Immobilization of lead and cadmium from aqueous solution and contaminated sediment using nano-hydroxyapatite.

The effectiveness and mechanism of nano-hydroxyapatite particles (nHAp) in immobilizing Pb and Cd from aqueous solutions and contaminated sediment were investigated. The maximum sorption amount (Q(max)) of Pb and Cd in aqueous solution was 1.17 and 0.57 mmol/g. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) surface and depth analysis indicated that dissolution-precipitation is the primary immobilization mechanism for Pb, while surface complexation and intraparticle diffusion account for Cd sequestration. Different amounts of nHAp (0-10% nHAp/dry weight) were added to the contaminated sediment. Sequential extraction showed that nHAp could effectively reduce the exchangeable fraction of Pb and Cd in the sediment and significantly reduce the concentration in porewater. The results in this study showed that nHAp can immobilize Pb and Cd in sediment effectively.