Fluoride ion-mediated differential coordination separation of Al (III) and Fe (III) for regeneration of low-aluminum, high-purity battery-grade iron phosphate

Deep removal of trace aluminum from lithium extraction slag (LES) is key to recovering high-purity battery-grade iron phosphate (FePO 4 ). Existing methods exhibit low aluminum removal due to the close solubility product constants of Al (III) and Fe (III). In this work, we propose a novel strategy for trace aluminum removal based on fluoride ion-mediated differential coordination of Al (III) and Fe (III). Through precise control of fluoride ion concentration in phosphoric acid solution, iron preferentially precipitates while aluminum predominantly forms soluble fluoride complexes. This distinct behavior enables precise elemental separation through fluoride content optimization. The developed separation technology achieved aluminum removal rate of 98.89 %. It is noteworthy that the aluminum content of precipitated FePO 4 is below 30 ppm, which meets the standard of battery-grade. This work provides a viable technical pathway for the industrialization of Al/Fe separation in the lithium extraction slag leachate and the regeneration of low-Al, high-purity FePO 4 .