Bioleaching of lithium-ion battery scrap at high pulp density with indigenous Acidithiobacillus ferriphilus

Bioleaching is regarded as an environmentally sustainable process for recycling spent lithium-ion batteries (LIBs). However, at high pulp densities, its application becomes challenging due to reduced microbial activity caused by the toxic metal components in the LIB black mass. Accordingly, the applicability of bioleaching under high pulp density conditions requires systematic evaluation. In this study, Acidithiobacillus ferriphilus 9-P1 was utilized, and leaching parameters, including inoculation rate, temperature, agitation speed, pulp density, and initial Fe²⁺ concentration, were tested in both 2 L and 10 L laboratory-scale reactors. Among the bioleaching factors, the bioleaching efficiency was enhanced by increasing the inoculation ratio to 50% and the iron concentration from 8.8 to 33 g/L. Elevating the temperature to 37.5°C significantly improved the leaching efficiencies to 99.2% for Li, 96.1% for Al, 96.8% for Mn, 98.7% for Co, 98.6% for Ni, and 95.8% for Cu within 168 h. Furthermore, at the 10 L reactor scale, leaching efficiencies exceeding 90% for Li, Al, Mn, Co, and Ni, and 81.6% for Cu were achieved within 168 h. These results demonstrate that bioleaching can serve as a practical and environmentally friendly alternative to traditional LIB recycling processes even under high pulp density conditions.