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.