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 hydroxyapatit es 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 e xperiments, X-ray diffraction, scanning electron microscopy and nuclear mic roprobe. Cadmium is incorporated into the hydroxyapatite structure via diff usion and ion exchange. Once cadmium is sorbed, cadmium-containing hydroxya patites can be separated from the liquid phase by flocculation. Thus hydrox yapatite can potentially be used for remediating contaminated water and ind ustrial 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 mat erial. (C) 1998 Kluwer Academic Publishers.