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

A general model that couples the diffuse-layer theory of surface complexation with an aqueous activity coefficient model based on the B-dot equation has been developed to study the adsorption of ions at the solid-water interface. The model takes into account the effect of changing aqueous speciation on the formation of surface complexes. It has been applied to determine the binding constants for the sorption of selected radionuclide cations, namely, 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 all 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 can be generalized to study the ionic adsorption effects in other waste-abatement processes at solid-water interfaces and in water streams where ion separation is required.