文摘
The phase equilibria of the quaternary system K+, Mg2+//Cl–, borate–H2O were studied at T = 298 K using an isothermal dissolution method. On the basis of the experimental data, the stable equilibrium phase diagram and the diagrams of the density versus composition and refractive indices versus composition of this quaternary system at 298 K were constructed. This phase diagram consists of three invariant points, seven univariant curves, and five crystallization fields corresponding to the single salt MgB4O7·9H2O, KCl, MgCl2·6H2O, K2B4O7·4H2O, and the double salt KCl·MgCl2·6H2O. The largest crystallization field is MgB4O7·9H2O; the smallest crystallization field is MgCl2·6H2O. By comparison with the stable phase diagram of system K+, Mg2+//Cl–, borate–H2O at 288, 298, and 323 K, the crystalline forms of salts are not changed, and the crystalline form of borate are B4O5(OH)42–. The crystallization field of MgB4O7·9H2O decrease obviously at 323 K. The crystallization region of KCl and K2B4O7·4H2O increases evidently, and the crystallization region of MgCl2·6H2O and KCl·MgCl2·6H2O changes slightly, meaning temperature has little impact on the solubility of KCl·MgCl2·6H2O and MgCl2·6H2O.