Bioleaching Process Research Articles

Bacterial biofilm-based bioleaching: Sustainable mitigation and potential management of e-waste pollution.

Significant advances in the electrical and electronic industries have increased the use of electrical and electronic equipment and its environmental emissions. The e-waste landfill disposal has deleterious consequences on human health and environmental sustainability, either directly or indirectly. E-waste containing ferrous and non-ferrous materials can harm the surrounding aquatic and terrestrial environments. Therefore, recycling e-waste and recovering metals from it before landfill disposal is an important part of environmental management. Although various chemical and physical processes are being used predominantly to recover metals from e-waste, the bioleaching process has gained popularity in recent years due to its eco-friendliness and cost-effectiveness. Direct contact between microbes and e-waste is crucial for continuous metal dissolution in the bio-leaching process. Biofilm formation is key for the continuous dissolution of metals from e-waste in contact bioleaching. Critical reviews on microbial activities and their interaction mechanisms on e-waste during metal bioleaching are scarce. Therefore, this review aims to explore the advantages and disadvantages of biofilm formation in contact bioleaching and the practical challenges in regulating them. In this review, sources of e-waste, available metallurgical methods, bioleaching process, and types of bioleaching microbes are summarized. In addition, the significance of biofilm formation in contact bioleaching and the role and correlation between EPS production, cyanide production, and quorum sensing in the biofilm are discussed for continuous metal dissolution. The review reveals that regulation of quorum sensing by exogenous and endogenous processes facilitates biofilm formation, leading to continuous metal dissolution in contact bioleaching.

Mechanism of surfactant effect on bacterial adsorption during bioleaching of lepidolite

Direct contact of bacteria with minerals can provide better leaching effect than indirect contact in the process of bioleaching. As a leaching assistant, surfactant can change the surface tension of ore leaching solution, improve the bacterial adsorption capacity and enhance the biological leaching effect. Thus, this study investigated the mechanisms by which chemical and biological surfactants influence bacterial metabolism, bacterial adsorption, and leaching in the bioleaching process of lepidolite. With the addition of the biosurfactant rhamnolipid and chemical surfactants sodium dodecyl sulfate and Tween-20, FTIR of leaching residues indicated that non-polar functional groups appeared, and the contact angles decreased from 75.22° to 10.64°, 6.8°, 43.18°. Surfactants reduced the surface tension at the solid-liquid interface through the combined action of their hydrophilic head groups and hydrophobic tail groups, thereby increasing the contact area and adsorption efficiency between bacteria and minerals. Additionally, surfactants weaken the chemical bonds of mineral metals and promote the complexation of -COOH and -OH groups in organic acids with minerals. Surfactants-assisted bacterial attachment altered mineral lattice structure via microenvironment creation and bacterial metabolized organic acids.

Bioleaching of Vanadium-Bearing Shale by Acidithiobacillus Ferrooxidans Using Pyrite as an Energy Resource

Abstract Bioleaching of vanadium (V)-bearing shale by Acidithiobacillus ferrooxidans using ferrous ions as the sole energy source rapidly decreases the V leaching efficiency. To reduce the formation of jarosite and improve leaching efficiency, we examined the bioleaching process of V-bearing shale-adapted A. ferrooxidans grown with pyrite, providing insight into the optimal conditions for V extraction and bioleaching. Experiments were conducted by varying the pulp density, grinding size, initial pH, initial cell concentration, and pyrite concentration. Under optimum process conditions (40 g/L pulp density, sample particle size of less than −400 mesh accounting for 56.95%, and 12 g/L initial pyrite at pH 2.00), V leaching rates were increased by 15%–25% compared to sterile controls. Moreover, this study describes the balance between V leaching from V-bearing shale by A. ferrooxidans, the synergistic effect of its oxidation products (Fe3+ and H+), and V loss by coprecipitation and adsorption of jarosite. Our findings indicate that using pyrite rather than ferrous ions as the sole energy source can reduce the influence of jarosite.

A novel approach for microbial activity assessment in bioleaching. Towards to a standardised fast starting up protocol

Biohydrometallurgy is a proven industrial method for extracting base metals from sulfidic ores with low-grade content and as a pre-treatment of Au ores. The lack of study of biological aspects related with microbial activity assessment makes it difficult to control and monitor these processes; and the multitude of experimental procedures described in the literature hinders cross-study comparisons among researchers. Experimental tools that allow a quick and reliable quantitative assessment of the iron oxidising capacity of the cells during the bioleaching process are needed. This work proposes monitoring microbial activity through a simple and reliable method based on the offline measurement of the Oxygen Uptake Rate (OUR). The methodology allows to quantify the microbial activity evolution of a growing culture under no-limiting conditions. By this methodology, the maximum potential bioleaching rate of the culture at any time is determined, assessing the occurrence of a biological or chemical limitation. The results obtained reveals that whether due to Fe2+ or O2 depletion, substrate availability significantly limits microbial activity. This aspect is key to assess a culture suitability for bioleaching bioreactor inoculation, preventing long lag phases. Furthermore, the methodology allows for quick disturbances correction, avoiding process shutdowns and enhances technological reliability of continuous bioleaching.

Study of the impurity dissolution kinetics, rheological characterization, and hydrodynamic aspects during the bioleaching of iron ore pulp in a bioreactor

AbstractThis research aims to study the rheological behavior and impurities dissolution kinetics in a bioleaching process of two particle sizes and three different pulp densities, which are analyzed and compared. It was found that the small particle size with 40% (w/w) pulp density provides the maximum dissolution of impurities in the shortest bioleaching time (in 2 days). Furthermore, through a CFD simulation in a system with 40% (w/w) pulp density and 44 μm particle size, a stirring speed of 700 rpm provides the best mixing conditions in the bioreactor, enabling good distribution of recirculation zones and adequate streamline patterns with a viscosity map that minimizes regions of high and low viscosity. Graphical abstract

A practical green methodology for metal extraction from electric arc furnace dust through Yarrowia lipolytica biolixiviant

The study addresses the management of electric arc furnace dust (EAFD) generated by steel manufacturers and the challenge of metal leaching from this waste. Recognizing the scarcity of rare earth elements (REEs) and the industrial importance of manganese, the study emphasizes the urgent need for their recovery from waste. The current study presents a green approach using a biolixiviant from Yarrowia lipolytica IBRC-M30168, with crude sunflower oil as a hydrophobic carbon source with buffering properties. LC-MS analysis reveals significant citric, malic, and succinic acids production, with the highest concentrations reaching 53.3, 17.4, and 1.0 g/l. Bioleaching experiments show biolixiviants with an initial pH of 7 and 80 g/l carbon source and 5.5 and 100 g/l outperform others, resulting in 92.4 %, 23.2 %, 19.6 %, and 84.8 %, 24.2 %, and 20.6 % of manganese, dysprosium, and erbium within 9 days, with a pulp density of 10 g/l at 60 °C and 140 rpm. The study also explores the potential for industrial adaptation, testing a higher pulp density of 50 g/l, which resulted in leaching of 65.7 %, 10.7 %, and 7.3 % for manganese, dysprosium, and erbium after 6 days. Ultimately, the study concludes that structural analyses of the residues provide added evidence for the bioleaching process’s effectiveness.

Study on the role of microbial metabolites in in-situ noncontact bioleaching of ion-adsorption rare earth ore

Ion adsorption rare earth ore nearly satisfy global market demand for heavy rare earth elements (HREEs). Bio-leaching has important potential for the clean and efficient extraction of ion-adsorption rare earth ore. However, the complexities of in-situ mining restrict the use of contact/direct bio-leaching, and non-contact/indirect bio-leaching would be the best choice. This study explore the potential of fermentation broths prepared by Yarrowia lipolytica (ATCC 30162) for the bio-leaching of ion-adsorption rare earth ore, and three typical metabolites (potassium citrate (K3Cit), sodium citrate (Na3Cit) and ammonium citrate ((NH4)3Cit) of Yarrowia lipolytica were further evaluated in simulated bioleaching (non-contact bioleaching) of ion-adsorption rare earth ore, including leaching behavior, seepage rule and rare earth elements (REEs) morphological transformation. The column leaching experiments shown that direct leaching of REEs using fermentation broths results in incomplete leaching of REEs due to the influence of impurities. Using the purified and prepared metabolites as lixiviant, REEs can be effectively extracted (leaching efficiency >90%) at cation concentration was only 10 % of the commonly used ammonium sulfate concentration (45 mM). Cation type had less effect on leaching efficiency. During the ion-adsorption rare earth ore leaching process, rare earth ions form a variety of complex chelates with citrate, thus transferring rare earth elements from the mineral surface to the leachate. Experimental results showed that pH and concentration together determined the type and form of rare earth chelates, which in turn affect the leaching behavior of REEs and solution seepage rule. This study helps to provide a theoretical basis for the regulation and enhancement of ion-adsorption rare earth ore non-contact bioleaching process.

Enhanced bioleaching of spent Li-ion batteries using A. ferrooxidans by application of external magnetic field

Recycling spent batteries is increasingly important for the sustainable use of Li-ion batteries (LIBs) and for countering the supply uncertainty of critical raw minerals (Li, Co, and Ni). Bioleaching, which uses microorganisms to extract valuable metals, is both economical and environmentally safe compared to other recycling methods, but its practical application is impaired by slow kinetics. Accelerating the process is a key for bioleaching spent LIBs on an industrial scale. Acidithiobacillus ferrooxidans (A. ferrooxidans), which thrives in extremely low pH conditions, has long been explored for bioleaching of spent LIBs. Metabolism of A. ferrooxidans involves the oxidation of magnetic Fe2+ and produces intracellular magnetic nanoparticles. The possibility of accelerating the leaching kinetics of A. ferrooxidans by the application of an external magnetic field is explored in this work. A weak static magnetic field is applied during the bioleaching of spent LIBs to recover Li, Ni, and Co using A. ferrooxidans. It is determined that 3 mT is the optimal field strength which allows the leaching efficiency of Li to reach 100% after only 2 days of leaching at a pulp density of 3 w/v % while without the external magnetic field, the leaching efficiency is limited to 57% even after 4 days. The leaching efficiency of Ni and Co also increases by nearly three-fold to >80% after 4 days of leaching. The proposed magnetic field-assisted bioleaching of spent LIBs using A. ferrooxidans substantially improves the leaching kinetics and thus the cost-effectiveness of the bioleaching process with minimal environmental impact, hence enabling environment-friendly recycling of raw materials that are increasingly becoming scarce. The positive effect of an external magnetic field on the metabolism of A. ferrooxidans demonstrated in this work provide a new set of tools to engineer the bioleaching process and the possibility for genetic modification of acidophile bacteria, especially targeted for magnetic enhancement.

Ways to improve kinetics of a chalcopyrite bioleaching process: a review

Ways to improve kinetics of a chalcopyrite bioleaching process: a review

Geochip 5.0 insights into the association between bioleaching of heavy metals from contaminated sediment and functional genes expressed in consortiums.

The heavy metal contamination in river and lake sediments endangers aquatic ecosystems. Herein, the feasibility of applying different exogenous mesophile consortiums in bioleaching multiple heavy metal-contaminated sediments from Xiangjiang River was investigated, and a comprehensive functional gene array (GeoChip 5.0) was used to analyze the functional gene expression to reveal the intrinsic association between metal solubilization efficiency and consortium structure. Among four consortiums, the Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans consortium had the highest solubilization efficiencies of Cu, Pb, Zn, and Cd after 15days, reaching 50.33, 29.93, 47.49, and 79.65%, while Cu, Pb, and Hg had the highest solubilization efficiencies after 30days, reaching 63.67, 45.33, and 52.07%. Geochip analysis revealed that 31,346 genes involved in different biogeochemical processes had been detected, and the systems of 15days had lower proportions of unique genes than those of 30days. Samples from the same stage had more genes overlapping with each other than those from different stages. Plentiful metal-resistant and organic remediation genes were also detected, which means the metal detoxification and organic pollutant degradation had happened with the bioleaching process. The Mantel test revealed that Pb, Zn, As, Cd, and Hg solubilized from sediment influenced the structure of expressed microbial functional genes during bioleaching. This work employed GeoChip to demonstrate the intrinsic association between functional gene expression of mesophile consortiums and the bioleaching efficiency of heavy metal-contaminated sediment, and it provides a good reference for future microbial consortium design and remediation of river and lake sediments.

Removal of Impurities from Refractory Gold Ore using Bio-reduction and Bio-oxidation processes

Gold in refractory gold ore is difficult to be extracted by conventional metallurgical method due to the presence of sulfide minerals with elevated levels of iron (Fe), sulfur (S), and arsenic (As) as impurities, resulting in low gold (Au) recovery. Conventional methods such as cyanide leaching has been proven ineffective for gold extraction from refractory ore due to gold being intricately bound within the sulfide minerals. Consequently, this study explores the application of bioleaching as an alternative to conventional cyanide leaching. Shewanella oneidensis (S. oneidensis) and Acidithiobacillus ferroxidans (A. ferroxidans) serve as bio-reduction and bio-oxidation agents, respectively in the bioleaching process. The composition of minerals in the ore was determined through XRD analysis (Model: Rigaku’s Miniflex 600) and EDX analysis (Model EDX 3). Meanwhile, SEM analysis (Zeiss EVO LS15 SEM) was utilized to examine the morphology structure. The concentrations of impurities (Fe, S, and As) were assessed using a spectrophotometer (Model: DR3900 Hach) meanwhile the Au concentration was determined through ICP-OES (Model: G8015A5110 ICP-OES). Sieved refractory gold ore samples with less than 32 um and varying in weight (0.5 g, 1.0 g, 1.5 g, 2.0 g), underwent bio-reduction and bio-oxidation processes. The results indicated a rougher surface morphology of raw sample as observed through SEM analysis. Furthermore, XRD and EDX results demonstrated a decrease in impurity concentrations, suggesting a potential increase in gold purity. Notably, the bio-reduction process exhibited a superior enhancement in Au concentration with the values of 138.89% compared to biooxidation with the value 122.22%. Thus, the bio-reduction process proved more effective in increasing Au concentration compared to bio-oxidation.

Investigating the acidophilic microbial community's adaptation for enhancement indium bioleaching from high pulp density shredded discarded LCD panels

As part of electronic waste (e-waste), the fastest growing solid waste stream in the world, discarded liquid crystal displays (LCDs) contain substantial amounts of both valuable and potentially harmful metal, offering valuable opportunities for resource extraction but posing environmental threats. The present comprehensive study is an investigation into the bioleaching of indium from discarded LCD panels, with a particular focus on high pulp density shredded (Sh-LCDs) and powdered (P-LCDs) materials. This study involved an acidophilic consortium, with two pathways, namely the mixed sulfur-iron pathways and sulfur pathways, being explored to understand the bioleaching mechanisms. Indium bioleaching efficiencies through the mixed sulfur-iron pathway were approximately 60% and 100% for Sh-LCDs and P-LCDs, respectively. Three mechanisms were involved in the extraction of indium from LCD samples: acidolysis, complexolysis, and redoxolysis. The microbial community adapted to a pulp density of 32.5 g/L was streak-plated and it was revealed that sulfur-oxizing bacteria dominated, resulting in the minimum indium extraction of 10% and 55% for both Sh-LCDs and P-LCDs samples, respectively. It was generally accepted that ferric ions as oxidants were effective for indium bioleaching from both the Sh-LCDs and P-LCDs. This implies that the cooperation or interaction within the microbial community used in the bioleaching process had a beneficial impact, enhancing the overall effectiveness of extracting indium from LCD panels. The adapted consortium utilizes a combination of microbial transformation, efflux systems, and chelation through extracellular substances to detoxify heavy metals. The adapted microbial community demonstrated better indium leaching efficiency (50%) compared to the non-adapted microbial community which achieved a maximum of 29% and 5% respectively from Sh-LCDs and P-LCDs at a pulp density of 32.5 g/L. The advantages of an adapted microbial community for indium leaching efficiency, attributing this advantage to factors such as high metabolic activity and improved tolerance to heavy metals. Additionally, the protective role of the biofilm formed by the adapted microbial community is particularly noteworthy, as it contributes to the community's resilience in the presence of inhibitory substances. This information is valuable for understanding and optimizing bioleaching processes for indium recovery, and by extension to possibly other metals.

Enhanced vanadium bioleaching from stone coal employing Aspergillus niger: Optimization of stone coal pretreatment method

Vanadium is a rare metal with excellent properties. The recovery of vanadium from low-grade stone coal and vanadium-containing solid wastes using microbial leaching, has become an increasingly popular technology. In this paper, Vanadium was obtained from stone coal using Aspergillus niger as the leaching strain, and the process of vanadium bioleaching was strengthened. Compared with plasma treatment and ultrasonic pretreatment of stone coal, the leaching effect of stone coal after roasting at 900 °C was the best, and the leaching rate of vanadium was as high as 94.52 %. The vanadium bioleaching mechanism was explored by SEM-EDS, XRD, XPS and FTIR analysis. The findings indicated that Aspergillus niger has the ability to adhere to the surface of stone coal, resulting in subsequent corrosion and degradation. The roasting treatment of stone coal and bioleaching of Aspergillus niger jointly lead to the decrease of crystallinity, the increase of interplanar spacing and the decrease of stability of stone coal. Meanwhile, the valence state and binding form of vanadium changed, and V (III) was oxidized to V (IV) and V (V). The mineral structure may be distorted as a result of the distinctive peak's vibratory stretching and the influence of functional categories that include oxygen, which in turn causes the change of the coordination form of the internal metal ions, which affects the symmetry of the mineral and facilitates the dissolution of vanadium from the stone coal. Research indicates that roasting and Aspergillus niger bioleaching have a great deal of promise to increase vanadium recovery from stone coal.

Potential and characteristics of rare-earth metals acid bioleaching from the rare-earth-rich tailings with the enriched functional bacterial consortium: Comparison between one-step and two-step processes

The irreplaceable roles of rare-earth metals (REMs) in modern technologies have renewed interest in the grand challenges of mineral processing and metallurgical engineering—the efficient extraction of REMs. However, traditional methods for extracting REMs are inefficient, costly and harmful to health and the environment. In this study, a method of biological extraction (bioleaching), which has been proved to be effective in the field of mineral processing for extraction of the metals, was employed for REMs bioleaching from Bayan Obo rare-earth-rich tailings (RERT) using the acid functional bacterial consortium, and the optimal culture and leaching conditions were optimized. Under the optimal conditions for 18 days, the total bioleaching rate of the five main REMs of La, Ce, Pr, Nd and Sm was obtained at 82.78 % for one-step process and 83.51 % for two-step process, which has a significant improvement comparing to previous studies. The results demonstrated that REMs could be efficiently bioleached by acid bioleaching functional bacterial consortium, and the difference in leaching efficiency between the one-step and two-step bioleaching process was not significant. In addition, by analyzing the mineral composition of the RERT and leaching residue, the extensively bioleach of REMs in bastnaesite are observed. To sum up, the rare-earth resources of Bayan Obo RERT could be effectively leached by acid bioleaching method.

Sustainable bioleaching of heavy metals from coal tailings using Bacillus inaquosorum B.4: Mechanistic insights and environmental implications

Coal tailings are byproducts of the coal washing process and pose significant environmental pollution issues due to the release of heavy metal elements. In this study, a sustainable bioleaching method was proposed, and a Bacillus inaquosorum B.4 strain with high Extracellular Polymeric Substances(EPS) production characteristics was isolated through mutagenesis. The importance of EPS in the adsorption of free heavy metals was validated, as EPS-covered (EPS-C) cells exhibited significantly higher removal rates of Cu (71.30 ± 1.10 %), Pb (79.90 ± 1.02 %), and Zn (64.90 ± 1.00 %) compared to EPS-removed (EPS-R) cells. The adsorption kinetics followed pseudo-second-order kinetics models. The significant bioleaching efficiency of this strain for heavy metals Pb, Zn, and Cu in coal tailings was investigated. Through shake flask experiments under conditions of a particle size of 45–74 μm, pH of 7, and a bacterial concentration of 15.00 %, the bioleaching rates of Pb, Zn, and Cu were found to be 91.88 mg/kg、23.21 mg/kg、8.06 mg/kg, respectively. The B.4 strain's mechanism of action was determined using techniques like SEM, XRD, FT-IR, and LA-ICP-MS. It involves absorbing organic compounds, disrupting the lattice structure of heavy metal minerals, and releasing metal ions. These metal ions are then immobilized by forming complexes with functional groups on the bacterial surface. The bioleaching process was primarily subject to a combination of chemical reaction and diffusion control. This research offers a practical bioremediation strategy to manage heavy metals in coal tailings and has important implications for environmental protection and sustainable resource utilization.

Mixed rare earth metals production from surface soil in Idaho, USA: Techno-economic analysis and greenhouse gas emission assessment

Rare earth elements are crucial for the development of cutting-edge technologies in various sectors, such as energy, transportation, and health care. Traditional extraction of rare earth elements from soil and ore deposits primarily involves chemical leaching and solvent extraction. Environmental-based biological rare earth element extraction, such as bioleaching, can be a promising alternative to mitigate pollution and hazardous wastes. We investigated the sustainability aspects (techno-economic and environmental impact) of mixed rare earth metals production from soil in Idaho, USA. We focused on the bioleaching of surface soil using techno-economic analysis and “cradle-to-gate” life cycle assessment. The system boundary included collection, transportation, bioleaching, and molten salt electrolysis. Our results revealed that the mixed rare earth metals (including Nd, Ce, and La) production costs approximately $10,851 per metric ton and generates 1.9 × 106 kg CO2 eq./ton. Our results showed that most emissions are due to energy consumption during bioleaching. Over a 100-year time horizon ultrasound-assisted bioleaching can reduce greenhouse gas emissions by approximately 91 % compared to the traditional bioleaching process by decreasing the organic acid leaching process time and energy consumption. Our work demonstrates that higher solids loading in leaching with biological reactions can promote economic feasibility and reduce chemical wastes.

Osmotic response in Leptospirillum ferriphilum isolated from an industrial copper bioleaching environment to sulfate

Iron and sulfur-oxidizing microorganisms play important roles in several natural and industrial processes. Leptospirillum (L.) ferriphilum, is an iron-oxidizing microorganism with a remarkable adaptability to thrive in extreme acidic environments, including heap bioleaching processes, acid mine drainage (AMD) and natural acidic water. A strain of L. ferriphilum (IESL25) was isolated from an industrial bioleaching process in northern Chile. This strain was challenged to grow at increasing concentrations of sulfate in order to assess changes in protein expression profiles, cells shape and to determine potential compatible solute molecules. The results unveiled changes in three proteins: succinyl CoA (SCoA) synthetase, isocitrate dehydrogenase (IDH) and aspartate semialdehyde dehydrogenase (ASD); which were notably overexpressed when the strain grew at elevated concentrations of sulfate. ASD plays a pivotal role in the synthesis of the compatible solute ectoine, which was identified along with hydroxyectoine by using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF). The relationship between IDH, SCoA, and ectoine production could be due to the TCA cycle, in which both enzymes produce metabolites that can be utilized as precursors or intermediates in the biosynthesis of ectoine. In addition, distinct filamentous cellular morphology in L. ferriphilum IESL25 was observed when growing under sulfate stress conditions. This study highlights a new insight into the possible cellular responses of L. ferriphilum under the presence of high sulfate levels, commonly found in bioleaching of sulfide minerals or AMD environments.

The advances in the recovery process for precious metals from nickel slag, a review

The creation of nickel-smelting products including important metals like nickel, cobalt, and copper is a persistent issue in the nickel mining business. Another secondary source of precious metals is nickel slag. In addition, the massive amounts of nickel slag generated by the nickel smelter sector will pollute the environment, particularly the soil, since the smelting slag contains hazardous materials. This study examines techniques for recovering precious metals from nickel slag by reviewing publications from Springer Link, Google Scholar, MDPI, ScienceDirect, Membrane Journal, and other authors. The two types of metal recovery techniques from nickel slag that were examined were hydrometallurgical and pyrometallurgical techniques. This review article describes a pyrometallurgical method that involves roasting and selective reduction. In the meantime, the hydrometallurgical techniques were examined in the high-pressure oxidative acid leaching process, the atmospheric acid leaching method, and the bioleaching process. A roadmap for research designs that can be used to recover valuable metals from nickel slag sustainably has been created due to the completed literature evaluation.

Ammonium-based bioleaching of toxic metals from sewage sludge in a continuous bioreactor

The broader reuse of sewage sludge as a soil fertilizer or conditioner is impeded by the presence of toxic metals. Bioleaching, a process that leverages microbial metabolisms and metabolites for metal extraction, is viewed as an economically and environmentally feasible approach for metal removal. This study presents an innovative bioleaching process based on microbial oxidation of ammonia released from sludge hydrolysis, mediated by a novel acid tolerant ammonia-oxidizing bacteria (AOB), Ca. Nitrosoglobus. Over a span of 1024 days, a laboratory-scale bioleaching reactor processing anaerobically digested (AD) sludge achieved an in-situ pH of 2.5 ± 0.3. This acidic environment facilitated efficient leaching of toxic metals from AD sludge, upgrading its quality from Grade C to Grade A (qualified for unrestricted use), according to both stabilization and contaminants criteria. The improved quality of AD sludge could potentially reduce sludge disposal expenses and enable a broader reuse of biosolids. Furthermore, this study revealed a pH-dependent total ammonia affinity of Ca. Nitrosoglobus, with a higher affinity constant at pH 3.5 (67.3 ± 20.7 mg N/L) compared to pH 4.5–7.5 (7.6 – 9.6 mg N/L). This finding indicates that by optimizing ammonium concentrations, the efficiency of this novel ammonium-based bioleaching process could be significantly increased.

Do ferrous iron-oxidizing acidophiles (Leptospirillum spp.) disturb aerobic bioleaching of laterite ores by sulfur-oxidizing acidophiles (Acidithiobacillus spp.)?

The extraction of nickel, cobalt, and other metals from laterite ores via bioleaching with sulfur-oxidizing and ferric iron-reducing, autotrophic, acidophilic bacteria (e.g. Acidithiobacillus species) has been demonstrated under anaerobic as well as aerobic conditions in experiments in different laboratories. This study demonstrated the bioleaching of laterites from Brazil with the addition of elemental sulfur in 2-L stirred-tank bioreactors with pure and mixed cultures of Acidithiobacillus and Sulfobacillus species under aerobic conditions. In particular, a potential disturbance of mineral dissolution under aerobic conditions by ferrous iron-oxidizing acidophiles likely introduced as contaminants in an applied bioleaching process was investigated with Leptospirillum ferrooxidans at 30°C and Leptospirillum ferriphilum at 40°C, at maintained pH 1.5 or without maintained pH leading to an increase in acidity (with pH values <1.0) due to the biological production of sulfuric acid. Despite the proportion of ferrous iron to the total amount of extracted iron in the solution being drastically reduced in the presence of Leptospirillum species, there was a negligible effect on the extraction efficiency of nickel and cobalt, which is positive news for laterite bioleaching under aerobic conditions.