Studies on Phase Equilibria of Ternary Systems KCl–PbCl2–H2O and MgCl2−PbCl2–H2O at 323 K

The solubility relationships of the ternary systems KCl–PbCl2–H2O and MgCl2−PbCl2–H2O at 323 K were studied by the isothermal dissolution equilibrium method in this article. In the KCl–PbCl2–H2O system, the phase diagram contains three invariant points, four solubility curves, and four crystallization regions (corresponding to KCl, KCl·2PbCl2, KCl·PbCl2, and PbCl2, respectively). Accordingly, two kinds of double salts, KCl·2PbCl2 and KCl·PbCl2, form in sequence with the increase of KCl concentration. In the MgCl2–PbCl2–H2O system, there are two invariant points, three solubility curves, and three crystallization regions (corresponding to MgCl2·6H2O, 3MgCl2·2PbCl2·18H2O, and PbCl2, respectively) in the phase diagram. In the two phase diagrams listed above, lead chloride has the largest crystallization region and it is most easily to deposit from the solution.