XANES AND LASER FLUORESCENCE SPECTROSCOPY FOR RARE-EARTH SPECIATION AT MINERAL-WATER INTERFACES

Sorption equilibria and kinetics involving Eu and Ce at the surface of hydroxylapatite and manganese oxide in aqueous solutions were examined by non-invasive spectroscopic techniques. The X-rays Absorption Near Edge Structure of Ce adsorbed on delta-MnO2(s) was determined using synchrotron radiation. A surface-mediated redox transformation of Ce(III) to Ce(IV) was observed. The rate of Eu adsorption and incorporation into the hydroxylapatite structure was studied by direct observation of the reacting suspension using Time Resolved Laser Induced Fluorescence. The process was found to be remarkably influenced by the aqueous speciation of Eu initially added to the mineral/water suspension.