Recovery of iron phosphate from waste activated sludge as a precursor for lithium-ion battery cathode materials

• FePO4 recovery approach from waste activated sludge (WAS) was proposed • Al- and Fe-bound P were the primary P-release contributors during WAS acidification • 78.9 % of P was precipitated from acidic leachate as FePO4 with 98.5 % purity • LiFePO4/C synthesized using recovered FePO4 exhibited high Li-battery capacity Phosphorus (P) recovery from waste activated sludge (WAS) offers a sustainable solution for resource management and circular economy in wastewater treatment. This study presents a novel approach that integrates acidic treatment of WAS with iron phosphate (FePO 4 ) precipitation to produce high-purity P for lithium battery cathode synthesis. Acidification using H 2 SO 4 (pH 2.0) released 40% of total P, mainly from Al- and Fe-bound fractions, as confirmed by sequential P fractionation. Subsequent precipitation at a Fe:P molar ratio of 1:1 and pH 1.6 achieved 78.9% P removal and yielded FePO 4 with 98.5% purity. The recovered FePO 4 was converted to LiFePO 4 /C, a cathode material that delivered an initial discharge capacity of 110.2 mAh/g at 200 mA/g and maintained 99% capacity retention over 300 cycles. The estimated P recovery cost was $6.04/kg, with a net economic benefit of $3.68/kg. This study demonstrates a promising pathway for integrated P recovery and value-added material production from WAS.