Radiocesium sorption behavior on illite, kaolinite, and their mixtures

Clay minerals are one of the most important components in soil for radiocesium sorption. There are many types of clay minerals in soil, and their capacities for cesium (Cs) sorption differ. However, the effects of differing clay mineral amounts and compositions on Cs sorption behavior have not been clarified yet. In this study, therefore, we studied Cs sorption on illite, kaolinite, and illite–kaolinite mixtures, carrying out batch sorption test and sequential extractions to investigate Cs sorption mechanisms. The amount of sorbed Cs in the mixtures did not depend on the illite content, but the amount of exchangeable Cs decreased as the illite content increased. Conversely, the amount of fixed Cs in the mixtures increased with increasing illite content. These results suggest that the distribution of Cs sorption between ion exchange sites and fixed sites may be dependent on the illite/kaolinite ratio. In addition, we can estimate the amount of sorbed Cs in an illite-kaolinite mixture from the amounts of sorbed Cs in illite and in kaolinite, and the abundance ratio of each clay mineral in the clay mixture. This is basic knowledge needed for long-term assessment of Cs mobility in soil.