Thermodynamic phase equilibria containing sodium, potassium, magnesium, strontium and chloride in underground brine environment and evaporation and salt precipitation behavior of strontium chloride

Abstract

The isothermal dissolution equilibrium method was employed to study the thermodynamic phase equilibria of the NaCl + KCl + MgCl2 + SrCl2 + H2O system at 298.2 K. The equilibrium solubilities and solid phase compositions of the quinary system at 298.2 K were determined by chemical analysis and X-ray diffraction, and the corresponding stable phase diagrams were drawn. The phase diagram of the quinary system has three invariant points, six solid phase crystallization fields and fifteen solubility curves. In the phase diagram, crystalline area of double salt KCl·MgCl2·6 H2O existed. Moreover, the Pitzer thermodynamic model was utilized to predict the phase equilibria of the quinary system at 298.2 K, and the predicted solubilities agreed well with the experimental values. The results demonstrate that the Pitzer model can accurately describe the thermodynamic properties in the quinary system at 298.2 K. Finally, based on the advantages of rich strontium in underground brine from Longnu Temple brine-bearing structure in Sichuan basin of China, the salt precipitation law of strontium chloride was studied.