Recycling Li-Ion Battery Cathode Materials in Iron-Fueled, Low-Sulfate Cultures of <i>Acidithiobacillus ferrooxidans</i>

The continuous demand for lithium-ion batteries (LIBs) in consumer products and electric vehicles (EVs) has raised concerns about their environmental impact when not disposed of properly. Among the components of a spent LIB, the recovery of heavy metals, such as nickel, manganese, and cobalt, from cathode materials is the most critical. While biohydrometallurgy is a promising method for this recovery, it relies on large quantities of chemicals such as iron sulfate (FeSO4) as the energy source, which can limit its scalability. In this work, we seek to develop a modified biohydrometallurgy process that is less dependent on external chemical fuels. For this purpose, we examined the feasibility of replacing the FeSO4 salt with metallic iron (Fe) or stainless steel (SS), which is readily available in spent batteries as protective cases. The modification of the culture growth through the utilization of abundant metallic Fe or SS is expected to lower costs and limit chemical transportation, which will likely decrease potential detrimental environmental impacts in comparison with other recycling methods. The growth profile of the autotrophic bacterium Acidithiobacillus ferrooxidans (Atf) was studied after the initial acidification with H2SO4 or HCl. The resulting culture was then used to leach model cathode materials made of NMC622 (Ni/Mn/Co = 6:2:2). Near-unity leaching efficiencies were measured on all four elements of interest, Li, Ni, Mn, and Co, when compared with those by aqua regia-based digestion. This new bioleaching process opens the door to efficiently recovering cathode metals while further simplifying the cultivation process, promising scaled-up applications.