Metal Extraction and Solid-Phase Evolution During Ammoniacal Leaching of Spent LiCoO₂ Cathodes

Ammonia leaching constitutes a selective route for the recovery of metals from used lithium-ion batteries, but the relationship between the extraction of metals and the evolution of residues remains insufficiently understood. This study focused on the leaching of used and pretreated LiCoO₂ cathodes, without the external addition of a reducing agent, by combining extraction measurements, kinetic modeling and X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX) XRD and SEM-EDX characterizations. The effects of ammonia concentration, liquid/solid ratio, temperature and leaching time were examined. With a concentration of 4 M in NH₃, a liquid/solid ratio of 20 mL/g and a temperature of 60 °C, approximately 90% of the Li and 80% of the Co was extracted in 240 min for the series of tests dedicated to the characterization of the residues. The preferential extraction of Li was accompanied by a weakening of the reflections of LiCoO₂, an intensification of the reflections of Co₃O₄ and a heterogeneous alteration of the residual particles. These observations relate the incomplete extraction of Co to the persistence of cobalt-containing domains. In a separate kinetic series conducted between 40 and 70 °C, Avrami’s model described the extraction better than the evaluated shrinking core models, making it possible to determine apparent activation energies of 36.5 kJ/mol for Li and 38.0 kJ/mol for Co. The extraction of Cu and Al reached 57% and 7%, respectively, under the conditions chosen, while the Fe and Si concentrations in the filtrate remained below the detection limits.