Solid–Liquid Phase Equilibria Determination of the Quaternary System Na⁺, K⁺, Ca²⁺//Cl^––H₂O at 348.2 and 363.2 K

Abstract

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 + , Ca 2+ //Cl − −H 2 O 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•CaCl 2 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 (CaCl 2 •4H 2 O) and two single salts (NaCl, KCl) in the phase diagram at 308.2 K. As the temperature fluctuates, CaCl 2 •4H 2 O (308.2 K) transitions to CaCl 2 • 2H 2 O (348.2−368.2 K). Additionally, with the increase in temperature, the crystal regions of NaCl, CaCl 2 •2H 2 O, and KCl•CaCl 2 gradually become larger and the crystal region of KCl decreases.

Solid–Liquid Equilibria of the Quaternary Water–Salt System K+, Mg2+, Ca2+ // SO42––H2O at 323.2 K

“…In the calcium-containing chloride system, we find that double salts 2MgCl 2 ·CaCl 2 ·12H 2 O and KCl·CaCl 2 are known to form in the quaternary systems Na + , Mg 2+ , Ca 2+ // Cl – –H 2 O and Na + , K + , Ca 2+ // Cl – –H 2 O at temperatures higher than 323.2 K. Two calcium-containing double salts, K 2 SO 4 ·CaSO 4 ·H 2 O and K 2 SO 4 ·MgSO 4 ·2CaSO 4 ·2H 2 O, are generated in the quaternary system K + , Mg 2+ , Ca 2+ // SO 4 2– –H 2 O at 323.2 K. We can see that the introduction of calcium ions, whether chloride or sulfate, makes the salting out of the solution very complicated. Therefore, detailed calcium-containing ion interaction is very important for the development of polyhalite.…”