A surface complexation model, the so-called diffuse double layer model (DLM), was used in the description of the multicomponent
system consisting of Czech sodium bentonite SABENYL and synthetic granitic water spiked with233U(VI). The experimental data were evaluated and the characteristic parameters, e.g., the equilibrium constants of all the
reactions considered, were obtained and used for the numerical simulation of sorption selectivity of the uranium in relation
to the total carbonate concentration. The values of separation factors indicate that the selectivity of uranium sorption in
such multicomponent systems can depend not only on the pH and composition of both phases, but also on the phase ratio and
starting concentrations of participating components.