Phosphate recovery from aqueous environment with recyclable nanoscale zero-valent iron coated with aluminum hydroxide

Recovery of phosphate (PO₄-P) from the aqueous environment is crucial for sustainable eutrophication and phosphorus resource management. In this study, aluminum hydroxide-coated nanoscale zero-valent iron (NZVI@Al(OH)₃) was developed as a magnetic-recyclable, air-stable, and efficient adsorbent for aqueous PO₄-P removal and recovery. The Al(OH)₃ shell could effectively protect the NZVI core from corrosion by O₂ and H⁺ under aerobic and anaerobic conditions, keeping the NZVI@Al(OH)₃ magnetically recyclable after adsorption. In addition, the Al(OH)₃ shell adsorbs PO₄-P efficiently via Al-O-P inner-sphere complexation, which was not affected by atmospheric conditions, pH conditions, and the co-existing anions and natural organic matter in real surface waters. After adsorption, PO₄-P can be readily desorbed by facile immersion of used NZVI@Al(OH)₃ in a highly alkaline solution and precipitated as hydroxylapatitle, with bare NZVI and dissolved AlO₂^- recovered for recycling. Therefore, NZVI@Al(OH)₃ is a robust and cost-effective adsorbent for PO₄-P recovery under real surface water conditions.