Application of microanalytical techniques to the study of aqueous ion sorption phenomena on mineral surfaces

Summary

Nuclear microprobe analysis has been used to study the aqueous sorption of cadmium and selenium at different solution pH values onto hydroxyapatite. By coupling Particle Induced X-ray Emission (PIXE) and Rutherford Backscattering (RBS) microanalyses, we have quantified the concentration and modeled the depth distribution of Cd and Se in particles of calcium hydroxyapatites (HAP). No cadmium precipitation was observed for those experiments in which the initial concentration was greater than the solubility of Cd(OH)₂ and CdCO₃ at solution pH=9 and 12. The observation of the solid by transmission and scanning electron microscopies, SEM and TEM, showed the polycrystalline nature of the particles; these particles were constituted by aggregated nanocrystals. This additional information allowed us to interpret the incorporation of Cd and Se into the apatitic substrate as a penetration in the intra-particle porosity generated by this aggregation of crystals and probably not as diffusion in the solid structure.