To enrich the thermodynamic data and exploit valuable components in polyhalite, we utilized the isothermal dissolution method to examine the solid–liquid phase equilibria of the quaternary Na⁺, K⁺, Ca²⁺//Cl^––H₂O at 348.2 and 363.2 K. The compositions of the equilibrium solid phases were analyzed utilizing X-ray particle diffraction (XRD). The formation of the double salt KCl·CaCl₂ occurred at temperatures of 348.2 and 363.2 K. The phase diagram illustrates this relationship with two invariant points, five univariate curves, and four crystal regions. By examining the phase diagrams of the quaternary system at 308.2, 348.2, and 363.2 K, it can be concluded that there are three crystal regions corresponding to a hydrate salt (CaCl₂·4H₂O) and two single salts (NaCl, KCl) in the phase diagram at 308.2 K. As the temperature fluctuates, CaCl₂·4H₂O (308.2 K) transitions to CaCl₂·2H₂O (348.2–368.2 K). Additionally, with the increase in temperature, the crystal regions of NaCl, CaCl₂·2H₂O, and KCl·CaCl₂ gradually become larger and the crystal region of KCl decreases.

中文翻译：

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348.2 和 363.2 K 下四元体系 Na+、K+、Ca2+//Cl––H2O 的固液相平衡测定

^{为了丰富杂卤石的热力学数据并开发有价值的成分，我们利用等温溶解法检测了季盐Na +}、K ⁺、Ca ²⁺ //Cl ^– –H ₂ O 在348.2 和363.2 下的固液相平衡。K. 利用 X 射线颗粒衍射 (XRD) 分析平衡固相的组成。复盐KCl·CaCl ₂的形成发生在348.2和363.2 K的温度下。相图通过两个不变点、五个单变量曲线和四个晶体区域说明了这种关系。通过检查 308.2、348.2 和 363.2 K 下四元系的相图，可以得出结论，存在对应于水合物盐 (CaCl ₂ ·4H ₂ O) 和两种单盐 (NaCl、KCl)的三个晶区。在308.2 K 的相图中。随着温度波动，CaCl ₂ ·4H ₂ O (308.2 K) 转变为CaCl ₂ ·2H ₂ O (348.2–368.2 K)。另外，随着温度的升高，NaCl、CaCl ₂ ·2H ₂ O、KCl·CaCl ₂的晶体区域逐渐变大，而KCl的晶体区域逐渐减小。