Constructing Fe(III)-bearing hydroxyapatite for Cr(VI) removal

Great importance has been attached to the utilization of low-cost, accessible, and high-pollution waste materials, particularly industrial solid wastes (i.e., steel slag) and hazardous solid wastes (i.e., spent adsorbents/catalysts). Herein, the transformation of Ca-containing whewellite precipitation originated from steel slag leaching solution into hydroxyapatite (Hap) nanorods is realized. Fe(III)-bearing Hap (xFe-Hap, x represents initial concentration of Fe3+ ions, mg/L) is then prepared via cation exchange between Fe3+ in solution and Ca2+ in Hap. The preferred 60Fe-Hap shows large specific surface area of 132.59 m2/g and 100% Cr(VI) photoreduction (60 mL, 40 mg/L Cr(VI)) with the assistance of oxalic acid (0.5 g/L) based on intramolecular charge transfer from oxalic acid to Fe(III) in [FeIII(C2O4)n]3-2n complex under visible light irradiation. This work thus offers a novel strategy for a high-efficient utilization of waste materials which may shift the waste materials into things of value in wastewater purification applications.