E-waste generated from end-of-life spent lithium-ion batteries (LIBs) is increasing at a rapid rate owing to the increasing consumption of these batteries in portable electronics, electric vehicles, and renewable energy storage worldwide. On the one hand, landfilling and incinerating LIBs e-waste poses environmental and safety concerns owing to their constituent materials. On the other hand, scarcity of metal resources used in manufacturing LIBs and potential value creation through the recovery of these metal resources from spent LIBs has triggered increased interest in recycling spent LIBs from e-waste. State of the art recycling of spent LIBs involving pyrometallurgy and hydrometallurgy processes generates considerable unwanted environmental concerns. Hence, alternative innovative approaches toward the green recycling process of spent LIBs are essential to tackle large volumes of spent LIBs in an environmentally friendly way. Such evolving techniques for spent LIBs recycling based on green approaches, including bioleaching, waste for waste approach, and electrodeposition, are discussed here. Furthermore, the ways to regenerate strategic metals post leaching, efficiently reprocess extracted high-value materials, and reuse them in applications including electrode materials for new LIBs. The concept of "circular economy" is highlighted through closed-loop recycling of spent LIBs achieved through green-sustainable approaches.

Green Recycling Methods to Treat Lithium-Ion Batteries E-Waste: A Circular Approach to Sustainability.

Much research has been carried out on the bacterial bioremediation of soil contaminated with petroleum hydrocarbons and toxic metals but much less is known about the potential of fungi in sites that are co-contaminated with both classes of pollutants. This article documents the roles of fungi in soil polluted with both petroleum hydrocarbons and toxic metals as well as the mechanisms involved in the biotransformation of such substances. Soil characteristics (e.g., structural components, pH, and temperature) and intracellular or excreted extracellular enzymes and metabolites are crucial factors which affect the efficiency of combined pollutant transformations. At present, bioremediation of soil co-contaminated with petroleum hydrocarbons and toxic metals is mostly focused on the removal, detoxification, or degradation efficiency of single or composite pollutants of each type. Little research has been carried out on the metabolism of fungi in response to complex pollutant stress. To overcome current bottlenecks in understanding fungal bioremediation, the potential of new approaches, e.g., gradient diffusion film technology (DGT) and metabolomics, is also discussed. KEY POINTS: • Fungi play important roles in soil co-contaminated with TPH and toxic metals. • Soil characteristics, enzymes, and metabolites are major factors in bioremediation. • DGT and metabolomics can be applied to overcome current bottlenecks.

/pdf/fungal-bioremediation-of-soil-co-contaminated-with-petroleum-4yl5o6i5xy.pdf

Fungal bioremediation of soil co-contaminated with petroleum hydrocarbons and toxic metals

This article has reviewed the progress that has been made in bioleaching research of metals using filamentous fungi. This review has focused on fungal bioleaching from various metal sources, including mine tailings, electronic waste, solid mine wastes, spent catalysts, and low-grade ores. Filamentous fungi are used in bioleaching due to their ability to secrete organic acids and facilitate the solubilization of metal ions from the solution phase. The information provided in this review shows that fungal species under different specific operating parameters (pH, temperature, substrate, incubation time) can be used in the recovery of essential metals. Several drawbacks that lie in fungal bioleaching have been listed in this review. However, we have put forward suggestions that might help counter these challenges and invigorate interest in this research line. The present review examines the gaps and summarizes the fundamental mechanisms of fungal bioleaching. Furthermore, fungal species' practical potentiality for the future development of enhanced bioleaching technology applications is underlined.

Overview of fungal bioleaching of metals

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Molybdenum is an essential element for life, with growing production due to a constantly expanding variety of industrial applications. The potentially harmful effects of Mo on the environment, and on human and ecosystem health, require knowledge of Mo behavior in mining-affected environments. Mo is usually present in trace amounts in ore deposits, but mining exploitation can lead to wastes with very high Mo concentrations (up to 4000 mg/kg Mo for tailings), as well as soil, sediments and water contamination in surrounding areas. In mine wastes, molybdenum is liberated from sulfide mineral oxidation and can be sorbed onto secondary Fe(III)-minerals surfaces (jarosite, schwertmannite, ferrihydrite) at moderately acidic waters, or taken up in secondary minerals such as powellite and wulfenite at neutral to alkaline pH. To date, no Mo-metabolising bacteria have been isolated from mine wastes. However, laboratory and in-situ experiments in other types of contaminated land have suggested that several Mo-reducing and -oxidising bacteria may be involved in the cycling of Mo in and from mine wastes, with good potential for bioremediation. Overall, a general lack of data is highlighted, emphasizing the need for further research on the contamination, geochemistry, bio-availability and microbial cycling of Mo in mining-affected environments to improve environmental management and remediation actions.

Geochemistry, Mineralogy and Microbiology of Molybdenum in Mining-Affected Environments

Struvite (magnesium ammonium phosphate-MgNH4 PO4 ·6H2 O), which can extensively crystallize in wastewater treatments, is a potential source of N and P as fertilizer, as well as a means of P conservation. However, little is known of microbial interactions with struvite which would result in element release. In this work, the geoactive fungus Aspergillus niger was investigated for struvite transformation on solid and in liquid media. Aspergillus niger was capable of solubilizing natural (fragments and powder) and synthetic struvite when incorporated into solid medium, with accompanying acidification of the media, and extensive precipitation of magnesium oxalate dihydrate (glushinskite, Mg(C2 O4 ).2H2 O) occurring under growing colonies. In liquid media, A. niger was able to solubilize natural and synthetic struvite releasing mobile phosphate (PO43- ) and magnesium (Mg2+ ), the latter reacting with excreted oxalate resulting in precipitation of magnesium oxalate dihydrate which also accumulated within the mycelial pellets. Struvite was also found to influence the morphology of A. niger mycelial pellets. These findings contribute further understanding of struvite solubilization, element release and secondary oxalate formation, relevant to the biogeochemical cycling of phosphate minerals, and further directions utilizing these mechanisms in environmental biotechnologies such as element biorecovery and biofertilizer applications.

/pdf/biotransformation-of-struvite-by-aspergillus-niger-phosphate-ij7ln338dd.pdf

Biotransformation of struvite by Aspergillus niger: phosphate release and magnesium biomineralization as glushinskite

In this research, the capabilities of culture supernatants generated by the oxalate-producing fungus Aspergillus niger for the bioprecipitation and biorecovery of cobalt and nickel were investigated, as was the influence of extracellular polymeric substances (EPS) on these processes. The removal of cobalt from solution was >90% for all tested Co concentrations: maximal nickel recovery was >80%. Energy-dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) confirmed the formation of cobalt and nickel oxalate. In a mixture of cobalt and nickel, cobalt oxalate appeared to predominate precipitation and was dependent on the mixture ratios of the two metals. The presence of EPS together with oxalate in solution decreased the recovery of nickel but did not influence the recovery of cobalt. Concentrations of extracellular protein showed a significant decrease after precipitation while no significant difference was found for extracellular polysaccharide concentrations before and after oxalate precipitation. These results showed that extracellular protein rather than extracellular polysaccharide played a more important role in influencing the biorecovery of metal oxalates from solution. Excitation–emission matrix (EEM) fluorescence spectroscopy showed that aromatic protein-like and hydrophobic acid-like substances from the EPS complexed with cobalt but did not for nickel. The humic acid-like substances from the EPS showed a higher affinity for cobalt than for nickel.

/pdf/biorecovery-of-cobalt-and-nickel-using-biomass-free-culture-46jk5lh7ye.pdf

Biorecovery of cobalt and nickel using biomass-free culture supernatants from Aspergillus niger.

The bioleaching efficiency and mechanism of recovery of cobalt (Co) and nickel from laterites and pyritic ores by Aspergillus niger were investigated. Recoveries of Co from laterites and pyritic or...

Direct and Indirect Bioleaching of Cobalt from Low Grade Laterite and Pyritic Ores by Aspergillus niger

In this study, the ability of the geoactive fungus Aspergillus niger to colonize and transform manganese nodules from the Clarion-Clipperton Zone in both solid and liquid media was investigated. Aspergillus niger was able to colonize and penetrate manganese nodules embedded in solid medium and effect extensive transformation of the mineral in both fragmented and powder forms, precipitating manganese and calcium oxalates. Transformation of manganese nodule powder also occurred in a liquid medium in which A. niger was able to remove the fine particles from suspension which were accumulated within the central region of the resulting mycelial pellets and transformed into manganese oxalate dihydrate (lindbergite) and calcium oxalate dihydrate (weddellite). These findings contribute to an understanding of environmental processes involving insoluble manganese oxides, with practical relevance to chemoorganotrophic mineral bioprocessing applications, and, to the best of our knowledge, represent the first demonstration of fundamental direct and indirect interactions between geoactive fungi and manganese nodules.

/pdf/colonization-penetration-and-transformation-of-manganese-3erb1z6z4h.pdf

Colonization, penetration and transformation of manganese oxide nodules by Aspergillus niger

There are a need for novel, economical and efficient metal processing technologies to improve critical metal sustainability, particularly for cobalt and nickel which have extensive applications in low-carbon energy technologies. Fungal metal biorecovery processes show potential in this regard and the products of recovery are also industrially significant. Here we present a basis for selective biorecovery of Co and Ni oxalates and phosphates using reactive spent Aspergillus niger culture filtrate containing mycogenic oxalate and phosphate solubilized from struvite. Selective precipitation of oxalates was achieved by adjusting phosphate-laden filtrates to pH 2.5 prior to precipitation. Co recovery at pH 2.5 was high with a maximum of ~96% achieved, while ~60% Ni recovery was achieved, yielding microscale polyhedral biominerals. Co and Ni phosphates were precipitated at pH 7.5, following prior oxalate removal, resulting in near-total Co recovery (>99%), while Ni phosphate yields were also high with a recovery maximum of 83.0%.

John Ferrier

Papers

Biotransformation of struvite by Aspergillus niger: phosphate release and magnesium biomineralization as glushinskite

Biorecovery of cobalt and nickel using biomass-free culture supernatants from Aspergillus niger.

Direct and Indirect Bioleaching of Cobalt from Low Grade Laterite and Pyritic Ores by Aspergillus niger

Colonization, penetration and transformation of manganese oxide nodules by Aspergillus niger

Selective fungal bioprecipitation of cobalt and nickel for multiple-product metal recovery