Acid Mine Drainage Remediation Research Articles

Adsorption of heavy metals from acid mine drainage using poly (hydroxamic acid) ligand

Acid mine drainage (AMD) causes severe environmental concerns worldwide due to its high acidity, toxic metals and sulphate contents. Conventional treatment methods may not be effective for AMD. There is a need for wastewater remediation; however, it requires cost-effective technologies for efficiently removing heavy metals. The current study reports the remediation of AMD using a modified pine cone powder. The surface of the biosorbent was improved by pre-treatment using Fenton reagent and then modified using chemical grafting of acrylic acid onto pine cone powder with free radical initiation. The modified adsorbent was used for adsorption of (Fe3+), (Cu2+), (Mn2+), (Zn2+), and (Pb2+) from single components solution and acid mine drainage sampled from an abandoned mine at Witbank. The adsorption behaviour of poly (hydroxamic acid) ligand has been studied to determine its application in treating Witbank acid mine drainage (AMD). The rate of adsorption and the uptake at equilibrium were investigated using batch conditions from single and multi-component solutions (AMD). The optimum pH for the poly (hydroxamic acid) ligand was 6 for all heavy metal ions investigated with the percentage removal of 79,83, 82,90 and 73% for Fe3+, Cu2+, Mn2+, Zn2+ and Pb2+ respectively. The ligand's binding capacity (qe) with metal ions such as iron, copper, manganese, zinc and lead were 13, 14, 11, 11 and 12 mg g−1, respectively. The adsorption of the heavy metal ions onto the ligand fitted well with the Langmuir isotherm model due to R2 > 0.99 compared to the Freundlich model. Additionally, RL values were in a range of 0,0020 to 0,0560, which indicates favourable adsorption. Furthermore, pseudo second-order kinetics was the best to describe adsorption kinetics for AMD metal ions using poly (hydroxamic acid) ligand. The AMD treatment using poly (hydroxamic acid) ligand showed great potential as a low-cost alternative material.

Insights into mechanisms governing the passive removal of inorganic contaminants from acid mine drainage using permeable reactive barrier

The permeable reactive barrier has been deemed as the most prudent and pragmatic way to passively manage and remediate acid mine drainage (AMD). Herein, insights into mechanisms governing the removal of inorganic contaminants from AMD using a permeable reactive barrier (PRB), i.e. pervious concrete, were reported. In particular, the effects of varying dosages, i.e., 6, 10, 30, and 60 g, of cementitious materials comprising CEM I 52.5R with or without fly ash, hydrated lime, and gypsum were evaluated whilst the fate of chemical species was underpinned using the state-of-the-art analytical techniques, along with PHREEQC geochemical modelling. The role of gypsum, a product formed from the interaction of PRB with AMD in heavy metals attenuation was also elucidated. Findings revealed cementitious materials to play an indispensable role in the removal of inorganic contaminants from AMD. Furthermore, alkalinity from used materials increases the pH (i.e. pH ≥ 12.5) of AMD leading to the precipitation of chemical species. Specifically, the efficacy registered the following sequence: Lime ≥ CEM I ≥ 30%FA ≥ Gypsum with ≥99 for Al and Fe except for Gypsum which attained ≥98 while the performance for Zn removal registered the following sequence, 97 ≥ 98 ≥ 88.8 ≥ 45% for CEM I ≥ Lime ≥30%FA ≥ Gypsum, respectively. Chemical species exist as divalent, trivalent, oxyanions, and other complexes in solution as predicted by PHREEQC. Moreover, they were removed as metal hydroxides, oxyhydrosulphates, and gypsum hence corroborating findings from XRD, SEM-EDS, and FTIR results. Mechanisms which were responsible for the removal of chemical species were precipitation, adsorption, co-adsorption, co-precipitation, ion exchange, and complexation. Henceforth, this study explicitly demonstrated mechanisms that underpin the removal of inorganic contaminants from AMD using PRB and findings from this study will be used to develop effective PRB for the management of acid mine drainage and the receiving environment.

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

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

Critical evaluation of the chemical composition of acid mine drainage for the development of statistical correlations linking electrical conductivity with acid mine drainage concentrations

• Significant metals concentrations were present in AMD in Mpumalanga Coalfields. • Seasonal variability and strong correlations between electrical conductivity and major parameters were noted. • Electrical conductivity is easily measured and data are immediately available. • Electrical conductivity can be used as a proxy to predict concentrations of other major parameters. • Derivation of electrical conductivity values corresponding to water quality limits for the predicted parameters may be used as a rapid method for testing compliance. The design an effective treatment processes for the remediation of acid mine drainage (AMD) requires an understanding of the composition of the AMD water. The pH and elemental composition of AMD waters are site specific and are dependent on the regional geology, and environmental factors. To establish the chemical and physical characteristics of two AMD sites located in the Mpumalanga coal mining region, South Africa, samples were taken between February 2018 to April 2019. These data were compared against regulatory legislation, and the potential health effects of exposure indicated. Strong correlations were noted between parameters and statistical evaluation demonstrated that electrical conductivity (EC) could be a useful correlative for prediction of total acidity, dissolved iron, and sulfur concentrations in acidic AMD waters. From these findings, empirical correlations were used to derive regression equations which were used to derive the EC values corresponding to the respective water quality limits for total dissolved solids (TDS), dissolved iron, and sulfur to provide a rapid method for testing compliance. Given the site specificity of AMD composition, this approach is intended as a proof of concept for the development of a methodology for adaption at other AMD sites. The regression equations should not be considered as universal to all AMD sites and EC should also not be used as a replacement for more complete chemical analysis. :

Assessing Alternative Supporting Organic Materials for the Enhancement of Water Reuse in Subsurface Constructed Wetlands Receiving Acid Mine Drainage

Acid mine drainage (AMD) is a global problem with severe consequences for the environment. South Africa’s abandoned mines are a legacy from the country’s economic dependence on the mining sector, with consequent negative impacts on ecosystems. AMD remediation includes active and passive techniques. Constructed wetlands (a passive technique) have lower operational costs but require larger spaces and longer timeframes to achieve the remediation of AMD, and are supported by anaerobic sulphate-reducing bacteria (SRB), which capable of remediating high-sulphate-laden AMD while precipitating dissolved metals from the AMD. Organic substrates supporting these activities are often the limiting factor. When enhancing existing passive AMD remediation technologies, alternative waste material research that may support SRB activity is required to support the circular economy through the reduction in waste products. Chicken feathers show potential as a substrate enhancer, boosting organic carbon availability to SRB, which sustains passive AMD treatment processes by achieving pH elevation, sulphate and metal reductions in AMD water for reuse. Microbial biodiversity is essential to ensure the longevity of passive treatment systems, and chicken feathers are proven to have an association with SRB microbial taxa. However, the longer-term associations between the AMD water parameters, microbial diversity and the selected substrates remain to be further investigated.

Active Physical Remediation of Acid Mine Drainage: Technologies Review and Perspectives

Active Physical Remediation of Acid Mine Drainage: Technologies Review and Perspectives

Effect of pH on oxygen-induced abio-oxidation and removal of As from As-rich acid mine drainage in the co-existence of Zn(II)

Zn(II) enhances the adsorption of arsenate in heavy metal wastewater onto iron oxides, but the effect of Zn(II) on the removal of As during the oxidation of As(III) to As(V), corresponding to remediation of As-rich acid mine drainage (AMD) via oxidation-precipitation method, is still unclear. The rapid and efficient removal of As from As-rich AMD in the co-existence of Zn(II) was conducted through oxygen-induced abio-oxidation of Fe(II) and As(III) at slightly acidic to alkaline pH in this work. After 8-h reactions, arsenic removal and arsenite oxidation efficiencies reached 91.9–99.9% and 34.6–63.8%, which showed an evident rise at first and then decreased as the pH increased from 3 to 9. Maximum As removal and oxidation with the As-leaching stable solid product was observed at pH 5. Reactive oxygen species (ROS) contents involving Fenton-like reaction degree and solid product species were controlled by pH for As(III), As(V), Fe(II), Fe(III) and Zn(II) liquid-solid distribution as the probable mechanism. Almost all of arsenic and zinc were mainly immobilized by the produced Zn(II)–As(III + V)-bearing SO4-ferrihydrite at pH 5 with the higher short-term stability of the final solid due to higher As(V) in solid-phase and a small amount of zinc hydrogen arsenate produced. At higher pH, adsorbed-Zn(II) competition with ROS for solid surface sites negatively affected the Fenton-like reaction process for unstable Zn(II)–As(III + V)-bearing magnetite, causing the decrease of As removal and oxidation.

Using chemometric models to predict the biosorption of low levels of dysprosium by Euglena gracilis.

The critical rare earth element dysprosium (Dy) is integral for sustainable technologies. What is concerning is that Dy is in imminent short supply and no current replacements yet exist, coupled with increasing environmental Dy levels influenced by anthropogenic activities. This study applies chemometric methods such as response surface methodology and artificial neural networks to predict low Dy removal levels using the biosorbent Euglena gracilis. A three-factor Box-Behnken experimental design was conducted with initial concentration (1 to 100µg L-1), contact time (30 to 180min), and pH (3 to 8) as the three independent variables, and percentage removal and sorption capacity (q) as dependent variables. Using Dy percentage removal as response, for the worst and best conditions ranged from 0 to 92% respectively, with an average removal of 66 ± 4%. Using sorption capacity (q) as a different response variable, q varied from 0 to 93µg/g with 27 ± 4µg/g capacity as average. Maximum removal was 92% (q = 93µg/g) was at pH 3, a contact time of 105min and at a concentration of 100µg/L. Using sorption capacity as the response variable for ANOVA, pH and metal concentrations were statistically significant factors, with lower pH and higher metal concentration having improved Dy removal, with a desirability near 1. Statistical tests such as analysis of variance, lack-of-fit, and coefficient of determination (R2) confirmed model validity. A 3-10-1 ANN network array was used to model experimental responses (q). RSM and ANN effectively modeled Dy biosorption. E. gracilis proved to be a cheap and effective biosorbent for Dy biosorption and has the potential to remediate acid mine drainage areas exhibiting low Dy concentrations.

Long-term treatment of acid mine drainage by alkali diffusion ceramic reactor: Simultaneous metal removal mechanisms

A novel alkali diffusion reactor using ceramic porous media (ceram-ADR) was designed for the long-term remediation of acid mine drainage (AMD) without external energy. The filling material was newly applied to improve the ceram-ADR for intensive long-term treatment of acidity and metals in AMD. Activated carbon (AC), polyurethane (PU), or MgO-incorporated polyurethane (PU–MgO) were inserted as filling materials into ceram-ADR. NaHCO3 was used as the alkaline chemical. PU did not enhance the neutralizing capacity of ADR and metal removal efficiency. Although the ceram-ADR with PU-MgO showed long-term removal efficiency for all metals up to 545 bed volumes (BVs), the effluent pH complied with the mineral mining and processing effluent guidelines during 45 BVs. Ceram-ADR with AC enhanced the long-term treatment (up to a year) of metals and acidity in AMD. Mn concentration in the effluent discharged from ceram-ADR exceeded the mineral mining and processing effluent guidelines, followed by Zn, Al, and Fe. The main removal mechanism for metals was precipitation as a metal hydroxide or metal carbonate. The ion exchange of metal ions on the surface of ceramic porous media and AC can influence the adsorption behavior, which is responsible for 15.3% of the total removal of metals. The ceram-ADR with AC could be reused at least five times with no appreciable loss in activity. These results highlight the hybrid operation of ADR for the best performance in mining areas where the passive and active system are insufficient because of low efficiency, budget limitations, and geological sites.

Novel approach for the management of acid mine drainage (AMD) for the recovery of heavy metals along with lipid production by Chlorella vulgaris

The treatment of acid mine drainage (AMD) is of paramount importance for environmental sustainability. A two-stage process involving AMD remediation and simultaneous lipid production represents a highly efficient approach with zero-waste generation. Alkaline (NaOH) treatment of AMD at pH 8.0, 10.0, and 12.0 had significantly reduced metal loads (copper (Cu), cobalt (Co), chromium (Cr), cadmium (Cd), nickel (Ni), and zinc (Zn)) compared to the acidic pH range (4.0 and 6.0). The concentration levels of sulfates (SO4 = 4520 mg/L), iron (Fe = 788 mg/L), aluminum (Al = 310 mg/L), and manganese (Mn = 19.4) were reduced to 2971 mg/L, 10.3 mg/L, 16.4 mg/L, and 1.3 mg/L, respectively at pH value 8.0. AMD with a pH value of 8.0 was later chosen as an ideal medium to favor the lipid accumulation by Chlorella vulgaris. Algal biomass was increasing to 5.5 g/L from 0.6 g/L of AMD-based medium within 15 days of cultivation. The FTIR and SEM-EDS studies revealed significant morphological changes in the microbial cell wall. The metals might positively impact lipid production in microalgae, where lipid yield achieved 0.18 g/g of glucose with lipid content of 0.35 g/g of biomass. The fatty acid profile presented 53.4% of saturated fatty acid content with a cetane value of 60.7. Thus, the efficiency of C. vulgaris was demonstrated with AMD treatment proving it to be a good candidate for bioenergy production.

Sustainability Evaluation of Immobilized Acid-Adapted Microalgal Technology in Acid Mine Drainage Remediation following Emergy and Carbon Footprint Analysis.

Sustainability evaluation of wastewater treatment helps to reduce greenhouse gas emissions, as it emphasizes the development of green technologies and optimum resource use rather than the end-of-pipe treatment. The conventional approaches for treating acid mine drainages (AMDs) are efficient; however, they need enormous amounts of energy, making them less sustainable and causing greater environmental concern. We recently demonstrated the potential of immobilized acid-adapted microalgal technology for AMD remediation. Here, this novel approach has been evaluated following emergy and carbon footprint analysis for its sustainability in AMD treatment. Our results showed that imported energy inputs contributed significantly (>90%) to the overall emergy and were much lower than in passive and active treatment systems. The microalgal treatment required 2–15 times more renewable inputs than the other two treatment systems. Additionally, the emergy indices indicated higher environmental loading ratio and lower per cent renewability, suggesting the need for adequate renewable inputs in the immobilized microalgal system. The emergy yield ratio for biodiesel production from the microalgal biomass after AMD treatment was >1.0, which indicates a better emergy return on total emergy spent. Based on greenhouse gas emissions, carbon footprint analysis (CFA), was performed using default emission factors, in accordance with the IPCC standards and the National Greenhouse Energy Reporting (NGER) program of Australia. Interestingly, CFA of acid-adapted microalgal technology revealed significant greenhouse gas emissions due to usage of various construction materials as per IPCC, while SCOPE 2 emissions from purchased electricity were evident as per NGER. Our findings indicate that the immobilized microalgal technology is highly sustainable in AMD treatment, and its potential could be realized further by including solar energy into the overall treatment system.

Increases in pH of acid mine drainage with coal fly-ash application

Coal fly-ash (CFA), waste materials resulted from coal processing in power plants, contains oxides that have capability to neutralize hydrogen ions of acid mine drainage (AMD). A batch reactor experiment was conducted by adding different amounts of CFA (0, 50, 100, 150, 200, and 250 Mg ha−1) to reclaimed mining soils (RMS) to quantify the effect of CFA addition on changes in the pH of AMD. AMD was then flowed into the reactors following the incubation of the mixtures of RMS and CFA for 7 days, and the changes in pH of AMD in the reactors were monitored over 35 days. Results of the study showed pH and specific surface areas (SSA) of soils increased significantly with the addition of CFA. pH of AMD over 35 days also improved with CFA application, in which the degree of pH improvement was controlled by the amounts of added CFA. The addition of CFA <200 Mg ha−1 was not able to result in pH of AMD >6.0, and AMD pH of 6.0 was obtained when the amount of applied CFA reached to 200 Mg ha−1. Increasing pH of AMD is attributed to the CaO and MgO contained in the CFA neutralizing the H+ ions of AMD. Results of the study demonstrate the potential of CFA in remediation of AMD, in particularly in increasing pH of AMD.

Experimental study of the remediation of acid mine drainage by Maifan stones combined with SRB.

The problems of acid mine drainage (AMD) in coal mine acidic wastewaters arise from a range of sources, including severe pollution with heavy metals and SO42- and difficulties during treatment. Based on the ability of Maifan stone to adsorb heavy metals and the dissimilatory reduction of SO42- by sulfate-reducing bacteria (SRB), Maifan stone-sulfate-reducing bacterium-immobilized particles were prepared via immobilization techniques using Shandong Maifan stone as the experimental material. The effects of Maifan stones containing SRB on mitigating AMD were investigated by constructing Dynamic Column 1 with Maifan stone-sulfate-reducing bacterium-immobilized particles and by constructing Dynamic Column 2 with SRB mixed with Maifan stones. By the use of adsorption isotherms, adsorption kinetics, a reduction kinetics model and X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies, the mechanism by which Maifan stone-sulfate-reducing bacterium-immobilized particles mitigate AMD was revealed. The results showed that the total effect of Maifan stone-sulfate-reducing bacterium-immobilized particles on AMD was better than that of biological Maifan stone carriers. The highest rates for the removal of Fe2+, Mn2+, and SO42- in AMD were 90.51%, 85.75% and 93.61%, respectively, and the pH value of the wastewater increased from 4.08 to 7.64. The isotherms for the adsorption of Fe2+ and Mn2+ on Maifan stone-sulfate-reducing bacterium-immobilized particles conformed to the output of the Langmuir model. The adsorption kinetics were in accordance with Lagergren first-order kinetics, and the kinetics for the reduction of SO42- conformed to those of a first-order reaction model.

Passive multi-unit field-pilot for acid mine drainage remediation: Performance and environmental assessment of post-treatment solid waste

This study evaluated the performance of a passive multi-unit field-pilot operating for 16 months to treat acid mine drainage (AMD) from a coal mine in Colombia Andean Paramo. The multi-unit field-pilot involved a combination of a pre-treatment unit (550 L) filled with dispersed alkaline substrate (DAS), and six passive biochemical reactors (PBRs; 220 L) under two configurations: open (PBRs-A) and closed (PBRs-B) to the atmosphere. The AMD quality was 1200 ± 91 mg L−1 Fe, 38.0 ± 1.3 mg L−1 Mn, 8.5 ± 1.6 mg L−1 Zn, and 3200 ± 183.8 mg L−1 SO42−, at pH 2.8. The input and output effluents were monitored to establish AMD remediation. Physicochemical stability of the post-treatment solids, including metals (Fe2+, Zn2+, and Mn2+) and sulfates for environmental contamination from reactive mixture post-treatment, was also assessed.The passive multi-unit field-pilot achieved a total removal of 74% SO42−, 63% Fe2+, and 48% Mn2+ with the line of PBRs-A, and 91% SO42−, 80% Fe2+, and 66% Mn2+ with the line of PBRs-B, as well as 99% removal for Zn2+ without significant differences (p < 0.05) between the two lines. The study of the physicochemical stability of the post-treatment solids showed they can produce acidic leachates that could release large quantities of Fe and Mn, if they are disposed in oxidizing conditions; contact with water or any other leaching solutions must be avoided. Therefore, these post-treatment solids cannot be disposed of in a municipal landfill. The differences in configuration between PBRs, open or closed to the atmosphere, induced changes in the performance of the passive multi-unit field-pilot during AMD remediation.

Performance and microbial response in a multi-stage constructed wetland microcosm co-treating acid mine drainage and domestic wastewater

Multi-stage constructed wetland microcosms (mixing and sedimentation pond (MS), vertical-flow constructed wetland (VFCW) and surface-flow constructed wetland (SFCW)) were designed to co-treat high-strength acid mine drainage (AMD) and domestic wastewater, with agricultural waste (straw and cow manure) fermentation liquor as stimulation substrate. The 270-day lab-scale study showed that this system was highly effective in enhancing effluent pH (from 2.5 to 8.1) and removing dissolved metals (89.4% of Mn, and 99% of Fe, Zn, Cd and Cu), sulfate (51.9%) and organic/nutrient pollutants (COD, NH4+-N, NO3--N, and TP). The mixing and sedimentation pretreatment could alleviate the burden (strong acidity and high-strength metals) and clogging of wetlands, and the formed metal-rich sludge offered the possibility of metals reclaiming. Quantitative supplementary of fermentation liquor promoted sulfidogenic activity in VFCW, also avoiding excessive release of organic/nutrient pollutants. SFCW was effective in treating residual metals (especially Mn) and organic/nutrients. High-throughput sequencing test showed that the diverse microbe (such as sulfate reducing bacteria, nitrifying bacteria, and denitrifying bacteria) co-existing in this multi-stage system predominantly contributed to the effective remediation. Metal amounts assimilated by wetland plants were very limited (e.g. 1% for Mn) for metals remediation. The multi-stage constructed wetlands co-treatment system quantitatively supplied with liquid waste as carbon source may offer a promising eco-technology for the remediation of AMD.

Mechanism of Acid Mine Drainage Remediation with Steel Slag: A Review.

Technologies for remediation of wastewater by industrial solid waste have recently attracted interest. Acid mine drainage is an extraordinarily acidic and highly heavy metal ions contaminated leachate which posed some challenges for the environment. Nonetheless, steel slag shows significant potential application prospects in wastewater treatment, due to its excellent physicochemical properties and structures. This paper elaborately reviewed the structure, properties, water treatment applications of steel slags, and the mechanism for removing heavy metal ions from acid mine drainage, discussed the problems existing in industrial wastewater treatment by steel slag, and proposed the solutions for future research, aiming to provide theoretical references for the practical application of steel slag in AMD treatment.

Effects of Contact Time and Flow Configuration on the Acid Mine Drainage Remediation Capabilities of Pervious Concrete

This paper investigates the Acid Mine Drainage (AMD) remediation capabilities of pozzolanic pervious concrete Permeable Reactive Barriers (PRBs) with a specific focus on the effects of flow configuration and contact time on the remediation efficiency. Raw AMD was collected from an abandoned coal mine. Two flow configurations, gravity flow and column flow, were tested at a laboratory scale with gradually increasing contact times. The gravity flow configuration with two orders of magnitude less liquid-concrete contact time achieved AMD treated water quality equivalent to the high retention column flow configuration. Concentrations of iron, aluminium, sulphate, magnesium and sodium were reduced by more than 99%, 80%, 17%, 22% and 20%, respectively, at the tested limits while calcium and potassium concentrations were increased by up to 16% and 300%, respectively. The study findings indicate that the lifecycle costs of pervious concrete PRBs can be significantly reduced when the PRBs are operated under gravity flow.

Application of biohydrometallurgical processes for heavy metals removal from acid mine drainage

The main scope of this study was to remediate Acid Mine Drainage (AMD) by application of biohydrometallurgical processes, environmentally friendly, to remove heavy metals such as Zn, Cu, Mn, Cd, Al and Fe. The processes studied have been electrowinning and bioprecipitation. The samples utilised were collected from the zinc mine located in Italy and from a cooper – iron ore deposit in Slovakia. By electrochemical experiments, high metals removal, with a low energetic consumption, has been achieved: in particular, by Zn electrodeposition, it was possible to achieve 95-99% Zn removal. Culture of sulphatereducing bacteria (SRB) of genera Desulfovibrio sp. was used for the bioprecipitation tests. The precipitation kinetic of metals at the original pH of aforementioned AMD by SRB has been investigated. This method has been performed in two interconnected reactors. Achieved results indicate the 98-99% selective elimination of Cd from AMD - Italian mine, and the 98-99% selective elimination of Cu from AMD - Slovak mine by bacterially produced H2S. Both the electrowinning and bioprecipitation processes have been demonstrated the technical feasibility to decrease the heavy metals concentration. The experimental work has been carried out in the framework of the agreement of scientific cooperation between the Institute of Environmental Geology and Geoengineering of the CNR, Italy and the Institute of&#x0D; Geotechnics of Slovak Academy of Sciences, Slovakia (years 2007-2009).

Bioremediation of acid mine drainage in constructed wetlands: Aspect of vegetation (Typha latifolia), loading rate and metal recovery

Two constructed wetlands, unplanted (CCW) and planted (PCW) units were investigated to assess the role of plants (Typha latifolia) and the impact of hydraulic loading rates in the remediation of acid mine drainage (pH ≤ 2) and metal attenuation. Results revealed significant differences (p < 0.05) between metal removal efficiencies of CCW and PCW, except for Al, Mn and Cr. CCW (92–42%) exhibited higher sulfate removal efficiency than PCW (85–30%), indicating significant impairment of microbial sulfate reduction in the presence of plants. The overall activity decreased from 2.55 and 2.21 to 2.04 and 1.90 mg chemical oxygen demand (COD) removed mg (total volatile solids) TVS–1 day−1, whereas specific sulfidogenic activity decreased from 0.79 and 0.76 to 0.62 and 0.59 mg sulfate reduced mg TVS–1 day−1 in CCW and PCW, respectively. Wetland media retaining metals (>90% of the total metal mass removed) was further extracted, good metal extraction efficiencies (%) were achieved for Fe (57.7–97.6), Al (39.2–61.3), Zn (65.9–98.8), Co (70.8–77.3), Ni (78.3–89.2) and Cr (82.2–87.1) using different chelating acids. Following extraction, metals were recovered as 49.1–97.6% Fe, 29.7–47.9% Al, 57.4–94.9% Zn, 50.3–73.6% Co, 67.0–86.5% Ni and 68.3–83.8% Cr.

Review of Remediation Solutions for Acid Mine Drainage Using the Modified Hill Framework

This paper reviews the Acid Mine Drainage (AMD) remediation potential and operational costs of twelve existing AMD remediation methods against Class 0 and Class I AMD geochemical characteristics as defined in the Modified Hill Framework. Of the twelve remediation options reviewed in this study, eleven required additional process steps either for further treatment to achieve the discharge limits or for the safe management of hazardous waste by-products. Chemical desalination showed the greatest potential with high quality treated water and operational costs between USD 0.25 and USD 0.75 per cubic meter treated. The management of the toxic metal and sulphide by-products remains a key challenge that requires further research for sustainable mine water remediation. Further development of end-to-end methods suitable for Class 0 AMD with economical operational costs is recommended in order to effectively address the ongoing environmental challenges posed by AMD globally.