GB778192A - Process for removing hafnium from zirconium - Google Patents

Abstract

Zirconium tetrahalide contaminated with hafnium tetrahalide is subjected to the action of a reducing agent to bring about preferential reduction of the zirconium tetrahalide and thereafter the unreduced hafnium tetrahalide is removed from the reaction mass. The reduction of the zirconium tetrahalide may be ffected by heating the compound in a sealed vessel in vacuo or an inert atmosphere with finely divided metallic zirconium, magnesium, aluminium, zinc or other reducing agent of sufficient oxidation reduction potential whereby the zirconium halide is reduced to the trihalide or dihalide. The temperature of the treatment may be as high as 500 DEG C. when zirconium is employed whilst for aluminium a temperature between 250 and 400 DEG C. is suitable. After reduction the unreduced hafnium tetrahalide may be separated by sublimation in vacuo at a temperature above 250 DEG C. and below the volatilization temperature of the reduced zirconium tetrahalides. The lower zirconium halide residue may be dissolved in water or dilute mineral acid to produce solutions of zirconium oxyhalides containing less than 0.1 per cent of hafnium or alternatively the unvolatilized residue may be converted into zirconium tetrahalide and metallic ziconium by heating in vacuo at above 600 DEG C. to bring about disportionation. According to an example, zirconium tetrachloride was mixed with twice its weight of finely divided metallic zirconium and heated at 420 DEG C. in a sealed evacuated vessel for one hour whereby zirconium trichloride was produced whilst the hafnium tetrahalide was substantially uneffected. Whilst maintaining the temperature the hafnium tetrachloride and unreduced zirconium tetrachloride was then pumped off and the volatile products condensed. The condensed material contained 28 to 30 per cent of hafnium calculated at dioxide and the residue in the vessel contained up to 90 per cent of the original zirconium. This residue consisted of zirconium dichloride, trichloride and tetrachloride, and on heating in an evacuated vessel to above 600 DEG C. the zirconium dichloride disproportionated and the resulting zirconium tetrachloride was pumped off and condensed. The zirconium metal remaining in the vessel was used for the treatment of further zirconium tetrachloride. The condensed purified zirconium tetrachloride may be subjected to a further similar purification treatment.