Analysis of sorption behavior of cesium and iodide ions on pumice tuff

Abstract

In the reliable safety assessment of radioactive waste disposal, the understanding and modeling of the sorption behavior onto the host rock under various groundwater conditions are indispensable. The influence of pH, ionic strength, and the initial concentrations of Cs and I on the sorption of Cs and I on tuff and pumice isolated from the original pumice tuff rock was investigated. For both rocks, the proton concentration has little effect on the Kd values for Cs in the pH range 3-10. As the ionic strength of the solution increases in the presence of sodium perchlorate as a matrix ion, the Kd value of cesium apparently decreases, reflecting the competition of the electrolyte Na+ with the specific sorption of Cs+ on the negatively charged sites. In contrast, no significant dependence of ionic strength on the Kd of anionic iodine was found. A simple surface complexation model without considering electrostatic works was applied to simulate the sorption of ions on rocks, and the model parameters were determined. The Kd values at the given chemical conditions were estimated using the parameters and compared with the ones in the literature. © 2011 Atomic Energy Society of Japan.