This dataset presents both isotopic and elemental data for a series of cation exchange experiments between mineral water, montmorillonite clay and seawater. These were a series of in-house experiments to determine isotopic fractionation and elemental distribution coefficients (if any) as the exchange pool switched from mineral water rich to seawater rich. Full details about this dataset can be found at https://doi.org/10.5285/8db593bf-cdc9-4256-ac28-e002814d636d
