Indirect bioleaching for metal recovery from battery black mass using microbially generated acid from a secondary sulfur resource.

Recycling critical metals from spent lithium-ion batteries (LIB) has attracted significant attention in recent years, driving the search for more sustainable and environmentally friendly recovery methods. Among emerging approaches, indirect bioleaching may be a very promising alternative for recovering valuable metals from spent LIB. In this study, sulfuric acid (H2SO4) was produced by using a mixed culture containing Acidithiobacillus thiooxidans and Acidithiobacillus caldus, supplemented with elemental sulfur recovered as a waste product from a biogas plant. The biogenic acid was subsequently used for leaching black mass derived from nickel manganese cobalt (NMC)-based lithium-ion batteries (LIB). First, the influence of different concentrations (0.2, 1, and 2 M) of hydrogen peroxide (H2O2) on metal dissolution was investigated. Subsequently, 2% (v/v) of rhamnolipids / phospholipids was added and the effect on the H2SO4-H2O2 system was studied. Finally, the best performing system was scaled up to a 1L reactor, achieving complete recovery of Mn and Li from 10% (w/v) NMC within 1 h. This result highlights the high potential of microbially produced H2SO4 as an effective leaching agent for recovering critical metals from spent LIB, while simultaneously valorizing a secondary sulfur waste stream, aligning with the broader objectives of circular and sustainable resource recovery approaches.