Zirconium-hafnium hydroxide chloride

Hafnium-free zirconium alloys, 26 6351 Hafnium halides, 73 91-93 Hafnium hydride, 73 93 Hafnium hydroxide chloride heptahydrate, 13 92... 

The crude tetrachloride mixture of zirconium and hafnium is dissolved in ammonium thiocyanate solution. The solution is extracted with methyl isobutyl ketone (MIBK). MIBK is passed countercurrent to aqueous mixture of tetrachloride in the extraction column. Halhium is preferentially extracted into MIBK leaving zirconium in the aqueous phase. Simultaneously, zirconium tetrachloride oxidizes to zirconyl chloride, ZrOCb. When sulfuric acid is added to aqueous solution of zirconyl chloride, the chloride precipitates as a basic zirconium sulfate. On treatment with ammonia solution the basic sulfate is converted into zirconium hydroxide, Zr(OH)4. Zirconium hydroxide is washed, dried, and calcined to form zirconium oxide, Zr02. 

Purified zirconyl chloride solution is then reacted sequentially with surfuric acid and ammonium hydroxide to precipitate a complex zirconium oxysulfate. The precipitate is washed, filtered, and stripped to remove traces of MIBK, and then calcined to drive off sulfur and convert the product to Zr02. The precipitation process leaves behind most of the aluminum and phosphorus. The hafnium stream leaving solvent extraction is treated similarly, producing a Hf02 byproduct. 

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