Cesium stability on the interlayers of K- or Rb-fixing micaceous minerals investigated by both experimental and...

The frayed edge site (FES) of micas, a partially weathered interlayer site, selectively adsorbs Cs radioisotopes. Despite extensive research on Cs⁺ adsorption, the interactive dynamics of FES elements remain unclear. This study employs experimental and computational methods to examine how interlayer cations at the FES affect Cs stability. We measured the solid-liquid distribution coefficients of Cs⁺ for partially expanded K- and Rb-fixed biotite using chemical extraction and adsorption methods. We evaluated the standard Gibbs free energy for the Cs exchange reaction between the FESs of K- and Rb-fixed muscovite models and bulk water, expanding the d₀₀₁ spacing from collapsed to fully expanded conditions. Our results reveal that the interlayer cation significantly influences Cs⁺ affinity for FES, with the substitution of K⁺ with Rb⁺ largely reducing Cs⁺ stability. The computational approach further disclosed that the K⁺ to Rb⁺ replacement only at the wedge-shaped part of the FES contributed to the decrease in Cs⁺ stability whereas the replacement at other interlayer sites caused little impact. Our studies offer microscopic structural insights into FES, highlighting the critical role of the wedge-shaped part of FES in Cs⁺ stability.