Phase Diagram Theory and Process Investigation of K ₂ SO ₄ Production via the Two-Stage Glauber’s Salt Method under Ambient- and Elevated-Temperature Conditions

To address high energy consumption caused by excessive water evaporation in the conventional two-stage Glauber’s salt method for K2SO4 production at 25 °C, this study determines solid–liquid phase equilibrium data of the quaternary Na+, K+//Cl–, SO42––H2O system and its subsystems at 90 °C and constructs corresponding phase diagrams. Based on these data, the ambient- and elevated-temperature cooperative circulation processes (25 °C + 75 °C, 25 °C + 90 °C, 25 °C + 100 °C) are proposed and evaluated by material and heat-balance calculations. Compared with the traditional process, the 25 °C + 90 °C process generates mother liquor with a higher K+ concentration, reduces water evaporation by 21.88% and total heat consumption by 16.23%, and exhibits a smaller mother liquor circulation amount and a lower K+ loss rate. This process provides a practical energy-saving pathway for industrial K2SO4 production.