Phase Equilibria of Quaternary Systems Containing the Chlorides of Ammonium, Strontium(Magnesium), and Aluminum at 298.2 K

The phase equilibria of the quaternary systems NH4Cl–SrCl2–AlCl3–H2O and NH4Cl–MgCl2–AlCl3–H2O at 298.2 K were investigated by using the isothermal dissolution method. The solubility, density, and refractive index of the systems were measured experimentally, and the related phase diagrams, density/refractive index versus composition diagrams, are plotted. There is one quaternary invariant point and three crystallization regions corresponding to single salts NH4Cl, AlCl3·6H2O, and SrCl2·6H2O in the phase diagram of the system NH4Cl–SrCl2–AlCl3–H2O at 298.2 K, which belongs to a simple system. In addition to the single salts NH4Cl, AlCl3·6H2O, and MgCl2·6H2O, the double salt NH4Cl·MgCl2·6H2O is formed in the quaternary system NH4Cl–MgCl2–AlCl3–H2O at 298.2 K, which indicates that the addition of magnesium makes the interaction relationship between Al3+, NH4+, and Mg2+ more complex and increases the difficulty of separation of magnesium. The crystallization region of NH4Cl is the largest in both the systems, which indicates that NH4Cl is much easier to separate than the other salts from the two systems.