Early-Stage Cultures of Acidithiobacillus ferrooxidans Enable Efficient Bioleaching of Li-ion Battery Cathode Material

Abstract

In response to the growing need to recycle E-waste, specifically that of lithium-ion batteries (LIBs), the development of sustainable recycling methodologies will be vital. As one of the most sustainable and low-cost options, biohydrometallurgy (BioHM) uses biological organisms to facilitate the recovery of critical metals from spent LIBs. Despite the advantages of BioHM, its slow kinetics, due to the reliance on the metabolic activity of microorganisms, limit its large-scale application for the closed-loop recycling of LIBs. In this work, we investigate the correlation between the incubation time of Acidithiobacillus ferrooxidans (Atf) and its leaching efficiency of four common elements in LIBs: Li, Ni, Mn, and Co. We assess how specific incubation times along the biological growth curve affect the leaching efficiency of Li[Ni0.6Mn0.2Co0.2]O2 (NMC622), a model electrode material. Our results show that pH alone is not an accurate descriptor of the leaching efficiency of Atf cultures used at different growth stages. The addition of NMC622 during the bacterial lag phase reaches similar or even improved extraction compared to cultures used after reaching the exponential or stationary phases. A simple model of leaching dynamics shows predictions consistent with our experimental observations under the condition that the inhibition of bacterial growth by NMC is not severe. Our findings indicate that early-stage cultures can alleviate the kinetic bottleneck and improve the throughput of recovering critical materials from spent batteries.