Sorption of radiocesium by active silica.

Cement and cement components have previously been shown to exhibit negligible sorption for cesium. Pyrogenic silica has been examined as an additive to cement materials for its ability to reduce the leachability of cesium and to provide a host material with permanent sorption sites. The incorporation of silica into cement composites can also improve the physical characteristics and strength of these materials as long ages. At neutral pH values, there is significant sorption of cesium by silica, but in high pH regimes, such as occur in cement environments, initial sorption is enhanced but this high level of sorption is followed by a gradual release of Cs. This apparent desorption is due to the consumption of SiO2 by Ca(OH)2 to form products which have little sorption potential for cesium. If, however, sufficient SiO2 is added to the system initially such that an excess remains after satisfying the demands of the Ca(OH)2 reaction, permanent sorption sites for cesium may be created.