Sulfuric acid leaching of ball-milling activated FePO4 residue after lithium extraction from spent lithium iron phosphate cathode powder

A mechanical-chemical process is proposed to recover the iron phosphate residue(IPR)of spent lithium iron phosphate(LFP)after lithium extraction. In this process, the IPR was pretreated by ball-milling and leached with the sulfuric acid solution. The results showed that, under the optimized ball-milling conditions (a mass ratio of the stainless-steel-ball to material to water of 2:1:2.5, a milling time of 20 min), the maximum particle size of IPR decreased from 34.265 um to 13.102 um, the specific surface increased from 11.41 m2/g to 13.74 m2/g, and the cell volume distortion rate could reach 0.331 %. Under the optimized leaching conditions (a temperature of 333 K, a concentrated acid-to-material ratio of 0.46 mL/g, a liquid-to-solid ratio of 5:1 mL/g, and a stirring speed of 600 rpm), the leaching efficiency of iron phosphate could reach 98 %. The kinetic study indicated that the leaching was controlled by diffusion and chemical reaction with the apparent activation energy of 29 kJ/mol. The dissolution-precipitation phase transition of IPR was also found at high temperatures. This study illustrates that such a mechanical-chemical process is an effective way to improve the leaching efficiency of IPR with a lower sulfuric acid dosage, which has great potential in industrial applications.