Glutamate Leaching of Spent Lithium-Ion Battery Cathode in Weak Acidic-Neutral Condition: New Insight on Kinetics and Dissolution Mechanism

Abstract

ABSTRACT Organic acid leaching receives less attention than inorganic acids for Li-ion battery recycling process at the industrial scale due to the high consumption rate of the acids as leaching reagents. This paper reports an effective leaching of cobalt (Co) and lithium (Li) from spent battery cathode using low concentration of monosodium glutamate as lixiviants. More than 95% of Co and Li could be dissolved at leaching conditions MSG 0.1 M (18 g/L), pH 5, sodium sulfite 0.5 M as reductant, pulp density 20 g/L, room temperature and leaching time 6 h. Increasing the temperature to 80°C sped up the leaching process, where maximum recovery could be attained within 1 h. pH played a major role in the leaching efficiency (effective range pH 4–6). pH lower than 4 led to neutral and cationic glutamate species, which were ineffective in attracting cobalt ion. pH higher than 6 initiated the surface passivation by Co(OH)2. In the absence of a passivation layer, cobalt dissolution mechanism followed the chemical reaction-controlled model, while in the presence of the layer, the mechanism switched to diffusion through product layer. Kinetic studies demonstrated that aside from pH, the formation of passivation layer was hypothetically regulated by adjusting the other leaching parameters. Aside from the observation on kinetic study, the proposed leaching mechanism was supported by characterization (particle size analysis, SEM-EDS, FT-IR) results.