Interlayer structure model of tri-hydrated low-charge smectite by X-ray diffraction and Monte Carlo modeling in the Grand Canonical ensemble

摘要: The present study aims primarily at refining a structure model for interlayer cations and H2O molecules in tri-hydrated (3W) smectite (d(001) = 18-19 angstrom). <2 mu m fraction of the SWy-2 source clay (low-charge montmorillonite) was saturated by Mg2+, Ca2+, Ba2+, or Na cations, before collection X-ray diffraction (XRD) patterns 98% relative humidity. Experimental d(001) values derived essentially homogeneous 3W hydrates provided volume constraints Grand Canonical Monte Carlo (GCMC) simulations. Computed atomic density distribution species were used turn to calculate XRD intensities 00l reflections. agreement between calculated experimental allowed validating GCMC results both content (cations molecules). profiles do not correspond usual three discrete planes but rather exhibit two sharp wetting surfaces (at similar 2.7 angstrom from layer surface). Additional belong cation hydration shells define poorly organized ensemble filling internal voids. This alternative suggests that stability hydrate dual interaction some with cation, through their second shell; 2:1 surface. approximated propose an smectite. simplified includes sets (symmetrical mid-plane) one set cations. allows reproducing different samples investigated thus represents valid parameters routine quantitative analysis effort determine reactivity close water-saturated conditions. Implications such studies are crucial provide on behavior main vector element transfer under conditions common surficial environments prevailing waste repositories. In addition, provides validation models widely ClayFF model, its use predict fate water clayey systems