Bioleaching of tungsten-rich spent hydrocracking catalyst using Penicillium simplicissimum

Scalable and Consolidated Microbial Platform for Rare Earth Element Leaching and Recovery from Waste Sources

Chemical methods for the extraction and refinement of technologically critical rare earth elements (REEs) are energy-intensive, hazardous, and environmentally destructive. Current biobased extraction systems rely on extremophilic organisms and generate many of the same detrimental effects as chemical methodologies. The mesophilic methylotrophic bacterium Methylobacterium extorquens AM1 was previously shown to grow using electronic waste by naturally acquiring REEs to power methanol metabolism. Here we show that growth using electronic waste as a sole REE source is scalable up to 10 L with consistent metal yields without the use of harsh acids or high temperatures. The addition of organic acids increases REE leaching in a nonspecific manner. REE-specific bioleaching can be engineered through the overproduction of REE-binding ligands (called lanthanophores) and pyrroloquinoline quinone. REE bioaccumulation increases with the leachate concentration and is highly specific. REEs are stored intracellularly in polyphosphate granules, and genetic engineering to eliminate exopolyphosphatase activity increases metal accumulation, confirming the link between phosphate metabolism and biological REE use. Finally, we report the innate ability of M. extorquens to grow using other complex REE sources, including pulverized smartphones, demonstrating the flexibility and potential for use as a recovery platform for these critical metals.

Unlocking the hidden value of industrial by-products: Optimisation of bioleaching to extract metals from basic oxygen steelmaking dust and goethite

In this study, the potential of bioleaching to extract valuable metals from industrial by-products, specifically basic oxygen steelmaking dust (BOS-D) and goethite was investigated. These materials are typically discarded due to their high zinc content and lack of efficient regeneration processes. By using Acidithiobacillus ferrooxidans, successful bioleaching of various metals, including heavy metals, critical metals, and rare earth elements was achieved. The Taguchi orthogonal array design was used to optimise the bioleaching process, considering four variables at three different levels. After 14 days, the highest metal extraction for the BOS-D (11.2 mg Zn/g, 3.2 mg Mn/g, 1.6 mg Al/g, 0.0013 mg Y/g, and 0.0026 mg Ce/g) was achieved at 1% solid concentration, 1% energy source concentration, 1% inoculum concentration, and pH 1.5. For goethite, the optimal conditions were 1% solid concentration, 4% energy source concentration, 10% inoculum concentration, and pH 2 resulting in a extraction of 26.6 mg Zn/g, 2.1 mg/g Mn, 1.8 mg Al/g, 0.01 mg Co/g, 0.0022 mg Y/g. These findings are significant, as they demonstrate the potential to extract valuable metals from previously discarded industrial by-products. The extraction of such metals can have substantial economic and environmental implications, while simultaneously reducing waste in the metallurgical industry. Furthermore, the preservation of initial concentration of iron in both BOS-D and goethite residues represents a significant step towards implementing more sustainable industrial practices.

An environmentally friendly method for extraction of cobalt and molybdenum from spent catalysts using deep eutectic solvents (DESs)

There has been a substantially increasing demand for energy critical elements (ECEs) in recent years as energy-related technology has advanced rapidly. Spent catalysts are known as potential sources of ECCs such as Ni, Co, Mo, W, V, and rare earth elements. This study developed a novel environmentally friendly process for recovering cobalt and molybdenum from spent hydroprocessing catalysts using deep eutectic solvents (DESs). DESs based on p-toluenesulfonic acid achieved high metal extraction at 100 °C and a pulp density of 20 g/L for 48 h which 93% of cobalt and 87% of molybdenum were dissolved. FT-IR and H-NMR analyses were conducted to determine whether hydrogen bonds form between p-toluenesulfonic acid-based DES components. Leaching kinetic models were also developed for DES systems. The experimental results were well-matched with the shrinking core models. The leaching controlling step of DES-1 was determined to be the diffusion through the product layer based on kinetic studies, with an activation energy of 22.56 kJ/mol for Co and 29.34 kJ/mol for Mo in DES-1. Similarly, the mixed control reaction with an activation energy of 38.09 kJ/mol for Co and 31.48 kJ/mol for Mo in DES-2 was found to control the leaching kinetic mechanism of the DES-2 sample.

Leaching of valuable metals from cathode active materials in spent lithium-ion batteries by levulinic acid and biological approaches

Recycling of valuable metals from spent lithium-ion batteries (LIBs) is of paramount importance for the sustainable development of consumer electronics and electric vehicles. This study comparatively investigated two eco-friendly leaching methods for recovering Li, Ni, Co, and Mn from waste NCM523 (LiNi_0.5Co_0.2Mn_0.3O₂) cathode materials in spent LIBs, i.e., chemical leaching by a green organic solvent, levulinic acid (LA) and bioleaching by an enriched microbial consortium. In chemical leaching, mathematical models predicting leaching efficiency from liquid-to-solid ratio (L/S; L/kg), temperature (°C), and duration (h) were established and validated. Results revealed that LA of 6.86 M was able to achieve complete leaching of all target metals in the absence of reductants at the optimal conditions (10 L/kg, 90 °C, and 48 h) identified by the models. The evaluation of direct one- and two-step and indirect bioleaching indicated that the latter was more feasible for metal extraction from waste NCM523. L/S was found to impact the indirect bioleaching most significantly among the three operating variables. Pretreatment of waste NCM523 by washing with 1 vol% methanesulfonic acid significantly improved indirect bioleaching. The side-by-side comparison of these two leaching approaches on the same cathode active material (CAM) thus provided the technical details for further comparison with respect to cost and environmental impact.

Environmentally-friendly biorecovery of manganese from electrolytic manganese residue using a novel Penicillium oxalicum strain Z6-5-1: Kinetics and mechanism

Bioleaching is a promising route for electrolytic manganese (Mn) residue (EMR) reutilization due to being eco-friendly and cost-effective. However, microbes with high bioleaching efficiency are scarce. This work aimed to isolate, screen, and characterize a novel fungal strain with high Mn-bioleaching efficiency from EMR, and study the kinetics and mechanism. The novel Penicillium oxalicum strain Z6-5-1 was found to selectively bioleach Mn from EMR. A maximum Mn²⁺ recovery of 93.3 % was achieved after 7 days and was mainly dependent upon acidolysis of the bio-organic acids, specifically gluconic acid and oxalic acid, as well as mycelial biosorption. This efficiency was the highest reported in the literature for a fungus over such a short time. EMR strongly induced P. oxalicum to produce gluconic acid and oxalic acid. The novel transcription factor PoxCxrE of P. oxalicum controlled the production of bio-organic acids by regulating the expression of rate-limiting enzyme genes involved in the biosynthesis of bio-organic acids. Scanning electron microscopy, laser particle size analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were employed to analyze EMR changes after bioleaching. This study provides an alternative fungal resource for Mn-bioleaching of EMR, and a novel target for metabiotic engineering to improve bio-organic acid production.

Fungal biotechnology for urban mining of metals from waste printed circuit boards: A review

Rapid surge in electronic waste (e-waste) and its unscientific handling has an adverse impact on humans and the environment. Waste printed circuit board (WPCB), an integrated component of e-waste, has a high metallic content that includes both toxic and precious metals. Therefore, metal recovery is essential not just to avoid environmental degradation but also for economic growth. The current literature analysis focuses on one such eco-friendly approach, known as fungal biotechnology, for extracting metals from WPCBs. Among diverse bioleaching agents, fungi have shown promising metal extraction efficiency (Al: 65-96%; Co: 45-90%; Cu: 34-100%; Ni: 8-95%; Mn: 70-95%; Pb: 27-95%; Zn: 54-99%) and the ability to work in a wide pH range. However, in terms of metal recovery from WPCBs, fungal bioleaching has been less explored. This review, thus, assesses the fungal biotechnology for metal extraction from WPCBs and discusses the associated mechanism and kinetics involved. Different process parameters affecting the fungal bioleaching have also been discussed briefly. The review highlights that, while this process has enough potential, some associated drawbacks hinder its practical applicability on an industrial scale. Lastly, some suggestions for scaling up and reducing the cost of the process have been made, which need to be addressed.

Insights into the polysaccharides and proteins production from Penicillium citrinum during bioleaching of spent coin cells

The essential role of polysaccharides and proteins of extracellular polymeric substances (EPS) has been well known in the bioleaching process. However, there is no information on the role of these compositions in the bioleaching of spent coin cells (SCCs). This study investigated protein and polysaccharide production as biological macromolecules during the bioleaching of SCCs at various pulp densities using adapted Penicillium citrinum. The adaptation improved the tolerance index of fungi for the bioleaching up to a pulp density of 30 g/L. The EPS analysis indicated that loosely bound EPS (LB-EPS) contained a high concentration of polysaccharides. Instead, the most protein content was concentrated at tightly bound EPS (TB-EPS). Both protein and polysaccharide keep growing up to 20 g/L of pulp density during the entire period of bioleaching, and the maximum binding rate of Mn and Li to EPS was 43% and 15%, respectively. Pearson correlation indicated the positive correlation of the protein and the polysaccharides content on bioleaching efficiencies. From the FTIR spectroscopy, the principal functional groups on Mn and Li binding were OH and carboxyl. The FE-SEM analysis revealed the deformation of EPS at 30 g/L of pulp density, which suggested the toxic effect of this pulp density.

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.

A sustainable approach on biomining of low-grade bauxite by P. simplicissimum using molasses medium

In order to find a sustainable and low-cost alternative route to the traditional recovery of aluminum, the filamentous fungus Penicillium simplicissimum was evaluated for aluminum recovery from low-grade bauxite ore. The oat-agar medium was carefully chosen as the foremost solid medium for fungal sporulation due to lower cost, ease in preparation, and high spore production in a short incubation time. To examine the acid production capability in submerged fermentation, P. simplicissimum was inoculated in a medium augmented with glucose and molasses as an energy source. High-performance liquid chromatography (HPLC) technique was used for the determination of the produced organic acids. Three different bioleaching approaches were evaluated using 1% bauxite pulp density. The culture containing P. simplicissimum spores grown in a medium supplemented with molasses leached 86.6% Al in the direct two steps on the fifth day, 56.5% in the direct one step on the fourth day, and 71.7% in the indirect bioleaching on the fourth day, while in the controlled sterile flasks, Al leaching was almost negligible. A maximal amount of Al was leached by the fungal strains using low-cost molasses as a substrate.

Microbial recovery of critical metals from secondary sources

The continuous development of technologies involving critical metals, both in Europe and over the world, and geopolitical challenges in areas rich in critical metal sources, imposed increased research efforts to recover them from secondary sources, by eco-efficient processes. Yet, microbes-metal interactions are not sufficiently exploited to recover metals from secondary sources, although they are already used in ore extraction. This review examines and compare strategies and processes involving microorganisms for critical metals recovery, since conventional physico-chemical methods are energy-intensive and often polluting. Two groups of microbial assisted recovery processes are discussed: metal mobilization from metal bearing waste, and selective metal separation from leaching solutions by immobilization on microbial biomass. Because most of the identified microbial technologies are developed on laboratory scale, the increase of biorecovery efficiency is compulsory for enhancing scaling-up potential. Future developments focused on novel microorganisms and high-performance strategies for critical metal recovery by microbial processes are considered.

Lithium bioleaching: An emerging approach for the recovery of Li from spent lithium ion batteries

The rapidly growing demand for lithium has resulted in a sharp increase in its price. This is due to the ubiquitous use of lithium-ion batteries (LIBs) in large-scale energy and transportation sectors as well as portable devices. Recycling of the LIBs for being the supply of critical metals hence becomes environmentally and economically viable. The presently used approaches for the recovery of spent LIBs like pyrometallurgical process can effectively recover nickel, cobalt, and copper, while lithium is usually lost in slag. Bioleaching process as an alternative method of extraction and recovery of valuable metals from the primary and secondary resources has been attracting a large pool of attraction. This method can provide higher recovery yield even for low concentration of metals which makes it viable among conventional methods. The bioleaching process can work with lower operating cost and consumed water and energy along with a simple condition, which produces less hazardous by-products ultimately. Here, we comprehensively review the biological and chemical mechanisms of the bioleaching process with a conclusive discussion to help how to extend the use of bioleaching for lithium extraction and recovery from the spent LIBs with a focus on recovery yields improvement. We elaborate on the three main types of the reported bioleaching with considering effective parameters including temperature, initial pH, pulp density, aeration, and medium and cell nutrients to sustain microorganism activity. Finally, practical challenges and future opportunities of lithium are discussed to inspire future research trends and pilot studies to realize the full potential of lithium recovery using sustainable bioleaching processes to extend a clean energy future.

Fungal bioleaching of metals from refinery spent catalysts: A critical review of current research, challenges, and future directions

Petroleum refining operations such as hydroprocessing and fluid catalytic cracking (FCC) generate huge quantities of spent catalysts containing toxic and valuable metals (Ni, V, Mo, Co, W, Al, etc.), the management of which is a serious environmental issue. Besides environmental concerns, the different metals present in the spent catalysts are also a valuable commodity to modern industries. Therefore, these spent catalysts also provide an opportunity to use it as a source of value to the refiners. In recent years, a biotechnological based leaching process 'bioleaching' has emerged as a promising eco-friendly technique for the extraction of metals from these refinery spent catalysts. Among various bioleaching agents such as archean, bacterial, or fungi, the process mediated by the fungi (Aspergillus niger, Penicillium simplicissimum, and many others) is gaining attention owing to the high metal extraction ability of the various fungal produced metabolites (organic acids) under moderately acidic conditions. Furthermore, the ability of these fungi to withstand wide process conditions (pH, spent catalyst concentration, substrate types, etc.), high metal toxicity and use of low-cost organic substrate make them an ideal candidate for bioleaching. In this review article, we shed light on the role and mechanisms of fungi involved in extracting different metals from spent hydroprocessing and FCC catalysts. Key process parameters that affect the efficiency of fungal based bioleaching are discussed. The techno-economic challenges associated with the process are elaborated, and the needed future research directions to promote its commercial applications are highlighted. Based on our analysis, it can be argued that the fungi bioleaching has potential, however, some challenges (slower kinetics, and health and safety) should be addressed before the process can be scaled up for the commercial application.

Tolerance of three fungal species to lithium and cobalt: Implications for bioleaching of spent rechargeable Li-ion batteries

AIMS

This paper aims to quantify the growth and organic acid production of Aspergillus niger, Penicillium chrysogenum and Penicillium simplicissimum when these fungi are exposed to varying levels of lithium (Li) and cobalt (Co). The study also tests whether pre-exposing the fungi to these metals enables the fungi to develop tolerance to Li or Co.

METHODS AND RESULTS

When cultures of A. niger, P. chrysogenum or P. simplicissimum were exposed to 250 mg l^-1 of Li or Co, biomass production and excretion of organic acids were significantly inhibited after 5 days of growth compared to cultures grown in the absence of these metals. Pre-exposing cultures of A. niger to 250 mg l^-1 of Li or Co for 20 days significantly increased biomass production when the fungus was subsequently sub-cultured into 250 or 500 mg l^-1 of Li or Co. However, pre-exposure of P. chrysogenum or P. simplicissimum to 250 mg l^-1 of Li or Co for 20 days did not increase biomass production.

CONCLUSIONS

Aspergillus niger, but not the Penicillium species, developed tolerance to Li and to Co during the 20-day pre-exposure period. Therefore, processes that utilize fungal bioleaching with A. niger to mobilize and recover valuable metals such as Li or Co should consider a pre-exposure step for fungi to improve their tolerance to metal toxicity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Fungi may have the ability to extract valuable metals such as Li and Co from spent rechargeable batteries. However, the toxicity of the extracted metals can inhibit fungal growth and organic acid production. Pre-exposure to metals may alleviate toxicity for some fungal species. This knowledge can be used to improve the design of bioleaching protocols, increasing the potential for fungal bioleaching to become an economical and environmentally friendly method of recovering Li and Co from spent batteries.

Enhanced bio-recovery of aluminum from low-grade bauxite using adapted fungal strains

Filamentous fungi have been proved to have a pronounced capability to recover metals from mineral ores. However, the metal recovery yield is reduced due to toxic effects triggered by various heavy metals present in the ore. The current study highlights the fungal adaptations to the toxic effects of metals at higher pulp densities for the enhanced bio-recovery of aluminum from low-grade bauxite. In the previous studies, a drastic decrease in the aluminum dissolution was observed when the bauxite pulp density was increased from 1 to 10% (w/v) due to the high metal toxicity and low tolerance of Aspergillus niger and Penicillium simplicissium to heavy metals. These fungi were adapted in order to increase heavy metal tolerance of these fungal strains and also to get maximum Al dissolution. A novel approach was employed for the adaptation of fungal strains using a liquid growth medium containing 5% bauxite pulp density supplemented with molasses as an energy source. The mycelia of adapted strains were harvested and subsequently cultured in a low-cost oat-agar medium. Batch experiments were performed to compare the aluminum leaching efficiencies in the direct one-step and the direct two-step bioleaching processes. FE-SEM analysis revealed the direct destructive and corrosive action by the bauxite-tolerant strains due to the extension and penetration of the vegetative mycelium filaments into the bauxite matrix. XRD analysis of the bioleached bauxite samples showed a considerable decline in oxide minerals such as corundum and gibbsite. Results showed a high amount of total Al (≥ 98%) was successfully bioleached and solubilized from low-grade bauxite by the adapted fungal strains grown in the presence of 5% pulp density and molasses as a low-cost substrate. Graphical abstract.

Enfoques microbiológicos para el tratamiento de catalizadores agotados

Los catalizadores, homogéneos o heterogéneos, son ampliamente utilizados para una gran variedad de procesos industriales, con el fin de producir combustibles limpios y muchos otros productos valiosos, siendo los catalizadores agotados provenientes del hidroprocesamiento los mayores residuos sólidos de la industria de la refinería y la contribución principal a la generación de catalizadores agotados. Debido a su naturaleza peligrosa, el tratamiento y la recuperación de metales de este tipo de residuos han ganado cada vez más importancia, debido al agotamiento de los recursos naturales y a la contaminación ambiental. Aunque ya existen técnicas disponibles para estos fines, éstas generan grandes volúmenes de desechos potencialmente peligrosos y producen emisiones de gases nocivos. Por lo tanto, las técnicas biotecnológicas pueden representar una alternativa promisoria para el biotratamiento y la recuperación de metales contenidos en los catalizadores agotados. Con este fin, se han analizado diversos microorganismos, que comprenden bacterias, arqueobacterias y hongos, capacitados para facilitar la eliminación de losmetales contenidos en estoscatalizadores. En estarevisión se presenta un amplio escenario sobre los avances con respecto al manejo de los catalizadores agotados y su tratamiento tradicional, seguido de una descripción detallada sobre los enfoques microbiológicos reportados hasta la actualidad.

Evaluation of molybdenum recovery from sulfur removed spent catalyst using leaching and solvent extraction

In this article a new spent catalyst sample preparation method was implemented for the purpose of molybdenum leaching in a single step. Further molybdenum and vanadium in the leach liquor were separated and their concentrations were enriched using the solvent extraction and stripping techniques. The impervious sulfur (S⁰) layer of the spent catalyst sample was removed using carbon disulfide (CS₂). The advantages of S⁰removal were evaluated by conducting different sets of the Mo leaching experiments and they were further examined by varying different conditions such as three lixiviants, hydrogen peroxide (H₂O₂) addition, and three leaching parameters. The leaching rate increased in an order, e.g. acetone washed < acetone-CS₂ washed < acetone washed-H₂O₂ < acetone-CS₂ washed-H₂O₂, for the experimental concentration range of different lixiviants with the maximum of 94.8%(w/w) Mo dissolution in a single step. Optimization of the pulp density was important as the interaction of lixiviant molecules with multiple reacting solid particles decreased the driving force of the chemical reactions. The solvent extraction followed by the stripping technique was found to be excellent as the concentration of vanadium and molybdenum enriched from 0.55 to 1.9 M and 0.0448 to 1.08 M, respectively.

Ultrasound-assisted leaching of vanadium from fly ash using lemon juice organic acids

In this work, vanadium (V) was selectively extracted from fuel-oil fly ash using a leaching process utilizing organic acids extracted from lemon juice with assistance from ultrasound and H₂O₂. Response Surface Methodology (RSM) was used to optimize the main operating factors. The V recovery was 88.7% at the optimal conditions: 27.9% (v/v) lemon juice, 10% (v/v) hydrogen peroxide (H₂O₂), solid/liquid (S/L) ratio 0.01% (w/v), ultrasound power 159 W at 20 kHz in 2 h, and initial temperature of 35 °C. The effect of time on the V recovery was examined. The maximum recovery was 100% after 3 h. Furthermore, the individual effects of ultrasound and H₂O₂ on V recovery were studied, and the results showed that without H₂O₂ and ultrasound, the V recovery decreased greatly, indicating that both factors were essential in the leaching process. According to the modified shrinking core model, test results indicated that mass diffusion was the controlling step of the overall reaction kinetics. The activation energy of the leaching reaction in the temperature range 25 to 65 °C was found to be 17.1 kJ mol⁻¹.

In this work, vanadium (V) was selectively extracted from fuel-oil fly ash using a leaching process utilizing organic acids extracted from lemon juice with assistance from ultrasound and H₂O₂.

Leaching of metals from end-of-life solar cells

The issue of recycling waste solar cells is critical with regard to the expanded use of these cells, which increases waste production. Technology establishment for this recycling process is essential with respect to the valuable and hazardous metals present therein. In the present study, the leaching potentials of Acidithiobacillus thiooxidans, Acidithiobacillus ferrooxidans, Penicillium chrysogenum, and Penicillium simplicissimum were assessed for the recovery of metals from spent solar cells, with a focus on retrieval of the valuable metal Te. Batch experiments were performed to explore and compare the metal removal efficiencies of the aforementioned microorganisms using spent media. P. chrysogenum spent medium was found to be most effective, recovering 100% of B, Mg, Si, V, Ni, Zn, and Sr along with 93% of Te at 30 °C, 150 rpm and 1% (w/v) pulp density. Further optimization of the process parameters increased the leaching efficiency, and 100% of Te was recovered at the optimum conditions of 20 °C, 200 rpm shaking speed and 1% (w/v) pulp density. In addition, the recovery of aluminum increased from 31 to 89% upon process optimization. Thus, the process has considerable potential for metal recovery and is environmentally beneficial.

Effects of Solid Content and Substrate Concentration on Bioleaching of Heavy Metals from Sewage Sludge Using Aspergillus niger

The presence of heavy metals in sewage sludge not only affects the performance of sludge anaerobic digestion process but also restricts the land application of treated sewage sludge. Therefore, a fungi-mediated bioleaching process for simultaneous metal leaching and sludge digestion by Aspergillus niger was developed to treat the sewage sludge containing heavy metals in this study. The effects of two important parameters, sludge solid content and substrate (sucrose) concentration, on the performance of fungal bioleaching were investigated in this study. The results showed that the rate of pH reduction increased with increasing sludge solid contents and sucrose concentrations. In this study, the efficiency of metal removal decreases in the order of Mn > Zn > Ni > Pb. The efficiencies of metal leaching and solid degradation (SS and VSS) were found to be decreased with an increase of sludge solid content and a decrease of sucrose concentration. At 2 days of reaction time, the maximum efficiency of metal solubilization was 95, 56, 21 and 13% for Mn, Zn, Ni and Pb, respectively.

Bioleaching of Al from spent fluid catalytic cracking catalyst using Aspergillus species

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Biogenically produced organic acids (citric acid) are used for the bioleaching of spent fluid catalytic cracking catalyst.

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Aspergillus strains-A. niger, A. foetidus, and A. carbonarius, were studied with varying catalyst loading for Al bioleaching.

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The highest Al leaching efficiency of 88.43% was obtained at 0.8% (w/v) catalyst loading using A. foetidus.

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A different carbon source, molasses was also investigated for Al bioleaching.

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Highest bioleaching efficiency of 60% (in molasses) for Al was obtained at 40 g/L sugar concentration.

Bioleaching uses biodegradable organic acids, thereby making the process environmental friendly as compared to chemical leaching. In this work, bioleaching of aluminium (Al) metal from spent catalyst was investigated by using three Aspergillus strains (A. niger, A. foetidus, and A. carbonarius). Bioleaching was performed in batch culture mode at different loading densities of spent catalyst (i.e., 0.4%, 0.8% and 1.2% (w/v)). The highest Al leaching efficiency of 88.43% was obtained at 0.8% ((w/v)) catalyst loading using A. foetidus, further increase in the catalyst loading decreased the efficiency. In addition to this, molasses was used as a carbon source (low-cost) at various concentrations for bioleaching of spent catalyst and the results were found to be significant at 40 g/L sugar concertation with 60% bioleaching efficiency. Overall, this study indicates that A. foetidus have the potential for leaching of Al from spent catalysts. Therefore, present research findings suggested that, instead of using mineral acids, organic acids (biodegradable) usage for metal leaching process is highly reliable and eco-friendly as well.

Bioleaching of Major, Rare Earth, and Radioactive Elements from Red Mud by using Indigenous Chemoheterotrophic Bacterium Acetobacter sp

The aim was to study the bioleaching performance of chemoheterotrophic bacterium involved in leaching of major, rare earth, and radioactive elements from red mud (RM), and to explore the underlying mechanism. An acid-producing bacterium, identified as Acetobacter sp., was isolated from RM impoundment and used in the bioleaching experiments under one-step, two-step and spent medium process at up to 10% pulp density. The results showed that the leaching ratios of Al, Lu, Y, Sc, and Th were 55%, 53%, 61%, 52%, and 53% respectively under one-step process at 2% pulp density. Under both one- and two-step processes at 2% pulp density, the radioactivity of bioleached RM can meet the relevant regulation in China. The total amount of organic acids excreted by Acetobacter sp. increased with an increase of RM pulp density. After bioleaching, contents of hematite and gibbsite decreased but perovskite increased in RM. Micromorphology analysis indicated that the cells of Acetobacter sp. adhered to RM particles and formed large-size aggregates, and a new crystal of weddellite emerged. In view of the shorter lag phase and smaller biomass comparing to fungi even under direct contact with RM, bacterium Acetobacter sp. is supposed to apply to in situ heap or dump bioleaching of RM.

Leaching of vanadium from waste V2O5-WO3/TiO2 catalyst catalyzed by functional microorganisms

Solid wastes are currently produced in large amounts. Although bioleaching of metals from solid wastes is an economical and sustainable technology, it has seldom been used to recycle metals from abandoned catalyst. In this study, the bioleaching of vanadium from V₂O₅-WO₃/TiO₂ catalyst were comprehensively investigated through five methods: Oligotrophic way, Eutrophic way, S-mediated way, Fe-mediated way and Mixed way of S-mediated and Fe-mediated. The observed vanadium bioleaching effectiveness of the assayed methods was follows: S-mediated > Mixed > Oligotrophic > Eutrophic > Fe-mediated, which yielded the maximum bioleaching efficiencies of approximately 90%, 35%, 33%, 20% and 7%, respectively. The microbial community analysis suggested that the predominant genera Acidithiobacillus and Sulfobacillus from the S-mediated bioleaching way effectively catalyzed the vanadium leaching, which could have occurred through the indirect mechanism from the microbial oxidation of S⁰. In addition, the direct mechanism, involving direct electron transfer between the catalyst and the microorganisms that attached to the catalyst surface, should also help the vanadium to be leached more effectively. Therefore, this work provides guidance for future research and practical application on the treatment of waste V₂O₅-WO₃/TiO₂ catalyst.

A statistical approach of zinc remediation using acidophilic bacterium via an integrated approach of bioleaching enhanced electrokinetic remediation (BEER) technology

The aim of the present study was to isolate an indigenous acidophilic bacterium from tannery effluent contaminated sludge (TECS) sample and evaluate its potentiality towards the removal of zinc using an integrated approach of bioleaching enhanced electrokinetic remediation (BEER) technology in zinc spiked soil at an initial concentration of 1000 mg/kg. The isolated acidophilic bacterium was characterized by biochemical and 16S rRNA molecular identification and was named as Serratia marcescens SMAR1 bearing an accession no. MG742410 in NCBI database. The effect of pH and inoculum dosage of SMAR 1 strain showed an optimal growth at pH 5.0 and 4% (v/v) respectively. Based on these experimental data, a statistical analysis was done using Design Expert computer software, v11 to study the interaction between the process parameters with respect to zinc reduction as an output response. Electrokinetic experiments were conducted in a customised EK cell under optimised process conditions, employing titanium electrodes. Experiments for zinc removal were demonstrated for bioleaching, electrokinetic (EK) and BEER technology. On comparing, the integrated process was found to evidence as an excellent metal remediation option with a maximum zinc removal of 93.08% in 72 h than plain bioleaching (72.86%) and EK (56.67%) in 96 h. This is the first report of zinc removal in a short period of time using Serratia marcescens. It is therefore concluded that the BEER approach can be regarded as an effective technology in cleaning up the metal contaminated environment with an easy recovery and reuse option within short period of time.

Biosurfactant-facilitated leaching of metals from spent hydrodesulphurization catalyst

AIMS

To investigate the capabilities of different types of biosurfactants (rhamnolipids, lipopeptides, sophorolipids) to remove metals and carbon from the hazardous spent hydrodesulphurization (HDS) catalyst generated by petroleum refineries.

METHODS AND RESULTS

Biosurfactants were prepared and used to treat spent HDS catalyst. Metal and carbon contents were analysed and compared with those from no-biosurfactant control treatments. All biosurfactant treatments increased carbon loss percentage from the spent HDS catalyst. The lipopeptide treatment LI, containing 17·34 mg ml^-1 of crude biosurfactants, caused the highest carbon loss percentage (44·5%). Rhamnolipids were, in general, better than sophorolipids and lipopeptides as metal-removing agents. The metal content decreased as the concentration of rhamnolipids decreased. The R5 treatment, which contained 0·4 mg l^-1 of crude rhamnolipids, caused the highest reduction in metal content. Molybdenum, nickle and vanadium contents were reduced by 90, 30 and 70% respectively.

CONCLUSIONS

Biosurfactants might have potential application for metals and coke removal from spent HDS catalysts. The bioleaching capability depends on the type and concentration of the biosurfactant.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study, after further in-depth investigations, might lead to the development of an eco-friendly and economic technology to treat or even regenerate the environmentally hazardous spent HDS catalysts, which are generated in huge amounts by the petroleum refineries.

An Aspergillus aculateus strain was capable of producing agriculturally useful nanoparticles via bioremediation of iron ore tailings

Mining waste such as iron ore tailing is environmentally hazardous, encouraging researchers to develop effective bioremediation technologies. Among the microbial isolates collected from iron ore tailings, Aspergillus aculeatus (strain T6) showed good leaching efficiency and produced iron-containing nanoparticles under ambient conditions. This strain can convert iron ore tailing waste into agriculturally useful nanoparticles. Fourier-transform Infrared Spectroscopy (FT-IR analysis) established the at the particles are protein coated, with energy dispersive X-ray Spectroscopy (EDX analysis) showing strong signals for iron. Transmission Electron Microscopy (TEM analysis) showed semi-quasi spherical particles having average size of 15 ± 5 nm. These biosynthesized nanoparticles when tested for their efficacy on seed emergence activity of mungbean (Vigna radiata) seeds, and enhanced plant growth at 10 and 20 ppm.

Chemical and petrochemical industry

The potential sources of various metals in chemical and petrochemical processes are discussed. Special emphasis is put on the catalysts used in the industry. Their main applications, compositions, especially metal contents are presented both for fresh and spent ones. The focus is on the main types of metals used in catalysts: the platinum-group metals, the rare-earth elements, and the variety of transition metals. The analysis suggested that chemical and petrochemical sectors can be considered as the secondary source of metals. Because the utilization of spent refinery catalysts for metal recovery is potentially viable, different methods were applied. The conventional approaches used in metal reclamation as hydrometallurgy and pyrometallurgy, as well as new methods include bioleaching, were described. Some industrial solutions for metal recovery from spent solution were also presented.

Comparison of bioleaching and electrokinetic remediation processes for removal of heavy metals from wastewater treatment sludge

Heavy metals prevent the growing amount of sewage sludge from being disposed as fertilizeron land. The electrokinetic remediation and bioleaching technology are the promising methods to remove heavy metals. In recent years, some innovation has been made to achieve better efficiency, including the innovation of processes and agents. This paper reviews the development of the electrokinetic remediation and bioleaching technology and analyses their advantages and limitation, pointing out the need of the future research for the heavy metals-contaminated sewage sludge.

Alkaline bioleaching of municipal solid waste incineration fly ash by autochthonous extremophiles

The increasing demand for energy and the generation of solid waste have caused an alarming rise in fly ash production globally. Since heavy metals continue to be in demand for the production of materials, resource recovery from the recycling of these wastes has the potential to delay the depletion of natural ores. The use of microorganisms for the leaching of metals, in a process called bioleaching, is an eco-friendly and economical way to treat the metal-laden wastes. Bioleaching of fly ash is challenging due largely to the alkaline nature and toxic levels of heavy metals which are detrimental to microbial growth and bioleaching activity. The present work reports the isolation of indigenous bacteria from a local landfill site and their bioleaching performance [corrected]. 38 autochthonous strains of bacteria were isolated from eight samples collected and plated on five different media. 18 of the isolates showed bioleaching potential, with significant alkaline pH or fly ash tolerance. Genetic characterization of the strains revealed a dominance of Firmicutes, with Alkalibacterium sp. TRTYP6 showing highest fly ash tolerance of up to 20% w/v fly ash, and growth over a pH range 8-12.5. The organism selectively recovered about 52% Cu from the waste. To the best of our knowledge, this is the first time a study on bioleaching with extreme alkaliphiles is reported.

Fungal leaching of valuable metals from a power plant residual ash using Penicillium simplicissimum: Evaluation of thermal pretreatment and different bioleaching methods

Each year a tremendous volume of V-Ni rich ashes is produced by fuel oil consuming power plants throughout the world. Recovery of precious metals existing in these ashes is very important from both economic and environmental aspects. The present research was aimed at investigating bioleaching potential of Penicillium simplicissimum for the recovery of metals from power plant residual ash (PPR ash) using different bioleaching methods such as one-step, two-step, and spent-medium bioleaching at 1% (w/v) pulp density. Furthermore, the effects of thermal pretreatment on leaching of V, Ni, and Fe, as major elements present in PPR ash, were studied. Thermal pretreatment at various temperatures removed the carbonaceous and volatile fraction of the ash and affected the fungal growth and metal leachability. The highest extraction yields of V and Ni were achieved for the original PPR ash, using spent-medium bioleaching in which nearly 100% of V and 40% of Ni were extracted. The maximum extraction yield of Fe (48.3%) was obtained for the pretreated PPR ash at 400°C by spent-medium bioleaching. In addition, the fungal growth in pure culture was investigated through measurement of produced organic acids via high performance liquid chromatography (HPLC). Chemical leaching experiments were performed, using commercial organic acids at the same concentrations as those produced under optimum condition of fungal growth (5237ppm citric, 3666ppm gluconic, 1287ppm oxalic and 188ppm malic acid). It was found that in comparison to chemical leaching, bioleaching improved V and Ni recovery up to 19% and 12%, respectively. Moreover, changes in physical and chemical properties as well as morphology of the samples utilizing appropriate analytical methods such as XRF, XRD, FTIR, and FE-SEM were comprehensively investigated.

Identification of Bacillus megaterium and Microbacterium liquefaciens genes involved in metal resistance and metal removal

Bacillus megaterium MNSH1-9K-1 and Microbacterium liquefaciens MNSH2-PHGII-2, 2 nickel- and vanadium-resistant bacteria from mine tailings located in Guanajuato, Mexico, are shown to have the ability to remove 33.1% and 17.8% of Ni, respectively, and 50.8% and 14.0% of V, respectively, from spent petrochemical catalysts containing 428 ± 30 mg·kg(-1) Ni and 2165 ± 77 mg·kg(-1) V. In these strains, several Ni resistance determinants were detected by conventional PCR. The nccA (nickel-cobalt-cadmium resistance) was found for the first time in B. megaterium. In M. liquefaciens, the above gene as well as the czcD gene (cobalt-zinc-cadmium resistance) and a high-affinity nickel transporter were detected for the first time. This study characterizes the resistance of M. liquefaciens and B. megaterium to Ni through the expression of genes conferring metal resistance.

V and Ni recovery from a vanadium-rich power plant residual ash using acid producing fungi: Aspergillus niger and Penicillium simplicissimum

Bioleaching of V and Ni from a vanadium-rich power plant residual (PPR) ash using Aspergillus niger and Penicillium simplicissimum was investigated.

Bioleaching of fuel-oil ash using Acidithiobacillus thiooxidans in shake flasks and a slurry bubble column bioreactor

This work investigated a bioleaching process to remove V, Ni and Cu from fuel-oil ash (FOA) using Acidithiobacillus thiooxidans.

Bioleaching of an oil-fired residual: process optimization and nanostructure NaV6O15 synthesis from the bioleachate

The main objective of this work was to optimize metals recovery from a residual oil-fired ash produced in a thermal power plant using Acidithiobacillus ferrooxidans.

Platinum and rhenium extraction from a spent refinery catalyst using Bacillus megaterium as a cyanogenic bacterium: statistical modeling and process optimization

The present study evaluated the potential of Bacillus megaterium as a cyanogenic bacterium to produce cyanide for solubilization of platinum and rhenium from a spent refinery catalyst. Response surface methodology was applied to study the effects and interaction between two main effective parameters including initial glycine concentration and pulp density. Maximum Pt and Re recovery was obtained 15.7% and 98%, respectively, under optimum conditions of 12.8 g/l initial glycine concentration and 4% (w/v) pulp density after 7 days. Increasing the free cyanide concentration to 3.6 mg/l, varying the pH from 6.7 to 9, and increasing the dissolved oxygen from 2 to 5mg/l demonstrated the growth characteristics of B. megaterium during bioleaching process. The modified shrinking core model was used to determine the rate limiting step of the process. It was found that diffusion through the product layer is the rate controlling step.

Cr and Ni recovery during bioleaching of dewatered metal-plating sludge using Acidithiobacillus ferrooxidans

This study determined the optimal conditions required to attain maximum metal recovery in the bioleaching process of dewatered metal-plating sludge using Acidithiobacillus ferrooxidans (A. ferrooxidans). Adaptation of this strain was carried up to 1% (w/v) of the sample. Three factors including initial pH, initial Fe(3+) concentration and pulp density were selected as the effective factors and were optimized using a central composite design of response surface methodology. An initial pH of 1, pulp density of 9 g/l and initial Fe(3+) concentration of 1g/l were determined to be optimum values by the statistical models. The highest extractions for Cr and Ni under optimal conditions were 55.6% and 58.2%, respectively. Bioleaching kinetics was investigated using a modified shrinking core model to better understand the mechanism of the leaching reaction. The model predictions indicate that the diffusion step controlled the overall dissolution kinetics and is the rate controlling step.

Bioleaching of rare earth and radioactive elements from red mud using Penicillium tricolor RM-10

The aim of this work is to investigate biological leaching of rare earth elements (REEs) and radioactive elements from red mud, and to evaluate the radioactivity of the bioleached red mud used for construction materials. A filamentous, acid-producing fungi named RM-10, identified as Penicillium tricolor, is isolated from red mud. In our bioleaching experiments by using RM-10, a total concentration of 2% (w/v) red mud under one-step bioleaching process was generally found to give the maximum leaching ratios of the REEs and radioactive elements. However, the highest extraction yields are achieved under two-step bioleaching process at 10% (w/v) pulp density. At pulp densities of 2% and 5% (w/v), red mud processed under both one- and two-step bioleaching can meet the radioactivity regulations in China.

Bioleaching mechanism of heavy metals in the mixture of contaminated soil and slag by using indigenous Penicillium chrysogenum strain F1

The ability and bioleaching mechanism of heavy metals by Penicillium chrysogenum in soils contaminated with smelting slag were examined in this study. Batch experiments were performed to investigate the growth kinetics of P. chrysogenum, organic acids production and to compare the removal efficiencies of heavy metals between bioleaching with P. chrysogenum and chemical organic acids. The results showed that the bioleaching had higher removals than chemical leaching, and the removal percentages of Cd, Cu, Pb, Zn, Mn and Cr reached up to 74%, 59%, 24%, 55%, 57% and 25%, respectively. Removal efficiencies of heavy metals (15.41 mg/50 mL) by bioleaching were higher than chemical leaching with 0.5% of citric acid (15.15 mg/50 mL), oxalic acid (8.46 mg/50 mL), malic acid (11.35 mg/50 mL) and succinic acid (10.85 mg/50 mL). The results of transmission electron microscope (TEM) showed that no damage was obviously observed on the surface of the living cell except for thinner cell wall, discontinuous plasma membrane, compartmentalized lumen and concentrated cytoplasm during bioleaching process. The activity of extracellular glucose oxidase (GOD) produced by P. chrysogenum is influenced severely by the multi-heavy metal ions. The result implied that P. chrysogenum can be used to remove heavy metals from polluted soil and smeltery slag.

Bioleaching of spent hydrotreating catalyst by acidophilic thermophile Acidianus brierleyi: Leaching mechanism and effect of decoking

Bioleaching of spent hydrotreating catalyst by thermophillic archae Acidianus brierleyi was investigated. The spent catalyst (containing Al, Fe, Ni and Mo as major elements) was characterized, and the effect of pretreatment (decoking) on two-step and spent medium leaching was examined at 1% w/v pulp density. Decoking resulted in removal of carbonaceous deposits and volatile impurities, and affected the solubility of metal compounds through oxidization of the metal sulfides. Nearly 100% extraction was achieved using spent medium leaching for Fe, Ni and Mo, and 67% for Al. Bioleaching reduced nickel concentration in the leachate below the regulated levels for safe waste disposal. Chemical (i.e. abiotic) leaching using equimolar concentration of sulfuric acid produced by the bacteria during two-step process achieved a lower leaching efficiency (by up to 30%). Results indicated that A. brierleyi successfully leached heavy metals from spent catalyst.

Bioleaching of heavy metals from a contaminated soil using indigenous Penicillium chrysogenum strain F1

Bioleaching of heavy metals from contaminated soil using Penicillium chrysogenum strain F1 was investigated. Batch experiments were performed to compare leaching efficiencies of heavy metals between one-step and two-step processes and to determine the transformation of heavy metal fractions before and after bioleaching. The results showed that two-step process had higher leaching efficiencies of heavy metals than one-step process. When the mass ratio of soil to culture medium containing P. chrysogenum strain F1 was 5% (w/v), 50%, 35%, 9% and 40% of Cd, Cu, Pb and Zn were removed in one-step process, respectively. The two-step process had higher removals of 63% Cd, 56% Cu, 14% Pb and 54% Zn as compared with one-step process. The results of the sequential extraction showed that the metals remaining in the soil were mainly bonded in stable fractions after bioleaching. The results of TEM and SEM showed that during bioleaching process, although the mycelium of P. chrysogenum was broken into fragments, no damage was obviously observed on the surface of the living cell except for thinner cell wall, smaller vacuoles and concentrated cytoplasm. The result implied that P. chrysogenum strain F1 can be used to remove heavy metals from polluted soil.