Fractionation of Zirconium and Hafnium

The mechanics of fractionation are the same as for complete precipitation except that an insufficient amount of precipitant is used. To determine what the optimum cutoff value for a given hafnia concentration should be, and to determine also what enrichment may be expected in each 

Comparison of optimum mol fraction of combined oxides precipitated and composition of starting material. 

By using the prediction curve (Fig. 16) it should be possible, theoretically, to proceed through the fractionation with no analyses other than the initial analysis. However, since actual operating conditions are not as reproducible as would be desired, deviations from the predicted enrichment are observed. Since small changes are additive an appreciable error may result within a few steps. It is therefore necessary to determine the hafnium content at frequent intervals. 

it is possible to obtain, in a series of seven fractionations, about a 10 per cent yield of a product with 0.9 mol fraction Hf02. Mother liquors of approximately equivalent concentration from the various steps are combined for re-treatment. 

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It should be noted that a partial fractionation of zirconium and hafnium may be obtained in the sublimation of the tetrachlorides.11,14... 

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