Solid–Liquid Phase Equilibria of the Quaternary System (NaCl + NH₄Cl + SrCl₂ + H₂O) and Subsystem (NaCl + NH₄Cl + H₂O) at 288.15 K and 0.1 MPa

Abstract—Solid–liquid phase equilibria of the quaternary system (NaCl + NH₄Cl + SrCl₂ + H₂O) and its subsystem are very important for the separation of ammonium and strontium salts from oilfield brines. In this paper, the solubilities of the quaternary system (NaCl + NH₄Cl + SrCl₂ + H₂O) and its subsystem (NaCl + NH₄Cl + H₂O) at 288.15 K and 0.1 MPa were determined by the isothermal solution equilibrium method. The experimental results show that the (NaCl + NH₄Cl + H₂O) system contains one invariant point and two single salt crystallization zones corresponding to NaCl and NH₄Cl. The crystallization zone of NH₄Cl was larger than that of NaCl. The quaternary system (NaCl + NH₄Cl + SrCl₂ + H₂O) contains one invariant points, three univariate solubility curves, and three single salt crystallization regions corresponding to NaCl, NH₄Cl, and SrCl₂⋅6H₂O.