Ability of micaceous minerals to adsorb and desorb caesium ions: Effects of mineral type and degree of weathering

Abstract To evaluate the effects of type of micaceous mineral and degree of weathering on the ability to adsorb and desorb radiocaesium (RCs) ions, various levels of weathering were induced (K‐depletion) in three types of micaceous minerals: biotite, muscovite and illite. The ability to adsorb RCs was represented by RCs interception potential (RIP) and a desorption ratio was determined by the amount of 137 Cs desorbed from the minerals by 1 M ammonium acetate ( 137 Cs desorption ratio). The RIP values were in the order of illite > biotite > muscovite. The RIP values for biotite gradually increased with the release of up to ~50% of the K + from interlayer sites but then decreased with the further release of K + , up to ~100%, which was associated with the formation of a fully expanded interlayer: vermiculite. The change from increasing to decreasing RIP due to the weathering of the biotite strongly indicated that the selective adsorption sites for RCs are not located in an expanded interlayer but in intermediate sites between non‐expanded and expanded interlayers: frayed edge sites (FES). In contrast, for both the muscovite and illite, the RIP only increased. The 137 Cs desorption ratio, <7% for all the samples, tended to decrease with increasing degrees of weathering and did not differ greatly by mineral type. These results contribute to a more accurate prediction of the risk of RCs transfer from soils to crops and the understanding of the weathering processes of micaceous minerals in soils. Highlights Radiocaesium adsorption and desorption was investigated for gradually K‐removed biotite, muscovite and illite. Vermiculitization of biotite via K removal firstly increased then decreased the frayed edge sites (FES). Adsorption was influenced by di/trioctahedral character and charge localization, and desorption by degree of weathering. These results lead to better understanding of the weathering processes of micaceous minerals and fate of RCs in soils.