GB790345A - Improvements in or relating to the separation of zirconium and hafnium compounds - Google Patents

Abstract

<PICT:0790345/III/1> Zirconium and hafnium halide vapours are separated by contacting the vapours with a solvent comprising molten alkali metal halide and thereafter separating and recovering the zirconium and hafnium halides by fractionation. Preferably the vapours are contacted in a fractionating zone or column with a counter-current flow of the molten alkali metal halide, the hafnium rich product being recovered from the upper part of said zone and the zirconium enriched product from the lower part of the zone. As shown in the drawing a fractionating column 1 is connected at its lower end to a receiver 2 and at its upper end to a reservoir 3; in addition a side arm 5 leading to a vessel 6 is provided. In operation the mixture of zirconium and hafnium halides to be separated is placed in the vessel 6 which is surrounded by a heater 7, the alkali metal halide is placed in vessel 3, also surrounded by a heater and heat is also applied to the fractionating column 1 and to the receiver 2. The mixed halide vapours pass through pipe 5 and to contact the flow of molten alkali metal halide running down the column whereby the zirconium halide collects in the receiver 2 and is refluxed whilst the hafnium halide concentrates in the upper part of the column 1 in the molten salt mixture. If the heating is discontinued and the upper part of the column is chilled, the hafnium-enriched alkali metal halide may be recovered therefrom whilst zirconium-enriched alkali metal halide is recovered from the receiver 2. Such a mixture may be added to molten magnesium to form metallic zirconium and a separable alkali metal chloride/magnesium chloride mixture. Alternatively the fractionation may be so conducted that the receiver is at a sufficiently high temperature, for example 600-900 DEG C., for the zirconium halide to be wholly vaporized from the receiver 2, in which case a bleed-off line is provided in the vapour space of the receiver 2 from which the zirconium halide free from alkali metal halide may be drawn off as vapour. According to examples: (1) the vessel 6 was filled with a zirconium tetrachloride containing 2.4 per cent hafnium on an oxide basis, and granular sodium chloride was placed in the salt reservoir 3. The heaters were turned on until the temperature in the salt reservoir 3 and the top and bottom of the column was 330 DEG C., the temperature in the receiver 2 was 340 DEG C. and that of the vaporizer 330 DEG C. When all sections of the column were wet with the molten salt-zirconium/hafnium tetrachloride mixture the receiver temperature was increased to 350 DEG and that of the bottom of the column increased to 340-350 DEG C. The vaporizer temperature was increased to 380 DEG C. and the top of the column maintained at 330-340 DEG C. At the end of operation the heating was stopped and the upper part of the column chilled. After cooling samples were taken from the bottom and top of the column and the receiver, dissolved in water and the Zr and Hf precipitated with ammonium hydroxide. The Hf content at top of the column was 4.4 per cent whilst the receiver sample contained 2.1 g 0 Hf, and consisted of the lowest melting eutectic for the zirconium tetrachloride-sodium chloride system. (2) a similar apparatus was used except that the heating was intensified to bring the receiver to a final temperature of 510 DEG C. whereby the temperature of the bottom of the column increased to about 370 DEG C. and the top of the column to about 340 DEG C. In such circumstances the final salt in the receiver consisted of a sodium chloride/zirconium chloride mixture melting at 331 DEG C. containing 1.7 per cent hafnium. A further example relates to the use of potassium chloride. The process is applicable to the tetrabromide, tetraiodide and tetrachloride of zirconium and hafnium; other alkali metal halides, such as the chloride, bromides and iodides of sodium, potassium, lithium may be employed.