Study of bromide salts solubility in the (m1KBr + m2CaBr2)(aq) system at T = 323.15 K. Thermodynamic model of solution behaviour and (solid + liquid) equilibria in the ternaries (m1KBr + m2CaBr2)(aq), and (m1MgBr2 + m2CaBr2)(aq), and in the quinary (Na + K + Mg + Ca + Br + H2O) systems to high concentration and temperature

Abstract

The bromide minerals solubility in the mixed system (m1KBr+m2CaBr2)(aq) have been investigated at T=323.15K by the physico-chemical analysis method. The equilibrium crystallization of KBr(cr), and CaBr2·4H2O(cr) has been established. The results from solubility measurements obtained have been combined with experimental equilibrium solubility data available in the literature at T=298.15K to construct a chemical model that calculates (solid+liquid) equilibria in the ternary (m1KBr+m2CaBr2)(aq) system. The solubility modelling approach based on fundamental Pitzer specific interaction equations is employed. Temperature extrapolation of the mixed system model provides reasonable mineral solubilities at low (273.15K) and high temperature (up to 373.15K). The reference solubility data for (m1MgBr2+m2CaBr2)(aq) system, which are available in the literature at T=(273.15, 298.15, and 323.15)K are used to evaluate mixing ion interaction parameters and to develop a model that calculates (solid+liquid) equilibria in this ternary system. The models for both ternary systems give a very good agreement with bromide salts equilibrium solubility data. Limitations of the mixed solution models due to data insufficiencies at high temperature are discussed. The mixed system models presented in this study expand the previously published temperature dependent sodium–potassium–magnesium–bromide model by evaluating potassium–calcium–bromide and magnesium–calcium–bromide mixing solution parameters and by evaluating a chemical potential of double salt 2MgBr2·CaBr2·12H2O(cr), and complete the temperature dependent thermodynamic model of solution behaviour and (solid+liquid) equilibria in quinary system (Na+K+Mg+Ca+Br+H2O). The results of Pitzer ion interaction model-based thermodynamic studies on binary, and mixed systems within the (Na+K+Mg+Ca+Br+H2O) system have been summarised. Important thermodynamic characteristics {solubilities (ms), thermodynamic solubility products (as lnK°sp), standard molar Gibbs free energy of formation (ΔfG°m), deliquescence relative humidity (DRH)} of the bromide minerals crystallizing from the saturated binary and ternary solutions are given. Model predictions on ms, lnK°sp, ΔfG°m, and DRH are compared with those available in the literature. Model calculations are in excellent agreement with the reference experimental data and recommendations.