Adsorption of Nuclides on Hydrous Oxides

Abstract

Hydrous oxides and minerals which have adsorbing groups that behave like hydrous oxides are ubiquitous components of geological formations and may dominate the adsorptive properties of the formations at conditions of natural groundwaters. An understanding of the adsorptive behavior of hydrous oxides is therefore necessary for reliable prediction of migration of nuclides through the formations. Various isotherms are derived from equilibrium ion-exchange theory for the sorption of non-hydrolyzed ions on hydrous oxides. These isotherms are compared with experimental isotherms for sorption of Cs+, Sr2+, Eu3+, and TcO4- on several hydrous oxides. The experimental isotherms for cations show little dependency of sorption on the ionic strength at intermediate pH values but considerable dependence at higher pH values. In the pH range of negligible hydrolysis, sorption increases with pH for cation sorption, and the slope of this dependency on pH increases with the charge of the cation. General features of these isotherms are predictable from ion-exchange equilibrium theory as applied to hydrous oxides. By combining isotherms for hydrous oxides with those for layer-type clay minerals, many unusual features of isotherms found on geological materials can be explained.