Adsorption of Chromium (VI) on Calcium Phosphate: Mechanisms and Stability Constants of Surface Complexes
Hydroxyapatite is a calcium phosphate in the apatite group. It has numerous applications due to its particular properties including the sorption of metallic ions. This makes it useful for the treatment of contaminated groundwater and for soil decontamination. The least expensive source of hydroxyapatite for synthesis is bovine bone, since this is a waste material. Vivianite is an iron phosphate which has received little study. Like hydroxyapatite, it has particular properties. This paper describes the method of obtaining these phosphates; calcium phosphate from bovine bone, and iron phosphate by synthesis. Also described are the methods of purifying the materials and characterization of these two phosphates by X-ray diffraction, infrared analysis, thermogravimetric and differential scanning calorimetric analysis, scanning electron microscopy, and surface area by the BET method. Physicochemical characteristics of hydroxyapatite obtained from bovine bone are described, and preliminary results are presented of an investigation into whether hydroxyapatite and iron phosphate are suitable as a permeable reactive barrier for the treatment of metallic and radionuclide contaminants.