Mixed interaction terms in the use of pitzer equations: application to the heat capacities of the reciprocal system Na +/K +/Cl −/SO 42−/H 2O at high temperatures

Abstract

Changes of heat content of aqueous solutions of Na 2SO 4 and of NaCl-Na 2SO 4 mixtures have been measured between 60 and 220°C by means of a drop calorimeter Standard procedure yielded the corresponding heat capacity data. These data were analyzed in terms of Pitzer's theory which enables the calculation of the parameters β 0, β 1 and C φ for Na 2SO 4(aq), which are valid up to 3 mol kg −1, and the binary mixed interaction term XXX CISO 4. These new data were utilized, in the framework of the ion interaction model, to reproduce experimental values of the heat capacity data of the quaternary system Na +/K +/Cl −/SO 4 2−/ H 2O. The critical points of this description are discussed.