Uranium(VI) and europium(III) speciation at the phosphate compounds-solution interface

Prediction of radionuclides migration through a geosphere is of fundamental interest in order to evaluate the safety of an underground radwastes repos itory. We have studied uranyl and europium(III) ion sorption mechanisms ont o three phosphate compounds: ZrP2O7; Zr2O(PO4)(2), and Th-4(PO4)(4)P2O7. A spectroscopic investigation which has been previously reported has allowed one to determine all species involved in the sorption processes under study . This paper presents the modeling of experimental retention data using FIT EQLv3.2 code (constant capacitance model). All sorption isotherms were succ essfully simulated with respect to the structural constraints. We have show n that uranyl sorption onto the solids under study is less influenced by el ectrostatic interactions between aqueous species and charges. on the surfac e than is that for europium(III) ion. Because; many experimental constraint s, obtained from independent spectroscopic techniques, have been taken into account for the fitting procedure, the sorption constant values can be det ermined accurately.