Separation of Te(IV) and Fe(III) by extraction methods using TBP

Abstract

In the analysis of steel it is of course necessary to separate iron from the other elements. As one of the investigations for this purpose, the authors have studied the separation of Fe(III) from Te (IV) in hydrochloric acid solution by means of extraction methods using 100% n-tributylphosphate (TBP).
When the acid concentration of the solution is lower than 0.1N, neither Fe nor Te is extracted by TBP, but with increasing concentration of hydrochloric acid Fe as well as Te are extrated into the TBP-phase. In the presence of potassium thiocyanate in the solution, however, Fe is nearly completely extracted into the TBP-phase as thiocyanate, while Te is extracted only partially (pH 0.4, ca. 5%; pH 1.0, ca. 20%). A little Te thus extracted can then be extracted back to the aqueous phase by shaking the TBP-phase with 0.1N hydrochloric acid solution. Ten ml of TBP is added to 10 ml of the hydrochloric acid solution, containing 250350 γ Te, 0.3535 mg Fe and 500 mg KSCN, and after adjusting the pH to 0.4, the mixture is shaken for 2 minutes. The TBP-phase is then separated and shaken with 10 ml of 0.1N hydrochloric acid solution for 1 minute. By this procedure the Te which escaped from the aqueous solution to the TBP-phase is extracted back into the former. This aqueous solution is combined with the original aqueous phase, and centrifuged. Te together with a small amount of Fe which remains in the aqueous phase are determined photometrically.
The results are as follows: Te in aq. phase ca. 99%, Fe in TBP-phase ca. 99.9%.