Process optimization of hydrothermal leaching of LiFePO4 cathode materials with organic acids and selective elemental separation for high-purity product recovery

In this study, hydrothermal leaching of LiFePO 4 (LFPO) cathode materials with citric acid was conducted with the purpose of achieving high leaching efficiencies of Li, Fe, and P at high pulp densities within 10 min. As two most critical parameters, the temperature and acid concentration were mainly optimized. The results indicate that conditions of 100 °C with 2 mol/L citric acid and 180 °C with 4 mol/L citric acid are conducive to maintaining high leaching efficiencies at high pulp densities. With consideration of reducing energy and chemical consumption, the former condition was selected, achieving high leaching efficiencies for Li, Fe, and P at 100%, 98.8%, and 95.3%, respectively, at a pulp density of 30 g/L. Furthermore, a process of separating elements from leachates obtained from hydrothermal leaching of LFPO with citric or oxalic acid was proposed. High-purity (>99.6%) Li 3 PO 4 microparticles were obtained with P separation efficiencies exceeding 92.5% using both leaching agents. Meanwhile, high-purity (99.4%) Fe products with 98.5% separation efficiency were recovered from the citric acid leachate in the form of iron hydroxides, FeOOH, and Fe 3 O 4 precipitates. In contrast, in the oxalic acid system, 99.0% of Fe was directly recovered as FeC 2 O 4 during the oxalic acid hydrothermal leaching process, with a purity of 99.2%. This work significantly advanced the hydrothermal leaching of LFPO using citric or oxalic acid, contributing to the sustainable recycling of spent lithium-ion batteries and promoting the potential industrial application of the organic acid-based hydrothermal leaching technology.