Low-temperature solid-phase calcination: Potassium persulfate oxidation enables efficient and selective separation of waste lithium iron phosphate and lithium iron

This study develops an innovative and low-energy process for recovering lithium from spent lithium iron phosphate (LFP) batteries, aiming to mitigate environmental pollution and address resource scarcity. Using potassium persulfate (K 2 S 2 O 8 ) as an oxidant, the calcination method enables selective lithium recovery and concurrent rejuvenation of iron phosphate. Under the optimizes conditioned of a calcination temperature of 205 °C,40 min roasting time, and a molar ratio of K 2 S 2 O 8 to LiFePO 4 of 3:1, the lithium extraction efficiency reaches 98.63%, the iron leaching rate is suppress to below 8.72%, and the selective separation ratio (molar ratio) of lithium to iron reaches 11.31. Mechanistic investigations reveal that K 2 S 2 O 8 disrupting the olivine structure and releasing Li + to form soluble LiKSO 4 , while retaining iron as insoluble FePO 4 . The lattice parameter expands from 0.38 nm to 0.572 nm. This study also constructs a closed loop recycling process from the leachate to the final products. By gradually adjusting the pH, Li and Fe are successfully separated. The Fe precipitates out in the form of hydroxide. Lithium is precipitated as lithium carbonate. This work provides an efficient strategy for recovering valuable metals from spent LFP cathodes and offers a sustainable, industrially feasible solution for closed loop recycling of lithium ion batteries.