Separation Of Th Research Articles

The mutual separation of thorium, protoactinium, and uranium by tributyl phosphate extraction from hydrochloric acid

The distribution behaviour of U(VI) and Pa(V) in the system aqueous HCl-TBP (tributyl phosphate) without diluent has been investigated at 22 ± 2°C and the results compared with those reported for Th(IV) in the same system. From the comparison, it is postulated that protoactinium extracts respectively as oxygenated and nonoxygenated entities in the regions of low and high concentration of HCl, the transition range being 4–5 M HCl in the aqueous phase. Although the data indicate the feasibility of mutual separation of Th(IV), Pa(V), and U(VI) in the HCl—TBP system, the separation of Pa(V) from U(VI) is much more readily achieved in the (HCl, HF)—TBP system; since the complexing action of fluoride ion is much more pronounced for Pa(V) than for U(VI), under the conditions investigated. A protoactinium sample stored in the form of an (HCl, HF) aqueous solution in a polyethylene container for five years exhibited reversible behaviour, the protoactinium extracting into TBP following addition of boric acid to destroy the fluoride complex. There was no evidence of deposition of protoactinium on the walls of the container. Equilibrium was attained rapidly in all protoactinium extractions in which no “nonextractable” protoactinium was involved. The “nonextractable” form converts slowly to the “extractable” form in the presence of hydrochloric acid. The rate of this conversion increases with increasing acid concentration and with increasing temperature. The mutual separation of Th(IV), Pa(V), and U(VI) has been demonstrated for both synthetic and “natural” feeds.