Fluoride removal by hydroxyapatite modified with anhydrous aluminum chloride

View large Download slide View large Download slide Close modal Efficient and low-cost removal of fluoride from water has attracted wide attention. Here, aluminum-modified hydroxyapatite (Al-HAP) was prepared by a homogeneous hydrothermal co-precipitation method. The physicochemical properties of the Al-HAP surface were characterized by SEM, XRD, FT-IR, BET, and zeta potential, and the adsorption performances were evaluated. It showed that Al-HAP has a larger specific surface area (121.97 m 2 /g, which is 2.3 times larger than that of HAP), more surface-active hydroxyls and positively charged at pH less than 7, which indicate that Al-HAP is beneficial to the adsorption of negatively charged fluoride. Al-HAP had a higher fluoride adsorption capacity (56.44 mg/g) than that of HAP (28.36 mg/g), and not sensitive to the interference of coexisting ions except CO 3 2- . Based on the adsorption kinetics and adsorption isotherm experiments, the proposed two-stage kinetic model and Freundlich isotherm model can better describe the adsorption process. From the results of XPS and FT-IR, it indicated that the ion exchange between hydroxyl group on the surface and fluoride ions is the main driven force for the adsorption, and electrostatic adsorption is also helpful. The present study provides an improved HAP to effectively remove fluoride from water. Aluminum-modified hydroxyapatite (Al-HAP) was prepared by a co-precipitation method. The adsorption efficiency of Al-HAP was 30% higher than that of HAP. Al-HAP belongs to mesoporous structure with larger specific surface area. The equilibrium adsorption capacity of Al-HAP is 56.44 mg/g at 298 K. The main mechanism is ion exchange.