Study on phase equilibria of aqueous ternary system of Na+(Mg2+),Ca2+∥Cl--H2O at 278.2 K
Study on the multitemperature phase equilibria of water-salt system containing sodium,magnesium and calcium can provide data support for the sustainable development of salt lakes containing magnesium and calcium.Therefore,the phase equilibria of two aqueous ternary system of Na+,Ca2+∥Cl--H2O and Mg2+,Ca2+∥Cl--H2O at 278.2 K were investi-gated by the isothermal dissolution method,the solubility,refractive index and density of these two systems were deter-mined,the corresponding phase diagrams were constructed based on the experimental data.The results showed that Na+,Ca2+∥Cl--H2O and Mg2+,Ca2+∥Cl--H2O were both belong to simple system without double salts or solid solution formed at 278.2 K.The crystallization regions of NaCl was much larger than CaCl2·6H2O in the system Na+,Ca2+∥Cl--H2O at 278.2 K,comparing the phase diagrams of the system at 273.2,278.2,298.2,348.2 K,it could be seen that with the increase of tem-perature,the crystallization area of NaCl was increased,and the crystal form of CaCl2 was changed from CaCl2·6H2O to CaCl2·2H2O.The crystallization region of MgCl2·6H2O was larger than CaCl2·6H2O in the system Mg2+,Ca2+∥Cl--H2O at 278.2 K,comparing the phase diagrams of the system at 273.2,278.2,303.2,308.2,348.2,383.2 K,it was found that the double salt tachyhydrite 2MgCl2·CaCl2·12H2O was formed at 303.2,308.2,348.2,383.2 K,and its crystallization region was increased with the increase of temperature.There were two double salts of 2CaCl2·MgCl2·6H2O and 2MgCl2·CaCl2·12H2O formed at 383.2 K.
phase equilibriaphase diagramsolubilityhydrate salt
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