Abstract:

The behavior of salt-forming under a non-equilibrium status was experimentally determined for the system of MgSO₄-K₂SO₄-H₂O during boiling evaporation. The experiments of solution evaporation were carried out at a constant boiling temperature of 75 ℃ by a heating agent with a fixed temperature of 105 ℃. The evaporation intensity used was about 240—260 g/(h·L). The compositions of liquid and solid phase were analyzed at the time when primary nucleation occurs and several points of further evaporation. According to the experimental results the concepts of primary, extend and conditional salt-forming regions were proposed. The experimental results show that: (1) the primary salt forming regions of K2SO4, Leonite, Langbenite and MgSO₄·H₂O were observably different from those in Equilibria Phase Diagram. The width of primary forming region of K₂SO₄ and Langbenite are reduced, and the width of primary forming regions of Leonite and MgSO₄·H₂O are extended in different degrees. (2) Under the condition of having crystal seed, the width of salt-forming region is larger than that of primary salt-forming region in different degrees for different salts. (3) The extend salt forming regions of each salt caused an overlap. In the overlay region, what kind of the salt is formed depending on the seed of crystal. This overlay region is defined as conditional salt forming region, which is a special character in the non-equilibrium state phase diagram, and does not exist in the Equilibria Phase Diagram and Metastable Phase Diagram.

Key words: Phase diagram, Boiling evaporation, Non-equilibrium state, Behavior of salt-forming, MgSO₄-K₂SO₄-H₂O system