Phase diagrams and thermodynamic modeling of solid-liquid equilibria in the system NaCl–KCl–SrCl2–H2O and its application in industry

Abstract

Combining of the determined solubilities of two ternary systems NaCl–SrCl2–H2O and KCl–SrCl2–H2O and Pitzer binary parameters obtained in the literature at different temperatures, the lacking Pitzer mixing parameters θNa,Sr, θK,Sr, ΨNa,Sr,Cl, and ΨK,Sr,Cl were fitted on the basis of the Pitzer model. The variable temperature chemical model for Pitzer mixing parameters including Sr2+ ion was built. The model was then used to calculate thermodynamic properties such as the solubilities, osmotic coefficients, ionic activity coefficients and dilution enthalpy of the quaternary system NaCl–KCl–SrCl2–H2O in the wider temperature range. The theoretical results using the model coincide with the experimental values. The phase diagrams and Pitzer model for the quaternary system were then used to conduct computer simulation of isothermal evaporation and brine separation. The evaporation-crystallization route and the order of salt crystallization were obtained using the model at 298.15 K. The pure salts KCl, NaCl and SrCl2·6H2O were separated from the solution with the model at 273.15 K and 323.15 K.