Rapid and effective removal of uranium (VI) from aqueous solution by facile synthesized hierarchical hollow hydroxyapatite microspheres

Rapidly increasing development of nuclear power stimulates the exploration of low-cost and highly efficient materials to selectively remove uranium (VI) from contaminated wastewater streams. Herein, we successfully developed a novel hydroxyapatite (HAP) adsorbent by using a facile and template-free hydrothermal method. The XRD results demonstrated that the HAP was crystallized in hexagonal structure (space group P63/m(176)), and the images of SEM and TEM indicated that the HAP possessed hollow and hierarchical nanostructure. A large BET specific surface area (182.6 m²/g) and average pore size of 10.5 nm, suggested that the hierarchical hollow HAP microspheres could provide sufficient active sites for highly efficient removal of uranium from aqueous solutions, indicated the HAP might be a prompt emergency material for the remediation of nuclear leakage accident. Freundlich isotherm and pseudo-second-order kinetics model fitted well to sorption experimental data. The study was further advanced by FT-IR and XPS. The sorption mechanism was mainly attributed to surface chemisorption between U(VI) and HAP, forming a new U-containing compound, viz., autunite (Ca(UO₂)₂(PO₄)₂·3H₂O).