Separation of neptunium from actinides by monoamides. A solvent extraction study

Separation of neptunium from a mixture of actinides viz. uranium, neptunium and plutonium was evaluated using two monoamides, viz. N,N,-dihexyl octanamide (DHOA) and N,N,-dihexyl decanamide (DHDA). The extraction of actinides with these ligands followed the order: U(VI)>Np(IV)>>Pu(III). Poor extraction of Pu(III) with both the amides (DHOA and DHDA) was exploited for the mutual separation of U, Pu and Np. At 3 M HNO${}_3$, DHDA was a better extractant for all the three metal ions while Pu(III) extraction was one order magnitude lower with DHOA as compared to that seen with DHDA. Consequently, better separation factor of U(VI)/Np(IV) over Pu(III) was obtained with DHOA. In the actinide mixed solution, Pu was reduced to its +3 state followed by selective extraction of U(VI) and Np(IV). Subsequently, the mutual separation of U(VI) and Np(IV) was carried out by selective complexation and stripping of Np(IV) by acetohydroxamic acid (AHA) at 2 M HNO${}_3$, where U(VI) remained in the organic phase. The purity of the separated actinides was confirmed by alpha spectrometry. A separation scheme for the separation of Np from radioactive waste/high level waste has been proposed.