Thermodynamic modeling of the adsorption of radionuclides on selected minerals. I: Cations

A general model that couples the diffuse-layer theory of surface complexati on with an aqueous activity coefficient model based on the B-dot equation h as been developed to study the adsorption of ions at the solid-water interf ace. The model takes into account the effect of changing aqueous speciation on the formation of surface complexes. It has been applied to determine th e binding constants for the sorption of selected radionuclide cations, name ly, Am(III), Pu(IV), Pu(V), and Np(V), on a number of (hydr)oxide minerals. The results show that the model accurately represents adsorption data in a ll examined cases. The binding constants of radionuclide cations were found to increase with their hydrolysis constants, and a linear correlation was developed to reproduce this behavior. The approach presented in this work c an be generalized to study the ionic adsorption effects in other waste-abat ement processes at solid-water interfaces and in water streams where ion se paration is required.