A fundamental understanding of the behavior of actinides in ionic liquids is required to develop advanced separation technologies.  Spectroscopic measurements indicate a change in the coordination of uranyl in the hydrophobic ionic liquid 1-ethyl,3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIM][Tf2N]) as water is added to the system.  Molecular dynamics simulations of dilute uranyl (UO22+) and plutonyl (PuO22+) solutions in water, [EMIM][Tf2N], and their mixtures have been performed in order to examine on a molecular level the coordination and dynamics of the actinide as the amount of water in the system changes.  The simulations reveal that water is a much stronger ligand for the actinide than the Tf2N anion, with the water found almost exclusively in the first and second coordination spheres.  In mixtures with little or no water, the Tf2N anion can bridge between two actinides; we thus see association between the actinides even in very dilute solutions. However, as the water content increases the relative binding strength of Tf2N decreases, and the Tf2N no longer bridges between the actinides.  We also find that the diffusion coefficient of the actinide in the ionic liquid increases as the water content increases.

Molecular dynamics simulations of uranyl and plutonyl coordination in water/ionic liquid mixtures

245th National Meeting (2013)

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