ELECTROCHEMICAL SYNTHESIS OF INTERMETALLIC U–Ga AND U–Cd COMPOUNDS IN MOLTEN LiCl–KCl–CsCl EUTECTIC

Abstract

The processes of cathodic reduction of U(III) ions to metal in a low–melting LiCl–KCl–CsCl eutectic at the temperature range 650–850 K on tungsten, gallium and cadmium electrodes in an inert gas atmosphere have been studied by non-stationary and stationary electrochemical methods. Reagents without contain impurities of moisture, oxygen and their compounds were used in the experiments. All major operations were performed in a dry glove box. The following methods were used to analyze the electrochemical processes: cyclic voltammetry, square-wave voltammetry and potentiometry at zero current. On cyclic voltammogram of the molten LiCl–KCl–CsCl–UCl3 solution on an inert tungsten electrode, one cathode current peak corresponding to the deposition of metallic uranium and one anode current peak associated with its dissolution were recorded. It was found that the potential of the cathode peak was shifted to a region of more negative values with an increase of the scan rate. The value of the cathode peak current was directly proportional vs. the square root of the polarization rate, but this dependence does not pass through the origin. Consequently, the system of U(III)/U(0) couple was irreversible and proceeds in one stage. It was found that on square-wave voltammograms in the studied “electrochemical window” the deposition of uranium on liquid reactive gallium and cadmium electrodes was carried out at more positive values than on inert tungsten electrode. It was established that this potential shift was associated with the formation of intermetallic compounds of uranium with the material of reactive electrodes. The values of the alloy formation potentials were determined. For identification of the composition of cathode deposits, potentiostatic electrolysis was performed. By X–ray diffraction analysis, it was found that the formation of the intermetallic compounds Ga3U and Ga2U occurs on the gallium reactive electrode, and Cd11U occurs on the cadmium one. The conditions of their formation during the electrolysis of molten LiCl–KCl–CsCl–UCl3 solutions were established. The reaction of the electrochemical extraction of uranium from molten LiCl–KCl–CsCl–UCl3 electrolyte was investigated on liquid reactive electrodes at different duration of electrolysis. It was found that the electrochemical extraction of uranium exceeds 97% on both Ga and Cd electrodes.