Catalytic potential of selected metal ions for bioleaching, and potential techno-economic and environmental issues: A critical review

Siderite and vivianite as energy sources for the extreme acidophilic bacterium Acidithiobacillus ferrooxidans in the context of mars habitability

Past and present habitability of Mars have been intensely studied in the context of the search for signals of life. Despite the harsh conditions observed today on the planet, some ancient Mars environments could have harbored specific characteristics able to mitigate several challenges for the development of microbial life. In such environments, Fe2+ minerals like siderite (already identified on Mars), and vivianite (proposed, but not confirmed) could sustain a chemolithoautotrophic community. In this study, we investigate the ability of the acidophilic iron-oxidizing chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans to use these minerals as its sole energy source. A. ferrooxidans was grown in media containing siderite or vivianite under different conditions and compared to abiotic controls. Our experiments demonstrated that this microorganism was able to grow, obtaining its energy from the oxidation of Fe2+ that came from the solubilization of these minerals under low pH. Additionally, in sealed flasks without CO2, A. ferrooxidans was able to fix carbon directly from the carbonate ion released from siderite for biomass production, indicating that it could be able to colonize subsurface environments with little or no contact with an atmosphere. These previously unexplored abilities broaden our knowledge on the variety of minerals able to sustain life. In the context of astrobiology, this expands the list of geomicrobiological processes that should be taken into account when considering the habitability of environments beyond Earth, and opens for investigation the possible biological traces left on these substrates as biosignatures.

Insights into metal tolerance and resistance mechanisms in Trichoderma asperellum unveiled by de novo transcriptome analysis during bioleaching

This study investigates the genetic responses of the fungus Trichoderma asperellum (T. asperellum) during bioleaching of ore and tailing samples, comparing one-step, two-step, and spent media bioleaching processes. HPLC analysis quantified oxalic acid, citric acid, and propionic acids, with oxalic acid identified as the primary organic acid involved in metal bioleaching. Metal analysis revealed differences in recovery between ore and tailing samples and among bioleaching processes. The two-step bioleaching process yielded the highest zinc (>54%) and nickel (>60%) recovery in tailings and ore, respectively. Nickel's efficient recovery in ore bioleaching was attributed to the presence of manganese, while its precipitation as nickel oxalate in tailings hindered recovery. Additional metals such as Co, Mn, Mg, Cu, and As were also successfully recovered. Transcriptomic analyses showed significant upregulation of genes associated with biological processes and cellular components, particularly those related to cell membrane structure and function, indicating T. asperellum's adaptation to environmental stresses during metal bioleaching. These findings enhance our understanding of the diverse mechanisms influencing metal recovery rates in bioleaching processes.

Current overview and future perspective in fungal biorecovery of metals from secondary sources

Microorganisms are intimately involved in many biogeochemical processes that underpin the transformation of metals and cycling of related substances, such as metalloids and radionuclides. Many processes determine the mobility and bioavailability of metals, thereby influencing their transfer to the environment and living organisms. These processes are closely related to global phenomena such as soil formation and bioweathering. In addition to environmental significance, microbial metal transformations play an essential role in both in situ and ex situ bioremediation processes for solid and liquid wastes. The solubilization of heavy metals from industrial waste and soil is commonly used in bioremediation. Moreover, immobilization processes are applicable to bioremediation of metals and radionuclides from aqueous solutions. This review provides an overview of critical metal extraction and recovery from secondary sources, applied microorganisms and methods, metal-microbe interactions, as well as a detailed description of known metal recovery mechanisms.

Advances in bioleaching of waste lithium batteries under metal ion stress

In modern societies, the accumulation of vast amounts of waste Li-ion batteries (WLIBs) is a grave concern. Bioleaching has great potential for the economic recovery of valuable metals from various electronic wastes. It has been successfully applied in mining on commercial scales. Bioleaching of WLIBs can not only recover valuable metals but also prevent environmental pollution. Many acidophilic microorganisms (APM) have been used in bioleaching of natural ores and urban mines. However, the activities of the growth and metabolism of APM are seriously inhibited by the high concentrations of heavy metal ions released by the bio-solubilization process, which slows down bioleaching over time. Only when the response mechanism of APM to harsh conditions is well understood, effective strategies to address this critical operational hurdle can be obtained. In this review, a multi-scale approach is used to summarize studies on the characteristics of bioleaching processes under metal ion stress. The response mechanisms of bacteria, including the mRNA expression levels of intracellular genes related to heavy metal ion resistance, are also reviewed. Alleviation of metal ion stress via addition of chemicals, such as spermine and glutathione is discussed. Monitoring using electrochemical characteristics of APM biofilms under metal ion stress is explored. In conclusion, effective engineering strategies can be proposed based on a deep understanding of the response mechanisms of APM to metal ion stress, which have been used to improve bioleaching efficiency effectively in lab tests. It is very important to engineer new bioleaching strains with high resistance to metal ions using gene editing and synthetic biotechnology in the near future.

Sulfur enhancement effects for uranium bioleaching in column reactors from a refractory uranium ore

The feasibility of sulfur enhancement for uranium bioleaching in column reactors was assessed with a designed mixed Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferriphilum from a refractory uranium ore. The uranium extraction reached 86.2% with the sulfur enhancement (1 g/kg) in 77 days leaching process, increased by 12.6% vs. the control without sulfur addition. The kinetic analysis showed that uranium bioleaching with sulfur enhancement in columns followed an internal diffusion through the product layer-controlled model. Ore residue characteristics indicated that sulfur enhancement could strengthen the porosity of passivation layer, improving the ore permeability. Notably, bacterial community analysis showed that sulfur enhancement at 1 g/kg could make the iron-oxidizing and sulfur-oxidizing bacteria on the ore surface maintain a good balance (approx. 1:1), and thus decomposing ore more effectively. Lastly, a possible mechanism model for uranium bioleaching with sulfur enhancement was proposed.

Alkaliphiles for comprehensive utilization of red mud (bauxite residue)-an alkaline waste from the alumina refinery

The mining industry has powered the human endeavor to make life more innovative, flexible, and comfortable. However, it has also led to concerns due to the increasing amount of mining and associated industrial waste. Special attention is highly desired for its proper management and safe disposal in the environment. The problem has only augmented with the increase in the mining costs because of the investments needed for ecological remediation after the mining operation. It is pertinent that the targeted technologies need to be developed to utilize mining and associated industrial waste as a secondary resource to ensure sustainable mining operations. Every perceived waste is a valuable resource that is needed to be utilized to create additional value. In this review, the case of alkaline bauxite residue (red mud)-alumina refinery waste has been discussed at length. The highlight of the proposed work is to understand the importance of alkaliphile-assisted biomining-a sustainable alternative to conventional metal recovery processes. Along with the recovery of metals, pH reduction of red mud is possible through biomining, which ultimately paves the way for its complete utilization. The unique adaptation strategies of alkaliphiles make them more suitable for biomining of red mud through bioleaching, biosorption, and bioaccumulation, which have been discussed here. Furthermore, we have focused on the potential of the indigenous microflora of red mud for metal recovery in addition to its neutralization. The study of indigenous alkaliphiles from red mud, including its isolation and propagation, is crucial for the industrial-scale application of alkaliphile-based technology and has been emphasized.

Will Vanadium-Based Electrode Materials Become the Future Choice for Metal-Ion Batteries?

Metal-ion batteries have emerged as promising candidates for energy storage system due to their unlimited resources and competitive price/performance ratio. Vanadium-based compounds have diverse oxidation states rendering various open-frameworks for ions storage. To date, some vanadium-based polyanionic compounds have shown great potential as high-performance electrode materials. However, there has been a growing concern regarding the cost and environmental risk of vanadium. In this Review, all links in the industry chain of vanadium-based electrodes were comprehensively summarized, starting with an analysis of the resources, applications, and price fluctuation of vanadium. The manufacturing processes of the vanadium extraction and recovery technologies were discussed. Moreover, the commercial potentials of some typical electrode materials were critically appraised. Finally, the environmental impact and sustainability of the industry chain were evaluated. This critical Review will provide a clear vision of the prospects and challenges of developing vanadium-based electrode materials.

Bioleaching of rare earths elements from phosphate rock using Acidothiobacillus ferrooxidans

Phosphate rock containing rare earth elements (REEs) is considered one of the most promising potential secondary sources of REEs, as evidenced by large tonnages of phosphate rock mined annually. The bioleaching of REEs from phosphate rock using A. ferrooxidans was done for the first time in this study, and it was found to be greater than abiotic leaching and was more environmentally friendly. The result showed that the total leaching rate of REEs in phosphate rock was 28.46% under the condition of 1% pulp concentration and pH=2, and the leaching rates of four key rare earths, Y, La, Ce, and Nd, were 35.7%, 37.03%, 27.92%, and 32.53%, respectively. The bioleaching process was found to be accomplished by bacterial contact and Fe²⁺ oxidation. The blank control group which contained Fe²⁺ was able to leach some of the rare earths, indicating that the oxidation of Fe²⁺ may affect the leaching of rare earths. X-Ray Diffraction (XRD)analysis showed that the minerals were significantly altered and the intensity of the diffraction peaks of dolomite and apatite decreased significantly after microbial action compared to the blank control, and it was observed that bacteria adhere to the mineral surface and the minerals become smooth and angular after bioleaching by Scanning electron microscope (SEM), indicating that bacteria have a further effect on the rock based on Fe²⁺ oxidation.Finally.Fourier Transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission matrix (3DEEM) fluorescence spectra analysis showed that extracellular polymeric substances (EPS) participate in the bioleaching process.

Accessing Metals from Low-Grade Ores and the Environmental Impact Considerations: A Review of the Perspectives of Conventional versus Bioleaching Strategies

Mining has advanced primarily through the use of two strategies: pyrometallurgy and hydrometallurgy. Both have been used successfully to extract valuable metals from ore deposits. These strategies, without a doubt, harm the environment. Furthermore, due to decades of excessive mining, there has been a global decline in high-grade ores. This has resulted in a decrease in valuable metal supply, which has prompted a reconsideration of these traditional strategies, as the industry faces the current challenge of accessing the highly sought-after valuable metals from low-grade ores. This review outlines these challenges in detail, provides insights into metal recovery issues, and describes technological advances being made to address the issues associated with dealing with low-grade metals. It also discusses the pragmatic paradigm shift that necessitates the use of biotechnological solutions provided by bioleaching, particularly its environmental friendliness. However, it goes on to criticize the shortcomings of bioleaching while highlighting the potential solutions provided by a bespoke approach that integrates research applications from omics technologies and their applications in the adaptation of bioleaching microorganisms and their interaction with the harsh environments associated with metal ore degradation.

Growth in ever-increasing acidity condition enhanced the adaptation and bioleaching ability of Leptospirillum ferriphilum

Low pH eliminated the jarosite accumulation and improved the interfacial reaction rate during the bioleaching process. However, high acidity tends to make environments less hospitable, even for organisms that live in extreme places, so a great challenge existed for bioleaching at low pH conditions. This study demonstrated that the adaption and bioleaching ability of Leptospirillum ferriphilum could be improved after the long-term adaptive evolution of the community under acidity conditions. It was found that the acidity-adapted strain showed robust ferrous iron oxidation activity in wider pH, high concentration of ferrous iron, and lower temperature. Although the enhancement for heavy metal tolerance was limited, the resistance for MgSO₄, Na₂SO₄, and organic matter was stimulative. More importantly, both pyrite and printed circuit board bioleaching revealed the higher bioleaching ability of the acid-resistant strain. These adaptation and bioleaching details provided an available approach for the improvement of bioleaching techniques.

Copper and Zinc Recovery from Sulfide Concentrate by Novel Artificial Microbial Community

Exploring efficient methods to enhance leaching efficiency is critical for bioleaching technology to deal with sulfide concentrate. In our study, a novel artificial microbial community was established to augment the bioleaching efficiency and recovery of copper (Cu) and zinc (Zn). The optimum parameters in bioleaching experiments were explored according to compare a series of conditions from gradient experiments: the pH value was 1.2, temperature was 45 °C, and rotation speed was 160 r/min, which were different with pure microorganism growth conditions. Under optimal conditions, the result of recovery for Cu and Zn indicated that the average leaching rate reached to 80% and 100% respectively, which almost increased 1.8 times and 1.2 times more than control (aseptic condition) group. Therefore, this method of Cu and Zn recovery using a new-type artificial microbial community is expected to be an environmentally-friendly and efficient bioleaching technology solution, which has the potential of large-field engineering application in the future.

Effect of Temperature on Biobeneficiation of Bulk Copper-Nickel Concentrate with Thermoacidophilic Microbial Communities

Bioleaching of the bulk copper–nickel sulfide concentrate was proposed as a method to remove nickel from it and to obtain a concentrate containing copper as chalcopyrite. This approach is based on the different refractoriness of sulfide minerals in ferric sulfate solutions and oxidation by acidophilic microorganisms. The bulk concentrate contained 10.8% copper in the form of chalcopyrite (CuFeS2) and 7.2% nickel that occurred in pentlandite ((Ni,Fe)9S8) and violarite (FeNi2S4). Three microbial communities grown at 35, 40, and 50 °C were used for bioleaching. The microbial community at 40 °C was the most diverse in the genus and species composition. At all temperatures of the process, the key roles in bioleaching belonged to mixotrophic and heterotrophic acidophiles. The highest levels of nickel leaching of 97.2 and 96.3% were observed in the case of communities growing at 40 and 50 °C, respectively. At the same time, the bioleach residue, which could be characterized as a marketable high-grade copper (chalcopyrite) concentrate, was obtained only at 40 °C. This solid contained 15.6% copper and 0.54% nickel. Thus, the biobeneficiation of bulk sulfide concentrates can be a promising field of biohydrometallurgy.

A review on the recycling of spent lithium-ion batteries (LIBs) by the bioleaching approach

This review discusses the latest trend in recovering valuable metals from spent lithium-ion batteries (LIBs) to meet the technological world's critical metal demands. Spent LIBs are a secondary source of valuable metals such as Li (5%-7%), Ni (5%-10%), Co (5%-25%), Mn (5-11%), and non-metal graphite. Recycling is essential for the battery industry to extract valuable critical metals from secondary sources to develop new and novel high-tech LIBs for various applications such as eco-friendly technologies, renewable energy, emission-free electric vehicles, and energy-saving lightings. LIB waste is currently undergoing high-temperature pyrometallurgical or hydrometallurgical processes to recover valuable metals, and these processes have proven to be successful and feasible. These methods, however, are not preferable due to the difficulties in controlling the process, secondary waste produced, high operational cost, and high risk of scaling up. Biotechnological approaches can be promising alternatives to pyrometallurgical and hydrometallurgical technologies in metal recovery from LIB waste. Microbiological metal dissolution or bioleaching has gained popularity for metal extraction from ores, concentrates, and recycled or residual materials in recent years. This technology is eco-friendly, safe to handle, and reduces operating costs and energy demands. The pre-treatment process (material preparation), microorganisms used in the bioleaching of LIBs, factors influencing the bioleaching process, methods of enhancing the leaching efficiency, regeneration of electrode materials, and future aspects have been discussed in detail.

Bioleaching for environmental remediation of toxic metals and metalloids: A review on soils, sediments, and mine tailings

Owing to industrial evolution, a huge mass of toxic metals, including Co, Cu, Cr, Mn, Ni, Pb, and Zn, and metalloids, such as As and Sb, has inevitably been released into the natural environment and accumulated in soils or sediments. Along with modern industrialization, many mineral mines have been explored and exploited to provide materials for industries. Mining industries also generate a vast amount of waste, such as mine tailings, which contain a high concentration of toxic metals and metalloids. Due to the low economic status, a majority of mine tailings are simply disposed into the surrounding environments, without any treatment. The mobilization and migration of toxic metals and metalloids from soils, sediments, and mining wastes to water systems via natural weathering processes put both the ecological system and human health at high risk. Considering both economic and environmental aspects, bioleaching is a preferable option for removing the toxic metals and metalloids because of its low cost and environmental safety. This chapter reviews the recent approaches of bioleaching for removing toxic metals and metalloids from soils, sediments, and mining wastes. The comparison between bioleaching and chemical leaching of various waste sources is also discussed in terms of efficiency and environmental safety. Additionally, the advanced perspectives of bioleaching for environmental remediation with consideration of other influencing factors are reviewed for future studies and applications.

Effects of dissolved oxygen on the sludge dewaterability and extracellular polymeric substances distribution by bioleaching

Bioleaching is a biological conditioning technology for sludge, which not only improves sludge dewatering performance but also removes heavy metals from sludge. As the bioleaching process is a comprehensive biological and chemical process, it is necessary to explore the effects of dissolved oxygen (DO) concentrations on bioleaching efficiency. Three bioleaching experiments with different DO concentrations (T1: 0.8-3.1 mg/L, T2: 3.1-5.5 mg/L, T3: 5.5-7.5 mg/L) were conducted for five days. The sludge dewatering efficiency was evaluated using capillary suction time (CST) and specific resistance to filtration (SRF). The relationship between sludge dewaterability and extracellular polymeric substance (EPS) fraction distribution was investigated. In the treatment with the highest DO concentration, the minimum values of SRF and CST were 4.31 × 10¹¹ m/kg and 13.5 s, which occurred earlier than the treatment with the lower DO concentrations by approximately 24-48 h. A significant decrease (83.4-93.2%) in tightly bound EPS (TB-EPS) protein (PN) was observed in all treatments, while a positive correlation (r = 0.924, P < 0.01) was observed between SRF and PN content in TB-EPS. A relatively higher abundance of Acidithiobacillus was found with the increase in DO concentration. Additionally, other genera including Metallibacterium, Alicyclobacillus, Acidibacter, Acidocella, and Luteococcus also played important roles in EPS biodegradation. These results revealed that increasing the DO concentration could improve sludge dewatering performance and heavy metal removal by enhancing bioleaching microbial activity, the degradation of PN in TB-EPS, and sludge floc fragmentation, but only if sufficient energy sources were provided.

Lithium bioleaching: An emerging approach for the recovery of Li from spent lithium ion batteries

The rapidly growing demand for lithium has resulted in a sharp increase in its price. This is due to the ubiquitous use of lithium-ion batteries (LIBs) in large-scale energy and transportation sectors as well as portable devices. Recycling of the LIBs for being the supply of critical metals hence becomes environmentally and economically viable. The presently used approaches for the recovery of spent LIBs like pyrometallurgical process can effectively recover nickel, cobalt, and copper, while lithium is usually lost in slag. Bioleaching process as an alternative method of extraction and recovery of valuable metals from the primary and secondary resources has been attracting a large pool of attraction. This method can provide higher recovery yield even for low concentration of metals which makes it viable among conventional methods. The bioleaching process can work with lower operating cost and consumed water and energy along with a simple condition, which produces less hazardous by-products ultimately. Here, we comprehensively review the biological and chemical mechanisms of the bioleaching process with a conclusive discussion to help how to extend the use of bioleaching for lithium extraction and recovery from the spent LIBs with a focus on recovery yields improvement. We elaborate on the three main types of the reported bioleaching with considering effective parameters including temperature, initial pH, pulp density, aeration, and medium and cell nutrients to sustain microorganism activity. Finally, practical challenges and future opportunities of lithium are discussed to inspire future research trends and pilot studies to realize the full potential of lithium recovery using sustainable bioleaching processes to extend a clean energy future.

Removal behavior and chemical speciation distributions of heavy metals in sewage sludge during bioleaching and combined bioleaching/Fenton-like processes

The removal and chemical speciation changes of heavy metals in the sewage sludge during the single bioleaching and combined bioleaching/Fenton-like processes were compared in this study. The improvement in the dewaterability of the treated sludge was also investigated. The single bioleaching led to a removal of Zn, Cu, Cd, Cr, Mn, Ni, As and Pb of 67.28%, 50.78%, 64.86%, 6.32%, 56.15%, 49.83%, 20.78% and 10.52% in 10 days, respectively. The chemical speciation analysis showed that the solubilization of heavy metals in mobile forms (exchangeable/acid soluble and reducible forms) and oxidizable form was the main reason for their removal. Subsequent Fenton-like treatment was carried out at different bioleaching stages when the bioleached sludge dropped to certain pH values (4.5, 4.0 and 3.0), by adding H₂O₂ at different dosages. The highest removal ratio of Zn, Cu, Cd, Cr, Mn and Ni could reach 75.53%, 52.17%, 71.91%, 11.63%, 66.29% and 65.19% after combined bioleaching/Fenton-like process, respectively, with appropriate pH and H₂O₂ dosages in less than 6 days. The solubilization efficiencies of these heavy metals in mobile forms were further improved by Fenton-like treatment. The removal efficiencies of As and Pb decreased due to their transformation into insoluble forms (mostly residual fraction) after Fenton treatment. The capillary suction times (CST) of the raw sludge (98.7 s) decreased by 79.43% after bioleaching and 87.44% after combined process, respectively.

Bioleaching and Electrochemical Behavior of Chalcopyrite by a Mixed Culture at Low Temperature

Low-temperature biohydrometallurgy is implicated in metal recovery in alpine mining areas, but bioleaching using microbial consortia at temperatures <10°C was scarcely discussed. To this end, a mixed culture was used for chalcopyrite bioleaching at 6°C. The mixed culture resulted in a higher copper leaching rate than the pure culture of Acidithiobacillus ferrivorans strain YL15. High-throughput sequencing technology showed that Acidithiobacillus spp. and Sulfobacillus spp. were the mixed culture's major lineages. Cyclic voltammograms, potentiodynamic polarization and electrochemical impedance spectroscopy unveiled that the mixed culture enhanced the dissolution reactions, decreased the corrosion potential and increased the corrosion current, and lowered the charge transfer resistance and passivation layer impedance of the chalcopyrite electrode compared with the pure culture. This study revealed the mechanisms via which the mixed culture promoted the chalcopyrite bioleaching.

Mineralogical phase transformation of Fe containing sphalerite at acidic environments in the presence of Cu2

Dissolution of the exposed sphalerite (marmatite) in abandoned mining sites and tailings may exacerbate acid and metalliferous drainage (AMD) hazards. Cupric ions are inevitable ions in AMD systems but its action mechanism on the dissolution of sphalerite is still unclear. In this work, the possible phase transition from sphalerite to chalcopyrite is firstly discovered in acidic cupric ions solution according to the results of Raman and (synchrotron radiation-based) X-ray (micro-) diffractometer spectra, which should be an important reason that mediates the dissolution of sphalerite. Results of DFT calculations reveal the underlying mechanism that Cu²⁺ can selectively replace zinc in marmatite lattices and further diffuse into the matrix. Additionally, a strong correlation between the cupric ion consumption with the pH value variation is discussed and the effects of the formed new phase on the dissolution kinetics of marmatite were researched. According to this work, the action mechanism of cupric ions on sphalerite dissolution in acidic environments is furtherly clarified.

Ultrasound-assisted leaching of spent lithium ion batteries by natural organic acids and H2O2

Ultrasound-assisted bioacid leaching was examined for the extraction of valuable metals from spent lithium ion batteries (LIBs). In this work, organic acids in lemon juice were used as the leaching agent together with H₂O₂. Three effective factors, namely solid/liquid (S/L) ratio, lemon juice percentage, and H₂O₂ volume percentage, were optimized using Response Surface Methodology (RSM). The optimal conditions were found to be 0.98% (w/v) S/L ratio, 57.8% (v/v) lemon juice and 8.07% (v/v) H₂O₂ in the leaching liquor, achieving recovery of 100% Li, 96% Co and 96% Ni. Furthermore, the individual effects of ultrasound, H₂O₂ and lemon juice on metal recovery were studied and the results showed that without H₂O₂ or lemon juice, the metal recovery rates decreased greatly while the absence of ultrasound reduced recovery rates to a much smaller extent, indicating that both H₂O₂ and lemon juice were essential in the leaching process. The effect of time on the metals recoveries was examined and results showed that Li and Co recovery reached 100% with the leaching time of 35 min. The modified shrinking core modeling results suggested that chemical reaction was the rate controlling step.

Catalytic effect of silver on copper release from chalcopyrite mediated by Acidithiobacillus ferrooxidans

Although silver ion in the solution is an important factor affecting the biodissolution of chalcopyrite, the effect of silver ion on the release of copper ion from chalcopyrite to the environment has not been explored until now. In order to fill this knowledge gap, the effect of silver ion on copper release from chalcopyrite in the presence of Acidithiobacillus ferrooxidans was investigated. The results indicate that silver ion significantly enhanced chalcopyrite biodissolution, thereby releasing more copper ion. In turn, this indicates that the release of copper ion from chalcopyrite to the environment was increased under these conditions. Biodissolution results, bacterial adsorption experiments, elemental composition analysis, and electrochemical analysis reveal that the enhancement of silver ion on copper ion release from chalcopyrite was mainly attributed to the improvement of electrochemical activity of chalcopyrite and the inhibition of the formation of passivation layer (S_n^2-/S⁰) on the chalcopyrite surface. This study provides a better understanding of the effect of silver ion on the release of copper ion from chalcopyrite to the environment. In the future, the influence of silver ion on chalcopyrite biodissolution should be considered in the evaluation of copper ion pollution to ensure reliability.

Tracing sources of natural organic matter, trihalomethanes and metals in groundwater from a karst region

Groundwater offers an important source for drinking water around the world; however, groundwater quality is under increasing pressure and is particularly vulnerable in karst areas. Total organic carbon (TOC) is significantly related to groundwater quality and when not removed by water treatment processes can give rise to the formation of disinfection by-products trihalomethanes (THMs) above the level of compliance. This study investigated the source of organic matter giving rise to the THM exceedances in a groundwater supply in a karst area. Results highlighted that source water for this groundwater supply was prone to surface water infiltration linked to rainfall events; was not accurately captured in the zone of contribution (ZoC); had inadequate treatment of natural organic matter (NOM) and suffered THM exceedances in 45% of sampling events. THMs were mostly represented by chloroform and caused by terrestrial delivered reprocessed organic matter. This work will support water managers tasked with decision-making.

Role of Ag+ in the Bioleaching of Arsenopyrite by Acidithiobacillus ferrooxidans

Arsenopyrite (FeAsS) is often associated with gold, but pre-treatment is necessary prior to gold leaching, mainly due to the gold encapsulation in the matrix of FeAsS. Bio-oxidation is attractive and promising, largely due to its simplicity, low cost and environmental friendliness. A critical problem that still impedes the large-scale applications of this green technology is its slow leaching kinetics. Some metal ions such as Ag+ have previously been found to expedite the bioleaching process. In this paper, the role of Ag+ in the arsenopyrite bioleaching by Acidithiobacillus ferrooxidans was investigated in detail by bioleaching experiments and a series of analyses including thermodynamics, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Experimental results suggested that addition of 5 mg/L Ag+ to the leaching system could significantly improve the final As leaching efficiency from 30.4% to 47.8% and shorten the bioleaching period from 19 days to 15 days. Thermodynamic analysis indicates that Ag+ destabilises As2S2, As2S3 and S0 via forming Ag2S, which is confirmed by the XRD analysis on the phase transformation during bioleaching. SEM and XPS analyses further showed that Ag+ removed the passivating film consisting mainly of As2S2, As2S3 and S0 because Ag2S formed on the arsenopyrite surface from the start bioleaching of 36 h. In the presence of Fe3+, Ag2S could easily be dissolved to Ag+ again, likely leading to the establishment of the Ag+/Ag2S cycle. The bacteria utilised the two synergistic cycles of Fe3+/Fe2+ and Ag+/Ag2S to catalyse the bioleaching of arsenopyrite.

Recent advances in the recovery of metals from waste through biological processes

Wastes containing critical metals are generated in various fields, such as energy and computer manufacturing. Metal-bearing wastes are considered as secondary sources of critical metals. The conventional physicochemical methods of metals recovery are energy-intensive and cause further pollution. Low-cost and eco-friendly technologies including biosorbents, bioelectrochemical systems (BESs), bioleaching, and biomineralization, have become alternatives in the recovery of critical metals. However, a relatively low recovery rate and selectivity severely hinder their large-scale applications. Researchers have expanded their focus to exploit novel strain resources and strategies to improve the biorecovery efficiency. The mechanisms and potential applicability of modified biological techniques for improving the recovery of critical metals need more attention. Hence, this review summarize and compare the strategies that have been developed for critical metals recovery, and provides useful insights for energy-efficient recovery of critical metals in future industrial applications.

Ultrasound-assisted leaching of vanadium from fly ash using lemon juice organic acids

In this work, vanadium (V) was selectively extracted from fuel-oil fly ash using a leaching process utilizing organic acids extracted from lemon juice with assistance from ultrasound and H2O2. Response Surface Methodology (RSM) was used to optimize the main operating factors. The V recovery was 88.7% at the optimal conditions: 27.9% (v/v) lemon juice, 10% (v/v) hydrogen peroxide (H2O2), solid/liquid (S/L) ratio 0.01% (w/v), ultrasound power 159 W at 20 kHz in 2 h, and initial temperature of 35 °C. The effect of time on the V recovery was examined. The maximum recovery was 100% after 3 h. Furthermore, the individual effects of ultrasound and H2O2 on V recovery were studied, and the results showed that without H2O2 and ultrasound, the V recovery decreased greatly, indicating that both factors were essential in the leaching process. According to the modified shrinking core model, test results indicated that mass diffusion was the controlling step of the overall reaction kinetics. The activation energy of the leaching reaction in the temperature range 25 to 65 °C was found to be 17.1 kJ mol-1.

Combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans

Although jarosite and visible light are important factors for the formation of acid mine drainage (AMD), the effects of combined jarosite and visible light on chalcopyrite biodissolution have not been explored until now. In order to fill this knowledge gap, the combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans were investigated. The results indicated that jarosite and visible light could significantly accelerate chalcopyrite biodissolution, thus releasing more copper ions, iron ions and producing more acid. This in turn suggests enhanced generation of AMD under these conditions. Biodissolution results, mineral surface morphology, mineralogical phase and elemental composition analyses revealed that the promotion of chalcopyrite dissolution by additional jarosite and visible light was mainly attributed to the acceleration of ferric iron/ferrous iron cycling and the inhibition of the formation of a passivation layer (jarosite and S_n^2-/S⁰) on the surface of chalcopyrite. This study provides a better understanding of the effects of jarosite and visible light on chalcopyrite biodissolution. In the future, the influences of jarosite and visible light on chalcopyrite dissolution should be considered in AMD evaluation to ensure reliability.

Prospective (Bio)leaching of Historical Copper Slags as an Alternative to Their Disposal

The aim of this study was to evaluate the feasibility of (bio)hydrometallurgical methods for metal extraction from historical copper slags. Two types of slags (amorphous slag—AS, and crystalline slag—CS) were subjected to 24 to 48 h of leaching with: (i) Sulfuric acid at 0.1, 0.5, and 1 M concentrations at 1%, 5%, and 10% pulp densities (PDs); and (ii) normality equivalent (2 N) acids (sulfuric, hydrochloric, nitric, citric, and oxalic) at pulp densities ranging from 1% to 2%. Bioleaching experiments were performed within 21 days with Acidithiobacillus thiooxidans accompanied by an abiotic control (sterile growth medium). The results demonstrated that the most efficient treatment for amorphous and crystalline slag was bioleaching at 1% PD over 21 days, which led to extraction of Cu at rates of 98.7% and 52.1% for AS and CS, respectively. Among the chemical agents, hydrochloric acid was the most efficient and enabled 30.5% of Cu to be extracted from CS (1% PD, 48 h) and 98.8% of Cu to be extracted from AS (1% PD, 24 h). Slag residues after leaching were characterized by strong alteration features demonstrated by the complete dissolution of fayalite in the case of CS and the transformation of AS to amorphous silica and secondary gypsum. Based on this study, we conclude that amorphous slag is a more suitable candidate for potential metal recovery because of its generally high susceptibility to leaching and due to the generation of residue significantly depleted in metals as the end product. The inventory of economically relevant metals showed that 1 ton of historical copper slag contains metals valued at $47 and $135 for crystalline and amorphous slag, respectively, suggesting that secondary processing of such materials can potentially be both economically and environmentally viable.

Bacterial-mediated recovery of copper from low-grade copper sulphide using acid-processed rice straw

Bacteria community and copper recovery in presence of acid-processed rice straw (ARW) were explored during low-grade copper sulphide bioleaching. The results indicated a strongly promoting response of appropriate-quality ARW with improved bacteria concentration and enhanced copper recovery. The highest bacteria concentration reached 9.54 × 10⁷ cells·mL^-1 with an increase by 69.15%. And a maximum of 95.32% copper leaching rate with a relatively low Fe³⁺ concentration (329.00 mg·L^-1) was obtained in presence of 1.0 g powdered ARW compared to only 83.40% in its absence. That is due to less development of passivation layer formed by Fe³⁺ hydrolysis, which is contributed by reducing ARW. 16S rDNA analysis illustrated the dominant leaching bacteria (Acidithiobacillus ferrooxidans) was influenced significantly, whose proportion reached 40.38% to the total bacteria when the ARW was added compared to 15.92% in its absence. And Stenotrophomonas accounted for the highest proportion of the bacteria community throughout bioleaching process.

Enhancing microbial community performance on acid resistance by modified adaptive laboratory evolution

A new strategy of three-step adaptive laboratory evolution (ALE) was developed to enhance the bioleaching performance of moderately thermophilic consortia. Through consortium construction, directed evolution and chemostat selection, an improved consortium (ALEend) that composed of Leptospirillum ferriphilum (80.32%), Sulfobacillus thermosulfidooxidans (15.82%) and Ferroplasma thermophilum (3.86%) was obtained, showing ferrous iron oxidation rate of 500 mgL^-1h^-1 and biomass production of 2.0 × 10⁸ cells/mL at pH 0.75. During batch culturing, the ALEend consortium exhibited stable ferrous iron oxidation in wider conditions. PCA indicated that the communities were similar under fluctuating culture conditions, which demonstrated the stable community structure and the reinforced synergistic interactions resulting in the enhanced community performance. Pyrite bioleaching conducted at pH 1.5 and 0.75 revealed that the ALEend consortium extracted 26% and 55% more total iron relative to the original consortium. These findings indicated that the modified ALE may be a promising strategy for microbial community modification to enhance bioleaching.

Effect of particle size on uranium bioleaching in column reactors from a low-grade uranium ore

This study evaluated the effectiveness of ore particle size on column bioleaching from low-grade uranium ore using an indigenous Acidithiobacillus ferrooxidans, isolated from local uranium ore. The uranium content was 0.033% by weight and ore particle size was crushed to <50 mm, <30 mm, and <15 mm. The additive content of sulfuric acid 5 g/L, Fe³⁺ dosage of 5.0 g/L, spray strength of 2.57 L/(h·m²) and temperature of 25 °C were controlled. After 150 days of leaching, acid consumption amounted to 2.73 g H₂SO₄ per kg ore, the obtained maximum uranium extraction was 64.85% with the ore particle size of <15 mm. The results showed that a smaller particle size ore had a higher uranium extraction and that an economic uranium extraction can be obtained by correctly controlling the ore granularity.

Potential use of Bacillus genera for metals removal from spent catalysts

The aim of the present study was to isolate microorganisms able to tolerate Ni²⁺ and V⁵⁺ from different sites located close to a mineral mine in Guanajuato, Mexico, and then to evaluate their ability to remove metals contained in a spent catalyst. Seventeen isolates were obtained; among them seven presented a minimum inhibitory concentration (MIC) higher than 200 mg/L of Ni²⁺ and V⁵⁺ each. Nickel and Vanadium removal was evaluated in 9 K liquid medium added with spent catalyst at 16% (s/v) pulp density and incubated at 30 °C, 150 rpm for 7 days. Only three isolates which were coded as PRGSd-MS-2, MNSH2-AH-3, and MNSS-AH-4 showed a significant removal at the end of treatment corresponding in mg kg^-1 (or percentage metal removal) of 138 (32%), 123 (29%), and 101 (24%) for Ni, respectively; and 557 (26%), 737 (34%), and 456 (21%) mg kg^-1 for V, respectively. The same isolates were capable to remove also Al, Fe, As, and Mg at different extent. Cell morphology changes were observed, in comparison to the control system at the end of biological treatment as a higher quantity of spores for MNSH2-AH-3, 2 μm cells in pairs for MNSS-AH-4, also long chain-vegetative cells having inclusions into the cell surface were observed for PRGSd-MS-2. The three isolated microorganisms were identified by sequencing of the 16S gene as Bacillus thuringiensis, Bacillus megaterium, and Bacillus sp, respectively, suggesting its potential use in the treatment of this solid industrial waste.

Enhancing the Leaching of Chalcopyrite Using Acidithiobacillus ferrooxidans under the Induction of Surfactant Triton X-100

Chalcopyrite is the richest copper sulfide mineral in the world, but it is also the most resistant to biohydrometallurgical processing. To promote the bioleaching of chalcopyrite, a nonionic surfactant, t-octyl phenoxy polyethoxy ethanol (Triton X-100), was employed in this paper. Action of Triton X-100 in chalcopyrite leaching using Acidithiobacillus ferrooxidans was explored in shake flasks. Results showed that 30 mg·L−1 of Triton X-100 increased the bioleaching yield of copper by 42.21% compared to the process without additive after 24 days. Under the stress of Triton X-100, the bioleaching efficiency of chalcopyrite slightly dropped at an early stage, but remarkably increased afterwards. XRD and XPS analysis of the leach residues demonstrated that potassium jarosite and elemental sulfur resulted in surface leaching passivation. Surfactant Triton X-100 appeared to induce the oxidation of elemental sulfur by bacteria owing to the increase in the sulfur surface hydrophobicity. These results suggest that Triton X-100 itself has no ability to leach chalcopyrite, but under its induction, the bioleaching of chalcopyrite can be enhanced due to the removal of the passivation layer.

Disentangling effects of temperature on microbial community and copper extraction in column bioleaching of low grade copper sulfide

The lack of knowledge about responses of microbial community to temperature in copper sulfide bioleaching, and subsequent effects on copper extraction hampered understanding of how to improve bioleaching efficiency. This study presents first detailed quantitative data on microbial diversity and dynamics during bioleaching of low grade copper sulfide at different temperatures. The results demonstrate that temperature had significant effects on microbial community and copper extraction. The microbial structures on the ore surfaces were independent of communities in the leachates. Different species dominated the communities at different temperatures and portions of laboratory scale heap column. Moderate thermophiles rather than extreme thermophiles dominated the communities at 65 °C. The height of ore bed was sufficient to affect microbial communities at 30 °C and 65 °C. Sulfur-oxidizers were very important to improve copper extraction. High microbial diversity also were beneficial to enhance copper extraction within a certain temperature range in the final stage.

Intensified bioleaching of chalcopyrite by communities with enriched ferrous or sulfur oxidizers

The chalcopyrite bioleaching by enriched ferrous or sulfur oxidizers was investigated. The bioleaching was also intensified three times by the enriched communities. The results indicated that copper recoveries extracted by the enriched ferrous and sulfur oxidizers (Fe-O and S-O) were 38.87% and 43.13%, compared with that by the original community (35.35%). The positive effects of re-introducing S-enriched community to Fe-O and S-O groups were observed with copper extraction rates up to 41.67% and 46.45%. CCA indicated that the community dynamics intensified by S-enriched community was closer to that of the no re-inoculated one, but the Fe-enriched community drove a great fluctuation. A mechanism model for S-enriched community intensifying chalcopyrite bioleaching was proposed. More sulfur oxidizers in community slowed down jarosite formation and maintained lower ORP, which was propitious to chalcopyrite dissolution. Meanwhile, they accelerated S⁰ decomposition and decreased pH, which promoted acid leaching of chalcopyrite at a low cost.

Application of capillary electrophoresis combined with conductometric and UV detection to monitor meteorite simulant bioleaching by Acidithiobacillus ferrooxidans

The importance of microorganisms and biotechnology in space exploration and future planets colonization has been discussed in the literature. Meteorites are interesting samples to study microbe-mineral interaction focused on space exploration. The chemolithotropic bacterium Acidithiobacillus ferrooxidans has been used as model to understand the iron and sulfur oxidation. In this work, capillary electrophoresis with capacitively coupled contactless conductivity detection and UV detection was used to monitor bacterial growth in a meteorite simulant by measuring the conversion of Fe²⁺ into Fe⁺³ . The effect of Co²⁺ and Ni²⁺ (metals also found in meteorites) on the bacterial growth was also evaluated. The presented method allowed the analyses of all metals in a single run (less than 8 min). The background electrolyte was composted of 10 mmol/L α-hydroxyisobutyric acid/Histidine. For comparison purpose, the samples were also analyzed by UV-Vis spectrophotometry. The Fe²⁺ conversion into Fe³⁺ by A. ferrooxidans was observed up to 36 h with the growth rate constant of 0.19/h and 0.21/h in Tuovinen and Kelly (T&K) and in meteorite simulant media, respectively. The developed method presents favorable prospect to monitor the growth of other chemolithotropic microorganisms for biotechnology applications.

Relationships between galvanic interaction, copper extraction and community dynamics during bioleaching of chalcopyrite by a moderately thermophilic culture

A moderately thermophilic culture was enriched and adapted to bioleach chalcopyrite at high pulp density. In order to further improve copper extraction, effects of galvanic interaction on bioleaching performance and community dynamics were investigated by adding pyrite. Copper extractions were improved by 2.91 and 1.97 times in the initial and the final stages when pyrite was present, respectively. However, it did not benefit chalcopyrite dissolution in the middle stage. Community dynamics analysis showed that succession of the attached cells was significantly different from community dynamics of the planktonic cells. One of planktonic populations always dominated the communities in most cases, while no species had absolutely competitive advantages in the attached communities. In addition, the presence of pyrite had significant effects on planktonic and attached community structures, and could accelerate planktonic community succession.

Advances in bioleaching for recovery of metals and bioremediation of fuel ash and sewage sludge

Bioleaching has been successfully used in commercial metal mining for decades. It uses microbes to biosolubilize metal-containing inorganic compounds such as metal oxides and sulfides. There is a growing interest in using bioleaching for bioremediation of solid wastes by removing heavy metals from ash and sewage sludge. This review presents the state of the art in bioleaching research for recovery of metals and bioremediation of solid wastes. Various process parameters such as reaction time, pH, temperature, mass transfer rate, nutrient requirement, pulp density and particle size are discussed. Selections of more effective microbes are assessed. Pretreatment methods that enhance bioleaching are also discussed. Critical issues in bioreactor scale-up are analyzed. The potential impact of advances in biofilm and microbiome is explained.

Improvement of sewage sludge dewaterability by bioleaching in a continuous plug flow bioreactor: optimization of process parameters

A novel process for sewage sludge bioleaching by mixed Thiobacilli (Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans) using a 12-stage, 180 L working volume continuous plug-flow bioreactor, is presented. The objective of the present study was to assess the impact of some parameters on the sludge dewaterability and to improve the sludge dewaterability by optimization of these parameters. The parameters examined were sludge moisture content, nutrients dosage, aeration rate, and the number of reactors. The order of the influence of these factors on sludge dewaterability was found to be sludge moisture content > nutrients dosage > aeration rate > number of reactors. The optimized conditions were: sludge moisture content, 98.0%, nutrients dosage, 9 g/L, aeration rate, 8 m³/h, and 10 reactors. Confirmation experiments conducted under optimum conditions demonstrate the sludge dewaterability to be remarkably improved. After 2 days of bioleaching, the moisture of bioleached sludge cake was reduced to below 60%.

Responses of microbial community to pH stress in bioleaching of low grade copper sulfide

The microbial diversity and dynamics in the leachates and on the ore surfaces of different depth of the column were analyzed during bioleaching of low grade copper sulfide at different pH, after inoculation with the same inoculum containing mesophiles and moderate thermophiles. The results indicate that low pH was beneficial to enhance copper extraction. The highest copper extraction (86%) was obtained when pH was controlled at 1.0-1.5. The microbial structures on the ore surfaces were independent of community structures in the leachate, even at the top portion of column. Microbial richness and evenness increased with decreasing pH during bioleaching. pH had significant effects on microbial community structure in the leachate and on the mineral surface of different depth of the column. Leptospirillum ferriphilum accounted for the highest proportions of the community at most times when pH was operated during bioleaching, especially at the end of run.

Bioleaching of Gold and Silver from Waste Printed Circuit Boards by Pseudomonas balearica SAE1 Isolated from an e-Waste Recycling Facility

Indigenous bacterial strain Pseudomonas balearica SAE1, tolerant to e-waste toxicity was isolated from an e-waste recycling facility Exigo Recycling Pvt. Ltd., India. Toxicity tolerance of bacterial strain was analyzed using crushed (particle size ≤150 µm) waste computer printed circuit boards (PCBs)/liter (L) of culture medium. The EC₅₀ value for SAE1 was 325.7 g/L of the e-waste pulp density. Two-step bioleaching was then applied to achieve the dissolution of gold (Au) and silver (Ag) from the e-waste. To maximize precious metal dissolution, factors including pulp density, glycine concentration, pH level, and temperature were optimized. The optimization resulted in 68.5 and 33.8% of Au and Ag dissolution, respectively, at a pH of 9.0, a pulp density of 10 g/L, a temperature of 30 °C, and a glycine concentration of 5 g/L. This is the first study of Au and Ag bioleaching using indigenous e-waste bacteria and its analysis to determine e-waste toxicity tolerance.