Novel approach for in situ recovery of cobalt oxalate from spent lithium-ion batteries using tartaric acid and hydrogen peroxide

Recycling Co resource from spent lithium-ion batteries (LIBs) is significant for Co deficiency and environmental protection. A novel approach for in situ recovery of cobalt oxalate (Co(II)-oxalate) from spent LiCoO2 cathodes is proposed. 98.9% Co and 99.6% Li were obtained under the optimized conditions of 1.0 mol/L L-tartaric acid with 5 vol.% H2O2, 10 g/L solid-to-liquid ratio, and 10 min leaching time at 80 °C. Meanwhile, the leaching of Co and Li fits well to Avrami equation model with apparent activation energy of 48.86 and 28.03 kJ/mol, respectively. The first and second stability constants of Co (II) and L-tartaric acid are 1.05 (log K1) and 0.26 (log K2), respectively. 91.8% of high-purity Co(II)-oxalate was regenerated using 5 vol.% H2O2 at 80 °C for 6 h. The whole reaction mechanism was investigated by time-dependent UV–Vis spectroscopy. The proposed in situ Co recovery process proceeds according to the following pathway: Co(III)-tartrate → Co(II)-tartrate → Co(II)-oxalate. In the process, L-tartaric acid mainly acts as a chelating agent and acts as a precursor to form oxalate. Meanwhile, H2O2 mainly acts as a reducing agent and an oxidant. The process may provide an effective and environmentally friendly route for the sustainable recovery of Co(II)-oxalate from spent LIBs.