A diglycolamide-functionalized task specific ionic liquid (TSIL) for actinide extraction: Solvent extraction, thermodynamics and radiolytic stability studies

• DGA-functionalized TSIL was used for actinide extraction.
• The extraction trend was: Am3+ > Pu4+ > Np4+ > UO22+∼NpO22+∼PuO22+.
• Nature of extracted species was found out to be 1:1.
• Thermodynamics studies indicated spontaneous reactions.
• Stripping was done by complexing agents and radiolytic degradation studied by EPR.

A diglycolamide (DGA)-functionalized task specific ionic liquid (TSIL) was used for the extraction of actinide ions such as Am3+, Pu4+, Np4+, UO22+, NpO22+, and PuO22+. Trivalent actinide ion extraction was about one order of magnitude higher than that of the tetravalent ions, which in turn was one order of magnitude higher than that of the hexavalent actinide ions. Typically, using 3.6 × 10−2 M solution of the DGA-TSIL in C4mim·NTf2, the D values at 3 M HNO3 for Am3+, Pu4+, Np4+, UO22+, NpO22+, and PuO22+ were 34, 5.9, 3.5, 0.44, 0.38, and 0.32, respectively. The extraction of the actinide ions decreased with increasing aqueous phase acidity, which supports an ion-exchange mechanism that often operates for this type of extraction systems. The number of DGA-TSIL molecules present in the extracted species was about one for all actinide ions studied, suggesting species of the type M(TSIL)ILn+. Both the extraction constants (log Kex) and the thermodynamic parameters were calculated. The ΔG values were negative in case of all actinide ions suggesting spontaneity of the extraction, which was reflected in very high D values for the tri- and tetravalent actinide ions. Stripping and radiolytic degradation studies were also carried out and EPR spectroscopic measurements were performed to understand the nature of the degraded free radical species.