Research on the Solubilities of Sodium Chloride and Sodium Sulfate Under Hydrothermal Conditions

Salt deposition under hydrothermal conditions can cause serious problems, such as equipment corrosion and pipe blockage. Therefore, the dissolution behavior of inorganic salts in sub-/supercritical water is an important subject. In this paper, a set of fluidity equipment was designed and employed to measure the solubility data of sodium chloride and sodium sulfate in water at 11–15 MPa and 553–613 K. The results show that for sodium chloride, the solubility decreases slightly before the phase transition point and decreases significantly after that. The overall trend of solubility was correlated with water density. For sodium sulfate, in the experimental region investigated, its solubility first increases, then decreases slightly, and finally decreases sharply after passing through the phase transition point. At the same time, six common empirical and semi-empirical models were applied to correlate the solubility data. The results show that the second-order polynomial model and the Cp model lead to relatively satisfactory fitting results for sodium chloride and sodium sulfate, respectively. Then, for the temperature and pressure range investigated, a new correlation model was proposed for obtaining better fitting result.