Mechanism of Strong Affinity of Clay Minerals to Radioactive Cesium: First-Principles Calculation Study for Adsorption of Cesium at Frayed Edge Sites in Muscovite

Molecular dynamics simulations of cesium adsorption on illite nanoparticles

“…Atomistic simulation techniques such as molecular dynamics (MD) simulations and density functional theory (DFT) calculations can, in principle, circumvent these difficulties by allowing a direct observation of individual Cs ions on different surface sites. Existing simulation studies have probed cesium adsorption in the interlayer nanopores of swelling clay minerals [64,97,78,79,10,44], in anhydrous clay interlayers [79,93], and at illite and vermiculite wedge sites [68,107]. However, no existing atomistic simulation study has examined cesium adsorption selectivity on different surfaces of a single illite particle, because of two methodological challenges.…”

“…Recent efforts have deployed a combination of wet chemistry experiments [102,4,26], high-resolution imaging [47,63,95,34], synchrotron Xray spectroscopy [29,42], and atomistic-level simulations [68,93,44,107] to gain detailed insight into Cs adsorption mechanisms, selectivity, and kinetics. The emerging view from these studies is that Cs adsorption involves at least three types of surface sites: basal sites located on the external basal surfaces of illite particles, slow sites located in anhydrous illite interlayers, and high affinity sites of unclear nature.…”

“…Despite the importance of the high-affinity and slow sites of illite for cesium fate and transport, important questions remain unanswered regarding the properties of these sites. First, the structure of the high affinity sites is a continuing topic of investigation [46,62,93,68]. The predominant hypothesis is that they occur in ''wedge" regions where illite or vermiculite interlayers transition from a collapsed state to an expanded state [18,102,68,107].…”

“…First, the structure of the high affinity sites is a continuing topic of investigation [46,62,93,68]. The predominant hypothesis is that they occur in ''wedge" regions where illite or vermiculite interlayers transition from a collapsed state to an expanded state [18,102,68,107]. The existence of these regions is supported by electron microscopy observations showing that weathering induces a discernible ''fraying" at the edges of illite and mica crystals [62,34], perhaps associated with the replacement of K by solvated Ca near the extremities of the anhydrous interlayers [34].…”

Local Structure Analysis of Li-substituted (Bi_0.5Na_0.5)TiO₃ and NaNbO₃

“…However, in order to avoid approaching oxygen too much, covalent bond nature arises between alkaline metal and oxygen [4]. In the case of Li ion, covalent bond nature does not occur even in the crystal field owing to its small ionic size.…”