A highly efficient solvent system containing functionalized diglycolamides and an ionic liquid for americium recovery from radioactive wastes

Three room temperature ionic liquids (RTILs), viz. C(4)mim(+)center dot PF6-, C(6)mim(+)center dot PF6- and C(8)mim(+)center dot PF6-, were evaluated as diluents for the extraction of Am(III) by N,N,N',N'-tetraoctyl diglycolamide (TODGA). At 3 M HNO3, the D-Am-values by 0.01 M TODGA were found to be 102, 34 and 74 for C(4)mim(+)center dot PF6-, C(6)mim(+)center dot PF6- and C(8)mim(+)center dot PF6-, respectively. The extraction of Am(III) decreased with increasing feed acidity for all three diluents, indicating an ion exchange mechanism for the extraction. The stoichiometry of the extracted species suggested that two TODGA molecules were associated with Am(III) during the extraction for all three RTILs and the conditional extraction constants have been determined. The DM-values for different metal ions followed the order: 75 (Am(III)) > 30.7 (Pu(IV)) > 3.9 (Np(IV)) > 1.19 (Pu(VI)) > 0.52 (U(VI)) > 0.12 (Cs(I)) > 0.024 (Sr(II)). The distribution behaviour of Am(III) was also studied with a recently synthesized calix[4] arene-4DGA (C4DGA) extractant dissolved in C(8)mim(+)center dot PF6-. Using this extractant diluent combination, the D-Am-value was 194 at 3 M HNO3 using 5 x 10(-5) M C4DGA, suggesting a very high distribution coefficient at very low extractant concentrations. The stoichiometry of the extracted species containing Am was found to be 1 : 2 (M: L) in C(8)mim(+)center dot PF6-. The thermodynamics of the extraction was also studied for both extractants in C(8)mim(+)center dot PF6-. The use of RTILs gives rise to significantly improved extraction properties than the commonly used n-dodecane and an unusual increase in separation factor values was seen for the first time which can lead to selective separation of Am from wastes containing a mixture of U, Pu and Am.