Biomass-Assisted Hydrometallurgy and Pyrometallurgy for Sustainable Recovery of Spent Lithium-Ion Battery Cathodes

Abstract Biomass-assisted metallurgy, defined as an umbrella term encompassing recycling technologies that utilize biomass in any form (living microorganisms, biomass-derived chemical compounds, or thermally converted biomass products) as lixiviants, reductants, and/or energy sources, has emerged as a cost-effective, sustainable, and carbon-neutral approach for recovering critical metals from spent lithium-ion battery (LIB) cathodes. Unlike previous reviews that address bioleaching or organic-acid leaching separately, this review establishes a unified framework categorizing biomass-assisted recycling into three distinct technological routes: (i) microbial bioleaching, where acidophilic bacteria (Acidithiobacillus spp.) and fungi (Aspergillus niger) generate biogenic acids and oxidants to solubilize metals via acidolysis and redoxolysis; (ii) biomass reduction leaching, where biomass-derived substances (e.g., polyphenols, reducing sugars, organic acids) serve as green reductants to replace hazardous H2O2, enabling efficient metal extraction under mild conditions; and (iii) biomass reduction roasting, where lignocellulosic wastes provide reducing gases (e.g., H2, CO) and biochar for in or ex situ carbothermal reduction, enabling selective lithium recovery as water-soluble Li2CO3. The distinctive contribution lies in the synergistic valorization strategy─biomass wastes (e.g., lignocellulose, fruit peels, food waste) address waste management challenges in both the battery and agricultural sectors while providing renewable reducing agents and energy sources. Mechanistic comparisons reveal contrasting roles of biogenic versus mineral acids and in situ versus ex situ reduction pathways, which are rarely discussed. Finally, critical bottlenecks and future strategies, including genetic engineering of microbial strains, mechanochemical activation, microwave-assisted heating, and techno-economic/life-cycle assessments, are proposed to advance these technologies toward industrial-scale urban mining applications.