Extraction of plutonium(IV) by diglycolamide extractants in room temperature ionic liquids

Extraction of Pu(IV) was investigated using solutions of two diglycolamide extractants viz., N,N,N^',N^'-tetra-n-octyldiglycolamide (TODGA) and its branched homolog, N,N,N^',N^'-tetra(2-ethylhexyl) diglycolamide (T2EHDGA), dissolved in two imidazolium based room temperature ionic liquids viz., 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C₄mim][NTf₂]) and 1-octyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C₈mim][NTf₂]) from aqueous nitric acid medium. The extraction kinetics was found to be extremely slow which is reported for the first time for analogous extraction systems and took as long as 30 h to attain equilibrium D_Pu values. In general, TODGA based solvents showed better extraction of Pu(IV) than the T2EHDGA based solvents, one order of magnitude higher, and though both the ionic liquids ultimately yielded comparable D_Pu values, attainment of equilibrium was slower with [C₄mim][NTf₂]. The extracted species conformed to 1:1 for TODGA in both the ionic liquids while a mixture of 1:1 and 1:2 species was observed for T2EHDGA at 1 M HNO₃ which changed to 1:1 species at 4 M HNO₃. The extracted species is proposed to be (Pu(L)_x⁴⁺)_IL (where, L is the extractant and x=1 or 2) at lower acidities suggesting a cation exchange mechanism which changes over to (Pu(NO₃)₄ .L)_IL at 4 M HNO₃ conforming to a solvation mechanism for all the systems except for T2EHDGA-[C₈mim][NTf₂]. UV-VIS spectroscopic studies were carried out to throw light on the nature of the extracted species.