Valorization of Wastewater Phosphorus into Battery-Grade FePO4 via In-Situ Anodic Precipitation in an Electro-Driven Membrane System

The exponential growth of the new energy vehicle market has precipitated an urgent demand for sustainable lithium iron phosphate (LiFePO 4 ) precursors. While recovering iron phosphate (FePO 4 ) from phosphorus-rich wastewater presents a viable supply chain solution, conventional precipitation and adsorption methodologies are critically limited by low product purity and inefficient separation. This study introduces an innovative electro-driven membrane separation technology that employs Fe 2 (SO 4 ) 3 as the anode electrolyte to achieve simultaneous phosphorus concentration and in situ FePO 4 recovery. The process exploits the electric field to drive PO 4 3– migration into the anode chamber, where it precipitates with Fe 3+ . Under the optimized conditions, using a mixed Fe 2 (SO 4 ) 3 /Na 2 SO 4 anolyte and an activated-carbon-containing catholyte at a current density of 2.6 A m –2 , the system achieved phosphate removal and recovery efficiencies of 82.4% and 74.1%, respectively. Mechanistic investigations, corroborated by mass transport simulations, reveal that the continuous in situ precipitation strategy effectively maintains a steep concentration gradient. When applied to actual wastewater, the system yielded a recovered FePO 4 product with a near-stoichiometric Fe/P molar ratio of 0.99 and substantially lower cationic impurity levels than those obtained by direct ferric-salt precipitation. The acidic anodic environment and ion-selective membrane jointly limited the association of coexisting cations with the recovered product and suppressed the formation of Fe(OH) 3 impurities. The strategy addresses the challenge of impurity incorporation and demonstrates the potential for value-added FePO 4 precursor recovery from phosphorus-rich wastewater.