Interactions of cesium and barium ions with calcium silicate hydrate under the condition saturated with saline water - 15247

The interaction of cesium (Cs) and barium (Ba) ions with calcium silicate hydrate (CSH gel) without drying processes was examined under the condition saturated with saline water, by monitoring the concentrations of Cs and Ba and using the Raman spectroscopy and the zeta potential. In the experiments, Ca/Si molar ratios of CSH gel were set to 0.4, 0.8, 1.2 and 1.6. Each sample was synthesized with CaO powder, SiO₂ powder and NaCl solution in given combinations. The concentration of NaCl solution was set to 0.006, 0.06 and 0.6 M. At the same time, CsCl or BaCl₂ solution was added to the sample in order to adjust its concentration to 1.0 mM. The curing period was set to 7, 14, 30 days. As a results, the sorption of Cs and Ba ions on CSH gel became stronger with lower Ca/Si molar ratio. On the other hand, even though the zeta potential showed the surface charge of higher Ca/Si ratio samples was positive charge which inhibits the sorption of cations, Cs and Ba ions significantly sorbed on CSH gel. In addition, Raman spectra of higher Ca/Si ratio samples showed that the degree of depolymerization of silicate chain increased with the sorption of Cs and Ba ions on CSH gel. In other words, even in higher Ca/Si ratio samples, Cs and Ba ions can sorb on CSH gel through the structural deformation of CSH gel. These results suggest that CSH gel might be able to contribute the migration retardation of Cs and/or Ba ions through the interaction with CSH gel, even if the near-field of the geological repository are saturated by saline groundwater. (authors)