Bioleaching of copper sulfide minerals assisted by microbial fuel cells

Fundamentals of bio-based technologies for selective metal recovery from bio-leachates and liquid waste streams

The number of metal-containing waste streams resulting from electronic end-of life products, metallurgical by-products, and mine tailings to name but a few, is increasing worldwide. In recent decades, the potential to exploit these waste streams as valuable secondary resources to meet the high demand of critical and economically important raw materials has become more prominent. In this review, fundamental principles of bio-based metal recovery technologies are discussed focusing on microbial metabolism-dependent and metabolism-independent mechanisms as sustainable alternatives to conventional chemical metal recovery methods. In contrast to previous reviews which have partially addressed this topic, a special focus will be given on how fundamental principles of bio-based recovery technologies can influence the selectivity and specificity of metal recovery. While conventional methods for metal recovery show benefits in terms of economic affordability, bio-based recovery technologies offer advantages in terms of efficiency and environmentally friendliness. Modifications and adaptations in the processes of biosorption, bioaccumulation and bioelectrochemical systems are highlighted, further emphasizing the application of metal-binding peptides and siderophores to increase selectivity in the recovery of metals. Single metal solutions or mixtures with a low complexity have been the focus of previous studies and reviews, but this does not reflect the nature of complex industrial effluents. Therefore, key challenges that arise when dealing with complex polymetallic solutions are addressed and the focus is set on optimizing bio-based technologies to recover metals efficiently and selectively from bio-leachates or liquid waste streams.

Multi-stress adaptive lifestyle of acidophiles enhances their robustness for biotechnological and environmental applications

Acidophiles are a group of organisms typically found in highly acidic environments such as acid mine drainage. These organisms have several physiological features that enable them to thrive in highly acidic environments (pH ≤3). Considering that both acid mine drainage and solfatara fields exhibit extreme and dynamic ecological conditions for acidophiles, it is crucial to gain deeper insights into the adaptive mechanisms employed by these unique organisms. The existing literature reveals a notable gap in understanding the multi-stress conditions confronting acidophiles and their corresponding coping mechanisms. Therefore, the current review aims to illuminate the intricacies of the metabolic lifestyles of acidophiles within these demanding habitats, exploring how their energy demands contribute to habitat acidification. In addition, the unique adaptive mechanisms employed by acidophiles were emphasized, especially the pivotal role of monolayer membrane-spanning lipids, and how these organisms effectively respond to a myriad of stresses. Beyond mere survival, understanding the adaptive mechanisms of these unique organisms could further enhance their use in some biotechnological and environmental applications. Lastly, this review explores the strategies used to engineer these organisms to promote their use in industrial applications.

Synergistic enzymatic mechanism of lepidolite leaching enhanced by a mixture of Bacillus mucilaginosus and Bacillus circulans

Numerous studies have demonstrated that the co-leaching of ores by different silicate bacteria significantly improves the performance of bioleaching systems. Nevertheless, the mechanism of different silicate bacteria synergistically or complementarily enhanced the leaching process of lithium-containing silicate remains unclear. This study discussed the leaching impact of the combined presence of two metabolically distinct silicate bacteria on lepidolite, with the aim of comprehending the synergistic effect resulting from the presence of Bacillus mucilaginosus and Bacillus circulans in the leaching process. The results indicated that the polysaccharides and proteins secreted by bacteria-containing functional groups such as -OH and -COOH, which played an important role in the complex decomposition of ores. Organic acids played the role of acid etching and complexation. Bacillus mucilaginosus and Bacillus circulans exhibited low individual leaching efficiency, primarily due to their weak organic acid secretion. Moreover, the prolific polysaccharide production by Bacillus mucilaginosus led to bacterial aggregation, diminishing contact capability with minerals. Bacillus circulans decomposed the excessive polysaccharides produced by Bacillus mucilaginosus through enzymatic hydrolysis in the co-bioleaching process, providing later nutrient supply for both strains. The symbiosis of the two strains enhanced the synthesis and metabolic capabilities of both strains, resulting in increased organic acid secretion. In addition, protein and humic acid production by Bacillus mucilaginosus intensified, collectively enhancing the leaching efficiency. These findings suggested that the primary metabolic products secreted by different bacterial strains in the leaching process differ. The improvement in bioleaching efficiency during co-leaching was attributed to their effective synergistic metabolism. This work contributes to the construction of an efficient engineering microbial community to improve the efficiency of silicate mineral leaching, and reveals the feasibility of microbial co-culture to improve bioleaching.

Bioleaching Modeling-A Review

The leaching of minerals is one of the main unit operations in the metal dissolution process, and in turn it is a process that generates fewer environmental liabilities compared to pyrometallurgical processes. As an alternative to conventional leaching methods, the use of microorganisms in mineral treatment processes has become widespread in recent decades, due to advantages such as the non-production of emissions or pollution, energy savings, low process costs, products compatible with the environment, and increases in the benefit of low-grade mining deposits. The purpose of this work is to introduce the theoretical foundations associated with modeling the process of bioleaching, mainly the modeling of mineral recovery rates. The different models are collected from models based on conventional leaching dynamics modeling, based on the shrinking core model, where the oxidation process is controlled by diffusion, chemically, or by film diffusion until bioleaching models based on statistical analysis are presented, such as the surface response methodology or the application of machine learning algorithms. Although bioleaching modeling (independent of modeling techniques) of industrial (or large-scale mined) minerals is a fairly developed area, bioleaching modeling applied to rare earth elements is a field with great growth potential in the coming years, as in general bioleaching has the potential to be a more sustainable and environmentally friendly mining method than traditional mining methods.

Copper extraction from low-grade chalcopyrite in a bioleaching column assisted by bioelectrochemical system

Low-grade ores, tailings, and solid wastes contain small amounts of valuable heavy metals. Improper disposal of these substances results in the waste of resources and contamination of soil or groundwater. Accordingly, the treatment and recycling of low-grade ores, tailings, and solid wastes attracted much attention recently. Bioelectrochemical system, an innovative technology for the removal and recovery of heavy metals, has been further developed and applied in recent years. In the current study, the low-grade chalcopyrite was bioleached with the assistance of microbial fuel cells. Copper extraction along with electricity generation from the low-grade chalcopyrite was achieved in the column bioleaching process assisted by MFCs. Results showed that after 197 days bioleaching of low-grade chalcopyrite, 423.9 mg copper was extracted from 200 g low-grade chalcopyrite and the average coulomb production reached 1.75 C/d. The introduction of MFCs into bioleaching processes promoted the copper extraction efficiency by 2.7 times (3.62% vs. 1.33%), mainly via promoting ferrous oxidation, reducing ORP, and stimulating bacterial growth. This work provides a feasible method for the treatment and recycling of low-grade ores, tailings, and solid wastes. But balancing energy consumption of aeration and circulation frequency and chemical consumption of acid to improve the copper extraction efficiency need further investigation.

Bio-Based Processes for Material and Energy Production from Waste Streams under Acidic Conditions

The revolutionary transformation from petrol-based production to bio-based production is becoming urgent in line with the rapid industrialization, depleting resources, and deterioration of the ecosystem. Bio-based production from waste-streams is offering a sustainable and environmentally friendly solution. It offers several advantages, such as a longer operation period, less competition for microorganisms, higher efficiency, and finally, lower process costs. In the current study, several bio-based products (organic acids, biomethane, biohydrogen, and metal leachates) produced under acidic conditions are reviewed regarding their microbial pathways, processes, and operational conditions. Furthermore, the limitations both in the production process and in the scale-up are evaluated with future recommendations.

Biofilm Formation Is Crucial for Efficient Copper Bioleaching From Bornite Under Mesophilic Conditions: Unveiling the Lifestyle and Catalytic Role of Sulfur-Oxidizing Bacteria

Biofilm formation within the process of bioleaching of copper sulfides is a relevant aspect of iron- and sulfur-oxidizing acidophilic microorganisms as it represents their lifestyle in the actual heap/dump mining industry. Here, we used biofilm flow cell chambers to establish laminar regimes and compare them with turbulent conditions to evaluate biofilm formation and mineralogic dynamics through QEMSCAN and SEM-EDS during bioleaching of primary copper sulfide minerals at 30°C. We found that laminar regimes triggered the buildup of biofilm using Leptospirillum spp. and Acidithiobacillus thiooxidans (inoculation ratio 3:1) at a cell concentration of 10⁶ cells/g mineral on bornite (Cu₅FeS₄) but not for chalcopyrite (CuFeS₂). Conversely, biofilm did not occur on any of the tested minerals under turbulent conditions. Inoculating the bacterial community with ferric iron (Fe³⁺) under shaking conditions resulted in rapid copper recovery from bornite, leaching 40% of the Cu content after 10 days of cultivation. The addition of ferrous iron (Fe²⁺) instead promoted Cu recovery of 30% at day 48, clearly delaying the leaching process. More efficiently, the biofilm-forming laminar regime almost doubled the leached copper amount (54%) after 32 days. In-depth inspection of the microbiologic dynamics showed that bacteria developing biofilm on the surface of bornite corresponded mainly to At. Thiooxidans, while Leptospirillum spp. were detected in planktonic form, highlighting the role of biofilm buildup as a means for the bioleaching of primary sulfides. We finally propose a mechanism for bornite bioleaching during biofilm formation where sulfur regeneration to sulfuric acid by the sulfur-oxidizing microorganisms is crucial to prevent iron precipitation for efficient copper recovery.

Submarine Tailings in Chile—A Review

This review aims to understand the environmental impact that tailings produce on the land and marine ecosystem. Issues related to flora, fauna, and the environment are revised. In the first instance, the origin of the treatment and disposal of marine mining waste in Chile and other countries is studied. The importance of tailings’ valuable elements is analyzed through mineralogy, chemical composition, and oceanographic interactions. Several tailings’ treatments seek to recover valuable minerals and mitigate environmental impacts through leaching, bioleaching, and flotation methods. The analysis was complemented with the particular legislative framework for every country, highlighting those with formal regulations for the disposal of tailings in a marine environment. The available registry on flora and fauna affected by the discharge of toxic metals is explored. As a study case, the “Playa Verde” project is detailed, which recovers copper from marine tailings, and uses phytoremediation to neutralize toxic metals. Countries must regularize the disposal of marine tailings due to the significant impact on the marine ecosystem. The implementation of new technologies is necessary to recover valuable elements and reduce mining waste.

Species identification and mutation breeding of silicon-activating bacteria isolated from electrolytic manganese residue

A strain of silicon-activating bacteria was isolated from electrolytic manganese residue (EMR); identified as a species of Ochrobactrum by integrated microscopic morphological characteristics, biochemical index determination, and clone analysis (i.e., results of 16S rRNA sequence); and temporarily named as Ochrobactrum sp. T-07 (T-07). The optimal growth conditions of the strain T-07 were obtained as follows: temperature of 30 °C, initial pH of 7.0, shaking speed of 180 rev. min^-1, and loading volume of 100 mL. In order to enhance its activation activity of silicon, T-07 went through the ultraviolet (UV) mutagenesis and nitrosoguanidine (NTG) mutagenesis breeding, and the mutant strain T-07-B with higher activity was obtained. Under the optimal fermentation condition (leaching time of 20 days, temperature of 30 °C, initial pH of 7, pulp concentration of 5%, shaking speed of 180 rev. min^-1, and particle diameter of EMR ≤ 180 μm), the available silicon content in the supernatant reached 98.8 mg L^-1, which was 2.4 times of the original strain T-07. Therefore, T-07 can be used as a good backup in developing biological silicon fertilizer for plants.

Copper uptake, essentiality, toxicity, detoxification and risk assessment in soil-plant environment

Copper (Cu) is an essential metal for human, animals and plants, although it is also potentially toxic above supra-optimal levels. In plants, Cu is an essential cofactor of numerous metalloproteins and is involved in several biochemical and physiological processes. However, excess of Cu induces oxidative stress inside plants via enhanced production of reactive oxygen species (ROS). Owing to its dual nature (essential and a potential toxicity), this metal involves a complex network of uptake, sequestration and transport, essentiality, toxicity and detoxification inside the plants. Therefore, it is vital to monitor the biogeo-physiochemical behavior of Cu in soil-plant-human systems keeping in view its possible essential and toxic roles. This review critically highlights the latest understanding of (i) Cu adsorption/desorption in soil (ii) accumulation in plants, (iii) phytotoxicity, (iv) tolerance mechanisms inside plants and (v) health risk assessment. The Cu-mediated oxidative stress and resulting up-regulation of several enzymatic and non-enzymatic antioxidants have been deliberated at molecular and cellular levels. Moreover, the role of various transporter proteins in Cu uptake and its proper transportation to target metalloproteins is critically discussed. The review also delineates Cu build-up in plant food and accompanying health disorders. Finally, this review proposes some future perspectives regarding Cu biochemistry inside plants. The review, to a large extent, presents a complete picture of the biogeo-physiochemical behavior of Cu in soil-plant-human systems supported with up-to-date 10 tables and 5 figures. It can be of great interest for post-graduate level students, scientists, industrialists, policymakers and regulatory authorities.

Intensified bioleaching of chalcopyrite concentrate using adapted mesophilic culture in continuous stirred tank reactors

The bioleaching of chalcopyrite concentrate, intensified by the adapted mesophilic culture in the continuous stirred tank reactors (CSTR) was investigated. The cumulative bioleaching efficiency of copper was found to be increased from 34.8% to 49.3% in CSTR-1, 40.3% to 71.2% in CSTR-2, and 44.3% to 73.8% in CSTR-3, while the temperature was elevated from 30 to 37 °C, respectively; whereas, the pulp density (10%, w/v), agitation speed (350 rpm), aeration (400 cc/min), and retention time (7 days across the three reactors) were also optimized to keep constant. Further, the activation energy calculated for copper dissolution under the continuous flow indicated that the surface-diffusion was the overall rate-limiting step for the bioleaching process. Instrumental analysis of solid samples could reveal the degradation pathways of chalcopyrite bioleaching as: CuFeS₂ → Cu₂S → Cu_0.3333Fe_0.6667S → H₉Fe₃O₁₈S₈. It follows a complex mechanism that includes the occurrence of polysulfide and cooperative mechanism along with the passivation onto mineral surfaces.

Simultaneous copper removal and electricity production and microbial community in microbial fuel cells with different cathode catalysts

With graphene oxide (GO), platinum carbon (Pt/C), and reduced graphene oxide (rGO) as cathode catalysts, three types of single-chamber microbial fuel cells (MFCs) were constructed for simultaneous Cu²⁺ removal and electricity production. Results indicated rGO-MFC and Pt/C-MFC had much better Cu²⁺-removing and electricity-generating performance than that of GO-MFC, and rGO-MFC presented preferable electrochemical characteristics compared with Pt/C-MFC. Microbial community analysis indicated Geobacter dominated anodic biofilms and was mainly responsible for organics degradation and electricity generation. The dual bio-selective effects by cathode catalyst and toxic Cu²⁺ resulted in different cathodic microbial communities. At high Cu²⁺ contents, Nitratireductor, Ochrobactrum, and Serratia as efficient Cu²⁺-removing genera played key roles in Pt/C-MFC, and Azoarcus predominant in cathodic biofilms of rGO-MFC might be important contributor for the favorable performance in this case.

Bioleaching for resource recovery from low-grade wastes like fly and bottom ashes from municipal incinerators: A SWOT analysis

Bioleaching (or microbial leaching) is a biohydrometallurgical technology that can be applied for metal recovery from anthropogenic waste streams. In particular, fly ashes and bottom ashes of municipal solid waste incineration (MSWI) can be used as a target material for biomining. Globally, approximately 46 million tonnes of MSWI ashes are produced annually. Currently landfilled or used as aggregate, these contain large amounts of marketable metals, equivalent to low-grade ores. There is opportunity to recover critical materials as the circular economy demands, using mesophile, moderately thermophile, and extremophile microorganisms for bioleaching. A Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis was developed to assess the potential of this biotechnology to recover critical metals from MSWI wastes. Bioleaching has potential as a sustainable technology for resource recovery and enhanced waste management. However, stakeholders can only reap the full benefits of bioleaching by addressing both the technical engineering challenges and regulatory requirements needed to realise and integrated approach to resource use.

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.

Simultaneously enhanced Cu bioleaching from E-wastes and recovered Cu ions by direct current electric field in a bioelectrical reactor

In this study, a proof-of-concept of bioleaching and recovery of copper (Cu) from E-wastes assisted by direct current (DC) electric field was proved in a bioelectrical reactor. Results showed that 40 mA electric current application could not only significantly shorten the leaching time of Cu from 5 (control) to 3 days with 100% leaching efficiency, but also recover about 97% leached Cu ions within 4 days. DC electric field improved the activity and growth of iron oxidizing bacteria and facilitated Fe²⁺ oxidation, which resulted in effective leaching of Cu from printed circuit boards (PCBs). The functional Acidithiobacillus was selectively enriched by DC electric field for enhancing the efficiency of bioleaching. At the same time, the leached Cu ions were rapidly electrodeposited on the cathode, achieving the recovery of Cu. Hence, this work provided a novel strategy for metals bioleaching and recovery from E-wastes.

A new strategy on biomining of low grade base-metal sulfide tailings

This study investigated the effect of designed microbial consortia on biomining of low grade base-metal sulfide tailings. The results show the amount of recycled metals were equal if the tailings were leached by mixed cultures of Leptospirillum ferriphilum and Acidithiobacillus thiooxidans at three different ratios or by pure culture of L. ferriphilum, which was better than the pure culture of Acidithiobacillus ferrooxidans. qPCR (quantitative polymerase chain reaction) demonstrated only L. ferriphilum functioned in the mixtures at initial stage. The results of extracellular polymeric substances (EPS) via three-dimensional excitation-emission matrix combined with parallel factor analysis (3DEEM-PARAFAC) collected from mixed or pure cultures indicated there were no interactions between two strains. Secondary minerals were formed, but did not influence the leaching process. A new strategy for tailings biomining was proposed: only ferrous oxidizers should be added during the initial and middle biomining stage, while sulfur oxidizers should be added at the end.