The Experimental Determinatinon And Prediction Of Freezing Point Of Salt-water Systems

In this paper, aiming at the single saline solution, Na+,K+//Cl-,NO3--H2 O and Na+//Cl-,SO42-,NO3--H2 O quaternary system and their subsystems, experiment device for measuring electrolyte solution freezing point have been established, solution freezing points, eutectic point, the relationship between eutectic point and the system composition have been studied using cooling curve method. On this basis to Extended UNIQUAC model theory as a foundation for research, freezing points of salt-water systems involved in this paper have been calculated, and compared with the experimental results.The results show that:For a single saline solution, when the concentration of solution does not reach the concentration of eutectic point, freezing point decreases with the increase of concentration, and if it is greater than the concentration of eutectic point, the freezing point will not change, namely the freezing point under the eutectic point concentration.For the ternary system and quaternary system with one ion, the relationship among the freezing point, eutectic point and composition can be described with triangular prism; For the mutual quaternary system, the relationship among the freezing point, eutectic point and composition can be described with quadrangular prism.Multivariate systems involved in this article, according to the relationship among the solution freezing point, eutectic point and the system composition, the corresponding three-dimensional phase diagrams were drawn, and the scope of application were determined; A mathematical model was built according to phase diagram.Compared with the experimental results, with Extended UNIQUAC model, the calculation results for most of the systems under the low concentration are good, but under the high concentration, the deviations are slightly larger, especially for a solution containing the high cation. On the whole calculation value is slightly largerthan the experimental value.Extended UNIQUAC model to calculate multiple freezing point of salt-water system, has the advantages that parameters are fewer, calculation process is simpler,the predicted results are more accurate.