Coprecipitation of Cadmium with Hydrosyapatite

The distribution behavior of the cadmium ion between hydroxyapatite precipitates and aqueous solution phase was studied, where the hydroxyapatite was prepared by the extremely slow addition of diammonium hydrogenphosphate to the solutions of cadmium and calcium nitrates buffered with ethylenediamine at 80°C. The cadmium ion was coprecipitated in the hydroxyapatite, obeying the Doerner and Hoskins logarithmic distribution law. Apparent distribution coefficient was remarkably affected by the ethylenediamine concentration and the pH value. The true distribution coefficient, A°, was calculated by using the stability constants of proton and cadmium ion with ethylenediamine at 80°C, and its value gave a constant, about 103.4, independently of the ethylenediamine amount and the pH value..