Interpretation of the interaction between cesium ion and some clay minerals based on their structural features

Cesium (Cs⁺) is known to have a strong interaction with various clay minerals; however, it is not interpreted from the structure of clay minerals and the adsorption isotherm. The adsorption interactions between Cs⁺ and hydrobiotite (H-Bio), biotite (Bio), vermiculite (Verm), and exfoliated vermiculite (E-Verm) were evaluated by analyzing adsorption isotherm, basal spacing, and adsorption/desorption experiments. The Cs⁺ adsorption of H-Bio and Verm fitted well to the Langmuir adsorption isotherm, while the Cs⁺ adsorption of Bio and E-Verm fitted well to the Freundlich adsorption isotherm. The basal spacing of H-Bio and Verm was approximately 1.4 nm, while Bio and E-Verm basal spacing was 1.0 nm. The adsorption experiment results for Cs⁺ under the coexistence of Ca²⁺ and K⁺ indicated that the contribution of the interlayer sites to Cs⁺ adsorption on H-Bio and Verm was 25–40%, while the contribution of the interlayer sites to that on Bio and E-Verm was almost 0%. The adsorption isotherms reflected this interlayer contribution to Cs⁺ adsorption, which was dependent on the basal spacing. Therefore, the basal spacing of clay minerals is one of the key structural properties controlling both the adsorption capacity and the adsorption mechanism of Cs⁺ in clay minerals.