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) and interlayer surface oxygens (O) 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.