Several of the actinides have higher oxidations states (e.g., V and VI) available under conditions in which they exist as linear dioxo cations, distinguishing their coordination environments from trivalent cations. While the stability of these oxidation states can be a challenge for some of the transuranic actinides under acidic conditions, studies suggest that these oxidation states may be stabilized by coordination of ligands to the equatorial plane of the actinyl ion. For example, studies indicate that Schiff bases have been able to stabilize U(V). In light of this we are exploring mixed (N,O) donor, water soluble Schiff bases as actinyl-selective ligands. Results of the extraction of Eu(III) and An(III, V/VI) cations from aqueous nitrate solutions containing the water-soluble Schiff bases N,N'-bis(5-sulfonato-salicylidene)ethylenediamine (H2salenSO3) and N,N’- bis(5-sulfonato-salicylidene)diethylenetriamine (saldienSO3) by bis(2-ethylhexyl)phosphoric acid in toluene suggest significant holdback of U(VI) and Np(V) and significant extraction of Eu(III) and Cm(III). Combined with spectroscopic results indicating strong complexation of U(VI) by H2salenSO3 and saldienSO3, and weak interaction with Ln(III) ions, these studies have illustrated that similar ligand frameworks may be useful as selective holdback reagents in the separation of actinyl and trivalent lanthanide/actinide cations from aqueous media. In this report, we present refined measurements of metal ion complexation, spectroscopic studies of Np speciation, and discuss our efforts to increase the hydrolytic stability of the Schiff bases. Possible improvements in Ln/An separation factors may afford the design of separation systems under conditions not commonly considered.

Aqueous complexation of actinyl ions by Schiff base ligands: Effects on solvent extraction

251st National Meeting (2016)

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