Efficient recovery of phosphorus and iron from the lithium extraction slag by the leaching precipitation method

The key to recovering waste LiFePO4(LFP) is the recovery of lithium; however, the effective and synchronous recovery of phosphorus and iron resources still needs to be achieved. In this paper, a new process was proposed for recovering phosphorus and iron from the lithium extraction slag (LES) of waste LFP by the leaching and precipitation method. Based on the thermodynamic analysis of Fe3+ and PO43− and XRD results, the experimental conditions were discussed in detail. There were three stable regions when the solution pH value was from 0 to 5, no precipitation at pH = 0–0.664, stable existence of FePO4(s) at pH = 0.664–1.203, coexistence of FePO4(s), and AlPO4(s) when pH > 1.203, respectively. The leaching solution of LES by hydrochloric acid could prepare FePO4·2H2O under the following optimal conditions: 95°C, pH 1.5, feeding speed 1.5 mL min−1. The synthesised iron phosphate was pure and distributed in flakes. Additionally, the discharge capacity of the LiFePO4/C prepared by the regenerative FePO4·2H2O was 147 mAh g−1 at 0.1 C and showed good cycle stability at 1 C. The method not only recovers FePO4 from the LES but also shows simple operation and high efficiency.