Study on deep synergistic leaching mechanism of spent lithium iron phosphate under the H2SO4-H2O2 system and precise chemical precipitation recovery strategy of lithium carbonate

Efficient leaching and recovery of LiFePO 4 (LFP) in spent lithium-ion batteries (LIBs) is a key step to realize the recycling of lithium resources. Herein, H 2 SO 4 -H 2 O 2 is selected as the leaching agent to achieve selective leaching of lithium from spent LFP cathode materials, and the response surface method (RSM) serves to define the optimal leaching process. The experimental findings signify that when the concentration of H 2 SO 4 is 0.315 mol·L -1 , H 2 O 2 /Li molar ratio of 2.13, H 2 SO 4 /Li molar ratio of 0.62 (solid–liquid ratio of 96.87 g·L -1 ), leaching temperature of 62 °C and leaching time of 90 min, the leaching rate of Li + can reach as high as 95.23 %. Thermodynamic analysis, infrared spectroscopy and Mössbauer spectrum are used to clarify the reaction mechanism, that is, Fe 2+ in LiFePO 4 is oxidized to Fe 3+ by H 2 O 2 in situ to form FePO 4 , and Li + is released into the solution. Moreover, chemical precipitation method is used to efficiently recover the lithium resources in the form of lithium carbonate. By applying Box-Behnken design (BBD) and RSM to optimize the recovery technology to reach the global optimal solution to achieve the highest recovery rate of Li + in spent LFP. The experimental results show that under the optimal conditions of a Na 2 CO 3 /Li molar ratio of 0.6, a reaction temperature of 90 °C, and a C (Li + ) of 20.28 g·L -1 , the precipitation rate of Li + reaches 89.22 %. Moreover, the physical properties of the recovered Li 2 CO 3 are analyzed, and the content of Li 2 CO 3 in the recovered product is as high as 99.62 %. Additionally, the economic analysis and environmental impact analysis of the whole process of hydrometallurgical recovery of cathode materials are carried out by EverBatt 2023 model, which confirmed that hydrometallurgy is the extremely satisfactory method for recovering spent LFP cathode materials.