Hexone-thiocyanate process

A similar hexone-thiocyanate process has been operated in the U.S.A., firstly by the Northwest Electrodevelopment Laboratories at Albany since 1952 and the Carborundum Metals Corporation plant near Akron, New York, since 1953. They use packed and unpacked columns and the difficulties associated with polymerization of thiocyanic acid were alleviated by using a solvent consisting of 80 per cent hexone and 20 per cent butyl acetate instead of solely hexone. > The zirconium product is precipitated as the acid sulphate, phthalate or salicylate, and a certain additional degree of purification is obtained at this stage. A typical analysis of pure zirconium oxide after hexone-thiocyanate extraction and salicylate precipitation is as follows ... 

Fig. 4.32. U.K. process for zirconium purification by hexone-thiocyanate route. Solvent A, bexone 2-7M in thiocyanic acid inititdly solvent B, texone...

Although the solvent purification process is adequate for the production of say reactor-grade zirconium, it is possible to modify it so that pure hafnium may also be obtained. Distribution data are available for various solutions containing thiocyanate, sulphate and chloride from which it is possible, for example, to deduce that both hafnium and zirconium will extract into hexone provided the aqueous phase has a high thiocyanate concentration and a low chloride concentration. The zirconium may then be selectively backwashed in a second extractor using say an aqueous phase of high thiocyanate concentration and moderate sulphate concentration, where the separation factor of the system is high. The hafnium can then... 

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