Sorption Behavior of Cesium on Calcium Silicate Hydrate under High Carbonate Ion Concentration Conditions

To assess radionuclide migration, Ca/Si ratio of calcium silicate hydrate (CSH) gel formed as a secondary mineral is a key factor because CSH gels effectively adsorb radionuclides, in particular cationic nuclides. However, the Ca/Si ratio of the CSH gel is changed by the leaching of Ca ions and the formation conditions. In this study, the influence of carbonate ions on the sorption of Cs ions on the CSH gel was preliminarily examined. For the sorption experiments, the concentrations of carbonate ions (NaHCO3) were adjusted to 0 mM-1000 mM at the synthesis of the CSH gel or after a 7-day curing period. As a result, the sorption of Cs ions on the CSH gel became larger with the increase in the concentration of carbonate ions. Such sorption behavior was also observed when carbonate ions were added after curing the CSH gel. These results suggest that CSH gel formed as a secondary mineral might be able to contribute to the retardation of radionuclide migration by interacting with carbonate ions.