Performance and mechanism of amino-functionalized hydroxyapatite for uranium removal from strong acidity uranium wastewater

Abstract

The extraction of uranium generates substantial volumes of acidic wastewater loaded with uranium, thereby posing imminent threats to ecological systems and human wellbeing. Consequently, the development of highly effective adsorbent materials for uranium sequestration under strong acidic conditions has become paramount. The amino group contains a lone pair of electrons and is a highly reactive nucleophilic group with a strong affinity for uranium. Herein, we report the amino-functionalized materials (HAP-L-1NH2, HAP-L-2NH2, and HAP-L-3NH2) derived from sodium citrate-modified hydroxyapatite (HAP-L) through a combination of ultrasonic heating and grafting with varying concentrations of 2-amino-1,3-propanediol. The study delved into their performance and underlying mechanisms for uranium removal from acidic wastewater. The findings indicate that an optimal pH of 3.0 favors uranium adsorption for all the materials, with adsorption equilibrium achieved within 30min. Their respective maximum uranium adsorption capacities stand at 826.44, 990.09, 1060.21, and 884.95mgg-1, significantly enhancing the adsorptive prowess of amino-functionalized HAP-L materials. The kinetics and thermodynamics manifest that spontaneous endothermic chemisorption occurs on a homogenous monolayer during the adsorption process. Notably, HAP-L-2NH2 robust resilience to interfering ions and exceptional recyclability. After eight cycles of adsorption-desorption, HAP-L-2NH2 retains a uranium adsorption rate of 93.96% with a stable chemical structure. Application of HAP-L-2NH2 in treating real-world acidic uranium wastewater led to a notable increase in pH from 2.87 to 3.92 and a substantial reduction in uranium concentration from 0.883mgL-1 to 0.0104mgL-1. Uranium removal by HAP-L-2NH2 is primarily governed by ion exchange, electrostatic interaction, and co-precipitation reactions.