Kinetics Study on Lithium Leaching of Spent Lithium Iron Phosphate Batteries in Low Concentration of Sulfuric Acid

Abstract

Recovery of valuable metals from spent lithium iron phosphate (LiFePO₄) batteries are quite challenging because it needs a lot of process. The recycling of these spent batteries can avoid environment contamination from the waste, meanwhile the valuable metallic components in the batteries including lithium can be treated as a resource for potential recovery of lithium. Low concentration of sulfuric acid (H₂SO₄) as a leachant and hydrogen peroxide (H₂O₂) as an oxidant, was used to leach elements from cathode materials of spent LiFePO₄ batteries that mainly contained Li, Fe and P. Li could be selectively leached into the solution and while Fe and P was assumed to remain in the residue. The significant effects of acid concentration, solid-liquid ratio, reaction temperature and reaction time on the leaching rate are determined. Under the optimum conditions of 0.1 M H₂SO_4, 2 vol% H₂O_2, S/L ratio of 75g/L, 60 °C and 60 min, the leaching efficiency determined were 74.74% for Li and 0.99% for Fe. A leaching mechanism of shrinking-core model with diffusion through product layer control was proposed. It was found that the apparent activation energy was 12.69 kJ mol^-1 as calculated by the Arrhenius equation together with an enthalpy (∆H) of 10 kJ mol^-1 and an entropy (∆S) of -264.54 Jmol^-1K^-1.