Studies of Phase Equilibria in Quaternary Systems NaCl + BaCl₂ + SrCl₂ + H₂O and NaCl + KCl + BaCl₂ + H₂O at 323.0 K

In order to reveal the mineralization process of salts in the gas field water, studies of the solid–liquid phase equilibria of the systems are essential. The solid–liquid phase equilibria of the systems NaCl + BaCl2 + SrCl2 + H2O, NaCl + KCl + BaCl2 + H2O, and NaCl + BaCl2 + H2O at 323.0 K were studied. The corresponding equilibrium solid phases were identified by chemical analysis and powder-crystal X-ray diffraction, and the isothermal phase diagrams were drawn. The phase diagram of the ternary system NaCl + BaCl2 + H2O at 323.0 K contains one invariant point and two isothermal solubility curves. The phase diagram of the quaternary system NaCl + BaCl2 + SrCl2 + H2O at 323.0 K contains one invariant point and three isothermal solubility curves. In the dry salt phase diagram of NaCl + KCl + BaCl2 + H2O at 323.0 K, three salts, NaCl, KCl, and BaCl2, reach equilibrium at the only invariant point. These above experimental results can provide a theoretical basis for the extraction of associated barium and strontium resources in the gas field water.