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 (LiFePO4) precursors. While recovering iron phosphate (FePO4) 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 Fe2(SO4)3 as the anode electrolyte to achieve simultaneous phosphorus concentration and in situ FePO4 recovery. The process exploits the electric field to drive PO43- migration into the anode chamber, where it precipitates with Fe3+. Under the optimized conditions, using a mixed Fe2(SO4)3/Na2SO4 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 FePO4 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 FePO4 precursor recovery from phosphorus-rich wastewater.