A. M. Potapov, V. A. Kesikopoulos, A. E. Dedyukhin, Yu. P. Zaikov.
ABSTRACT
The equilibrium composition of (LiCl-KCl)eut. + 1 mol % UCl3 system during its titration with lead chloride at the temperatures of 773, 873 and 973 K was calculated by thermodynamic modeling methods. The calculations were carried out taking into account the activity coefficients of lead and uranium chlorides in the molten LiCl–KCl eutectic. At 773 K, the activity coefficients g(PbCl2) = 0.42; g(UCl3) = 5.73·10-3 и g(UCl4) = 7.54·10-5 were used. As the temperature rises, the activity coefficients increase. Thus, at 973 K the activity coefficients are already g(PbCl2) = 0.49; g(UCl3) = 0.020 and g(UCl4) = 3.04·10-4. It was found that in the LiCl-KCl melt, lead chloride only partially oxidizes UCl3 to UCl4. This is due to the fact that the difference between the formal standard potentials and is only about 0.2 V. Therefore, PbCl2 is a weak oxidizing agent in this case. The difference between и potentials increases with increasing temperature. Therefore, UCl4 equilibrium fraction increases with increasing temperature and also with excess of PbCl2. For example, at 773 K and a threefold excess of PbCl2 against the stoichiometry, the average uranium valence is n = 3.27. And at 973 K and the same excess of PbCl2, the average valency of uranium increases to n = 3.36.
Also, the process of reduction of UCl4 to UCl3 by metallic uranium in the molten LiCl-KCl eutectic was modeled taking into account the activity coefficients of the components. In the considered interval, 773–973 K, the reduction has no thermodynamic difficulties and proceeds completely.
The HSC-9.9 software package was used for thermodynamic calculations.
KEYWORDS
Thermodynamic modeling, Uranium, Uranium chlorides, Lead chloride, “soft” chlorination.
DOI: 10.31857/S0235010622060111