Sorption behavior of cesium ions to Mg-containing calcium silicate hydrate in a co-precipitation process

The sorption behavior of Cs to Mg-containing calcium silicate hydrate (C–S–H) was examined to consider C–S–H formation under the water-saturated conditions around a radioactive waste repository. The amount of Cs sorption was slightly lower for Mg-containing C–S–H than for C–S–H, because Mg leads to a decrease in sorption sites by facilitating the polymerization of silicate chains. However, the apparent sorption distribution coefficient Kd of Cs on C–S–H with a Ca/Si molar ratio of 0.8 and Mg contents up to 20% was estimated to be 3.4–6.1 mL/g. Furthermore, the amount of Cs sorption was not decreased by the presence of Ba. The apparent Kd obtained in this study was about 10 times higher than that conventionally estimated for host rocks in the plutonic repository, indicating that C–S–H retains the effect of Cs immobilization even when it contains Mg. Graphical abstract