Refractory metals such as Zr, HF, Nb, Mo, and Ta can be purified as metals by first vacuum vaporizing the impure halide to form an integrated solid mass which, despite a sublimation temperature of 300 deg. C, can be plunged into a molten electrolyte of an alkali metal halide at 500 deg.-700 Deg. C, and can then be electrodeposited on a cathode as pure metal. Combinations of the chlorides of li, rb, k, cs, and na can be used as the electrolyte. Some 1,000 g of hfc is chlorinated in an evacuated flask by heating it to 250 deg.-300 Deg. C in a current of cl2. The hfcl4 was formed in a dense ball weighing 800 g with a density of 3 g/cm3. The ball was placed in a cell with a graphite anode and a ni cathode with 15 kg of molten electrolyte at 700 deg. C in an inert atmosphere. An initial cathode current density of 216 a/ft2 was used and cl2 was vented at the anode. With a current efficiency of 94 pct, the test was operated for 10 a-h. The cathode deposits were leached with dilute hcl, washed, filtered, and dried, and the coarser 95 pct component of the hf had an o content of <40 ppm.
U.S. Pat. 3,600,284; Aug. 17, 1971; Chem. Abstr. 75:157,663Q