Sequential Leaching of Strategic Metals from Exhausted LNCM-Cathode Batteries Using Oxalic and Sulfuric Acid Lixiviants

Abstract

Hydrometallurgical extraction of strategic metals from exhausted Li-ion batteries has been explored using sequential application of biodegradable oxalic acid and sulfuric acid solutions. Following L25 orthogonal design of experiment (DoE), optimized extraction of > 99% Li and Cu with organic acid was achieved using a H2C2O4 concentration of 0.25 mol L−1, solid–liquid ratio of 10%, H2O2 at 0.5%, temperature of 80°C, and duration of 90 min. Subsequently, leaching of the residual mass in mineral acid yielded 99% efficiency of Ni, Co, and Mn at the optimal condition of H2SO4 concentration of 3.0 mol L−1, solid–liquid ratio of 6%, H2O2 at 2%, temperature of 60°C, and duration of 120 min. Fitting of the kinetic data using a logarithmic rate law revealed that, except for Cu that followed an intermediate-controlled mechanism with Ea = 27.6 kJ mol–1, all the other metals exhibited a diffusion-controlled mechanism with Ea < 12 kJ mol–1. Not only does this study demonstrate selectivity that will be beneficial to downstream processing, but the use of DoE also makes it applicable industrially.