We seek to understand and model the effects of salinity on geochemical processes occurring in aqueous environments including nanopores and interlayers in clay media, thin water films in unsaturated porous media, and solutions in which mineral nanoparticles nucleate, aggregate and grow. The overall goal is to identify conceptual models of salinity effects on complex geochemical processes including mineral growth and aggregation; diffusion in thin films and nanopores; and charge-transfer reactions. A specific objective is the development of predictive models for ion diffusion linking molecular and continuum descriptions and spanning relevant time scales. This research addresses a long-standing fundamental topic in geochemistry that is vital to understand core processes involving minerals, nutrients and contaminants in groundwater and how these processes will be affected by environmental change. Moreover, this research will provide basic knowledge and new methodologies for understanding the properties and evolution of geochemical systems anticipated to be relevant to the DOE mission for many years ahead.