Study of Pu(IV) and Am(III) sorption to clay minerals. Laboratory experiments and modeling

Sorption of Pu(IV) and Am(III) to natural clay from a mixture of synthetic rainwater - cement water was studied by batch and sequential extraction experiments as a function of pH and ionic strength These experiments were intended to simulate the effect of cement dissolution, causing the release of K+, Ca2+ and other cations from solidified radioactive waste into the aqueous phases. The results indicated a complex sorption behavior of the elements studied. It was found that iron oxides play an important role in the uptake of Pu(IV), whereas ion exchange and CaCO3 are mainly responsible for the binding of Am(III) on the clay. Simplified sorption experiments were conducted with clay minerals and iron oxides, using 0.01 and 0.1 mol/L NaNO3 as background electrolyte under an Ar atmosphere, for a better understanding of the sorption mechanisms. The experimental data were interpreted using the combination of surface complexation and ion-exchange models. (orig.)