A surface complexation model based on the diffuse-layer theory has been applied to study the adsorption of radionuclide anions (I-, IO3-, SeO32-, SeO42-, and TcO4-) on various minerals. The model is coupled with an aqueous activity coefficient model based on the B-dot equation and takes into account the effect of aqueous speciation on adsorption. Binding constants for the selected radionuclide anions on minerals have been determined. In all examined cases, the model is shown to accurately represent the adsorption data. The selected radionuclide anions have been identified as potentially significant contributors for dosing in high-level nuclear waste because of their high solubilities and reduced interactions with aquifer minerals; the methodology presented in this work can be generalized to the study of ion adsorption effects at water-mineral interfaces in natural systems that implicitly regulate the fate of environmental contaminants.