Neptunium(IV) and uranium(VI) complexation by hydroxamic acids

Hydroxamic acids complex more readily with Ac(IV) than Ac(VI). Formohydroxamic acid (FHA) is a hydrophilic organic ligand which can readily complex with Np(IV), as indicated by near infrared spectroscopy. Distribution experiments have also shown that FHA can strip Np(IV) from 30% TBP/OK into aqueous nitric acid. In contrast U(VI) does not complex as strongly with FHA and the reaction is greatly inhibited by nitric acid, as observed by UV-Vis spectroscopy. After stripping Np(IV) it has also been proven, by 13C NMR spectroscopy, that FHA can be decomposed to gaseous products in concentrated nitric acid leaving no organic waste products in solution. This experimental evidence proves that FHA can be used to selectively strip Np(IV) from a 30% TBP/OK solution of Np(IV) and U(VI) into aqueous nitric acid and is thus a viable new reagent for inclusion in an advanced PUREX process. (orig.)