Exploring biosynthesis strategies to boost the yield of exopolysaccharide-protein blend from Bacillus arachidis SY8(T), an isolated native strain, as a potent adsorbent for heavy metals removal.

This investigation centers on the synthesis of a polysaccharide-protein blend produced by an isolated native strain (99.12 % phylogenetic affinity with Bacillus arachidis SY8(T)). The primary objective was to investigate the production of extracellular polymeric substances (EPS) under diverse stress conditions, encompassing exposure to heavy metal ions, salt, and toxic agents. Additionally, the impact of environmental parameters, namely pH, inoculation percentage, and time, on the production was investigated. Subsequently, the study examined the biosorption potential of the EPS produced for Pb(II), Cu(II), and Mn(II). The EPS obtained was thoroughly characterized via various tests. Rheological evaluations of an EPS solution (2 wt%) confirmed its pseudo-plastic and non-Newtonian fluid properties, while TGA analysis demonstrated its thermal stability up to 600 °C. Additional analyses, including GPC, FTIR, and H-NMR, provide further insights into the produced EPS. The best conditions for EPS production are determined: 5 % NaCl salt, serving as an effective stress inducer, and 37 °C, pH 6, with a 5 % inoculation, over 96 h. EPS demonstrates remarkable removal efficiencies of 99.9, 99.4 and 78.9 % for Pb(II), Cu(II), and Mn(II), respectively. These findings highlight the potential of EPS as an effective agent for removing heavy metal ions.

Maximization of uricase production in a column bioreactor through RSM based optimization.

Uricase (EC 1.7.3.3) is an oxidoreductase enzyme which is widely exploited for diagnostic and treatment purposes in medicine. This study has been focused on producing recombinant uricase from E. coli BL21 in a bubble column bioreactor (BCB) and finding the optimal conditions for maximum uricase activity. The three most effective variables on uricase activity were selected through Plackett-Burman design from 8 different variables and were further optimized by central composite design of RSM. The selected variables included the inoculum size (%v/v), IPTG (Isopropyl ß-d-1-thiogalactopyranoside) concentration (mM) and the initial pH of culture medium. The activity of uricase, final OD600 (Optical Density at 600nm wave-length) and final pH were considered as the responses of this optimization and were modeled. As a result, the activity of 5.84 U.ml-1 and final OD600 of 3.42 were obtained at optimum conditions of 3 %v/v of inoculum size, IPTG concentration of 0.54 mM and pH=6.0. By purifying the obtained enzyme using a Ni-NTA agarose affinity chromatography column, 165±1.5 mg uricase was obtained from a 600 mL cell culture. The results of this study show that bubble column bioreactors can be a highly effective option for large scale uricase production.

A hybrid thermal-biological recycling route for efficient extraction of metals and metalloids from end-of-life liquid crystal displays (LCDs).

Waste liquid crystal displays (LCDs) are one of the most substantial and rapidly growing e-waste streams that contain a notable amount of critical, precious, and toxic elements. This study presented a novel thermal-biological hybrid method for resource recovery from waste LCDs. Through the design of a multistage thermal treatment process with the addition of optimized 20 wt% B2O3 to waste, the LCD's glass structure was separated into two interconnected phases, resulting in the transfer of metals from the LCD's glass phase to the B2O3 phase that can solubilize in the acid solution. Following the thermal treatment step, the biometabolites of Aspergillus niger were used for bioleaching of In, Sr, Al, and As from the obtained thermally treated product. The optimal bioleaching parameters were a pulp density of 10 g/L, temperature of 70 °C, and leaching time of 2 days, which led to the highest extraction of 82.6% Al, 70.8% As, 64.5% In, and 36.2% Sr from thermally treated LCD waste, representing a multifold increase in Al, As, and Sr extraction levels compared to untreated waste. This study demonstrated that the proposed hybrid method could successfully overcome waste complexities and ensure effective element extraction from discarded LCDs.

A sustainable solution for alleviating hexavalent chromium from water streams using Lactococcus lactis AM99 as a novel Cr(VI)-reducing bacterium.

Chromium, extensively used in various industries, poses significant challenges due to its environmental impact. The threat of Cr(VI) causes critical concerns in aquatic ecosystems as a consequence of the fluidity of water. The conventional approach for the treatment of effluents containing Cr(VI) is reducing Cr(VI) to low-noxious Cr(III). This research is related to a Gram positive bacterium newly isolated from tannery effluent under aerobic conditions. To characterize functional groups on the isolate, Fourier transform infrared spectroscopy was utilized. The effect of different factors on Cr(VI) bioreduction was investigated, including temperature, initial Cr(VI) concentration, acetate concentration, and Tween 80 surfactant. Under optimal conditions (37 °C and 0.90 g/L sodium acetate), the bioreduction rate of the isolate, identified as Lactococcus lactis AM99, achieved 88.0 % at 300 mg/L Cr(VI) during 72 h (p < 0.05). It was observed that Cr(VI) bioreduction was enhanced by the acetate in both the quantity and intensity, while Tween 80 had no impact on the reaction. The strain AM99 exhibited remarkable characteristics, notably a marginal decrease in growth at elevated concentrations of hexavalent chromium and an exceptional potential to reduce Cr(VI) even at very low biomass levels, surpassing any prior findings in the associated research. Furthermore, The isolate could tolerate 1400 mg/L Cr(VI) in a solid medium. These distinctive features make the isolate a promising and well-suited candidate for remediating Cr(VI)-polluted environments. Additionally, the impact of biogenic extracellular polymer produced by the strain AM99 on reduction was examined at different temperatures.

Performance evaluation of a novel multi-metal catalyst solution obtained from electronic waste bioleaching on upgrading and enhancing oil recovery.

Due to the high costs and associated high CO2 emissions of thermal methods, this study focuses on upgrading heavy oil and enhancing oil recovery within reservoir temperature ranges. In this research, a novel, low-cost, and environmentally friendly multi-metal catalyst has been used, which is actually extracted from electronic waste (E-waste). At optimal conditions, which include 80 °C, 12 h of retention time, and 0.2 % v/v of the multi-metal catalyst, this catalyst effectively reduced the viscosity of heavy oil from 687 to 580 mPa.s. To analyze heavy oil before and after the process, Fourier transform infrared spectroscopy (FTIR) was conducted. FTIR spectra indicates that the multi-metal catalyst has reduced the amount of aromatic compounds, shortened hydrocarbon chains, and decreased double and triple bonds. Micromodel tests were conducted by multi-metal catalyst flooding at optimal temperature and retention time obtained from static experiments. Heavy oil recovery through multi-metal catalyst flooding reached 38 %, which is a 10.5 % increase compared to deionized water flooding. The contact angle of the rock was measured after contact with the multi-metal catalyst. The multi-metal catalyst reduced the contact angle by 55 °, changing the wettability of carbonate rock from oil-wet to water-wet. The absorption test indicates that the multi-metal catalyst dissolves certain metals in the rock, most likely due to the high pH of the catalyst. As a result, the permeability of the rock may increase due to the dissolution of the rock metals.

An efficient approach for enhancement of gold and silver bioleaching from spent telecommunication printed circuit boards using cyanogenic bacteria: Prevention of biofilm formation.

Environmentally friendly bioleaching of gold and silver from electronic waste using cyanogenic bacteria has emerged as a promising approach. In the process of cyanide bioleaching, cyanide ions produced by cyanogenic bacteria form complexes (such as AuCN and AgCN) with metals in the waste structure and lead to their dissolution. The recovery rate of these valuable elements during bioleaching is influenced by extracellular polymeric substances (EPS). For the first time, this study presents an investigation into the role of EPS from Pseudomonas atacamensis in the bioleaching of gold and silver from spent telecommunication printed circuit boards (STPCBs). The experimental results demonstrate that, after 6 days of bioleaching, gold and silver recoveries reached 22% and 36.2%, respectively. Complementary analyses employing FE-SEM and attachment tests shed light on the interactions between EPS, bacterial attachment to particle surfaces, and biofilm development stages during gold and silver bioleaching. Notably, the most significant bacterial attachment occurred on the fourth day of bioleaching. Zeta potential tests conducted on bacteria and EPS provided insights into the potential absorption of soluble cations such as Au+ and Ag+ by EPS. Furthermore, 250 mg/L polyvinylpyrrolidone (PVP) effectively removed EPS from the particle surfaces, improving gold and silver recovery rates, reaching 26% and 43.2%, respectively. These findings highlight the importance of understanding the role of EPS in bioleaching processes and offer insights into enhancing gold and silver recovery from electronic waste.

Regulatory-systemic approach in Aspergillus niger for bioleaching improvement by controlling precipitation.

In the context of e-waste recycling by fungal bioleaching, nickel and cobalt precipitate as toxic metals by oxalic acid, whereas organic acids, such as citric, act as a high-performance chelating agent in dissolving these metals. Oxalic acid elimination requires an excess and uneconomical carbon source concentration in culture media. To resolve this issue, a novel and straightforward systems metabolic engineering method was devised to switch metabolic flux from oxalic acid to citric acid. In this technique, the genome-scale metabolic model of Aspergillus niger was applied to predicting flux variability and key reactions through the calculation of multiple optimal solutions for cellular regulation. Accordingly, BRENDA regulators and a novel molecular docking-oriented approach were defined a regulatory medium for this end. Then, ligands were evaluated in fungal culture to assess their impact on organic acid production for bioleaching of copper and nickel from waste telecommunication printed circuit boards. The protein structure of oxaloacetate hydrolase was modeled based on homology modeling for molecular docking. Metformin, glutathione, and sodium fluoride were found to be effective as inhibitors of oxalic acid production, enabling the production of 8100 ppm citric acid by controlling cellular metabolism. Indirect bioleaching demonstrated that nickel did not precipitate, and the bioleaching efficiency of copper and nickel increased from 40% and 24% to 61% and 100%, respectively. Bioleaching efficiency was evaluated qualitatively by FE-SEM, EDX, mapping, and XRD analysis. KEY POINTS: • A regulatory-systemic procedure for controlling cellular metabolism was introduced • Metformin inhibited oxalic acid, leading to 8100 ppm citric acid production • Bioleaching of copper and nickel in TPCBs improved by 21% and 76.

A comprehensive review of bioleaching optimization by statistical approaches: recycling mechanisms, factors affecting, challenges, and sustainability.

A serious environmental problem is associated with the accumulation of solid waste on the Earth. Researchers are encouraged to find an efficient and sustainable method to recover highly profitable heavy metals and precious and base metals. Bioleaching is a green method of recovering valuable metals from solid waste. Optimizing the variables and conditions of the bioleaching process is crucial to achieving maximum metal recovery most cost-effectively. The conventional optimization method (one factor at a time) is well-studied. However, it has some drawbacks, such as the necessity of more experiments, the need to spend more time, and the inability to illuminate the synergistic effect of the variables. Optimization studies are increasingly utilizing response surface methodology (RSM) because it provides details about the interaction effects of variables with fewer experiments. This review discusses the application of RSM for bioleaching experiments from other solid wastes. It discusses the Central Composite and Box-Behnken designs as the most commonly used designs for optimizing bioleaching methods. The most influential factors for increasing the heavy metal recovery rate in applying RSM using the bioleaching process are recognized, and some suggestions are made for future research.

Ecofriendly recovery of copper from spent telecommunication printed circuit boards using an indigenous cyanogenic bacterium.

In recent years, electronic waste (e-waste) production has increased due to the population's growth and high consumption. As a result of the high concentration of heavy elements in these wastes, their disposal has posed many environmental problems. On the other hand, due to the non-renewability of mineral resources and the presence of valuable elements such as Cu and Au in electronic waste, these wastes are considered secondary minerals for recovering valuable elements. Among electronic waste, recovery of metals from spent telecommunication printed circuit boards (STPCBs) is significant, which has not been addressed despite their high production worldwide. This study isolated an indigenous cyanogenic bacterium from alfalfa field soil. The 16S rRNA gene sequencing results showed that the best strain has 99.8% phylogenetic affinity with Pseudomonas atacamenisis M7DI(T) with the accession number SSBS01000008 with 1459 nucleotides. The effect of the culture medium, initial pH, glycine concentration, and methionine on the cyanide production of the best strain was investigated. The results showed that the best strain could produce 12.3 ppm cyanide in NB medium with an initial pH of 7 and a concentration of glycine and methionine of 7.5 g/L and 7.5 g/L, respectively. The one-step bioleaching method was performed, which led to the recovery of 98.2% of Cu from STPCBs powder after 5 days. Finally, XRD, FTIR, and FE-SEM analyses were performed to investigate the structure of the STPCBs powder before and after the bioleaching process, confirming the high Cu recovery.

Bioleaching of valuable metals from spent LIBs followed by selective recovery of manganese using the precipitation method: Metabolite maximization and process optimization.

Despite the increased demand for resource recovery from spent lithium-ion batteries (LIBs), low Mn leaching efficiencies have hindered the development of this technology. A novel process was devised to enhance the dissolution of metals by producing citric acid using a molasses medium by Penicillium citrinum. This investigation used response surface methodology to investigate the influence of molasses concentration and media components on citric acid production, which demonstrated that molasses (18.5% w/w), KH2PO4 (3.8 g/L), MgSO4.7H2O (0.11 g/L), and methanol (1.2% (v/v)) were the optimum values leading to the production of 31.50 g/L citric acid. Afterward, optimum inhibitor concentrations (iodoacetic acid: 0.05 mM) were added to accumulate citric acid, resulting in maximum bio-production (40.12 g/L) of citric acid. The pulp density and leaching time effect on metals dissolution was investigated in enriched-citric acid spent medium. The suitable conditions were a pulp density of 70 g/L and a leaching duration of 6 days, which led to the highest dissolution of Mn (79%) and Li (90%). Based on the results of the TCLP tests, the bioleaching residue is non-hazardous, suitable for safe disposal, and does not pose an environmental threat. Moreover, nearly 98% of Mn was extracted from the bioleaching solution with oxalic acid at 1.2 M. XRD, and FE-SEM analyses were utilized for further bioleaching and precipitation mechanism analysis.

Production and characterization of a polysaccharide/polyamide blend from Pseudomonas atacamensis M7D1 strain for enhanced oil recovery application.

Bio-based polymers have better salt and temperature tolerance than most synthetic polymers. The biopolymer solutions have high viscosity, which can lead to reducing the fingering effect and soaring the oil recovery rate. This work aims to produce and characterize a biopolymer from Pseudomonas Atacamensis M7D1 strain, modify the biopolymer yield using Printed Circuit Boards (PCBs) powder as an outer tension in the growth medium, and finally, evaluate the produced biopolymer function for Enhanced Oil Recovery (EOR) purposes. Using PCBs powder to trigger bacteria for higher production yield increases the biopolymer production rate eleven times higher than pure growth medium without additives. Different analyses were performed on the biopolymer to characterize its properties; Gel Permeation Chromatography (GPC) indicated that the produced biopolymer has an average molecular weight of 3.6 × 105 g/mol. This macromolecule has high thermal resistivity and can tolerate high temperatures. Thermal analysis (TGA/DSC) shows only 69.27 % mass lost from 25 °C to 500 °C. The viscosity of 0.5 wt% biopolymer solution equals 3cp, 3 times higher than water. The glass micromodel flooding result shows that biopolymer solution with 0.5 wt% concentration has a 42 % recovery rate which is 24 % higher than water flooding.

Improvement of gold bioleaching extraction from waste telecommunication printed circuit boards using biogenic thiosulfate by Acidithiobacillus thiooxidans.

Cyanide usage in gold processing techniques has become increasingly challenging due to its toxicity and environmental impact. It is possible to develop environmentally friendly technology using thiosulfate because of its nontoxic characteristics. Thiosulfate production requires high temperatures, resulting in high greenhouse gas emissions and energy consumption. The biogenesized thiosulfate is an unstable intermediate product of Acidithiobacillus thiooxidans sulfur oxidation pathway to sulfate. A novel eco-friendly method was presented in this study to treat spent printed circuit boards (STPCBs) using biogenesized thiosulfate (Bio-Thio) obtained from Acidithiobacillus thiooxidans cultured medium. To obtain a preferable concentration of thiosulfate among other metabolites by limiting thiosulfate oxidation, optimal concentrations of inhibitor (NaN3: 3.25 mg/L) and pH adjustments (pH= 6-7) were found to be effective. Selection of the optimal conditions has led to the highest bio-production of thiosulfate (500 mg/L). The impact of STPCBs content, ammonia, ethylenediaminetetraacetic acid (EDTA), and leaching time on Cu bio-dissolution and gold bio-extraction were investigated using enriched-thiosulfate spent medium. The suitable conditions were a pulp density of 5 g/L, an ammonia concentration of 1 M, and a leaching time of 36 h, which led to the highest selective extraction of gold (65 ± 0.78%).

Bioleaching of indium from spent light-emitting diode monitors and selective recovery followed by solvent extraction.

The spent light emitting diode (LED) monitors are one of the fastest-growing waste streams that could provide indium, an essential element for the industry. This study presents a comprehensive strategy for indium extraction from spent LED monitors, including bioleaching followed by solvent extraction, stripping, and precipitation. Effects of A. thiooxidans and A. ferrooxidans inoculum percentage in mixed culture, pulp density, and time on indium, aluminum, and strontium bioleaching were investigated. In this regard, at optimized inoculum percentages (1.5 and 0.5% (v/v) of A. ferrooxidans and A. thiooxidans, respectively) and pulp density (60 g/L) at initial pH of 2, approximately 100% indium recovery was obtained in 18 days. The solubilized indium in the bioleaching solution has been extracted by the organic solvent of 20% (v/v) D2EHPA in kerosene. Following extraction, the stripping step was carried out to recover indium rather than iron selectively. The effect of two-phase contact time and aqueous to organic phase volume ratio in the extraction step and the acid type and concentration in the stripping step on indium and iron recovery percentages have been evaluated. For indium extraction, the optimum ratio of aqueous to organic phase volume and time were determined as 1 and 30 min, respectively, recovering 91.5% of indium. Using 5 M sulfuric acid has also resulted in an efficient stripping process. Finally, sodium hydroxide performed indium precipitation and a final precipitate of 94% (w/w) indium was obtained.

Environmentally sustainable and cost-effective recycling of Mn-rich Li-ion cells waste: Effect of carbon sources on the leaching efficiency of metals using fungal metabolites.

Metals recovery from spent lithium coin cells (SCCs) is enjoying great attention due to environmental problems and metal-rich contents such as Mn and Li. Fungi can generate many organic acids, and metals can be dissolved, but sucrose is not an economical medium. The main objective of this study is to find a suitable carbon substrate in place of sucrose for fungal bioleaching. We have developed an environmentally friendly, cost-effective, and green method for recycling and detoxifying Mn and Li from SCCs using the spent culture medium fromPenicillium citrinumcultivation. Sugar cane molasses and sucrose were selected as carbon sources. Based on the extracted fungal metabolites, the effects of pulp density, temperature, and leaching time were assessed on metal dissolution. The most suitable conditions were 30 g/L of pulp density, a temperature of 40 °C, and 4 days of leaching time in spent molasses medium, which led to a high extraction of 87% Mn and 100% Li. Based on EDX-mapping analyses, it was found that the initial concentration of ∑ (Mn + C) in the SCCs powder was almost 100% while reaching nearly 6.4% after bioleaching. After bioleaching, an analysis of residual powder confirmed that metal dissolution from SCCs was effective owing to fungal metabolites. The economic study showed that the bioleaching method is more valuable for the dissolution of metals than the chemical method; In addition to improving bioleaching efficiency, molasses carbon sources can be used for industrial purposes.

Comprehensive characterization and environmental implications of spent telecommunication printed circuit boards: Towards a cleaner and sustainable environment.

The management and prevention of environmental risks associated with spent telecommunications printed circuit boards (STPCBs) is a concerning issue worldwide. Recycling might be proposed as a proper method to overcome this issue. Despite knowing that, choosing a sustainable method is challenging because of STPCBs complexity. This problem was overcome by analyzing STPCBs using different analytical methods and metal speciation. Understanding these data is essential in selection strategies to maximize selective recycling of metals and to minimize environmental impact. This research focused on characterizing STPCBs based on their structural, morphological, physiochemical, surface, and thermal properties. The accurate measurement of metal contents, indicating 187,900 mg kg-1 Cu, 22,540 mg kg-1 Pb, 1320 mg kg-1 Ag, and 205 mg kg-1 Au elements, plus other base metals, revealed a remarkable potential value in STPCBs. The results of structural analyses indicated that the powder has a crystalline structure and consists of Cu, Sn and Pb phases as well as different functional groups. In addition, after evaluating the zeta potential of the sample, the isoelectric pH of the sample was observed to be 5.6, which indicates that the powder particles have a negative surface in an environment with a pH higher than this value. Further, the metal speciation via sequential extraction procedure was performed, which showed that a unique harsh recycling strategy is required due to the stable structure of STPCBs. According to the results of this analysis, the global contamination factor (GCF) value was 83.48, which indicates STPCBs have a high degree of contamination. Leaching tests and environmental criteria were also conducted on this waste. The findings suggest that STPCBs needs pretreatments before landfilling to lower the concentration of toxic metals. Also, waste extraction test was the most aggressive procedure to assess mobility. Achieving this information is considered an essential step to choosing the most efficient recycling methods that minimize environmental impact while maximizing selective recycling of metals.

Antimicrobial resistance patterns and virulence gene profiles of Salmonella enteritidis and Salmonella typhimurium recovered from patients with gastroenteritis in three cities of Iran.

This study evaluated distribution of virulence factors and antibiotic resistance in clinical isolates of Salmonella enteritidis and Salmonella typhimurium in three cities of Iran. Altogether 48 S. enteritidis and S. typhimurium isolates were collected from patients at certain Iranian hospitals between May 2018 and September 2021. Antimicrobial susceptibility testing was performed by disk diffusion and broth microdilution methods. The presence of antibiotic-resistance genes (blaTEM,blaSHV,blaCTX-M,blaNDM,strA, strB, aadA1, tetA, tetB, floR, sul1, sul2, dfrA), integrons (classe 1 and 2), and virulence-associated genes (invA, stn, sopB, spvC, rck, phoPQ) was investigated by PCR and sequencing. Antimicrobial agents like trimethoprim-sulfamethoxazole and imipenem represent highly efficient agents with 97% susceptibility. S. enteritidis and S. typhimurium exhibited high resistance to ciprofloxacin (n = 20, 71.43%) and ceftazidime (n = 9, 45%), respectively. Overall, 3 (6.25%), 13 (27.08%), and 6 (12.5%) isolates were divided into strong, moderate, and weak biofilm producers, respectively. Moreover, blaCTX-M,blaTEM, blaSHV, sul1, sul2, tetA, tetB, floR, strA, and strB resistant genes were detected in 10 (20.8%), 5 (10.4%), 1 (2.08%), 7 (14.58%), 1 (2.08%), 3 (6.25%), 2 (4.1%), 1 (2.08%), 2 (4.1%), 2 (4.1%), respectively. Furthermore, 7 (14.58%) strains had classe 1 integron. All tested S. enteritidis strains had invA and sopB, and all S. typhimurium strains had invA and phoPQ. However, spvC remained undetected in all isolates. Extensive surveillance and efficient control measures against infection help to stop the upsurge of various antibiotic-resistant isolates.

Structural study and metal speciation assessments of waste PCBs and environmental implications: Outlooks for choosing efficient recycling routes.

Environmental protection from risks and disposal management of discarded mobile phone printed circuit boards (MPhPCBs) is a global issue. Although recycling is proposed as a solution, it is challenging to choose a sustainable method due to the insufficient recognition from extreme structural heterogeneity of these wastes based on their types. To this end, a thorough study on the structural characterization of PCBs using different analyses and metal speciation by sequential extraction procedure were performed. Understanding these information is an essential step in order to choose efficient methods to maximize selective recycling of metals and minimize environmental implications. PCBs were found to be potent metallic reservoirs after all metal content of PCBs were precisely measured. The structural analysis results of the sample included identification of different phases, functional groups, 45.1 % of the crystalline and 54.9 % of amorphous, the mesoporous nature (pore diameter mean âˆ¼ 7.24 nm), hydrophobic property (contact angle âˆ¼93.4°), the positive ζ-potential of particles at pH < (isoelectric point âˆ¼5.4) and vice versa, and the particle size that were not oversized. The metal speciation outcome indicated over 80 % of the total content of elements such as Si, Sn, Ag, Au, Sr, Al, Cr, Nd, Ca, Ba, and P was in a solid crystal structure/residual fraction, which were hard recycled. The assessment of contamination levels of waste indicated the considerable contamination for the environment at global contamination factor âˆ¼27.7, the moderate ecological risk at potential ecological risk assessment âˆ¼82.9, and threats to public health. In addition, the metals of Pr, Mn, and Zn pose high risks because of their risk assessment code values of 42.7 %, 36.7 %, and 33.1 %, respectively. Leaching tests proved Waste Extraction Test was an aggressive method. ANC4 proposed high level of H+ consumption are required for metal leaching in future works.

Complete bioleaching of Co and Ni from spent batteries by a novel silver ion catalyzed process.

In the present work, bioleaching of two valuable metals of cobalt (Co) and nickel (Ni) from spent lithium-ion batteries (LIBs) of laptop by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans through a novel adaptation procedure was investigated. Different bioleaching methods including A. ferrooxidans and A. thiooxidans spent medium, A. ferrooxidans one-step and two-step bioleaching were carried out. The effect of silver ion on the bioleaching of Co and Ni in these methods was evaluated. Moreover, a novel strain adaptation approach to the toxic solid content of the battery powder was chosen, which resulted in a very short adaptation time and bioleaching (2 days). Even though silver ion did not have a significant effect on the spent medium method, it had an increasing effect of 26% and 7%, for Co and Ni recovery, respectively, on two-step bioleaching with silver ion-adapted A. ferrooxidans, in gradual addition of the battery powder. The highest extraction results in the spent medium method were 45.2% and 71.5% for Co and Ni, respectively, and a very high extraction yield of 99.95% for these metals was achieved in a short time of only 3 days by two-step bioleaching with gradual addition of the solid content and in the presence of Ag+. KEY POINTS: • Mixed spent medium of acidophilic bacteria resulted in higher Ni and Co extraction. • Adaptation to Ag+ has enhanced the strain capability for Co and Ni extraction. • With Ag+ presence, Co and Ni extraction reached 99.95% in two-step bioleaching.

A novel green strategy for biorecovery of valuable elements along with enrichment of rare earth elements from activated spent automotive catalysts using fungal metabolites.

Metals recovery from spent automotive catalytic converters (SACCs) has gained great attention due to high metal content of SACCs and their potential to pollute the environment. This study presented a novel green strategy for treating SACCs using oxalic acid-enriched spent culture medium from Aspergillus niger cultivations. To enhance oxalic acid production, the Central Composite Design (CCD) was applied, which demonstrated that glucose (27.06 g/L), NaNO3 (0.9 g/L), disodium oxalate (7.7 g/L), MnSO4·H2O (0.28 g/L), and ethanol (0.65%(v/v)) were the optimum values leading to production of 15.3 g/L oxalic acid. The results of metals biorecovery with the fungal metabolites showed that pulp density of 15 g/L, temperature of 60 °C, and leaching time of 6 h resulted in the highest extraction of 99.1% Al, 99.3% Si, 82.2% Mn, 91.9% Zn, 17.6% Ba, 99.5% Fe, 92.2% Sr, 35.7% Ti, 60.9% Pt, and 73.7% Pd, as well as maximum enrichment of rare earth elements (REEs) in the residual powder. The EDX-mapping analysis indicated that the concentration of ∑REEs was nearly 8% in the initial waste powder, while it reached around 81% in the residual powder after bioleaching. The bioleaching mechanism was further analyzed by characterizing the bioleaching residues through XRD, FTIR, and FESEM analyses.