SOME THERMODYNAMIC ASPECTS OF MOLTEN SALTS: HALIDES OF URANIUM, ZIRCONIUM, THORIUM, AND CERIUM IN ALKALI HALIDE EUTECTICS*

Preparation and Application of a NaCl-KCl-CsCl-Cs2ZrCl6 Composite Electrolyte

Using ternary molten salt with a molar ratio of NaCl:KCl:CsCl = 30:24.5:45.5 and ZrCl₄ as raw materials to prepare a NaCl-KCl-CsCl-Cs₂ZrCl₆ composite electrolyte. Characterizing by XRD, ICP-AES, optical microscopy and SEM-EDS, the results showed that when the molar ratio of CsCl:ZrCl₄ ≥ 2:1, Cs₂ZrCl₆ was generated according to the stoichiometric reaction; when the molar ratio of CsCl:ZrCl₄ < 2:1, CsCl in molten salt was almost completely converted to Cs₂ZrCl₆, and there was a ZrCl₄ phase. When the molar ratio of CsCl:ZrCl₄ = 2:1, with the increase of the reaction temperature and reaction time, the concentration of zirconium ions first increased and then decreased. The optimized preparation process conditions are: the 2:1 molar ratio of CsCl to ZrCl₄ in NaCl-KCl-CsCl, 500 °C of reaction temperature of and 3 h of reaction time. Under this condition, 99.68% conversion rate from ZrCl₄ to Cs₂ZrCl₆ was obtained. Taking the prepared NaCl-KCl-CsCl-Cs₂ZrCl₆ composite electrolyte as a raw material, a preliminary study of molten salt electrolytic refining zirconium was carried out, and a refined zirconium product with a dendrite of 10.61 mm was obtained under the conditions of a zirconium ions concentration of 5%, an electrolysis temperature of 750 °C, a current density of 0.1 A/cm², and an electrolysis time of 9 h, indicating that the composite electrolyte can be used for the electrolytic refining of zirconium.

ELECTRODE POTENTIALS OF THE URANIUM CHLORIDES IN FUSED ALKALI CHLORIDE SOLUTIONS

Using a silver – silver chloride reference electrode, the electrode potentials of the system U, UCl3(KCl, NaCl) and the redox potentials of the system Pt, UCl3, UCl4(KCl, NaCl) were measured at various concentrations of the uranium chlorides and at temperatures between 650 and 850 °C.From the results, the electrode potential of the system U, UCl4(KCl, NaCl) was calculated. In addition, the activity coefficients and partial molal properties of dilute solutions of UCl3 and UCl4 in the equimolar mixture of potassium and sodium chlorides were calculated.