A study of Eu2O3 solubilization in K2SrCl4 melt at 973 K under the action of CCl4 vapor

Abstract A comparative study of carbochlorination processes (treatment with CCl4 vapor in argon flow) of K2SrCl4 melt and K2SrCl4+Eu2O3,solid mixture at 973 K was performed by the potentiometric method with the use of Pt(O2)|ZrO2(Y2O3) membrane oxygen electrode as reversible to oxide ion. Solid Eu2O3 interacts with K2SrCl4 melt that results in partial transformation of the oxide into oxochloride, EuOCl (the degree of Eu2O3 transformation is 0.54) and the process is completely suppressed at oxide ion (SrO) concentration ca. 3∙10-3 mol kg-1; here the melt becomes saturated with respect to both Eu2O3 and EuOCl. The course of interaction of Eu2O3 with K2SrCl4 melt at 973 K obeys the Shchukarev equation. The analysis of van’t Hoff diagrams for these processes showed that the stage of Eu2O3 solubilization under the action of CCl4 is clearly detected. The data corresponding to the finishing of Eu2O3 solubilization in K2SrCl4 melt allowed to estimate the solubility product of Eu2O3 as 1.2·10-22 mol5·kg-5 in molality scale and 3.2·10-26 in mole fractions. The corresponding values for EuOCl are 1.47·10-7 mol3·kg-3 ( m C l - = 13.1 mol kg-1) or 1.05·10-9 (mole fractions). An application of the Shreder-Le Chatelier equation for the recalculation of some literature data on the solubilization of rare-earth metal oxides and oxochlorides at different temperatures allowed us to compare them with the results obtained in this work. It was confirmed that the running of the carbochlorination process at low oxide ion concentrations was determined by the rare earth oxide (oxochloride) dissolution similarly to the situation observed in other chloride melts where HCl was used as a chlorinating agent. The literature data and data of this work expressed in units of oxoacidity function Ω and reduced to the same temperature (973 K) are in a good agreement.