The prediction of mineral solubilities in natural waters: A chemical equilibrium model for the Na-K-Ca-Cl-SO4-H2O system to high concentration from 0 to 250°C

A chemical equilibrium model is described which is used to calculate solubilities within experimental uncertainties in the Na-K-Ca-Cl-SO4-H2O system from zero to high ionic strength and from 0 to 250°C. This model is an expansion of the variable temperature Na-Ca-Cl-SO4-H2O model of Møller (1988). It is parameterized by fitting available osmotic and solubility data in all common ion systems involving the potassium ion: Na-K-Cl-H2O, Na-K-SO4-H2O, K-Cl-SO4-H2O, K-Ca-Cl-H2O, and K-Ca-SO4-H2O. Limitations of the model due to data insufficiencies are discussed and comparisons of model calculations with the available data are given. Model predictions for solubility in the complex reciprocal systems, Na-K-Cl-SO4-H2O and K-Ca-Cl-SO4-H2O, are compared with experiment. Data for the two systems were available only in the temperature ranges 0–100°C and 25–55°C, respectively. The phase diagram predicted for the halite-saturated Na-K-Ca-Cl-SO4-H2O quinary system at 100°C is also presented. This model will be used to extend the Harvie et al. (1984) model for the Na-K-Ca-Mg-Cl-SO4-CO2-H2O seawater system to high temperature.