Isothermal evaporation of quaternary system Li⁺, K⁺, Mg²⁺//Cl⁻-H₂O at 348 K

Abstract

The solubilities of the quaternary system Li⁺, K⁺, Mg²⁺//Cl⁻-H₂O were investigated at 348 K via isothermal evaporation. The densities and refractive indices of its equilibrated solution were also determined experimentally. On the basis of the obtained data, the metastable phase diagram, the water content diagram, the diagrams of the density and refractive index against the composition of this quaternary system were constructed. The quaternary system Li⁺, K⁺, Mg²⁺//Cl⁻-H₂O at 348 K belongs to a complex type with the formation of two carnallite double salts, which are potassium carnallite(K-carnallite) and lithium carnallite(Li-carnallite). There are five salts like potassium chloride (KCl), lithium chloride monohydrate(LiCl·H₂O), bischofite(MgCl₂·6H₂O), K-carnallite(KCl·MgCl₂·6H₂O) and Li-carnallite(LiCl·MgCl₂·7H₂O), seven unvariant curves named AH₃, BH₂, CH₃, DH₁, EH₁, H₁H₂ and H₂H₃, and three invariant points, namely H₁, H₂ and H₃, included in this metastable phase diagram. Comparisons between the stable phase diagram at 298 K and metastable phase diagram at 348 K of this quaternary system show that all the crystalline forms of the salts are not changed, whereas the crystallization areas of salts are changed significantly with temperature. The scope of KCl crystallization increases from 82% to 95% and that of K-carnallite decreases from 15.80% to 0.32% along with the temperature increasing from 298 K to 348 K, respectively.