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.