Preparation and characterization of nano-hydroxyapatite and its competitive adsorption kinetics of copper and lead ions in water

Abstract

In this work, microemulsion and hydrothermal methods were combined to synthesize hydroxyapatite nanomaterials. Competitive adsorption kinetics of aqueous Pb2+ and Cu2+ on nano-hydroxyapatite surfaces were investigated by performing adsorption kinetic experiments. Results showed that the adsorption quantity of Pb2+ on nano-hydroxyapatite was higher than that of Cu2+ in the single system. However, the competitive adsorption of Pb2+ and Cu2+ occurred in the coexistence system of Pb2+ and Cu2+. The adsorption quantity of Cu2+ on nano-hydroxyapatite increased, whereas that of Pb2+ decreased. The adsorption quantities of Pb2+ and Cu2+ on nano-hydroxyapatite presented a marked linear relationship with Ca2+ release from nano-hydroxyapatite (R2 0.861 to 0.954). The adsorption kinetics were fitted with the first-order, second-order, parabola, Elovich, double-constant, and Lennard–Jones function equations. Among these equations, the second-order equation and power function kinetics fitted the results optimally. Overall, the results indicate that the adsorption kinetics of Pb2+ and Cu2+ on nano-hydroxyapatite represent complex adsorption processes with both chemical reaction and physical adsorption.