Due to their low volatility, favourable solvent properties and tunable phase behaviour, ionic liquid (IL) technology continues to attract interest in a wide variety of applications. Over the last few decades, the term ‘task specific ionic liquid’ (TSIL) has appeared, the meaning of which is that the application has been considered more carefully in the design and structure of one or both of the constituent IL ions.
In this ChemComm communciation, researchers from the Los Alamos National Laboratory, New Mexico, USA, describe advances in the application of ILs in the area of nuclear fuel reprocessing. The authors describe how neptunium may exist in solution in +III, +IV, +V and + VI oxidation states. The pentavalent state is the most stable and common, but interestingly, usually the most reluctant to coordinate with ligands, or take part in ion exchange processes.
Ionic liquid molecular structure and stabilizing behaviour towards Np(V) in aqueous solution
In aqeuous solution, in the presence of the ionic liquid betaine bistriflimide, the lifetime of the Np(IV) solution species is significantly increased. This is followed by the presence of a characteristic electronic adsorption at 970nm. Without the IL, an anti-oxidant is required to keep the metal from converting to its +V form. Np(V) has a rich and complex coordination chemistry at room temperature, so the authors repeated experiments with sources of Np(V) at 60oC. After 3 days, 90% of the starting neptunium compound had been converted to the betaine complexed form, compared with a 15% conversion at room temperature. Again the material was stable in solution, not resulting in Np(IV) species unless a reducing agent such as hydrazine was deliberately added.
With this detailed study, the authors significantly add to the body of knowledge of competitive coordination chemistry of actinides in aqueous solutions of ionic liquids. This should, in turn, enable new separation technology R&D for the important task of nuclear fuel reprocessing.
Read this ChemComm communication for free* today!
Unusual redox stability of neptunium in the ionic liquid [Hbet][Tf2N]
Kristy Long, George Goff and Wolfgang Runde
DOI: 10.1039/C4CC01835D
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