Improvement of Li and Mn bioleaching from spent lithium-ion batteries, using step-wise addition of biogenic sulfuric acid by Acidithiobacillus thiooxidans

Conventional spent lithium-ion battery (LIB) recycling procedures, which employ powerful acids and reducing agents, pose environmental risks. This work describes a unique and environmentally acceptable bioleaching method for Li and Mn recovery utilizing <i>Acidithiobacillus thiooxidans</i>, a sulfur-oxidizing bacteria that may produce sulfuric acid biologically. The novel feature of this strategy is the step-by-step addition of biogenic sulfuric acid, which differs significantly from conventional methods that use chemical reagents. We expected that gradually introducing biogenic sulfuric acid produced by <i>A. thiooxidans</i> would improve metal leaching at high pulp density. To investigate this, LIBs were disassembled and bioleached with or without a step-wise addition of the biogenic sulfuric acid approach. The impact on leaching efficiency, time, and ultimate product quality was assessed. Direct bioleaching yielded modest Li (43 %) and Mn (15 %) recoveries. However, bioleaching greatly increased metal recovery with the step-wise addition of biogenic acid. Li and Mn leaching efficiency were 93 % and 53 %, respectively, at a high pulp density of 60 g/L, while leaching time was reduced from 16 to 8 days. Following bioleaching, Mn(OH)₂ and Li₂CO₃ were successfully precipitated from the leachate at more than 90 % purity. This study shows that gradually adding biogenic sulfuric acid can efficiently recover Li and Mn from waste LIBs. This approach has several environmental and economic advantages over conventional methods. The step-wise addition optimizes the leaching environment, increasing metal recovery rates while reducing the development of hazardous byproducts. This approach is environmentally friendly because it decreases greenhouse gas emissions and chemical waste. Economically, this technology offers potential cost savings through less chemical usage, shorter processing times, and lower energy needs, making it a more sustainable and cost-effective option for LIB recycling. This study shows that the step-wise addition of biogenic sulfuric acid may efficiently recover Li and Mn from wasted LIBs. This method provides a sustainable alternative to traditional procedures by limiting environmental impact while reducing process time and energy consumption.