Complexation and extraction studies of high valency actinides by Schiff base ligands - 5168

Full text of publication follows. Increased knowledge of actinide coordination chemistry and the development of advanced actinide separation processes are essential to reducing the radiotoxicity of used nuclear fuel. Commercial separation techniques for nuclear fuel have focused on the selective extraction of U(VI) and Pu(IV), while contemporary efforts are aimed at extracting the minor actinides, e.g. Np and Am. These four mid-actinides (U, Np, Pu, Am) have accessible higher oxidation states (+V, +VI) at which they exist as linear dioxo actinyl ions [AnO₂]n⁺, offering the possibility of co-extraction, or back-extraction of all 4 actinide cations. The An=O bonds permit ligand coordination in the equatorial plane of the metal ion center, affording a geometry for unique bonding characteristics. Schiff bases can be prepared with synthetic ease and offer essentially planar chelation around the equatorial plane of actinyl ions through their N(2)O(2) binding site, presenting the possibility that this distinct coordination environment may facilitate the selective solvent extraction or aqueous retention of pentavalent and hexavalent actinides. Preliminary results indicate that these ligands show promise for group solvent extraction or retention of the mid-actinides. Lipophilic salen-based ligands prepared in our labs are able to extract uranium from nitrate media with 90% or higher extraction in one contact. These ligands have been shown to form 1:1 complexes with U(VI), Np(VI) and Pu(VI) which have been structurally and spectroscopically characterized. Such ligands show promise for group solvent extraction or retention of the mid-actinides and recent results will be presented. (authors)