New tools and concepts for understanding the evolution of mineral surface area for extrapolation of environmental kinetics

To extrapolate geochemical kinetics of abiotic mineral-water reactions across scales, one must quantify the rate constants for reaction, activities of solution species involved in the reaction, and the surface area or reactivity of the mineral-water interface. While significant effort has focused on modeling rate constants as a function of mineral and solution composition, the complexities involved in measuring and predicting the mineral-water interfacial area and reactivity have not been systematically addressed. In general, the surface area and reactivity are coupled to dissolution since we know that roughness and reactivity vary as the dissolving surface evolves. In some cases, however, roughness, reactivity, and surface site density may reach steady state values. We have begun an investigation to compare the reaction kinetics of clusters of molecules modeled with ab initio techniques to the stochastic evolution of model mineral surfaces and to NMR measurements related to reactive surface area. Such a comparison will yield conceptual tools to predict temporal evolution of the surface area and reactivity terms, and should further our capacity to predict environmental kinetics.