Solid-Liquid Phase Equilibria of the Pb, Ca, Mg//Cl-HO Quaternary System and Its Subsystems at 303.2 K.

The solid-liquid phase equilibria of the ternary systems Pb, Ca//Cl-HO, Pb, Mg//Cl-HO, and Ca, Mg//Cl-HO were investigated at atmospheric pressure and = 303.2 K using the isothermal dissolution equilibrium method. Additionally, solid phase equilibria of the quaternary system Pb, Mg, and Ca//Cl-HO were determined, and the corresponding stable phase diagrams and density-composition diagrams were constructed. The results indicate that the phase diagrams of Pb, Ca//Cl-HO mainly consist of a ternary invariant point, two solubility curves, and four crystalline regions, while there are two ternary invariant points, three solubility curves, and six crystalline regions in the Pb, Mg//Cl-HO and Ca, Mg//Cl-HO systems. The results of the density-versus-(CaCl) plots of the various ternary systems confirm that the density of the equilibrium solution tends to go upward with the increase in the mass fraction of CaCl. The density of various ternary systems reaches the maximum and equilibrium at the corresponding invariant point, and there is no significant change with the further increase in the CaCl mass fraction. Furthermore, the phase diagram of the Pb, Mg, Ca//Cl-HO quaternary system includes two invariant points, five isothermal dissolution curves, and five crystalline regions. The order of the relative areas of the crystalline regions for the five salts is PbCl > CaCl·2MgCl·12HO > 2PbCl·3MgCl·18HO > MgCl·6HO > CaCl·4HO.