Polyethyleneglycol (PEG) and its derivatives of high molecular weight were found to be employed as useful extractants for
the solvent extraction of uranium. The extraction behaviors of uranium and neptunium were investigated, particularly concerning
the dependence of the extractibility of uranium(VI) on the molecular weight of PEG. A dominating species of the extracted
uranium(VI) thiocyanate complexes was assumed to be NH4 UO2(SCN)3·(PEG). The extraction of protactinium was also preliminarily studied. The extraction of these actinides from an acidic thiocyanate
solution increased in the order: uranium(VI)>protactinium(V)>neptunium(V).