Liquid-solid equilibria in the quaternary system NaCl–Na2SO4–Na2B4O7–H2O and the quinary system NaCl–NaBr–Na2SO4–Na2B4O7–H2O at 348 K

Abstract

According to the compositions of the underground brines in the Sichuan Basin, solid-liquid equilibria in the quinary system NaCl–NaBr–Na2SO4–Na2B4O7–H2O and its quaternary subsystem NaCl–Na2SO4–Na2B4O7–H2O at 348 K were measured by isothermal solution saturation method. The solubilities of salts and the densities of saturated solutions in the systems listed above were determined. Using the experimental data, phase diagrams, water content diagrams and density-composition diagrams were constructed, respectively. The quaternary system NaCl–Na2SO4–Na2B4O7–H2O belongs to a simple type, which consists of three univariant curves, one invariant point and three crystallization regions of NaCl, Na2B4O7 · 5H2O and Na2SO4. The equilibrium phase diagram (saturated with Na2SO4) in the quinary system NaCl–NaBr–Na2SO4–Na2B4O7–H2O is a type of solid solution and has not invariant point. There are two crystallization regions (saturated with Na2SO4): Na2B4O7 · 5H2O and solid solution Na(Cl,Br), one univariant curve.