An experimental study on phase equilibria in the system (K+, NH4+//Cl-, SO42--H2O) and (K+, NH4+//Cl-, SO42--(CH2OH)2-H2O) is done by the method of isothermal solution saturation. In these systems, the initial mass fraction of ethylene glycol is 30% in the salt-free binary solvent water + ethylene glycol. The solubilities, densities, viscosities, and refractive indices of saturated solutions have been measured for the two systems. On the basis of the experimental data, corresponding phase diagrams and diagrams of physical properties versus composition were plotted. All the physical properties of both systems change regularly with concentration change of the liquid phase. The phase diagram of (K+, NH4+//Cl-, SO42--H2O) consists of one invariant point, four univariant curves, and four solid phase crystallization regions at 333.15 K. The phase diagram of (K+, NH4+//Cl-, SO42--(CH2OH)2-H2O) is similar to the previous one, which contains one invariant point, four univariant curves, and four solid phase crystallization regions at 333.15 K. Comparisons of the stable phase diagrams for (K+, NH4+//Cl-, SO42--H2O) and (K+, NH4+//Cl-, SO42--(CH2OH)2-H2O) at 333.15 K are shown that they all have four solid solutions[respectively (K, NH4)Cl, (NH4, K)Cl, (K, NH4)2SO4 and (NH4, K)2SO4)]. These changes between phase diagrams at different solvents will be very useful for extracting the salts. According to this work, the measured data and phase equilibrium diagrams can be used for a new technology to design and optimize the production of K2SO4, from mother liquor of calcium carbonate whiskers prepared by FGD gypsum. At the same time, it can provide fundamental data support for chemical industry development.