Adsorption of CsCl on porous SiO2 glass surface: Experimental results and ab-initio calculations

Abstract

The disposal of nuclear wastes is an issue of global concern due to the physicochemical and radiologic properties of some isotopes. Cesium radionuclides exhibit high solubility and some of them pose a long half-life. This work focuses on the study of Cs+ adsorption on the surface of a porous silica glass. Adsorption experiments were done at room temperature using aqueous solutions with concentrations of 0.1 and 0.5 M of CsCl at pH = 5 and surface area to volume of 0.1 cm- 1. In these conditions, 14 and 18 mgCs/gSiO2 were adsorbed, respectively. The adsorbed quantity of Cs+ was determined by atomic absorption spectroscopy (AAS) analyzing the quantity of Cs+ contained in the solution before and after adsorption experiments. The Cs+/Cl- ratio at a glass cross section surface, determined by energy dispersive spectroscopy analysis, is near 6. In addition, first principle calculations were performed, in order to determine charge transfer and location of the active sites for Cs+ and Cl-. Adhesion energy values are presented, which explain the experimental values found for the Cs+/Cl- concentration ratio at the silica glass surface. The parameters calculated from experimental and ab-initio calculations results were used to explain the adsorption mechanism.