Crystallization of hydroxyapatite from aqueous solutions in the presence of cadmium

Abstract

The interaction of cadmium with apatite, the model compound for hard tissues, is of interest as it may affect the structure and the kinetics of its formation. The seeded growth of hydroxyapatite was investigated at pH 7.40 and 25 °C, and at plethostatic conditions in the presence of cadmium ions at concentrations ranging from 0.01 to 1 µmol dm^–3. The presence of 0.05 µmol dm^–3 of Cd²⁺ caused a significant reduction in the rate of crystal growth, whilst at 0.5 µmol dm^–3 a plateau in the growth rate retardation was observed. Although the mechanism of growth in the presence of Cd²⁺ ions did not show any difference as compared to the pure system, the interaction of Cd with HAP cannot be explained by simple adsorption considerations, as was observed both by the analysis of kinetic data and by the electrophoretic mobility of HAP particles, in the absence and in the presence of Cd²⁺ ions.