The results of a study on the composition and rheological properties of solutions after separation of glaserite, as well as the influence of technological parameters on the process of evaporation of mother liquors in the production of potassium sulfate by conversion of flotation potassium chloride with mirabilite of the Tumryuk deposit, are presented. The most intensive process of evaporation of the mother liquor, after separation of the glaserite, proceeds at a temperature of 100°C. In this case, after 60 minutes, the volume of the solution decreases by more than 50%, while at 80 and 60°C these figures are 20 and 5%, respectively. With an increase in the volume of the evaporated liquid from 5% to 40%, the amount of precipitated sodium chloride increases from 3.1% to 22.9% of the mass of the initial mother liquor containing (wt.%): K2O-6.86; Na2O-11.67; SO4-2-3.46, CI--16.02; H2O-66.26 at 20°C. The density of the mother liquors with an increase in the volume of the evaporated solution increases from 1.250 g/cm3 to 1.358 g/cm3 at a temperature of 20°C and from 1.210 g/cm3 to 1.330 g/cm3 at 80°C, the viscosity decreases from 2.126 mPa s to 2.007 mPa s upon evaporation of 40% moisture and up to 0.914 mPa s when the temperature rises from 20°C to 80°C.