The solvent extraction of hafnium(IV)—II extraction of Hf(IV) by some dialkylphosphoric acids from perchloric medium

The distribution of 175+181Hf(IV) was studied between aqueous solutions of perchloric acid and solutions of dibutyl-, diamyl-, diethylhexyl- and dioctylphosphoric acids (=HA) in benzene, chloroform, CCl4, cyclohexane and n-octane. In the region of existence of mononuclear complexes (up to 1 × 10−7 M Hf) Hf is extracted predominantly as Hf(ClO4)A3·(HA)2. At higher initial concentration of Hf, polymeric complexes are formed in the aqueous phase, which cause a decrease in the value of the distribution ratio of the Hf (=D). In strongly acidic media (above 4 M HClO4), the primary ion-exchange reaction mechanisms is replaced by an addition type of reaction, which results in the formation of very extractable complexes of Hf(ClO4)4(HA)4. Consequently a considerable increase in the value of D occurs. When using diamyl- and dibutylphosphoric acids in this medium, the results are affected by adsorption of Hf on the walls. Addition of TBP caused a decrease in D. This antagonistic effect can be explained by the interaction of TBP with the HA.