Compared with salt lake brine, deep brine features high temperature and high calcium content, which alters potassium’s phase equilibria behavior. Accordingly, the phase equilibria of the quaternary system K+, Mg2+, Ca2+//Cl–-H2O at 323.2 and 348.2 K were investigated using the isothermal dissolution method. The phase diagrams at both temperatures consist of four quaternary invariant points, nine univariate curves, and six crystallization regions. Three double salts chlorocalcite (KCl·CaCl2), carnallite (KCl·MgCl2·6H2O), and tachyhydrite (2MgCl2·CaCl2·12H2O) were identified. In this system, potassium crystallizes as KCl, KCl·MgCl2·6H2O, and KCl·CaCl2, with KCl having the largest crystallization region, followed by KCl·MgCl2·6H2O and then KCl·CaCl2. A multitemperature comparison (298.2 to 348.2 K) of K+, Mg2+, Ca2+//Cl–-H2O reveals that at 298.2 K, potassium crystallizes only as KCl and KCl·MgCl2·6H2O, and the crystallization phase region of KCl has the largest region, which is favorable for the separation and extraction of potassium. When at 323.2 and 348.2 K, in addition to KCl and KCl·MgCl2·6H2O, the double-salt KCl·CaCl2 also forms, and the crystallization region of KCl·CaCl2 increases with increasing temperature, which may affect the stability of potassium extraction raw materials such as KCl and KCl·MgCl2·6H2O.
Yu et al. (Sat,) studied this question.