Sorption behavior of iodine on calcium silicate hydrates formed as a secondary mineral

This study examined the sorption behaviors of iodine into CSH gel without dried processes, considering the repository system saturated with groundwater after the backfilling. In glove box saturated with N₂ gas, each sample of CSH gel was synthesized with CaO, SiO₂, and distilled water with liquid/solid ratio 20. Then, 1 mM iodine solution is added into the aqueous solution including the CSH gel with various Ca/Si molar ratios under the isothermal condition (298 K). In the results, even if the Ca/Si ratio is relatively small (<1.0), the distribution coefficients (K_d) of iodine on CSH gel without dried processes were two-order of magnitude larger than those with dried processes. For example, the value of K_d (ml/g) was about 380 in the case of 0.5 in Ca/Si molar ratio. Furthermore, it was confirmed the sorption behavior attain equilibrium in 24 hours. These suggest secondary mineral of CSH gel would retard the migration of anionic nuclides under the condition saturated with groundwater. In comparison, this study prepared also the co-precipitated samples of CSH gel and iodine, where the 1 mM iodine solution is added before curing the CSH gel. These distribution coefficients and the kinetics almost agreed with those mentioned above.