Phase Equilibria in the ZnSO4–H2O System at Temperatures to 444°C and Pressures to 34 MPa

Abstract

Phase equilibria in the binary system ZnSO₄–H₂O at temperatures of 240–450°C and pressures to 34 MPa were studied by various methods (visual observation of phase transformations in water–salt systems of various compositions (30–60 wt%) in thick-walled quartz ampules (3 mm i.d.), taking samples of solutions and their chemical analysis, and autoclave measurements of P–V–T parameters in phase transitions). It was shown that the decrease in the ZnSO₄ solubility with increasing temperature, which is observed to 350–370°C, gives way to its abrupt increase with further heating; i.e., the negative temperature coefficient of solubility, which is characteristic of type 2 systems, changes to a positive one, as in type 1 systems. The ZnSO₄–H₂O system is of type 1 complicated by phase separation of saturated (and unsaturated) solutions, which leads to the sharp increase in the salt solubility above 375°C.