Search Results (67)

The aim of this study was to investigate the potential for co-bioleaching of ground printed circuit boards (PCBs) and flotation tailings using a single-stage biohydrometallurgical process. The ground PCB sample was a finely divided waste product from industrial shredding, which was collected using an air filtration system. The flotation tailings sample was mainly composed of pyrite (49%), quartz (29%), gypsum (8%), feldspar (8%), and chlorite (6%). The experiment was carried out in laboratory-scale reactors at 35 °C with constant aeration and a flotation tailings pulp density of 5% (solid-to-liquid ratio). In a control reactor, only flotation tailings were leached. In an experimental reactor, both flotation tailings and ground PCBs were leached simultaneously. The experiment was conducted in two stages. In the first stage, the experiment was carried out in a batch mode. The second stage involved two reactors operating continuously in cascade. During the experiment, we monitored the dynamics of several key parameters as a function of PCB concentration, including pH, redox potential, the concentrations of Fe³⁺ and Fe²⁺ ions, and the number of microbial cells. The 16S rRNA gene analysis revealed that the presence of PCBs had a significant effect on the composition of the microbial community. The concentration of PCB was gradually increased in order to examine the limits of the process and optimize potential economic benefits. The increase was done in 3 stages: 5 g/L in the first stage, from 5 to 12 g/L in the second stage, and up to 35.5 g/L in the third stage. However, this increase had a negative effect on the pyrite oxidation rate and the effectiveness of PCB bioleaching in continuous mode. The bioleaching efficiency of copper from printed circuit boards (PCBs) was above 70% in batch mode and above 80% in continuous mode at PCB concentrations up to 12 g per liter. Copper recovery decreased to around 53.1–61.6% as the PCB concentration continued to increase. The nickel leaching efficiency in batch mode was 46.3 ± 4.8%. In continuous mode, the nickel recovery decreased as the PCB concentration increased, reaching 48.53% in the first stage, then declining to 37.62% in the second stage and finally dropping to 27.06% in the third stage, depending on the higher concentration of PCB. Full article

Aspergillus fijiensis is an industrially important filamentous fungus, whose genetic analysis has been limited by the absence of species-specific tools. This study establishes an optimized CRISPR–Cas9 genome editing platform for A. fijiensis, from protoplast preparation to DNA repair pathway engineering. Antibiotic screening first identified hygromycin B and 5-FOA (5-fluoroorotic acid) as effective positive and counter-selection markers. A high-efficiency protoplast regeneration protocol was developed depending on specific osmotic stabilization and mycelial competence. Evaluation of a plasmid-based CRISPR system revealed that while autonomous replication was feasible, gene editing was constrained by low efficiency and a predominant bias toward NHEJ (non-homologous end joining). We implemented a Cas9–sgRNA RNP (ribonucleoprotein) delivery approach, with RNP delivery alone producing frequent indels. However, targeted integration remained inefficient when using conventional MMEJ (Microhomology-mediated end joining) donors. By employing donors containing short (5 bp) microhomology arms between cleavage sites, we effectively engaged the MMEJ pathway, enabling precise insertions and large-fragment deletions in 92% of the analyzed transformants. Donor templates containing minimal 5 bp microhomology sequences could effectively shift the predominant repair pathway from NHEJ to MMEJ. These findings demonstrate that MMEJ is the superior pathway with a unique mechanism for genome engineering in A. fijiensis, providing a versatile toolkit for unlocking the biotechnological potential of this recalcitrant species and a successful paradigm for establishing genetic systems in other species. Full article

Thorium (Th), a naturally occurring actinide, is gaining renewed attention due to its dual role as a strategic nuclear resource and a potential environmental contaminant. This review critically reassesses thorium valorization pathways by integrating extraction technologies, environmental behavior, toxicological risks, and regulatory constraints. While thorium is primarily recovered as a by-product of rare earth element (REE) processing, conventional hydrometallurgical methods—though mature—generate significant secondary waste and pose environmental challenges. Emerging technologies, such as functionalized adsorbents, membrane systems, and biohydrometallurgy, show promise but remain largely confined to laboratory-scale studies due to scalability and stability issues. A key finding is that thorium’s environmental mobility and toxicological impact are directly influenced by the extraction processes used, creating species with distinct bioavailability and risk profiles. This work highlights the disconnect between high laboratory efficiencies and real-world applicability, emphasizing the need for integrated approaches that consider lifecycle impacts, waste minimization, and occupational safety. We propose a circular economy framework for sustainable thorium management, connecting green primary processing, secondary recovery from industrial residues, smart environmental stewardship, and supportive policy. The review concludes that successful thorium valorization depends not on incremental efficiency gains but on holistic designs that reconcile technological performance with environmental and health safeguards. Full article

Silicon nitride is a type of bioceramic with great application potential. However, the brittleness of silicon nitride can be addressed through toughening. In this study, various proportions of TiC were incorporated into the sintering additive system to explore the effects of different amounts of TiC on the mechanical properties, cell compatibility, and antibacterial properties of silicon nitride. Silicon nitride was prepared by gas pressure sintering, with TiC addition amounts of 3%, 5%, 8%, and 13% wt. Among the four types of silicon nitride, the mechanical properties of silicon nitride with 3% and 5% wt TiC addition were improved, with the flexural strength and fracture toughness of the former being 571 MPa and 8.35 MPa·m^1/2, respectively, and the flexural strength and fracture toughness of the latter being 532 MPa and 8.53 MPa·m^1/2, respectively. The surface of all four types of silicon nitride was enriched with Ti as the amount of TiC added increased, and the surface properties of the four silicon nitrides were the same. All four types of silicon nitride could continuously release Si ions in liquid. In vitro cell experiments showed that all four types of silicon nitride could enable normal cell proliferation and adhesion. Silicon nitride with different TiC addition amounts all exhibited good cell compatibility. Compared with the control material, each of the four types of silicon nitride demonstrated robust antibacterial efficacy against Staphylococcus aureus and Escherichia coli, with comparable potency across all types. These findings indicate that the incorporation of titanium carbide (TiC) within the silicon nitride matrix, particularly within the 3–5% weight ratio range, not only enhances mechanical integrity and cellular compatibility, but also confers notable antibacterial attributes. Consequently, these results demonstrate the promising viability of TiC-modified silicon nitride as a prospective material for the fabrication of bone implants. Full article

The growing demand for lithium, driven by its key role in rechargeable batteries and its use in electric vehicles, highlights the need for sustainable and environmentally friendly recovery strategies. Conventional methods, such as pyrometallurgy and hydrometallurgy, are effective but costly and harmful as they emit toxic compounds. Biohydrometallurgy has emerged as a promising alternative, as it uses microorganisms and their metabolites to solubilize metals under milder conditions. Biohydrometallurgy has emerged as a promising alternative, as it relies on microorganisms and their metabolites to solubilize metals under mild operating conditions. Nevertheless, challenges related to process efficiency and selectivity remain, particularly for lithium recovery. In this context, recent advances in metal-binding peptides have attracted increasing attention due to their inherent selectivity and the possibility of rational design and heterologous expression in well-established microbial hosts such as Escherichia coli, Bacillus subtilis, and Saccharomyces cerevisiae. This review critically analyzes current biotechnological strategies and explores the integration of microbial bioleaching with peptide-based approaches as a complementary and environmentally friendly framework for the selective recovery of lithium and other metals from spent batteries and waste electrical and electronic equipment. Overall, this review provides an integrative conceptual framework that highlights the potential of combining microbial processes with metal-binding peptides to guide the development of more selective and sustainable biotechnological strategies for lithium recovery from secondary sources. Full article

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. Full article

Acid mine drainage (AMD) environments feature extreme acidity (pH ≤ 2) and high heavy metal concentrations. Acidophiles survive these conditions through unique genetic adaptations and secondary metabolite (SM) pathways. Leptospirillum ferriphilum, known for its acid and heavy metal resistance, serves as a model for AMD bioremediation, though systematic multi-omics studies on its key SMs and biosynthesis pathways remain underexplored. In this study, L. ferriphilum YR01 was isolated and identified from the AMD of the Zijinshan copper mine, China. Pangenomic analysis revealed that YR01 possesses the largest number of genes (2623) among the eight sequenced L. ferriphilum strains. Comparative genomics, antiSMASH, BiG-SCAPE, and metabolomic analyses (LC-MS and HPLC-MS) were integrated to comprehensively explore its biosynthetic capacity. A total of 39 biosynthetic gene clusters (BGCs) were identified, of which 60% shared <50% similarity with known clusters, indicating substantial novel biosynthetic potential. The sequence alignment of SM biosynthetic gene clusters (BGCs) demonstrated the potential of L. ferriphilum to synthesize conserved clusters for ectoine, choline, carotenoids, terpenoids, and terpene precursors. YR01 harbors complete BGCs for all five SM types. Notably, key nonribosomal peptide synthetase (NRPS) modules implicated in N-acyl homoserine lactone (AHL) synthesis were identified. Untargeted metabolomics (LC-MS) revealed the production of diverse SMs (18 types) putatively involved in environmental adaptation, including phosphocholine, carotenoids (e.g., anteraxanthin), cholera autoinducer-1 (CAI-1), and multiple AHLs. Targeted detection (HPLC-MS) further confirmed that YR01 could produce ectoine (0.10 ng/mL) and specific AHLs (C₁₄-HSL, C₁₂-HSL, C₁₂-OH-HSL), which were beneficial for the survival of the strain in extremely acidic environments and interspecies communication through SMs. This study represents the first comprehensive multi-omics characterization of BGCs in L. ferriphilum and experimentally validates the production of key SMs. Collectively, this study provides a comprehensive elucidation of the SM biosynthetic repertoire and environmental adaptation strategies in L. ferriphilum, advancing our understanding of microbial adaptation and interspecies communication in AMD systems, and offering potential implications for biomining applications. Full article

Extremely acidophilic iron- and sulfur-oxidizing bacteria and archaea are used in the processing of different sulfide ores and concentrates (biohydrometallurgical technologies); therefore, studying their metabolic pathways and regulation is an urgent task. Thus, the goal of this work was to compare differential gene expression in the thermoacidophilic archaeal strain, representative of the genus Acidiplasma, a predominant microbial group in bioleach reactors, during growth in the presence of ferrous iron and elemental sulfur as well as pyrite and arsenopyrite, which are the most widespread sulfide minerals, and to obtain novel data on the mechanisms of interaction of microorganisms and sulfide minerals. Transcriptomic analysis revealed metabolic pathways involved in ferrous iron and sulfur oxidation (key processes in sulfide mineral oxidation) and determined their expression dependence on different substrates. It was shown that the blue copper protein sulfocyanin may play an important role in both iron and sulfur oxidation, while sulfur oxidation also involves genes encoding well-known proteins for reduced inorganic sulfur compounds (RISC), sulfur oxygenase reductase (SOR), and thiosulfate quinone oxidoreductase (TQO). The results obtained in the present study may be used in further work to improve biohydrometallurgical technologies. Full article

This paper presents a case study on heap bioleaching at the Monywa copper mine in Myanmar. Through mineralogical characterization and leaching tests, specific heap bioleaching technologies were developed and implemented at the mine. These technologies include acidification and start-up of heap bioleaching without external acid addition, ore classification with process optimization, and selective inhibition of pyrite oxidation for acid/iron balance during heap bioleaching. The optimized heap bioleaching technologies implemented at the Monywa copper mine have reduced both capital and operating costs. These advantages are specifically reflected in the use of multi-lift pads for both heap bioleaching and final residue storage, optimized processing based on ore characteristics, and the implementation of a solution closed cycle process without the need for additional acid or neutralization. These findings demonstrate a cost-effective approach to heap bioleaching and provide practical insights for operational optimization in similar copper mines. Full article

Rare earth elements (REEs), as necessary elements in many industries, have driven increased demand for mineral exploitation. However, understanding the occurrence states of REEs is crucial for their extraction. Therefore, this work primarily investigated the differences in the occurrence states of REEs and the thermal decomposition behavior of carbonatite rare earth deposits in China using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. The results showed that the bastnaesite concentrate from the M deposit in southwestern China (referred to herein as B-ore), contained REEs accounting for 53.59%, and was associated with small amounts of wulfenite, barite, and iron ore. In contrast, the contents of REEs in the raw ores of N deposit in northern China (referred to herein as R-ore) was relatively low (3.71%), but were also enriched in Fe. R-ore consisted of small particle, with 32.44% sized between 0.075 and 0.11 mm, and 26.38% below 0.075 mm. The contents of Fe, La, and Ce in these smaller particles were higher than those of larger particles. Fe might be substituted with Ce, La, and other REEs in magnetite crystals, forming isomorphic structures. This research was expected to provide assistance in the efficient extraction of REEs from carbonatite deposits. Full article

Purely electric and hybrid vehicles are emerging as the transport sector’s response to meet climate goals, aiming to mitigate global warming. As the adoption of transport electrification increases, the importance of recycling components of the electric propulsion system at the end of their life grows, particularly the battery pack, which significantly contributes to the vehicle’s final cost and generates environmental impacts and CO₂ during production. This work presents an overview of the recycling processes for lithium-ion automotive batteries, emphasizing the developing Brazilian scenario and more established international scenarios. In Brazil, companies and research centers are investing in recycling and using reused cathode material to manufacture new batteries through the hydrometallurgical process. On the international front, pyrometallurgy and physical recycling are being applied, and other methods, such as direct processes and biohydrometallurgy, are also under study. Regardless of the recycling method, the main challenge is scaling prototype processes to meet current and future battery demand, driven by the growth of electric and hybrid vehicles, pursuing both environmental gains through reduced mining and CO₂ emissions and economic viability to make recycling profitable and support global electrification. Full article

The rising demand for lithium-ion batteries (LIBs), driven by the growing consumption of electronic devices and the expansion of electric vehicles, is leading to a concerning depletion of primary metal resources and a significant accumulation of electronic waste. This urgent challenge highlights the need for sustainable recovery methods to extract valuable metals from spent LIBs, aligning with circular economy principles. In this study, the preparation of spent batteries for the bioleaching process was achieved with minimal manipulation. This included a preliminary discharge to ensure safety in subsequent processes and a brief crushing to facilitate the access of leaching agents to valuable metals. Unlike most studies that grind batteries to obtain powders between 70 and 200 microns, our approach works with particles sized around 5 mm. Additionally, our preparation process avoids any thermal or chemical treatments. This straightforward pre-treatment process marks a significant advancement by reducing the complexity and cost of processing. A systematic study was conducted on various fractions of the large particle sizes, using Fe (III) produced through bio-oxidation by A. ferrooxidans and biogenically obtained H2SO4 from A. thiooxidans. The highest metal extraction rates were achieved using the unsorted fraction, directly obtained from the black mass after the grinding process, without additional particle separation. When treated with bio-oxidized Fe (III), this fraction achieved a 95% recovery of Cu, Ni, and Al within 20 min, and over 90% recovery of Co, Mn, and Li within approximately 30 min. These recovery rates are attributed to the combined reducing power of Al and Cu already present in the black mass and the Fe (II) generated during the oxidation reactions of metallic Cu and Al. These elements actively facilitate the reduction of transition metal oxides into their more soluble, lower-valence states, enhancing the overall metal solubilization process. The extraction was carried out at room temperature in an acidic medium with a pH no lower than 1.5. These results demonstrate significant potential for efficient metal recovery from spent batteries with minimal pre-treatment, minimizing environmental impact. Additionally, the simplified residue preparation process can be easily integrated into existing waste management facilities without the need for additional equipment. Full article

The genus Acidithiobacillus has been widely used in bioleaching, and novel strains in this genus, such as A. ferriphilus, have also been confirmed to possess bioleaching capabilities. In this study, an Acidithiobacillus ferriphilus strain, QBS3, was isolated from zinc-rich sulfide mine drainage using the gradient dilution method. QBS3 is a Gram-negative, 1.3 µm rod-shaped bacterium with small red colonies. It showed a high iron oxidation efficiency of 0.361 g/(L·h) and a sulfur oxidation efficiency of 0.206 g/(L·d). QBS3 has sphalerite bioleaching ability; using QBS3 for pure sphalerite bioleaching, 18.8% of zinc was extracted in 14 days at 1% pulp density. Whole genome sequencing was performed on QBS3. Functional prediction showed that 9.13% of the genes were involved in replication, recombination, and repair. Bioleaching-related genes were analyzed, including iron and sulfur oxidation genes, and carbon and nitrogen fixation genes. For iron oxidation, the Cyc2→RusA pathway and Iro→RusB pathway were found in QBS3. In terms of sulfur oxidation, QBS3 has an incomplete SOX system and lacks the SDO gene, but Rho and Trx may complement the SOX system, enabling QBS3 to oxidize sulfur. QBS3 has multiple sets of carbon fixation genes, and nitrogen fixation genes were also identified. A hypothetical sphalerite bioleaching model is proposed; this study provides a theoretical basis for the zinc sulfide ore bioleaching industry. Full article

As arsenopyrite is a typical arsenic-bearing sulfide ore, the biooxidation process of arsenopyrite is of great significance for the extraction of gold from arsenic-bearing gold ores and the generation of arsenic-bearing acid mine drainage. During the biooxidation of arsenopyrite, a large amount of arsenic is produced, which inhibits the growth and metabolism of microorganisms and thus affects the extraction of gold from arsenic-bearing gold ores. Therefore, the screening and enrichment of microorganisms with high arsenic resistance have become important aspects in the study of arsenopyrite biooxidation. As described in this paper, through arsenic acclimation, the maximum arsenic tolerance concentration of Acidithiobacillus ferriphilus QBS 3 isolated from arsenic-containing acid mine drainage was increased to 80 mM As(Ⅲ) and 100 mM As(V). Microorganisms with high arsenic resistance showed better bioleaching performance for arsenopyrite. After 18 days of bioleaching, the leaching rate of arsenopyrite reached 100% at a pulp concentration of 0.5%, and after 30 days of bioleaching, the leaching rate of arsenopyrite was 79.96% at a pulp concentration of 1%. Currently, research on arsenopyrite mainly focuses on the control and optimization of environmental conditions, but there have been few studies on the biooxidation process of arsenopyrite at the protein and gene levels. Therefore, combining the results of a one-month bioleaching experiment on arsenopyrite by A. ferriphilus QBS 3 and the analysis of arsenic resistance genes, a bioleaching model of arsenopyrite was constructed, which laid an experimental basis and theoretical foundation for improving the gold recovery rate from refractory arsenic-bearing ores and exploring the arsenic resistance mechanism of microorganisms during the arsenopyrite leaching process. Full article

Acid mine drainage (AMD) is the result of the oxidation of pyrite and other sulfide ores, and the catalytic action of microorganisms accelerates the generation of AMD. In this paper, the interaction between 2-mercaptobenzimidazole (MBI) and pyrite in the presence of Acidithiobacillus ferrooxidans (At. ferrooxidans) was studied. The results of leaching experiments showed that when the dosage of MBI was more than or equal to 6 g/kg, the oxidation of pyrite was obviously inhibited, and the inhibition rate of 9 g/kg MBI was the best, reaching 97.1%. Electrochemical tests show that when the amount of MBI exceeds 16.8 mg, the pyrite surface treated with MBI will show good oxidation corrosion resistance, and the corrosion resistance will be enhanced with the increase in MBI dosage. Subsequently, the influence of MBI on bacterial growth was ruled out by experiments, and the surface of passivated pyrite was observed and characterized. The results showed that MBI could chelate with iron on the surface of pyrite through -C=N and -SH in the molecule, which enhanced the hydrophobicity of pyrite, thus reducing the contact between pyrite and the external environment and effectively inhibiting the oxidation of pyrite. Full article