An experimental study on picromerite equilibrium in the five-component brine system K-Na-Mg-C1-SO4-H-2O

This paper presents the results of experiments on the physicochemical conditions for the formation of picromerite in the five-component brine system K-Na-Mg-Cl-SO₄-H₂O and the process of isothermal evaporation-crystallization of picromerite from brines. The metastable phase fields of picromerite at 15.10 and 5°C and its stable equilibrium phase field at -5°C have been established. In addition. the phase equilibrium relationships have also been established for other salt minerals. The lower limit of formation temperature of picromerite has been deduced on the basis of experimental results. The isothermal evaporation crystallization path of the invariant assemblage (point D) of picromerite, epsomite. sylvite and halite at 25, 15, 10 and 5°C has been revealed. Furthermore, some controversial problems are approached concerning the 25°C “solar” diagram and the 25°C metastable phase diagram of this system.