The kinetics of dissolution of calcium hydroxyapatite in water at constant pH

Abstract

The rate of dissolution of microcrystals of pure calcium hydroxyapatite in aqueous suspension was studied at 25°C and at constant pH. The effect of fundamental parameters such as (1) the initial sample mass, (2) the mass fraction remaining at later times, (3) the pH and (4) the concentration of the solute is reported. Specially prepared pyrophosphate-free orthophosphate solution was used in the preparation of the crystals. Carbon dioxide contamination was effectively avoided both in the preparation of crystals and in the kinetic experiments. The pH range studied was 6.6–7.2. An empirical equation representing the dependence of the rate of dissolution on the above-mentioned parameters is determined. The rate is found to be controlled by processes taking place in the surface of the crystals and not by transport processes.