Extrapolating investigations of ion and molecular adsorption at the muscovite (001)-water interface to systems in Earth, environmental, and materials science

Complete text of publication follows: Over ten years ago, we began investigating adsorption processes at the muscovite (001)-water interface using in situ X-ray reflectivity to understand the reactivity of this unique representative charged surface, which occurs in soils and sediments in the form of detrital micas and clays. Advances in experimental design and measurement along with implementation of resonant anomalous X-ray reflectivity have led to acquisition of data for monovalent cation, divalent cation, and dissolved organic matter systems over a range of pH at ambient conditions. From the data, which provide bulk and element-specific electron density in layers parallel to the (001) surface with Angstrom-scale resolution, a new detailed picture of the distributions of and interactions among ions, water, and organic molecules has emerged. We are developing quantitative expressions for the energetic balance between hydration and electrostatic attraction in the interfacial region that enhance models of the electrical double layer. We show how the results apply to the disposition of toxic metals and nutrients in soils and sediments, the mobility of cations in natural waters, the formation of mineral and organic colloidal aggregates in natural waters, and the general behavior of charged surfaces in materials science