Evaporation crystallization for the extraction of potassium bromide from bitters by phase equilibrium

Abstract

Aiming at the problems of complex process and high cost in the production of potassium bromide at present, the solubility data and the phase diagram of the quaternary system KBr–MgBr₂–K₂SO₄–MgSO₄–H₂O at 298.15 K were studied using the isothermal dissolution equilibrium method. The results showed that there are eight invariant points, sixteen univariant curves, and nine crystallization regions in the phase diagram which is complex and contains two double salts (K₂SO₄·MgSO₄·6H₂O and KBr·MgBr₂·6H₂O) and a metastable phase (MgSO₄·5H₂O). On the basis of the Pitzer model and HW model, the solubilities of the quaternary system were calculated, with which the corresponding phase diagram was plotted. By comparison, the evaluated phase diagram is in accordance with the measured one. Through analysis, the phase diagrams of the quaternary system at (298.15 and 323.15) K were combined to put forward a process to separate KBr from the system by evaporation and crystallization, which realized the full circulation of the mother solution.