Membrane technology applied to acid mine drainage from copper mining

Selective separation of light and heavy rare earth elements from acidic mine waters by integration of chelating ion exchange and ligand impregnated resin

This study addresses the potential of sourcing Critical Raw Materials (CRMs) using Acidic Mine Waters (AMWs) as a secondary resource. AMWs, often viewed as waste, contain valuable metals like zinc and copper, as well as critical metals like magnesium and cobalt. Moreover, recent studies also reported the presence of Rare Earth Elements (REEs) at concentrations (mg/L) that make their extraction both technically and economically viable. The research focuses on a circular process to recover these metals from AMWs, specifically from the Aznalcóllar open-pit mine, which contains 216 mg/L of Al, 47 mg/L of Fe, 547 mg/L of Zn, and 18.56 mg/L of REEs. The proposed method involves pre-treating the AMW to remove Fe and Al, achieving removals of over 99.9 % and 90 %, respectively, at pH 4.5. Following this, transition metals like Zn, Cd, and Cu were removed as sulphides with a removal efficiency exceeding 99 %. This pre-treatment step reduced the concentration of competing metals in the ion-exchange process, thereby enhancing the recovery and purity of REEs. To separate heavy and light REEs, two types of resins in series were used: an impregnated resin (TP272) and a chelating resin (S930), which can be regenerated using sulphuric acid (H2SO4). The final recovery of REEs as oxalates was achieved using oxalic acid and ammonia at pH 1, with further optimization of the elution process to minimize ammonia consumption and undesired precipitation of other oxalates. Finally, REE oxalates with purities exceeding 90 % were obtained. This research demonstrates a sustainable method for efficiently recovering valuable REEs from AMWs, while also addressing environmental concerns related to hazardous sludge generation.

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

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

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.

Investigations on Strategic Element Recovery by an Underground Membrane Pilot Plant from In-Situ Extracted Bioleaching Solutions

Focusing on the selective extraction of the critical raw materials indium and germanium from real bioleaching solutions, extended studies have been carried out using Europe’s first underground hybrid membrane pilot plant (TRL6). In order to transfer former laboratory experiments to pilot scale, NF99 (Alfa Laval) was used for the evaluation of membrane permeance and ion retention. A performance test of microfiltration (MF) and nanofiltration (NF) showed high permeances with low root-mean-square deviation under feed variation (5.2% for MF, 4.7% for NF). Depending on the feed load, a significant permeance drop of up to 57% for MF (3 bar) and 26% for NF (10 bar, 1.1 m s−1) was observed. The NF retention performance showed that, without regular chemical cleaning, the selectivity between the target elements degraded. By introducing acidic-basic cleaning steps, it was possible to keep the retention behavior at an approximately constant level (In 91.0 ± 1.3%; Ge 18.2 ± 5.5%). In relation to the specified target, the best results could be achieved at low pressure (7.5 bar) and a maximum overflow velocity of 1.1 m s−1, with a retention of 88.4% for indium and 8.8% for germanium. Moreover, the investigations proved the functionality and long-term stability of the underground membrane device.

Long-term operation of a permeable reactive barrier with diffusive exchange

In this study, we evaluate the long term operation of a bench-scale reactor which simulates a permeable reactive barrier with sulfidic diffusive exchange (SDES PRB) to treat acid mine drainage (AMD), considering that treatment costs are very sensitive to the useful life for passive reactors. Its functioning was evaluated for a much longer period of 591 days compared to previous SDES PRB studies, with two influents simulating moderately and highly acid groundwater contaminated by AMD. First, we fed water amended with 200 mg/L Zn²⁺ and 3300 mg/L SO₄^2- at pH 4.9; and after, water with 450 mg/L Fe²⁺, 100 mg/L Zn²⁺, 10 mg/L Ni²⁺, 5 mg/L Cu²⁺ and 3600 mg/L SO₄^2- at pH 2.5. Biologically produced sulfide and alkalinity were enough to remove both metals and acidity (~99%) from the moderately acidic water, while with the highly acidic water, they resulted in significant removal of the metals reaching up to 87% and 79% of total Fe and Zn, respectively. Furthermore, no inhibitory effect was apparent, as the sulfate reduction rates in the two experiments did not vary significantly (averages close to 0.2 mol/m³-d), despite the much higher acidity and metal load in the second case. Hence, the SDES PRB protected the microbial consortium from metal toxicity and acidity in the long-term, and thus is suitable for remediation of AMD contaminated groundwater with high concentrations of metals, extending the operational range of conventional biological PRBs. Furthermore, an economic evaluation shows that SDES costs can be competitive with the costs of conventional chemical precipitation if the enhanced reactivity that SDES technology offers is realized.

A membrane-biofilm system for sulfate conversion to elemental sulfur in mining-influenced waters

A system of two membrane biofilm reactors (MBfRs) was tested for the conversion of sulfate (1.5 g/L) in mining-process water into elemental sulfur (S⁰) particles. Initially, a H₂-based MBfR reduced sulfate to sulfide, and an O₂-based MBfR then oxidized sulfide to S⁰. Later, the two MBfRs were coupled by a recirculation flow. Surface loading, reactor-coupling configuration, and substrate-gas pressure exerted important controls over performance of each MBfR and the coupled system. Continuously recirculating the liquid between the H₂-based MBfR and the O₂-based MBfR, compared to series operation, avoided the buildup of sulfide and gave overall greater sulfate removal (99% vs 62%) and production of S⁰ (61% vs 54%). The trade-off was that recirculation coupling demanded greater delivery of H₂ and O₂ (in air) due to the establishment of a sulfur cycle catalyzed by Sulfurospirillum spp., which had an average abundance of 46% in the H₂-based MBfR fibers and 62% in the O₂-based MBfR fibers at the end of the experiments. Sulfate-reducing bacteria (Desulfovibrio and Desulfomicrobium) and sulfur-oxidizing bacteria (Thiofaba, Thiomonas, Acidithiobacillus and Sulfuricurvum) averaged only 22% and 11% in the H₂-based MBfR and O₂-based MBfR fibers, respectively. Evidence suggests that the undesired Sulfurospirillum species, which reduce S⁰ to sulfide, can be suppressed by increasing sulfate-surface loading and H₂ pressure.

Graphene Oxide-ZnO Nanocomposites for Removal of Aluminum and Copper Ions from Acid Mine Drainage Wastewater

Adsorption technologies are a focus of interest for the removal of pollutants in water treatment systems. These removal methods offer several design, operation and efficiency advantages over other wastewater remediation technologies. Particularly, graphene oxide (GO) has attracted great attention due to its high surface area and its effectiveness in removing heavy metals. In this work, we study the functionalization of GO with zinc oxide nanoparticles (ZnO) to improve the removal capacity of aluminum (Al) and copper (Cu) in acidic waters. Experiments were performed at different pH conditions (with and without pH adjustment). In both cases, decorated GO (GO/ZnO) nanocomposites showed an improvement in the removal capacity compared with non-functionalized GO, even when the pH of zero charge (pH_PZC) was higher for GO/ZnO (5.57) than for GO (3.98). In adsorption experiments without pH adjustment, the maximum removal capacities for Al and Cu were 29.1 mg/g and 45.5 mg/g, respectively. The maximum removal percentages of the studied cations (Al and Cu) were higher than 88%. Further, under more acidic conditions (pH 4), the maximum sorption capacities using GO/ZnO as adsorbent were 19.9 mg/g and 33.5 mg/g for Al and Cu, respectively. Moreover, the removal percentages reach 95.6% for Al and 92.9% for Cu. This shows that decoration with ZnO nanoparticles is a good option for improving the sorption capacity of GO for Cu removal and to a lesser extent for Al, even when the pH was not favorable in terms of electrostatic affinity for cations. These findings contribute to a better understanding of the potential and effectiveness of GO functionalization with ZnO nanoparticles to treat acidic waters contaminated with heavy metals and its applicability for wastewater remediation.

Low-Energy Method for Water-Mineral Recovery from Acid Mine Drainage Based on Membrane Technology: Evaluation of Inorganic Salts as Draw Solutions

In this work, a novel study for acid mine drainage remediation and reutilization by means of a forward osmosis technology is addressed. The proposed process is a potential alternative path, which allows to recover high-quality water and to concentrate metals for its possible reutilization as synthetic minerals. This novel process will help in the mining industry evolving toward more sustainable processes and favors circular economy policies. Four inorganic salts (NaCl, KCl, CaCl₂, and MgCl₂) were evaluated as draw solutions from 1 to 5 M concentrations, in terms of water flux, water recovery, and metal rejection, using a thin-film composite (TFC) membrane. Water flux obtained was in the range of 14-53 L/(m² h). The highest water flux was found for MgCl₂, whereas the lowest correspond to KCl. The metal rejection obtained was greater than 99%. After a discussion and comparison of the results, MgCl₂ was chosen for evaluating long-term assay performance. Scanning electron microscope images of the thin-film composite membrane after long-term assays were taken. The tendency of Mg-Ca and Al-Fe fouling was observed over the membrane surface. The energy consumption was estimated from 4.84-22.3 kWh_e/m³, assuming that osmotically assisted reverse osmosis is used to regenerate the draw solution.

Sustainable resolutions for environmental threat of the acid mine drainage

Acid Mine Drainage (AMD) caused by abandoned mines is an enormous source of negative impact on the environment and the species that inhabit it. The low levels of pH and high concentration of metals and metalloids (copper, gadolinium, lithium, etc.) in mining pits with standing water lead to changing the balance of surrounding organisms and ecosystems. The scale of the issue and the quantity of AMD sites throughout the globe are factors that make AMD a critical environmental threat. Many AMD treatments have been implemented to reduce the negative impact of AMD, with many solutions being very costly and only suited for particular project situations. Policymakers have strong leverage in correcting AMD problems by developing regulations and laws. This study proposes three more sustainable solutions for reducing and eventually eliminating the impact of AMD with less capital investment while also resolving the landfill problem as well. Also, some governmental strategies are suggested for forming collaborative relationships between industry professionals from different perspectives with the goal to resolve the AMD issue through innovative ideas. Implementation of previous strategies and suggested ones, as well as the further involvement of more communities, can enhance the sustainability of life exposed to AMD.

Biological remediation of acid mine drainage: Review of past trends and current outlook

Formation of acid mine drainage (AMD) is a widespread environmental issue that has not subsided throughout decades of continuing research. Highly acidic and highly concentrated metallic streams are characteristics of such streams. Humans, plants and surrounding ecosystems that are in proximity to AMD producing sites face immediate threats. Remediation options include active and passive biological treatments which are markedly different in many aspects. Sulfate reducing bacteria (SRB) remove sulfate and heavy metals to generate non-toxic streams. Passive systems are inexpensive to operate but entail fundamental drawbacks such as large land requirements and prolonged treatment period. Active bioreactors offer greater operational predictability and quicker treatment time but require higher investment costs and wide scale usage is limited by lack of expertise. Recent advancements include the use of renewable raw materials for AMD clean up purposes, which will likely achieve much greener mitigation solutions.

Selection and evaluation of water pretreatment technologies for managed aquifer recharge (MAR) with reclaimed water

Managed aquifer recharge with reclaimed water is a promising strategy for indirect potable reuse. However, residual contaminants in the treated wastewater effluent could potentially have adverse effects on human health. Hence, adequate water pretreatment is required. A multi-criteria approach was used to select and evaluate suitable water pretreatment technologies that can remove these critical contaminants in wastewater effluent for MAR identified in a previous study (Yuan et al., 2017). The treatment efficiency targets were calculated based on the concentrations and the suggested limits of critical contaminants. Treatment efficiency credits were then assigned to each treatment option for the removal of critical contaminants based on literature data. Treatment units that resulted in the highest efficiency credit scores were selected and combined into treatment train options, which were evaluated in terms of treatability, cost, and sustainability. This paper proposes an approach for the selection and evaluation of water treatment options, which will be helpful to guide the future implementation of MAR projects with reclaimed water.

Acid mine drainage treatment by integrated submerged membrane distillation-sorption system

Acid mine drainage (AMD), an acidic effluent characterized by high concentrations of sulfate and heavy metals, is an environmental and economic concern. The performance of an integrated submerged direct contact membrane distillation (DCMD) - zeolite sorption system for AMD treatment was evaluated. The results showed that modified (heat treated) zeolite achieved 26-30% higher removal of heavy metals compared to natural untreated zeolite. Heavy metal sorption by heat treated zeolite followed the order of Fe > Al > Zn > Cu > Ni and the data fitted well to Langmuir and pseudo second order kinetics model. Slight pH adjustment from 2 to 4 significantly increased Fe and Al removal rate (close to 100%) due to a combination of sorption and partial precipitation. An integrated system of submerged DCMD with zeolite for AMD treatment enabled to achieve 50% water recovery in 30 h. The integrated system provided a favourable condition for zeolite to be used in powder form with full contact time. Likewise, heavy metal removal from AMD by zeolite, specifically Fe and Al, mitigated membrane fouling on the surface of the hollow fiber submerged membrane. The integrated system produced high quality fresh water while concentrating sulfuric acid and valuable heavy metals (Cu, Zn and Ni).

How to tackle the stringent sulfate removal requirements in mine water treatment-A review of potential methods

Sulfate (SO₄^2-) is a ubiquitous anion in natural waters. It is not considered toxic, but it may be detrimental to freshwater species at elevated concentrations. Mining activities are one significant source of anthropogenic sulfate into natural waters, mainly due to the exposure of sulfide mineral ores to weathering. There are several strategies for mitigating sulfate release, starting from preventing sulfate formation in the first place and ending at several end-of-pipe treatment options. Currently, the most widely used sulfate-removal process is precipitation as gypsum (CaSO₄·2H₂O). However, the lowest reachable concentration is theoretically 1500 mg L^-1 SO₄^2- due to gypsum's solubility. At the same time, several mines worldwide have significantly more stringent sulfate discharge limits. The purpose of this review is to examine the process options to reach low sulfate levels (< 1500 mg L^-1) in mine effluents. Examples of such processes include alternative chemical precipitation methods, membrane technology, biological treatment, ion exchange, and adsorption. In addition, aqueous chemistry and current effluent standards concerning sulfate together with concentrate treatment and sulfur recovery are discussed.