Specific electrical conductivity of molten (LiCl–KCl)eut – HfCl4 mixtures

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Abstract

Electrical conductivity is one of the most important properties that are required for the proper organization of electrolytic processes occurring in molten salts, in particular, during the production and refining of metallic hafnium and its separation from zirconium. In this work, we have measured for the first time the electrical conductivity of molten HfCl4 mixtures with a low-melting solvent (LiCl-KCl)eut, which makes it possible to lower significantly (by hundreds of degrees) the temperature of technological processes. The liquidus line of this pseudobinary system has been also constructed for the first time at the HfCl4 concentrations up to 30 mol. %. A specially designed capillary quartz cell with a constant in the range of 95.2–91.9 cm–1 and high-purity chlorides were used to measure the electrical conductivity. The resistances of the molten mixtures in the HfCl4 concentration ranges of 0–30 mol.% and temperatures of 780–1063 K were recorded using an AC bridge P-5058 at a frequency of 10 kHz, and the melt temperature was measured with a Pt/Pt–Rh thermocouple. It was found that the values of electrical conductivity of the molten (LiCl–KCl)eut.-HfCl4 mixtures increase as the temperature increases from 0.86 to 2.08 S/cm. This occurs as a result of the increased ion mobility (simple and complex) and decreased melt viscosity. With an increase in the HfCl4 concentration, the electrical conductivity decreases. In the same direction, the concentration of relatively low-mobility complex groups HfCl62– containing 6 chlorine anions tightly bound to the tetra-charged metal, increases in the melts. The concentration of the main current carriers, Li+, K+ and especially the mobile Cl– anions, decreases more and more, which leads to a decrease in the electrical conductivity of the melt. In the molten (LiCl–KCl)eut.–ZrCl4 mixtures that we studied earlier, the electrical conductivity decreases less as the tetrachloride concentration increases, which indicates a lower strength of the ZrCl62– complexes compared to HfCl62–.

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About the authors

A. B. Salyulev

Institute of High-Temperature Electrochemistry, Ural Branch of the Russian Academy of Sciences

Author for correspondence.
Email: salyulev@ihte.ru
Russian Federation, Ekaterinburg

A. M. Potapov

Institute of High-Temperature Electrochemistry, Ural Branch of the Russian Academy of Sciences

Email: salyulev@ihte.ru
Russian Federation, Ekaterinburg

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2. Fig. 1. Electrical conductivity of molten and heterogeneous (melt + solid phase) mixtures (LiCl-KCl)eut.-HfCl4 and (LiCl-KCl)eut.-ZrCl4 [16].

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3. Fig. 2. Liquidus lines of the quasi-binary systems (LiCl-KCl)eut.-HfCl4 and (LiCl-KCl)eut.-ZrCl4 [16].

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4. Fig. 3. Specific conductivity isotherms of molten mixtures (LiCl-KCl)eut.-HfCl4 (dark dots) and (LiCl-KCl)eut.-ZrCl4 (light dots) [16].

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