Microbial Bioleaching of Critical Metals from Spent Lithium-Ion Batteries: A Biohydrometallurgical Approach

Biohydrometallurgical processing of spent lithium-ion batteries offers a low-impact route for critical metal recovery compared with conventional hydrometallurgy. In this work, the iron-oxidizing bacterium Acidithiobacillus ferrooxidans was evaluated for the bioleaching of cobalt (Co), nickel (Ni), lithium (Li) and copper (Cu) from the black mass of spent LiCoO₂ batteries. Batch experiments were conducted in 9K medium at 30 °C, varying pulp density (1-2 %, w/v), inoculum volume (10-20 mL in 200 mL medium) and initial pH (with and without adjustment). At 1 % pulp density and 10 % v/v inoculum, metal recoveries after 6-7 days reached about 64-70 % Co, 57-72 % Ni, 52-60 % Li and 81-100 % Cu, with most dissolution occurring in the first 6 days. Higher inoculum loads without initial pH adjustment increased Li recovery up to 79 %, but did not further improve Co and Cu, indicating a trade-off between microbial activity, metal toxicity and ferric iron availability. The temporal evolution of pH and metal dissolution is consistent with indirect redoxolysis by biogenic Fe³⁺ and sulfuric acid generated during ferrous iron and elemental sulfur oxidation. Overall, the results confirm the feasibility of A. ferrooxidans-assisted bioleaching as a green option for Co, Ni, Li and Cu recovery from spent LiCoO₂ batteries and provide operating windows for subsequent process optimization and scale-up.