Precise recovery of highly-purified iron phosphate from complex lithium extraction slag leach solution: Theory guiding experiment

Abstract

Different decommissioned lithium iron phosphate (LiFePO4) battery models and various recycling technologies resulted in lithium extraction slag (LES) with multiple and complex compositions, necessitating ongoing experimentation and optimization to recover iron phosphate (FePO4). This work proposes a one-step precise selective precipitation strategy for recovering high-purity FePO4 from complex LES acid leach solution by guiding experiments through theoretical analysis. Thermodynamic simulations and dynamic precipitation-dissolution equilibrium calculations elucidated metals' migration and transformation patterns. Under optimal conditions, the precipitation rate for Fe exceeds 94 %, whereas the levels of impurities such as Ni, Cu, and Al are significantly low, at 3.2 %, 0.9 %, and 9.7 %, respectively. Quantitative analysis of XRD patterns through Rietveld refinements confirms high crystallinity and Low impurities in recovery FePO4 at pH = 1.0. The recovered FePO4 closely approximates battery-grade specifications, demonstrating superior electrochemical performance characterized by an initial charge–discharge capacity of 159.34/151.68 mAh g−1 and maintaining a capacity retention rate of 94.4 % after 100 cycles at 0.5C. The life cycle analysis reveals that this process reduces 29.3 % of energy consumption and 28.4 % of greenhouse gas (GHG) emissions compared to traditional processes. This work presents a theory-guided optimization strategy that promises to achieve full component closed-loop recycling of decommissioned LiFePO4.