Adsorption performance and its mechanism of uranium using rod-like hydroxyapatite by one-step hydrothermal method

Abstract

Rod-like Hydroxyapatite (HAP) was synthesized using a one-step hydrothermal method. The successful synthesis of HAP has been confirmed based on the results of XRD and EDS. TEM images show that the HAP synthesized through the one-step hydrothermal method exhibits a rod-like morphology with good dispersion and minimal stacking. There was no significant aggregation observed and the diameter is about 25 nm. Both single-factor experiments and orthogonal experiments were conducted to determine the optimal conditions for adsorbing uranium from wastewater with an initial concentration of 10 mg·l−1. The optimized parameters included a pH of 5.0, a HAP dosage of m = 0.01 g, a reaction time of t = 30 min, a temperature at room temperature, and an agitation speed of R = 120 r·min−1. Under these conditions, the uranium removal efficiency exceeded 98%. The impact of anions and cations in the solution on uranium adsorption by HAP was investigated, revealing that cations with higher valence and anions with higher charge density had a more pronounced effect on the adsorption process. The fitting results obtained using adsorption isotherm and kinetic models indicated that the primary mechanism of uranium adsorption was surface monolayer chemical adsorption. Thermodynamic parameters suggested that the adsorption of uranium onto HAP was a spontaneous, endothermic process driven by entropy. Characterization results from EDS, XRD, FTIR, and XPS techniques indicated that the mechanism of uranium adsorption by HAP involved electrostatic adsorption, dissolution–precipitation, and ion exchange processes.