Solid–Liquid Phase Equilibria in the Quinary System Na+, K+, Mg2+//Cl−, $${\text{NO}}_{3}^{ - }$$–H2O and Its Subsystems at 258 K

Abstract

The phase equilibrium of the quaternary system Na+, K+, Mg2+//Cl−–H2O and the quinary system Na+, K+, Mg2+//Cl−, $${\text{NO}}_{3}^{ - }$$ –H2O were investigated at 258 K using the isothermal dissolution equilibrium method. The phase diagrams were obtained based on the measured data. Double salt KCl·MgCl2·6H2O was found in the quaternary and the quinary systems at 258 K. In the quaternary system Na+, K+, Mg2+//Cl−–H2O, there are two invariant points, five univariant curves, and four crystallization fields. The quinary system saturated with NaCl·2H2O contains four invariant points, nine univariant curves, and six crystallization fields corresponding to KCl, NaNO3, KNO3, Mg(NO3)2·6H2O, KCl·MgCl2·6H2O and MgCl2·8H2O. Mg(NO3)2·6H2O and MgCl2·8H2O that have higher concentrations and stronger salting-out effect on other salts. Therefore, low-temperature pretreatment can offer an alternative treatment of brines in accordance with the necessity for current brine treatment processes to reduce the presence of double salts and be crucial for purer products to be separated.