engleski

Structure and chemistry of the calcite-water- interface

Calcite is the most stable polymorph of CaCO3 at ambient conditions. It is ubiquitous in natural systems and controls to a large degree the geochemistry of terrestrial soils and sediments, but also of lacustrine- and seawater. Due to the reactivity of its surface, calcite has impact on the mobility of nutrients and contaminants in subsurface environments. Electrostatic phenomena at the calcite-water- interface provide a link between surface chemistry on the one hand side and hydrogeophysical methods like streaming potential or induced polarization measurements on the other hand side. In this study we present an updated view of the structure of the calcite(104)-water interface on the basis of a new extended crystal truncation rod data set, which allows to resolve previous ambiguities with respect to the coordination sphere around the surface Ca-ions and the relaxation of surface carbonate groups. On the basis of resonant surface diffraction data we investigate the interaction between calcite and weakly / non adsorbing Rb+ alkali metal cations. The structural aspects will be related to a newly developed electrostatic surface complexation model (SCM), describing the calcite-water-interface chemistry. For the first time, direct information on the inner surface potential of calcite, as measured with a calcite single crystal electrode, is included in the data constraining the calcite SCM, besides zeta potential data. Potential links between the calcite SCM and hydrogeophysical measurements will be highlighted.

calcite ; electrokinetic potential ; inner surface potential ; surface complexation model

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