Selective adsorption and irreversible fixation behavior of cesium onto 2:1 layered clay mineral: A mini review

In this study, we reviewed the selective adsorption and irreversible fixation of cesium (Cs⁺) on clay minerals. The selective adsorption of Cs⁺ results from reactions with frayed edge sites (FES) of clay minerals. The content of FES is about 0.1-2.0% of the total cation exchange capacity (CEC). The fractionation of Cs⁺ in actual accident sites mainly exists as a residue, which is important because it is closely related to the strong binding between Cs⁺ and soils. Cs⁺ adsorbed onto FES can move into the deeper interlayer via weathering processes, thereby Cs⁺ can be irreversibly fixed in the interlayer of non-expanding 2:1 layered clay mineral. Additionally, Cs⁺ can be adsorbed in the interlayer of the expanding clay mineral and can be fixed by interlayer collapse. For this reason, Cs⁺ adsorption onto FES is defined as 'selective adsorption' subsequent sorption in the interlayer as 'irreversible fixation'. Furthermore, the extended X-ray absorption fine structure (EXAFS) analysis can confirm that Cs⁺ bound to illite is coordinated with the outer surface (O_OS) and interlayer surface oxygens (O_IS) through FES or interlayer sites. Through these processes, Cs⁺ is adsorbed selectively onto FES, while Cs⁺ can subsequently move into the interlayer and become more strongly fixed.