Effect of pH and anions on hydroxyapatite-Cu2+ solid-liquid interactions

Abstract

The reaction of synthetic Ca₅(PO₄)₃OH (HAP) with Cu²⁺ ions is investigated by means of pH, pCu and pCa measurements as a function of the time, pH and electrolyte type (NaCl, NaHCO₃, Na₂HPO₄). The solid phases separated after different reaction times are investigated with X-ray diffraction (XRD) and IR techniques. The Cu²⁺ does not form mixed compounds with Ca²⁺ and does not replace Ca²⁺ in the HAP structure. The presence, in an appropriate concentration, of anions which form very insoluble Cu²⁺ compounds favours the precipitation of the latter with no involvement of HAP. If the concentration of the anions is low, the precipitation of Cu²⁺ also involves HAP and this behaviour is particularly enhanced with Na₂HPO₄.