Temperature variable chemical model of bromide–sulfate solution interaction parameters and solid–liquid equilibria in the Na–K–Ca–Br–SO4–H2O system

Abstract

The experimental solubility data of bromide and sulfate minerals available in the literature are used to construct a chemical model that calculates solid–liquid equilibria in mixed systems NaBr–Na2SO4–H2O, KBr–K2SO4–H2O, and CaBr2–CaSO4–H2O from low to high solution concentration within the T=(0–100) °C temperature range. The solubility modeling approach based on fundamental Pitzer specific interaction equations is employed. The resulting model for mixed systems gives a very good agreement with bromide and sulfate salts equilibrium solubility data available in the literature. Temperature extrapolation of the mixed system models provides reasonable mineral solubilities at low (0 °C) and high temperature (up to 100 °C). Limitations of the mixed solutions models due to data insufficiencies at high temperature are discussed. The model for mixed system CaBr2–CaSO4–H2O at T=(0–50) °C was developed using pure electrolyte parameters of Ca–SO4 interactions and without including into a model aqueous species CaSO4 °(aq). It was showed that solution parameters fully account possible association reactions in low calcium sulfate molality regions of binary CaSO4–H2O and mixed solutions. The model presented here expands the previously published temperature dependent sodium–potassium–calcium–sulfate model by evaluating bromide–sulfate mixing solution parameters and inclusion of 5 bromide minerals precipitating within Na–K–Ca–Br–SO4–H2O system. The model predictions on the effect of bromide–sulfate mixing on the equilibrium deliquescence relative humidity (DRH) in NaBr–Na2SO4–H2O and KBr–K2SO4–H2O solutions are also given.