Efficient removal of uranium in aqueous solution by Al-doped hydroxyapatite: Static/dynamic adsorption behaviors and mechanism study

Abstract

The development of efficient adsorbents is critical for the removal of uranium from aqueous solution. In this study, lamellar hydroxyapatite (HAP) was synthesized and further functionalized by aluminum doping through ion exchange, which was applied as adsorbents for uranium removal from aqueous solution. In batch static adsorption process, the optimized Al-doped hydroxyapatite (Al-HAP-5) exhibited good performances for uranium removal, including high uptake capability (222.22 mg g−1), favorable selectivity against co-existing ions (Na+, K+, Mg2+, F−, etc.) and good reusability (93.32% removal efficiency in 8th recycle run). Further continuous dynamic adsorption study proved that Al-HAP adsorbent possessed great potential for practical application with a maximum adsorption capacity calculated to be 220.00 mg g−1. The breakthrough time was measured up to be 69.0 h with a column bed height of 9.6 mm. Various adsorption models were adopted to fit the experimental data, which helped to understand the adsorption process and mechanism. Single layer adsorption dominated by chemisorption was suggested. Spectroscopy study indicated that Al doping brought more hydroxyl groups on the surface of HAP, which favored the complexation between uranium and adsorbent. The strong interaction between Ca2＋ and UO22+ was evidenced by the formation of autunite (Ca(UO2)2(PO4)2 ⋅3H2O), which also contributed to the high efficiency of uranium adsorption.