Study On Thermodynamics And Equilibrium Phase Of Cesium Alkali Metal Salts In Aliphatic Aqueous System

Abstract The rare alkali-metals rubidium and cesium had active chemical properties as well as the special physical merits of optics and electricity and they have been widely available in the realm of living and production application. Accordingly, the study of separation and purification of these metals could be extremely significance.In recent years, the researcher have applied the systems comprised alkali-metal salts and mixed solvents to separate the rare metals, to desalinate the sea water, to make a comprehensive utilization of the salt lake resources. What's more, the aim of the study of the system's phase behavior and thermodynamics properties was not only to provide the plenty of basic data for the applied research which would develop the solution chemistry, but also to make a foundation for the construction of thermodynamics model.This experimental work mainly includes two parts:In the one part, we have used the semi-micro phase equilibrium apparatus as well as the corresponding technology of the sample withdrawing and the analysis to study the isothermal equilibrium phase behavior.First, the "cloud point" and "tie-line" methods have been used to study the ternary system involved the water + propan-1-ol + cesium chloride and water + propan-2-ol + cesium chloride at 298.15 K, 308.15 K and 318.15 K. While we got the compositions of binodal curves and tie lines, draw the completely phase diagram. And the compositions have been correlated by using the Othmer-Tobias and Bancroft equations;the result could be satisfactory. At the same time, the liquid-liquid equilibrium has been fitted by the NRTL model which shows the interaction parameters.Second, we have studied the isothermal solubility of two quaternary systems. In the base of former ternary systems, we have performed the salt effect for liquid-liquid region in the quaternary system (cesium carbonate + cesium chloride + ethanol + water) with the different two salts ratios at 293.15 K. And we got the compositions of three sectional phases. At the same time, we have studied the whole phase diagram of another quaternary system (water + propan-1-ol + cesium sulfate + cesium chloride) at 298.15 K. And the data were correlated by Eisen-Joffe equations which show the influence of two salts for the liquid-liquid region. On the basis of the standard deviations, we concludedthat the equation may be satisfactorily used for the investigated systems. Last, we made an explanation for the mechanism of liquid-liquid equilibrium.In the other part, we have combined the cesium ion selective electrode and the chloride ion selective electrode to establish a galvanic cell and determined the electromotive force of cesium chloride in Methanol-Water mixtures at 298.15 K. While the Pitzer model was adopted to describe the behavior of electrolyte. The activity coefficient, E° and the related model parameter were calculated in different ratios of Methanol-Water mixtures. The Pitzer-Simonson-Clegg model was also applied to correlate the data and found superior than the Pitzer model;the reason could be that the ionic association was appeared in the mixed solvent along with the increase of the content of cesium chloride.Finally, on the foundation of models, the osmotic coefficient was determined at 298.15 K as well as the free energies of transfer of cesium chloride from water to Methanol-Water mixtures. The figure of the osmotic coefficient vs. the content of Methanol showed the superiority of Pitzer-Simonson-Clegg model;and the theory of Born electrostatic attraction could be used to explain the behavior of osmotic coefficient. Furthermore, we have made a prediction of solubility of cesium chloride in mixed Methanol-water solutions on the basis of Pitzer-Simonson-Clegg model.