P-Fe coupling behavior and mechanistic insights during selective Lithium extraction from spent LiFePO4

In the recycling of spent lithium iron phosphate (SLFP), the purity of lithium carbonate, the primary lithium product, is severely constrained by the co-leaching of impurity elements, particularly phosphorus, which has long been overlooked in conventional selective leaching studies. In this study, a selective lithium extraction strategy was developed in the H 2 SO 4 -H 2 O 2 system by simultaneously targeting high Li recovery and suppression of Fe/P dissolution. Guided by E -pH diagrams and response surface methodology, the optimal leaching domain was identified, achieving 99.52% Li extraction while limiting Fe and P dissolution to 0.04% and 1.36%, respectively. Mechanistic investigations reveal that Fe and P are not simply retained in the solid phase as traditionally assumed, but undergo a coupled dissolution-oxidation-reprecipitation process, ultimately forming FePO 4 ·xH 2 O. In contrast, Li leaching follows an interfacial chemical reaction-controlled mechanism ( E a  = 56.49 kJ mol −1 ). The decoupling of these pathways is the fundamental origin of high selectivity. Kilogram-scale experiments further confirmed the process stability and enabled the production of battery-grade Li 2 CO 3 with a purity of 99.74%. Furthermore, the migration of residual fluorine-containing species was evaluated, and corresponding strategies for safety management and emission control were proposed. This study reveals the previously overlooked leaching behavior of phosphorus during selective lithium extraction and clarifies the coupled immobilization mechanism of P Fe, providing a new theoretical basis and technical route for the high-selectivity and scalable recycling of spent LiFePO 4 .