An isopiestic study of aqueous NaBr and KBr at 50 °C: Chemical equilibrium model of solution behavior and solubility in the NaBr–H 2O, KBr–H 2O and Na–K–Br–H 2O systems to high concentration and temperature

Abstract

The isopiestic method has been used to determine the osmotic coefficients of the binary solutions NaBr–H 2O (from 0.745 to 5.953 mol kg −1) and KBr–H 2O (from 0.741 to 5.683 mol kg −1) at the temperature t = 50 °C. Sodium chloride solutions have been used as isopiestic reference standards. The isopiestic results obtained have been combined with all other experimental thermodynamic quantities available in literature (osmotic coefficients, water activities, bromide mineral’s solubilities) to construct a chemical model that calculates solute and solvent activities and solid–liquid equilibria in the NaBr–H 2O, KBr–H 2O and Na–K–Br–H 2O systems from dilute to high solution concentration within the 0–300 °C temperature range. The Harvie and Weare [Harvie C., and Weare J. (1980) The prediction of mineral solubilities in naturalwaters: the Na–K–Mg–Ca–Cl–SO 4–H 2O system from zero to high concentration at 25 °C. Geochim. Cosmochim. Acta 44, 981–997] solubility modeling approach, incorporating their implementation of the concentration-dependent specific interaction equations of Pitzer [Pitzer K. (1973) Thermodynamics of electrolytes. I. Theoretical basis and general equations. J. Phys. Chem. 77, 268–277] is employed. The model for binary systems is validated by comparing activity coefficient predictions with those given in literature, and not used in the parameterization process. Limitations of the mixed solutions model due to data insufficiencies are discussed. This model expands the variable temperature sodium–potassium model of Greenberg and Moller [Greenberg J., and Moller N. (1989) The prediction of mineral solubilities in natural waters: a chemical equilibrium model for the Na–K–Ca–Cl–SO 4–H 2O system to high concentration from 0 to 250 °C. Geochim. Cosmochim. Acta 53, 2503–2518] by evaluating Br − pure electrolyte and mixing solution parameters and the chemical potentials of three bromide solid phases: NaBr–2H 2O (cr), NaBr (cr) and KBr (cr).