Electrolyte layering at the calcite(104)-water interface indicated by Rb(+)- and Se(VI) K-edge resonant interface diffraction.
Calcite-water interface reactions are of major importance in various environmental settings as well as in industrial applications. Here we present resonant interface diffraction results on the calcite(104)-aqueous solution interface, measured in solutions containing either 10 mmol L(-1) RbCl or 0.5 mmol L(-1) Se(VI). Results indicate that Rb(+) ions enter the surface adsorbed water layers and adsorb at the calcite(104)-water interface in an inner-sphere fashion. A detailed analysis based on specular and off-specular resonant interface diffraction data reveals three distinct Rb(+) adsorption species: one 1.2 Å above the surface, the second associated with surface adsorbed water molecules 3.2 Å above the surface, and the third adsorbed in an outer-sphere fashion 5.6 Å above the surface. A peak in resonant amplitude between L = 1.5 and L = 3.0 is interpreted as signal from a layered electrolyte structure. The presence of a layered electrolyte structure seems to be confirmed by data measured in the presence of Se(VI).
Institut für Nukleare Entsorgung, Karlsruher Institut für Technologie, P.O. Box 3640, 76021 Karlsruhe, Germany. frank.heberling@kit.edu johannes.luetzenkirchen@kit.edu horst.geckeis@kit.edu.
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Heberling
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Eng
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Denecke
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Lützenkirchen
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Geckeis