Studies on the metastable phase equilibrium of Na+, K+, Mg2+//Cl-, SO42-H2O quinary system at 35°C

This paper presents the experimental data of metastable phase equilibrium of Na+, K+, Mg2+ //Cl-, SO42--H2O quinary system at 35 degreesC , from which the metastable phase diagram is drawn. It consists of nine regions of crystallization saturated with sodium chloride, potassium chloride, glasserite (3K(2)SO(4) . Na2SO4), leonite(K2SO4 . MgSO4 . 4H(2)O), kainite (KCl . MgSO4 2.75H(2)O), thenardite (Na2SO4), astrankit (MgSO4 . Na2SO4 . 4H(2)O), carnallite(KCl . MgCl2 . 6H(2)O), magnesium sulfate hexahydrite (MgSO4 . 6H(2)O) and bischofit (MgCl2 . 6H(2)O). A large difference is found between the obtained metastable phase diagram at 35 degreesC and Van' t Hoff's stable phase diagram at 25 degreesC. The crystallization regions of schoenite (K2SO4 . MgSO4 . 6H(2)O), epsomite (MgSO4 . 7H(2)O), magnesium sulfate pentahydrite (MgSO4 . 5H(2)O) and starkeyite (MgSO4 . 4H(2)O) disappear and the crystallization regions of leonit and astrankit are greatly incresed. Also there is much difference between the obtained metastable phase diagram at 35 degreesC and the metastable phase diagram at 25 degreesC. The crystallization regions of schoenite (K2SO4 . MgSO4 . 6H(2)O) and epsomite disappear and arise the crystallization regions of leonite and kainite. It is found that the crystallization region of low hydrate kainite (KCl . MgSO4 . 2.75H(2)O) exists in the metastable phase equilibrium of Na+, K+, Mg2+ //Cl-, SO42-H2O quinary system at 35 degreesC.