Determination of Solid–Liquid Phase Equilibria of Na₂SO₄–(NH₄)₂SO₄–MgSO₄–H₂O at T = 318.15 K

Abstract

The solubility data of the quaternary system Na+, NH4 +, Mg2+∥SO4 2––H2O and its subsystems Na+, NH4 +∥SO4 2––H2O and Mg2+, NH4 +∥SO4 2––H2O were measured by an isothermal dissolution method at T = 318.15 K. The physical property data (density and viscosity) of the supernatant were also obtained. The experimental results show that both ternary systems contain two invariant points, which are complex systems. The quaternary system (Na+, NH4 +, Mg2+∥SO4 2––H2O) has four invariant points, nine univariate curves, and six crystallization regions. The crystal area of double salt (NH4)2Mg­(SO4)2·6H2O is the largest, and it is the easiest to crystallize from the saturated solution. Density and viscosity varies regularly with solution composition in each system. The translation method is used to predict the quaternary system, and the results are consistent with the experiment. Based on the phase diagram of Na+, Mg2+, NH4 +∥SO4 2––H2O, the process of producing a nitrogen–magnesium compound fertilizer was designed, which provided a theoretical basis for guiding the industrial crystallization of salt lakes.

Solid–Liquid Phase Equilibria of Aqueous Quaternary System Na+, K+, Mg2+//SO42––H2O at T = 298.2 and 323.2 K

“…3 and Figure 1, respectively. [6][7][8][9][13][14][15][16]25,30 It can be seen from Table 3 that the solubility data of invariant points in ternary subsystems of system Na + , K + , Mg 2+ //SO 4 2− −H 2 O at 298.2 and 323.2 K in this work are in good agreement with the related literature. 6,7,13,25 From Figure 1 Based on the Janecke index, the stable phase diagram of the quaternary system Na + , K + , Mg 2+ //SO 4 2− −H 2 O is plotted in Figure 2.…”

“…To ensure the reliability of the experimental data of this work, the solubility data and physicochemical properties (density and refractive index) of invariant points in ternary subsystems in the literature of the Na + , K + , Mg 2+ //SO 4 2 – –H 2 O system are compared and listed in Table and Figure , respectively. − ,− ,, It can be seen from Table that the solubility data of invariant points in ternary subsystems of system Na + , K + , Mg 2+ //SO 4 2 – –H 2 O at 298.2 and 323.2 K in this work are in good agreement with the related literature. ,,, From Figure , the experimental data of density and the refractive index of the ternary subsystem (Na + , K + //SO 4 2 – –H 2 O, Na + , Mg 2+ //SO 4 2 – –H 2 O) in this work are consistent with the literature data, ,,− , and the changing trends of density and refractive index are basically the same.…”

“…Graphical comparison of the density (a) and refractive index (b) of invariant point data of the ternary subsystems Na + , K + //SO 4 2– –H 2 O (red stands for experimental data of this work and other colors stands for reference data): red box solid, red triangle down solid, red tilted square solid, red circle solid: in this work, blue triangle up solid, blue triangle right-pointing solid: ref , black box solid, black triangle left-pointing solid: ref ; graphical comparison of the density (c) and refractive index (d) of invariant point data of the ternary subsystems Na + , Mg 2+ //SO 4 2– –H 2 O: red box solid, red triangle down solid, red tilted square solid, red circle solid: in this work, blue triangle down solid, blue box solid: ref , black triangle up solid, black box solid: ref , green tilted square solid, green triangle down solid, green triangle up solid, green triangle left-pointing solid: ref , yellow box solid, yellow triangle right-pointing solid: ref , purple box solid: ref .…”

“…Among them, the interaction between ions in the sulfate system containing sodium, potassium, magnesium, and calcium is complex, and many kinds of double salts may be formed, which is the key to the research. So far, a series of experimental studies have been carried out on the sulfate system containing sodium, potassium, magnesium, and calcium, as described below: binary systems of Na 2 SO 4 –H 2 O at 272–514 K, K 2 SO 4 –H 2 O at 271.6–562.15 K, and MgSO 4 –H 2 O at 269.28–511.15 K; ternary systems of Na + , K + //SO 4 2– –H 2 O at 298.2, 303.2, 313.2, 323.2, and 348.2 K; − Na + , Mg 2+ //SO 4 2– –H 2 O at 298.2, 313.2, 318.2, 323.2, and 348.2 K; ,− and K + , Mg 2+ //SO 4 2– –H 2 O at 298.2, 308.2, 318.2, 323.2, and 348.2 K; ,− and quinary system Li + , Na + , K + , Mg 2+ //SO 4 2– –H 2 O at 298.2 K . By analysis of the above phase diagram, the results indicated that (1) the crystallization areas of single salts and double salts are different at different temperatures.…”