Mitsubishi Nuclear Fuel Co., Ltd.

Tomoo Kirihara

Ippei Nakagawa

Yutaka Honda

Yoshinobu Seki

Yasuo Ichihara

Separation of hafnium tetrachloride from zirconium tetrachloride by introducing zirconium tetrachloride containing about 2-4 wt percent of hafnium tetrachloride into an electrolytic cell filled with a molten salt and dissolving it to make an electrolytic bath. Running first phase electrolysis which produces zirconium trichloride containing a lower hafnium content than the dissolved zirconium tetrachloride at the cathode. Running second phase electrolysis using the first cathode, but switching the first cathode to become an anode and using a second cathode. Producing zirconium trichloride of a lower hafnium content than the dissolved zirconium tetrachloride at the second cathode. Evolving a gaseous zirconium trichloride at the anode by electrolytic oxidation of the zirconium trichloride produced in the first phase electrolysis. Recovering this evolved zirconium tetrachloride which has a lower hafnium content than the dissolved zirconium tetrachloride and the zirconium trichloride produced at the cathodes. Continuing this second phase electrolysis by changing over polarities of the cathode and the anode, when the concentration of zinc trichloride at the anode decreases to a predetermined concentration when the vapor pressure valve of hafnium tetrachloride, which has become concentrated in the electrolytic bath reaches about 1/10 of that of zirconium tetrachloride in the electrolytic bath. Transferring the hafnium enriched electrolytic bath to a separate vessel and separating it from the molten salt by raising the temperature of the electrolytic bath to a predetermined temperature.

Process for separation of hafnium tetrachloride from zirconium

A process for separation of hafnium tetrachloride from zirconium tetrachloride and electrode is disclosed. Zirconium tetrachloride containing hafnium tetrachloride in natural ratio dissolved in a molten salt is reduced in the first phase electrolysis using an anode composed of a substance formed by firing a mixture of more than one kind of compound selected from the group consisting of silica, silicate containing zirconium or zirconium oxide and carbon with a binder under maintenance of an initial concentration of the zirconium tetrachloride in order to produce zirconium trichloride containing a hafnium content lower than that of the zirconium tetrachloride at a cathode. Next, by using the former cathode as an anode and another cathode in the second phase electrolysis the zirconium tetrachloride is further reduced to yield zirconium trichloride of a lower hafnium content at another cathode and evolve on the anode gaseous zirconium tetrachloride having a high pressure by oxidizing the zirconium trichloride produced in the first phase electrolysis. The evolved zirconium tetrachloride is recovered as zirconium tetrachloride with a low hafnium content. Further, the zirconium tetrachloride with a low hafnium content and the zirconium trichloride with a lower hafnium content are produced by exchanging polarities of the cathode and the anode when the zirconium trichloride on the anode decreases. The second phase electrolysis is carried out repeatedly. After hafnium tetrachloride is concentrated to an expected value in the molten salt in the above mentioned electrolysis, the molten salt is transferred to a separate vessel and is heated to evaporate the tetrachloride highly concentrated hafnium. Thus, zirconium tetrachloride and hafnium tetracholoride are respectively separated with high efficiency. A hafnium content of zirconium tetrachloride separated is able to reduce to less than 100 ppm, and a zirconium content of hafnium tetrachloride separated is also reduced to less than 25 wt %.

A process of separation of hafnium from zirconium by molten salt electrolysis in which zirconium tetrachloride with ordinary hafnium tetrachloride content is dissolved in a molten salt and the zirconium tetrachloride is electrolytically reduced to zirconium trichloride with lower hafnium content at a cathode in the molten salt and hafnium tetrachloride is remained. Next, the cathode on which the zirconium trichloride is formed by the cathode reaction is used as an anode. The electrolytic reduction of zirconium tetrachloride at another cathode in the molten salt is carried out and at the same time the zirconium trichloride formed on the anode is oxidized to zirconium tetrachloride with a low hafnium content and the zirconium tetrachloride is evaporated for separation. The obtained zirconium tetrachloride containing a low hafnium content is suitable for production of reactor grade zirconium containing about 100 ppm of hafnium.

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Hirakocho-Higashi, Japan

Tomoo Kirihara