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.