Extraction of plutonium(IV), uranium(VI) and some fission products by di-n-hexyl sulphoxide

The extraction from nitric acid solution of plutonium, uranium and fission products such as zirconium, ruthenium and europium has been investigated using di-n-hexyl sulphoxide in Solvesso-100. Equal volumes (generally 2 cm3) of the aqueous and preequilibrated organic phases containing the required tracer were stirred mechanically in 20 ml stoppered centrifuge tubes for 10-15 min at room temperature. After settling for half an hour and centrifuging, suitable aliquots of the two phases were removed for radioassay. Equilibrium was found to be reached within 10 min. Results indicate that Pu(IV), U(VI), Zr(IV) and RuNO(III) are extracted as disolvates, whereas Eu(III) is extracted as the trisolvate. The absorption spectra of the plutonium(IV) and uranium(VI) complexes extracted are similar to those of the species extracted by TBP, which indicate the similarity of the species involved. Preliminary studies show that irradiated di-n-hexyl sulphoxide extracts zirconium to a smaller extent than irradiated TBP suggesting the use of long chain aliphatic sulphoxides as promising extractants for the recovery of plutonium in high radiation fields. (T.G.)