Battery-grade FePO4 recovery from P-rich urine via field-induced electro-Fenton in a compartmental electrolytic cell.

The recovery of ferric phosphate (FePO4) from wastewater offers a promising application as a valuable precursor in the new energy industry due to the substantial demand for the LiFePO4 battery. However, conventional FePO4 recovery from the massive neutral wastewaters is constrained by pH adjustment and the formation of low-purity precipitation. In this study, a new compartmental electrolytic cell was developed to recover high-purity FePO4 from phosphorus (P)-rich urine via an electric field-induced electro-Fenton process. The membrane-separated induced electro-Fenton (M/I-EF) system enabled the urine pH to decrease to < 3.0 within 5.0 min without pH pre-adjustment. Under the best conditions (H2O2 concentration, 10 mM; current density, 10 mA/cm2; initial pH, 6.0; reaction time, 40 min), the system achieved a total phosphorus (TP) recovery efficiency of 95.67%. Compared to the membrane-separated electro-Fenton (M/EF), the M/I-EF system exhibited a more rapid decrease in pH and ensured that Fe2+ was released from the induced Fe foam at a slow rate, resulting in the high-purity FePO4. Elemental analysis of the recovered products confirmed that the material obtained from the M/I-EF system was FePO4 with a purity of 98.41%, whereas the precipitate from the M/EF system exhibited a purity of only 87.72%. The effects of initial H2O2 concentration, current density, initial pH, and initial TP concentration were evaluated in this study. The recovered FePO4 was employed as a precursor to synthesize LiFePO4/C cathode material, which delivered a high specific discharge capacity of 161.7 mAh g-1 at 0.1C and maintained 99.55% of its initial capacity after 100 cycles at 0.5C, thereby demonstrating excellent electrochemical performance and cycling stability. Ultimately, the system demonstrated a TP recovery efficiency of 95.12% when treating real urine, with the recovered product being FePO4. The compartmental electrolytic cell offers an effective strategy for phosphorus recovery from urine, providing significant economic and environmental benefits.