and metals recovery by means of selective precipitation using magnesium oxide (MgO): An experimental study

The treatment of acid mine drainage (AMD) by metals precipitation and neutralization releases a huge volume of highly polluted toxic sludge which can be valorized by the recovering of chemical species. In this study, the treatment of AMD and chemical species recovery by means of selective precipitation using magnesium oxide (MgO) was explored. One litre and half (1500 mL) of AMD from coal mine was used for the experiment. The pH of AMD water was gradually increased using an overhead stirrer and chemical species recovered at different pH gradients via a sequential precipitation technique. The results revealed that Fe(III) was recovered at pH 2.9–4 interval, Al at pH ≥ 4, Cu at pH ≥ 6.5, gypsum at pH 2.9–9.5 interval, Fe(II) at pH ≥ 7.5, Mn, Ni and Zn pH ≥ 8. The results further revealed significant removal of inorganic pollutants in the following order: Cu (100%) = Ni (100%) ≥ Fe (99.9%) ≥ Al (99%) ≥ Mn (98.6%) ≥ Zn (97.2%) ≥ SO42─ (76%). Reduction of electrical conductivity (EC) and total dissolved solid (TDS) were also observed in the order of 82% and 85% respectively. Characterization studies were used to underpin and succinct the fate of chemical species of pure MgO and sludge recovered at different pH gradients. The product water obtained at pH 9.5 conformed to the prescribed standard for effluent discharge as prescribed by regulatory bodies.

A novel sulfidogenic process via sulfur reduction to remove arsenate in acid mine drainage: Insights into the performance and microbial mechanisms

Biological sulfidogenic processes based on sulfate-reducing bacteria (SRB) are not suitable for arsenic (As)-containing acid mine drainage (AMD) treatment because of the formation of the mobile thioarsenite during sulfate reduction. In contrast, biological sulfidogenic processes based on sulfur-reducing bacteria (S0RB) produce sulfide without pH increase, which could achieve more effective As removal than the SRB-based process. However, the reduction ability and toxicity tolerance of S0RB to As remains mysterious, which may substantially affect the practical applicability of this process when treating arsenate (As(V))-containing AMD. Thus, this study aims to develop a biological sulfur reduction process driven by S0RB, and explore its long-term performance on As(V) removal and microbial community evolution. Operating under moderately acidic conditions (pH=4.0), the presence of 10 mg/L As(V) significantly suppressed the activity of S0RB, leading to the failure of As(V) removal. Surprisingly, a drop in pH to 3.0 enhanced the tolerance of S0RB to As toxicity, allowing for efficient sulfide production (396±102 mg S/L) through sulfur reduction. Consequently, effective and stable removal of As(V) (99.9 %) was achieved, even though the sulfidogenic bacteria were exposed to high levels of As(V) (42 mg/L) in long-term trials. Spectral and spectroscopic analysis showed that As-bearing sulfide minerals were present in the bioreactor. Remarkably, the presence of As(V) induced notable changes in the microbial community composition, with Desulfurella and Clostridium identified as predominate sulfur reducers. The qPCR result further revealed an increase in the concentration of functional genes related to As transport (asrA and arsB) in the bioreactor sludge as the pH decreased from 4.0 to 3.0. This suggests the involvement of microorganisms carrying asrA and arsB in an As transport process. Furthermore, metagenomic binning demonstrated that Desulfurella contained essential genes associated with sulfur reduction and As transportation, indicating its genetic potential for sulfide production and As tolerance. In summary, this study underscores the effectiveness of the biological sulfur reduction process driven by S0RB in treating As(V)-contaminated AMD. It offers insights into the role of S0RB in remediating As contamination and provides valuable knowledge for practical applications.

Comparison of individual and ensemble machine learning models for prediction of sulphate levels in untreated and treated Acid Mine Drainage

Machine learning was used to provide data for further evaluation of potential extraction of octathiocane (S8), a commercially useful by-product, from Acid Mine Drainage (AMD) by predicting sulphate levels in an AMD water quality dataset. Individual ML regressor models, namely: Linear Regression (LR), Least Absolute Shrinkage and Selection Operator (LASSO), Ridge (RD), Elastic Net (EN), K-Nearest Neighbours (KNN), Support Vector Regression (SVR), Decision Tree (DT), Extreme Gradient Boosting (XGBoost), Random Forest (RF), Multi-Layer Perceptron Artificial Neural Network (MLP) and Stacking Ensemble (SE-ML) combinations of these models were successfully used to predict sulphate levels. A SE-ML regressor trained on untreated AMD which stacked seven of the best-performing individual models and fed them to a LR meta-learner model was found to be the best-performing model with a Mean Squared Error (MSE) of 0.000011, Mean Absolute Error (MAE) of 0.002617 and R2 of 0.9997. Temperature (°C), Total Dissolved Solids (mg/L) and, importantly, iron (mg/L) were highly correlated to sulphate (mg/L) with iron showing a strong positive linear correlation that indicated dissolved products from pyrite oxidation. Ensemble learning (bagging, boosting and stacking) outperformed individual methods due to their combined predictive accuracies. Surprisingly, when comparing SE-ML that combined all models with SE-ML that combined only the best-performing models, there was only a slight difference in model accuracies which indicated that including bad-performing models in the stack had no adverse effect on its predictive performance.

Unlocking water potential in drylands: Quicklime and fly ash enhance soil microbiome structure, ecological networks and function in acid mine drainage water-irrigated agriculture

In water-stressed regions, treated acid mine drainage (AMD) water for irrigated agriculture is a potential solution to address freshwater scarcity. However, a significant knowledge gap exists on the short and long-term effects of treated AMD water on soil health. This study used high-throughput Illumina sequencing and predictive metagenomic profiling to investigate the impact of untreated AMD (AMD), quicklime- (A1Q and A2Q) and quicklime and fly ash-treated AMD water (AFQ) irrigation on soil bacterial diversity, co-occurrence networks and function. Results showed that untreated AMD water significantly increased soil acidity, electrical conductivity (EC), sulfate (SO42−), and heavy metals (HM), including reduced microbial diversity, disrupted interaction networks, and functional capacity. pH, EC, Cu, and Pb were identified as key environmental factors shaping soil microbial diversity and structure. Predominantly, Pseudomonas, Ralstonia picketti, Methylotenera KB913035, Brevundimonas vesicularis, and Methylobacteriumoryzae, known for their adaptability to acidic conditions and metal resistance, were abundant in AMD soils. However, soils irrigated with treated AMD water exhibited significantly reduced acidity (pH > 6.5), HM and SO42− levels, with an enrichment of a balanced bacterial taxa associated with diverse functions related to soil health and agricultural productivity. These taxa included Sphingomonas, Pseudoxanthomonas, Achromobacter, Microbacterium, Rhodobacter, Clostridium, Massillia, Rhizobium, Paenibacillus, and Hyphomicrobium. Moreover, treated AMD water contributed to higher connectivity and balance within soil bacterial co-occurrence networks compared to untreated AMD water. These results show that quicklime/fly ash treatments can help lessen impacts of AMD water on soil microbiome and health, suggesting its potential for irrigated agriculture in water-scarce regions.

Investigation of the migration of natural organic matter-iron-antimony nano-colloids in acid mine drainage

Colloids can potentially affect the efficacy of traditional acid mine drainage (AMD) treatment methods such as precipitation and filtration. However, it is unclear how colloids affect antimony (Sb) migration in AMD, especially when natural organic matter (NOM) is present. To conduct an in-depth investigation on the formation and migration behavior of NOM, iron (Fe), Sb and NOM-Fe-Sb colloids in AMD, experiments were performed under simulated AMD conditions. The results demonstrate significant variations in the formation of NOM-Fe-Sb colloids (1–3–450 nm) as the molar ratio of carbon to iron (C/Fe) increases within acidic conditions (pH = 3). Increasing the C/Fe molar ratio from 0.1 to 1.2 resulted in a decrease in colloid formation but an increase in particulate fraction. The distribution of colloidal Sb, Sb(III), and Fe(III) within the NOM-Fe-Sb colloids decreased from 68 % to 55 %, 72 % to 57 %, and 68 % to 55 %, respectively. Their distribution in the particulate fraction increased from 28 % to 42 %, 21 % to 34 %, and 8 % to 27 %. XRD, FTIR, and SEM-EDS analyses demonstrated that NOM facilitates the formation and crystallization of Fe3O4 and FeSbO4 crystalline phases. The formation of the colloids depended on pH. Our results indicate that NOM-Fe-Sb colloids can form when the pH ≤ 4, and the proportion of colloidal Sb fraction within the NOM-Fe-Sb colloids increased from 9 % to a maximum of 73 %. Column experiments show that the concentration of NOM-Fe-Sb colloids reaches its peak and remains stable at approximately 3.5 pore volumes (PVs), facilitating the migration of Sb in the porous media. At pH ≥ 5, stable NOM-Fe-Sb colloids do not form, and the proportion of colloidal Sb fraction decreases from 7 % to 0 %. This implies that as pH increases, the electrostatic repulsion between colloidal particles weakens, resulting in a reduction in the colloidal fraction and an increase in the particulate fraction. At higher pH values (pH ≥ 5), the repulsive forces between colloidal particles nearly disappear, promoting particle aggregation. The findings of this study provide important scientific evidence for understanding the migration behavior of NOM-Fe-Sb colloids in AMD. As the pH gradually shifts from acidic to near-neutral pH during the remediation process of AMD, these results could be applied to develop new strategies for this purpose.

Replacing rice bran with low-molecular-weight substrates affected the performance and metabolic feature of sulfate-reducing bioreactors treating acid mine drainage

The sulfate-reducing bioreactor presents an auspicious approach for eradicating toxic metals from acid mine drainage (AMD). In earlier studies, the incorporation of rice bran as a substrate in bioreactors was observed to foster the proliferation of a diverse range of microorganisms, consequently leading to the undesirable development of biofilms atop the bioreactor. To selectively stimulate sulfate-reducing bacteria (SRB) within the bioreactor, we examined the consequences of introducing three low-molecular-weight substrates in lieu of rice bran under 12 varying conditions. The sulfate reduction performance was marginally impacted by the incorporation of lactate with corn steep liquor (CSL) compared to ethanol or glucose with CSL, and the microbial composition in the presence of lactate differed significantly from those containing ethanol or glucose. The integration of ethanol and glucose with/without CSL efficiently lowered oxidation-reduction potential and promoted the proliferation of Desulfosporosinus-related SRB (relative abundance: ∼26.6%). Given that the employment of glucose initially activated fermentative bacteria such as Clostridium spp., ethanol emerged as an efficacious alternative substrate to rice bran, which directly fosters the accumulation of Desulfosporosinus sp. without encouraging the growth of other microorganisms that contribute to the unwanted formation of biofilms within the sulfate-reducing bioreactors employed in AMD treatment.

Potato (Solanum tuberosum L.) cultivars physiological, biochemical performance and yield parameters response to acid mine water irrigation and soil physiochemical properties

This paper aimed to analyse the potato cultivar’s response to physiological, biochemical performance, yield parameters and soil physiochemical properties when subjected to quicklime (un)treated acid mine drainage (AMD) irrigation. A randomized design experiment was conducted with five water treatment levels: TW1; TW2; TW3; TW4 to TW5 replicated four times. The results showed that the quicklime treatment increased the pH of the AMD water, reduced the concentration of EC, NO3−, SO42− and ameliorated heavy metals. However, unsafe levels of heavy metals above the maximum permissible (WHO/FAO) levels were found in Pb, Mg and Mo for water (TW4 and TW5), while As, Cd and Cr for soils (ST4 and ST5) respectively. For potato tubers (TT4 and TT5) concentrations of As, Cd, Cr, and Pb were above the maximum levels. Stomatal conductance, chlorophyll content and yield parameters responded positively by increasing significantly on TW4 and TW5 treatments, but negatively (reduced) towards TW2 and TW3 treatments. A higher bioaccumulation factor was obtained for Zn ˃ Cu ˃ Mg ˃ Pb ˃ Mn, which was an indication of the contamination status of soil, with Zn being more concentrated than other metals. The findings indicate that quicklime-treated AMD is usable for potato irrigation with regular monitoring of heavy metal levels and strict observation of water reuse protocols. The use of this large source of ameliorated (AMD) water will go a long way in improving food security in South Africa and/or in countries where agriculture production is around mining areas.

Needs and Options for Improving Gold Mining Waste Management Practices for Sustainable Development in Tanzania

The main objective of this study was to evaluate current mining waste management practices and their challenges. This study aimed to identify existing technologies and practices, and to present improvement needs and options for environmentally sustainable practices for mining operations. Other researchers have reported many practices and technologies for managing mining waste, but the efficiency, applicability, and need for customization were not specifically addressed for developing countries. This study used field observations, measurement methods, and laboratory analysis to collect data. This study showed a large amount of mine waste rock compared to the tailings wastewater from gold processing plant produced annually. This comprises approximately 5.2 million m3 of mine contaminated water generated by leaching from the waste rock dump (WRD) and 2.3 million m3 from the tailings storage facility (TSF). The study also identified the use of TSF cut-off trenches for seepage collection, the use of lime to treat acid mine drainage (AMD), the discharge of AMD into the TSF, and the recycling of TSF water as the best practices for managing mining waste. Furthermore, the study also found that the most common environmental problems were caused by TSF water and AMD water. However, mining waste management can be improved by modifying existing practices and adopting cost-effective technologies and practices to control and treat excess mining water.

Application of Active and Passive Treatment of Acid Mine Drainage to Comply with the Threshold Parameter of Coal Mining Wastewater

Most of the coal mining in Indonesia that uses the open pit mining method faces serious problems, namely the treatment of acid mine drainage. This constitutes a relatively large volume of wastewater, especially in areas that have rainfall in the range of 2000–4000 mm yearly. Acid mine drainage as acidic wastewater formed during excavation cannot be avoided due to the oxidation process during overburden removal. The acidic wastewater that has formed must be managed strictly and appropriately prior to being released into public waters. There are two methods of treating acid mine wastewater, namely active and passive treatments. Active treatment is generally used more frequently during operations, considering the time, effort, and costs; however, when entering the mine closure period, natural processes must be used at lower costs. Undertaking passive treatment in this area has shown a reduction in the chemical materials used and has enabled a greater amount of wastewater to be managed. The purpose of this research is to describe the active and passive treatment processes in the management of acid mine drainage and to analyze the results of passive treatment in preparation for the mine closure stage. Development of passive treatment by swampy forest system can reduce cost of treatment, naturally process and more environment friendlier by reducing the quicklime materials.

Comparison of Artificial Neural Fuzzy Inference System (ANFIS) and Response Surface Methodology (RSM) Model in Predicting the Outlet Flow Rate of Passive Treatment System Column

Acid mine drainage (AMD) is one of the major environmental problems the mining and mineral processing industries face. Treatment of AMD involves active and passive treatment. In the long term, passive treatment is the most effective way to treat acid mine drainage, but it can be expensive. if handled properly. Therefore, the study of flow rate in a passive treatment system is one of the important ways to identify optimum hydraulic retention time to ensure the maximum percentage of heavy metal removal can be achieved while keeping the cost to a minimum level. This study focused on developing and comparing the Response Surface Methodology (RSM) model and Artificial Neural Fuzzy Inference System (ANFIS) model to predict the outlet flow rate of the passive treatment system column based on three parameters inlet flow time, thickness of peat soil bed, and inlet flow rate. The RSM model was created by Design-Expert software whereas MATLAB created the ANFIS model with 80% of data used for the model training and 20% of the data for model testing. The models' performances were compared in terms of statistical errors (AAPE, RMSE, R2, STD, minimum error, and maximum error). It was found the ANFIS model has performed better in predicting the outlet flowrate with R2 value of 0.99 RSM model with the value of 0.97. The inlet flow rate was an insignificant parameter affecting the outlet flow rate of the passive treatment column. From the 3-D surface response plot, the highest outlet flow rate is predicted to be 524 mL/min.

Source reduction and end treatment of acid mine drainage in closed coal mines of the Yudong River Basin

Abstract After the closure of the Yudong coal mine, the pH value was approximately 3.0, and the Fe and Mn concentrations reached 380 and 69 mg/L, respectively, in the acid mine drainage (AMD), causing serious pollution to the water bodies in the nearby watershed. Combined with the formation conditions of AMD, the comprehensive treatment technology of source reduction–end treatment is adopted to treat the AMD. The treatment area of the goaf is 0.3 km3, the filling and grouting volume is about 6.7 m3, and the curtain grouting volume is 4,000 m3. Through the grouting and sealing treatment in the goaf, the water volume is reduced to less than 85% of the initial volume (100 m3/h). After the end treatment, the pH value of the effluent is around 7.0, the content of Fe and Mn is less than 0.1 mg/L, and the removal rate is above 99%. The project was subsequently operated at RMB 0.85 yuan/t. This project is aimed at the treatment of AMD from small coal mines in complex terrain conditions. It has the characteristics of low cost and high efficiency and can provide an effective treatment technology for AMD in southwestern China and areas with the same geological conditions.