Genetic and transcriptomic analysis of microbial electro-extraction for releasing metals from spent Lithium-Ion...

Sustainable recycling strategies are urgently needed to address the rapidly growing accumulation of spent lithium-ion batteries. Current strategies for the first step in recycling, the solubilization of lithium and other metals, are energy intensive and/or generate toxic waste. This study critically evaluated the option of 'microbial electro-extraction' (MEE), a process in which electroactive microbes supply electrons to reduce the nickel, cobalt, and manganese in spent lithium-ion battery powder, releasing the soluble reduced ions of these metals along with soluble Li⁺. Shewanella oneidensis supplied with lactate as the electron donor was the MEE catalyst. It substantially increased solubilization of all metals compared with abiotic controls. Mutations that eliminated key components of the primary S. oneidensis porin-cytochrome conduit greatly inhibited metal solubilization, suggesting that the metal release could be attributed to extracellular electron transfer. Introducing the gene for OmcS, a Geobacter sulfurreducens outer-surface c-type cytochrome, enhanced S. oneidensis metal oxide reduction and substantially increased the release of all metals from battery powder. However, as the concentration of battery powder in the incubations was increased, the extent of metal solubilization plateaued. Transcriptomic analysis, metal toxicity studies, and analysis of residual solids revealed that the poor scalability of the process could be attributed to the accumulation of soluble nickel and cobalt that were toxic to S. oneidensis. These results suggest that additional engineering of S. oneidensis to further enhance extracellular electron transport capabilities and improve heavy metal resistance could advance MEE toward a scalable, sustainable process for extracting valuable metals from spent lithium-ion batteries.