Solid-liquid phase equilibria of quaternary systems LiCl+KCl+NaCl+H2O and LiCl+KCl+MgCl2+H2O at 308.2K

Abstract

The phase equilibria of quaternary systems LiCl+KCl+NaCl+H2O and LiCl+KCl+MgCl2+H2O at 308.2 K were investigated by isothermal dissolution equilibrium method. The results reveal that the phase diagram of the quaternary system LiCl+KCl+NaCl+H2O consists of one invariant point, three univariable curves and three equilibrium solid crystallization fields (LiCl·H2O, NaCl and KCl). Two double salts appear in the quaternary system LiCl+KCl+MgCl2+H2O, namely KCl·MgCl2·6H2O and LiCl·MgCl2·7H2O, and the phase diagram is composed of three invariant points, seven univariable curves and five crystallization fields (LiCl·MgCl2·7H2O, MgCl2·6H2O, LiCl·H2O, KCl and KCl·MgCl2·6H2O). Moreover, the solubilities of salts in two quaternary systems are predicted by applying the Pitzer model. The calculated phase diagrams were in good accordance with the experimental phase diagrams. The results clearly show that lithium chloride crystallizes as LiCl·2H2O at low temperatures; however, it is precipitated as LiCl·H2O at 308.2 K. Compared with KCl·MgCl2·6H2O, LiCl·MgCl2·7H2O has a smaller crystallization zone. The phase equilibria in invariant points of quaternary systems LiCl+KCl+NaCl+H2O and LiCl+KCl+MgCl2+H2O at 308.2 K have been explored for the first time.