Comparison of performance differences in metal leaching from spent lithium-ion batteries using different...

In recent years, bioleaching of metals from spent LIBs has been considered a green method with mild reaction conditions and low energy consumption. However, the efficiency of this process is highly dependent on the selection of effective leaching microorganisms. To address this, this study systematically investigated the bioleaching efficiency of spent LIBs using three types of bacteria: iron- and sulfur-oxidizing bacterium Acidithiobacillus ferrooxidans (A. ferrooxidans), the iron-oxidizing bacterium Leptospirillum ferrooxidans (L. ferrooxidans), and the sulfur-oxidizing bacterium Acidithiobacillus thiooxidans (A. thiooxidans). The results showed A. thiooxidans outperformed the other two strains. After only one day of bioleaching, A. thiooxidans achieved complete (100 %) leaching of Co, Mn, Ni, and Li. Mechanistic analysis revealed that the A. thiooxidans system generated the highest concentrations of the reducing agent Fe²⁺ and of H⁺. Thus, Fe²⁺ acts as an electron donor, reducing the insoluble high-valence metals Ni(III), Co(III), Mn(IV), and Mn(III) to their soluble divalent forms (Ni²⁺, Co²⁺, Mn²⁺). These soluble ions are then readily leached out by H⁺. In addition, the extracellular polymeric substances (EPS) produced by A. thiooxidans exhibited a greater diversity of protein types and a higher protein concentration in the loosely bound extracellular polymeric substance (LB-EPS) fraction, which helps mitigate the toxic effects of metals and other stressors on the cells. Overall, these findings indicate that sulfur-oxidizing bacteria should be preferentially selected as leaching bacteria to achieve a high bioleaching efficiency of spent LIB.