Calcium hydroxyapatites: evaluation of sorption properties for cadmium ions in aqueous solution

The efficiency and mechanisms of cadmium sorption on two synthetic calcium hydroxyapatites from aqueous solution were investigated. Both hydroxyapatites remove cadmium from aqueous solutions with an efficiency higher than 99.5% at pH 5-6. The mechanisms of cadmium sorption were studied using batch experiments, X-ray diffraction, scanning electron microscopy and nuclear microprobe. Cadmium is incorporated into the hydroxyapatite structure via diffusion and ion exchange. Once cadmium is sorbed, cadmium-containing hydroxyapatites can be separated from the liquid phase by flocculation. Thus hydroxyapatite can potentially be used for remediating contaminated water and industrial wastes. The fact that cadmium is incorporated into the bulk of the apatite is important in the context of the safe storage of used sorbent material. (C) 1998 Kluwer Academic Publishers.