A Sustainable Complexation Leaching of Critical Metals from Spent Lithium-Ion Batteries by Glycine in a Neutral Solution

To reduce the environmental footprint of hydrometallurgical processing of black mass from spent lithium-ion batteries (LIBs), a green leaching system based on glycine and sodium metabisulfite (Gly-SMS) was proposed. The novel leaching system was validated using black mass from end-of-life batteries and manufacturing scrap from battery producers, representing the two dominant black mass types processed in the market. The leaching study demonstrated that the highest cobalt and lithium recoveries of 100% and 99.8% were achieved under optimal conditions. The leaching mechanism revealed that the dissolution of LiCoO₂ in the Gly-SMS solution followed the shrinking core model. The apparent activation energies for cobalt and lithium were determined as 48.05 kJ/mol and 41.51 kJ/mol, respectively, indicating a surface chemical reaction controlling mechanism. The leachate was then processed by an acidification-precipitation technique with oxalic acid as the precipitant to remove cobalt. Glycine complexes with metal ions by zwitterionic ligand and recycles in the leaching-precipitation circuit, reducing the reagent cost. Compared to other studies, this leaching system has near-neutral operating conditions and is cost-effective, making it an economically viable alternative for treating cathode materials from spent LIBs.