Solubilities of Magnesium and Cadmium Sulfates in Water at High Temperatures and Pressures

Abstract

The solubilities of salts in the MgSO₄–H₂O and CdSO₄–H₂O systems are studied at 276–500°C using various methods (visual examination of phase transformations in water–salt mixtures in sealed quartz ampoules, collecting solution samples and performing chemical analysis, and measuring p–V–T dependences in an autoclave) to determine temperature dependence and classify the compounds as one the of two types (type 1 or type 2) according to the classification of inorganic salts. In the studied temperature range, the solubility of these salts is very low at pressures below 157 MPa and decreases when approaching the critical point of water. The systems under study are found to be classified as type 2 water–salt systems having the critical point (G = L – S) lying near the critical point of water. No separation of fluid into two liquid phases was detected at temperatures below 500°C and pressures below 157 MPa, thus indicating that the second critical point (L₁ = L₂ – S) has very high parameters. The resulting data can be used for elaborating methods for raw material processing.