Selective bioleaching of lithium from waste lithium iron phosphate batteries using spent medium produced by Acidithiobacillus thiooxidans

The increased accumulation of spent lithium iron phosphate (LFP) batteries promotes the need for efficient and sustainable recycling strategies to recover lithium, graphite and phosphorus. This study explores a spent medium bioleaching approach for the recycling of LFP black mass to extract lithium. Experiments were conducted using floated and unfloated LFP black mass. In a first step, spent medium was generated by the sulfur-oxidizer Acidithiobacillus thiooxidans in a 1 L-stirred tank reactor until a pH value of 1.0 was achieved after six days. In the second process step, the produced spent medium was used to leach LFP black mass. Various process parameters were optimized to enhance metal leaching, including the addition of H 2 O 2 to enable selective leaching. The reproducibility of spent medium production and subsequent leaching was validated through multiple tests. Optimal parameters were determined as follows: 7% ( w / v ) LFP black mass, 1.5 M H 2 O 2 , 60 °C and 60 min reaction time. Lithium leaching efficiencies of 85% were achieved in 1 L scale using unfloated LFP black mass. Using floated LFP black mass improved selective leaching, yielding an 88% lithium recovery. The XRD analysis of residues confirmed the successful precipitation of FePO 4 . Additionally, a hybrid leaching approach through combination of spent medium and sulfuric acid was tested at 10% ( w / v ) solid load, with a final concentration of 0.25 M H 2 SO 4 , resulting in a 91% lithium recovery. This study highlights the potential of bioleaching as a viable method for recycling LFP black mass at higher solid loads which requires low sulfuric acid concentrations and short process time.