Abstract:The valuable metals, lithium and iron, were recovered from spent LiFePO₄ cathode powder by hydro- metallurgy, and the recycled products were used as raw materials for the preparation of lithium iron phosphate. By the optimization of the leaching process parameters, the leaching efficiency of Li reached 96.56% at pyruvic acid concentration of 3.0 mol/L, volume of H₂O₂ of 2 mL, solid-to-liquid ratio of 0.1 g/mL, reaction temperature of 80 °C, and reaction time of 20 min. The leached residue was characterized by XRD, XPS, and FE-SEM coupled with EDS, and the results showed that the leached residue was FePO₄ with an Fe/P molar ratio of 0.974. After adjusting the pH of the leaching solution to 12.0 and stirring for 2 h at 80 °C, the recovery of Li from the leaching solution was enabled by in-situ precipitation in the form of Li₃PO₄ with a purity of 96.5 wt.%. The reaction kinetic data of Li leaching using the pyruvic acid/H₂O₂ solution were fit to the Avrami model with R²>0.95. The low activation energy of the Li leaching process indicated that diffusion step limited the reaction rate during the leaching process.

Key words: spent LiFePO₄; pyruvic acid; leaching kinetics; Avrami model; lithium ion batteries