Electroplating sludge (ES), a hazardous waste rich in toxic heavy metals, is produced through CaO/Ca(OH)2 precipitation. Despite its hazardous nature, the sludge is also a valuable secondary source of metals, making its recycling crucial both environmentally and economically. This study introduces an innovative ultrasonic-assisted ferric sulfate bio acid (FSBA) process to leaching of chromium (Cr), copper (Cu), and nickel (Ni) from ES. The bacterial supernatant of Acidithiobacillus ferrooxidans was employed to produce ferric ion and sulfuric acid for the ultrasonic-assisted leaching experiments. The impact of various parameters on the leaching efficiency in the presence of biogenic acids was systematically investigated. Ultrasonication significantly improved metal extraction rates and reduced the leaching time, achieving extraction efficiencies of 92.51% for Cr, 86.91% for Cu, and 91.25% for Ni within 8min at an S/L ratio of 10g/L, 400rpm agitation speed, and 45°C. Elemental analyses confirmed the enhanced metal extraction facilitated by ultrasonic. Furthermore, field emission scanning electron microscopy and X-ray diffraction analyses have detected the formation of hydronium jarosite on residue surfaces at 75°C temperature. Finally, both the synthetic precipitation leaching procedure and toxicity characteristic leaching procedure tests demonstrated effective detoxification of the ES through FSBA.

Digital and green energy transitions are driving an unprecedented demand for Strategic and Critical Raw Materials (S-CRMs), necessitating the identification of alternative sources such as secondary raw materials from exploration and mining residues. This study investigates an integrated, multi-scale approach to map and recover S-CRMs from an abandoned exploration stockpile in Zlatá Baňa, Slovak Republic. A key aspect of the methodology is comprehensive chemical and mineralogical characterization (XRF, PXRD, FTIR, LIBS, and SEM-EDS), which provided scientific validation for the diagnostic absorption features observed in laboratory reflectance spectra. These laboratory-acquired signatures were then used as endmembers to classify Sentinel-2 imagery via the Spectral Angle Mapper (SAM) algorithm. This integration enabled the identification of three distinct residue classes, with classA (jarosite-rich residues) emerging as the most reactive facies. Subsequent bioleaching experiments using Acidithiobacillus ferrooxidans demonstrated that microbial activity more than doubled Zn mobilization compared to abiotic controls. This cross-disciplinary strategy confirms that the synergy between advanced analytical characterization and remote sensing provides a robust, cost-effective pathway for the sustainable recovery of S-CRMs in regions affected by historical and mining activities.

Synergistic bioleaching by thiobacillus consortia for simultaneous heavy metal removal mechanisms and sludge dewaterability enhancement.

High concentrations of copper ions have long been recognized as a key factor limiting the efficiency of bioleaching due to the metal toxicity to microorganisms. In order to identify new determinants of copper resistance, we assessed the impact of different copper ion concentrations on the bioleaching model organism Acidithiobacillus ferrooxidans. Furthermore, we employed 6mA IP-seq technique to evaluate changes in the 6mA methylation levels of A. ferrooxidans under two conditions: iron oxidation and sulfur oxidation, both under copper stress. The results indicated that as the concentration of copper ions in the growth environment increased, the copper toxicity significantly inhibited the growth of A. ferrooxidans. The maximum tolerable copper ion concentration for iron-grown and sulfur-grown A. ferrooxidans was found to be 100 mM. Under 100 mM Cu2+ exposure, 184 and 242 differentially methylated genes were identified in the iron oxidation and sulfur oxidation A. ferrooxidans, respectively(P < 0.01). From the Kyoto Encyclopedia of Genes and Genomes (KEGG) functional analysis, under iron oxidation conditions, 130 differentially methylated genes were annotated and mapped into 7 KEGG pathways, while under sulfur oxidation conditions, 188 differentially methylated genes were annotated and mapped into 4 KEGG pathways (P < 0.05). Several differentially methylated genes were found to be associated with the following responses to copper stress: iron-sulfur oxidation acceleration, amino acid synthesis, and activation of the RND-type efflux system, polypeptide-based copper resistance systems, and metal ATPases to expel copper ions. In summary, the 6mA methylation levels in A. ferrooxidans change under copper stress, and these changes are widely present in various copper resistance genes. This study reveals a novel copper resistance mechanism in A. ferrooxidans, providing new insights for enhancing bioleaching efficiency and demonstrating significant implications for advancing biometallurgy.

Effect of pyrite on the bio-oxidation and arsenic migration of realgar mediated by Acidithiobacillus ferrooxidans

Extracellular polymeric substances - mediated hydrophobic/hydrophilic differentiation of chalcopyrite and pyrite by Acidithiobacillus ferrooxidans for enhanced selective flotation

Comparison of performance differences in metal leaching from spent lithium-ion batteries using different metabolically functional bacteria.

Effects of different energy sources (ferrous iron, elemental sulfur and their mixture) on the bioleaching efficiency of rare earth elements (REEs) from phosphogypsum (PG) by using Acidithiobacillus ferrooxidans CL (A. ferrooxidans) were investigated in this paper. Potassium and ammonium jarosite was detected in the residues of bioleaching experiments using the ferrous iron and the mixture as the energy source. XRD patterns and SEM images showed that jarosite intercepted the microbial attachment to the mineral surfaces because it was formed as a passivation layer. During the bioleaching process using ferrous iron as the energy source, redoxolysis reaction of PG by ferric iron produced in the oxidation of ferrous iron doesn’t perform. In the bioleached residue of using elemental sulfur as the sole energy source, jarosite was not detected and the pH value was 1.25, much lower than that of using the ferrous iron. REEs in PG exist in the form of phosphate and the dissolution of REEs from PG is described as the acidolysis process. The maximum total REEs extraction was found in the test using the elemental sulfur due to the lowest pH value and no formation of jarosite.

N-tetradecanoyl-L-homoserine lactone (C14-HSL) is a long-chain signaling molecule belonging to acyl-homoserine lactones (AHLs), which is widely present in the quorum sensing (QS) system of Gram-negative bacteria. In this study, the effects of C14-HSL on chalcopyrite bioleaching mediated by Acidithiobacillus ferrooxidans (A. ferrooxidans) were investigated. After cultivating A. ferrooxidans with different energy substrates and exploring the potential mechanisms of signal molecule production, chalcopyrite was selected as the energy substrate for further study. Molecular docking analysis revealed that the high binding affinity between AHL and the receptor protein AfeR in A. ferrooxidans was beneficial for the activation of transcription by the AfeR-AHL complex, promoting their biological impact. The variations in the physicochemical parameters of pH, redox potential, and copper ions revealed that after adding C14-HSL, the leaching rate of chalcopyrite increased (1.15 times during the initial 12 days). Further analysis of the mechanism of extracellular polymers formation indicated that the presence of C14-HSL could promote the formation of biofilms and the adhesion of bacteria, facilitating mineral leaching rate of A. ferrooxidans. This research provides a theoretical basis for regulating the biological leaching process of chalcopyrite and metal recovery using signaling molecules, which could also be used to control environmental damage caused by acid mine/rock drainage.

This study investigates the sustainable recovery of nickel from chromite beneficiation plant waste using bioleaching with Acidithiobacillus ferrooxidans. The research addresses the increasing demand for nickel, a critical resource for clean energy technologies, by optimizing recovery process through Taguchi L9 orthogonal design and ANOVA analysis. The key parameters, including solid ratio (1%–5%) and leaching time (5–15 days), were evaluated to determine their effects on metal extraction efficiency. The results demonstrated maximum recoveries rates of 89.20% Ni, 77.05% Fe, and 23.66% Co under optimal conditions (5% solid ratio, 15 days). Statistical analysis revealed that solid ratio had the most significant influence on Ni recovery (52.06% contribution), followed by leaching time (35.70%). These findings contribute to advancing secondary resource utilization and minimizing the environmental impacts associated with nickel extraction. Overall, the study highlights the potential of bioleaching as an eco-friendly alternative to conventional hydrometallurgical methods, aligning with circular economy principles.

In this study, bioleaching experiments on Kastamonu Hanönü copper ore were conducted using the bacterium Acidithiobacillus ferrooxidans in the presence of seawater. The characterization of the sample was performed using XRD, XRF, and SEM analysis methods. During the bioleaching experiments, bacteria concentration, pH, copper and iron concentrations were monitored over the 360-hour test period. The results demonstrated that an appropriate proportion of seawater significantly promoted copper recovery, with the solid-to-liquid ratio playing a key role. A maximum copper recovery of 81.43% was achieved in the presence of 30.00% seawater, 7% solid rate compared to only 71.02% in its absence. This study highlights the potential of seawater as an alternative solvent medium, offering both environmental and economic benefits. Moreover, the findings emphasize the applicability of the bioleaching method as an environmentally friendly and efficient process.

This article conducts a comprehensive study about how microbial gold recovery constitutes a sustainable alternative over expensive traditional extraction systems. Bioleaching involves bacteria such as Chromobacterium violaceum, Pseudomonas aeruginosa, Bacillus spp. and fungi such as Aspergillus niger for dissolving gold through mechanisms which include biooxidation using Acidithiobacillus ferrooxidans and biocyanidation through C. violaceum and organic acid production through fungal citric and oxalic acid production. The treatment methods show high performance when working with refractory gold ores and electronic waste by minimizing toxic byproducts and energy usage. The extraction process moves at a slow pace because it requires environmental conditions suitable for microbial activity and it generates harmful byproducts of cyanide among other things. Scientists plan to use genetics to boost microbial performance while nanotechnology will help extract gold nanoparticles better and they aim to create comprehensive biorefineries for extracting several metals from waste. Bioleaching stands as an environmentally friendly process which meets circular economy standards and should function as a primary sustainable mining method for upcoming years.

Soils heavily contaminated with potentially toxic elements (PTEs) pose substantial risks to the environment and human health. However, conventional remediation methods are often plagued by high energy consumption and the potential for secondary pollution. To address this challenge, this study developed a synergistic system combining acidophilic bacteria with a Fe-modified anode, aiming to enhance the remediation of PTEs in such contaminated soils. This system integrates the following three core components: the catalytic function of Fe3O4–graphene-oxide (Fe3O4–GO) nanocomposites, the acclimation of microbial communities, and the optimization of process parameters—specifically, applied electric current, pH, and oxidation–reduction potential (ORP). Experimental treatments were designed to assess the individual and combined effects of three key factors: bacterial inoculation, the Fe-modified anode, and the addition of Fe3O4–GO. The results revealed that the integrated synergistic system effectively reduced the soil pH from 2.9 to 2.0 and maintained the ORP at approximately 600 mV. For PTE removal, the system achieved efficiencies of 89% for Zn, 85.89% for Cu, 66.3% for Pb, 77.89% for Cd, and 40.63% for Cr, respectively. In contrast, control groups lacking bacteria, applied current, or Fe3O4–GO exhibited significantly lower metal removal efficiencies. Notably, the bacteria-free treatment led to a more than 50% reduction in Cr removal. Additionally, the group with an unmodified anode only achieved 1/3 to 1/2 of the removal efficiencies observed in the full synergistic system; this discrepancy is likely attributed to reduced electron transfer efficiency and compromised microbial adhesion on the anode surface. These findings demonstrate that the coupling of electrochemical enhancement, acidophilic microbial activity, and Fe3O4–GO catalysis constitutes an effective and energy-efficient approach for remediating soils contaminated with high concentrations of PTEs while simultaneously minimizing the risk of secondary pollution.

Acidithiobacillus ferrooxidans is a chemolithoautotrophic acidophilic bacterium widely found in industrial biomining operations. The cells obtain energy through iron and/or sulfur oxidation, and the resulting ferric iron can solubilize copper and other critical materials. The genetic engineering of acidophiles including A. ferrooxidans remains challenging due to limited molecular tools. In this study, we explored the feasibility of retron-based genetic engineering tools in A. ferrooxidans ATCC23270, leveraging a pBAD promoter system for inducible gene expression. We successfully expressed retron elements in Escherichia coli using the broad host pJRD215 plasmid and demonstrated both RNA and DNA antisense interference. We then expressed retron elements in A. ferrooxidans and targeted RNA antisense interference of the PetA2 gene, which is a bc1 complex gene involved in the sulfur metabolism electron transport chain. Engineered strains exhibited reduced expression of sulfur oxidation genes and increased iron oxidation under high sulfur conditions, demonstrating retron-mediated regulation. While transcriptional interference was evident, genome editing in concert with the addition of a single-stranded annealing protein (SSAP), or recombineering, was not detected in A. ferrooxidans. These findings establish retrons as a viable new tool for genetic modulation in A. ferrooxidans, suggesting a new capability for metabolic engineering of acidophilic extremophiles.

Pioneer phytoremediation of highly acidic mineral soil: O-glycoside components of rhizosphere exudates inhibit Acidithiobacillus ferrooxidans.

Biogenic jarosite coating as an innovative passivator for acidic uranium residue stabilization using Acidithiobacillus ferrooxidans.

A comprehensive investigation of the continuous oxidation of pyrrhotite by micromolar hydrogen peroxide in near neutral and acidic solutions

Chloride leaching is considered as a promising alternative method to recover copper from chalcopyrite and other copper sulfides, because it favors the leaching kinetics and avoids passivation of minerals. However, chloride ions inhibit the growth of acidophilic bacteria used in biomining. Biomining bacteria are unable to survive in highly saline environments and colonize a mineral surface, and would be unsuitable for application in biomining with seawater. This study aimed to establish the effect of sodium chloride on the growth and iron (II) oxidation of some biomining bacteria and evaluate their potential for use in saline bioleaching applications. All tested strains showed reduced cell numbers and a decrease in iron (II) oxidation rates in the presence of NaCl. Meanwhile, it was demonstrated that there was a range of sensitivities between genera of biomining bacteria to chloride, with Acidithiobacillus ferrooxidans being the most sensitive. Among the tested genera, Sulfobacillus exhibited the highest tolerance to NaCl, with robust growth and high iron (II) oxidation activity, making it suitable for metal bioleaching in saline environments. Leptospirillum spp. bacteria showed moderate tolerance, while Acidithiobacillus spp. demonstrated the lowest tolerance, with significant reductions in growth and iron oxidizing activity as NaCl concentrations increased. The limited tolerance of these bacteria restricts their use in biomining unless adaptations are explored. The role of chloride ion in the performance of the adapted moderate thermophiles from the genus Sulfobacillus in bioleaching of copper sulfide was investigated. It was revealed that Sulfobacillus sp. bacteria demonstrated the improved bioleaching of chalcopyrite (CuFeS2) in the presence of high concentration of sodium chloride significantly enhancing the copper leaching process.

The growing demand for electronic devices, combined with their increasingly short lifespans, has resulted in a sharp rise in electronic waste (e-waste), creating serious environmental and resource recovery challenges. Printed circuit boards (PCBs), a key component of electronic devices, are rich in valuable base and precious metals such as copper, aluminum, and gold - often in concentrations much higher than those found in natural ores. This study explores how particle size influences the bioleaching efficiency of metals from PCBs using a two-step approach. Bioleaching was carried out with biogenic ferric ions produced by Acidithiobacillus ferrooxidans 61. PCBs were crushed into four size fractions (≤125 µm, 125–630 µm, ≥800 µm, and 1000–1500 µm), pretreated, and subjected to bioleaching. The highest copper recovery was observed in the 125–630 µm fraction, where a balance between surface area and minimal particle agglomeration enhanced leaching efficiency. Zinc and aluminum recovery were also influenced by particle size: zinc leaching was more effective with larger particles (&gt;800 µm), while aluminum dissolution was higher in the finest fraction (≤125 µm). Most of the metal recovery occurred during the first stage of bioleaching, which corresponded with higher oxidation-reduction potential (ORP) values and more active bacterial performance. These findings emphasize the importance of particle size optimization in improving bioleaching outcomes and support the viability of bioleaching as an eco-friendly alternative to traditional metal recovery methods. Through precise control of particle size and process conditions, bioleaching can contribute to sustainable e-waste recycling and effective resource recovery.

Thermophilic lipase-producing microorganism’s present important industrial benefits owing to their stability and catalytic activity under extreme environmental conditions. This study sought to isolate and somewhat purify thermostable lipases from thermophilic bacteria collected from geothermal soils in (Hajj Yousef and Qaymawa, Iraq). A total of 68 samples were collected from hot springs at various depths and analyzed for lipase production utilizing tributyrin agar. Promising isolates were identified as Bacillus subtilis, Bacillus thermoleovorans, and Acidithiobacillus ferrooxidans. The lipase enzyme was purified using ammonium sulfate precipitation trailed by size-exclusion chromatography, yielding a 12-fold purification with 65% recuperation. SDS-PAGE revealed a single protein band of ~35 kDa. The enzyme exhibited optimum activity at 70°C and pH 9.0 and retained 85% activity at 80°C and in alkaline pH. Kinetic analysis showed a Km of 2.1 mM and Vmax of 120 U/mg. The enzyme demonstrated substrate specificity toward olive oil and stability in methanol, Ca2+, and SDS. Application trials confirmed 92% conversion of used oil to biodiesel and 80% fat degradation in wastewater. These findings highlight the enzyme's potential in sustainable biotechnology.