Chemical studies of tervalent neptunium and uranium.

Tervalent neptunium in aqueous acid solutions has been little studied and no efficient method of achieving complete reduction has been reported. This work reports a clean, efficient and reproducible method for the preparation of neptunium(III) in aqueous acid solution by electrolytic reduction. The electronic absorption spectra of the resulting solutions have been recorded. The stability of the hydrated uranium(III) and neptunium(III) cations in the presence of a number of inorganic and organic ions and organic complexing agents has been investigated in aqueous acid solution. Aqueous solutions of neptunium(III) have been shown to be more stable towards oxidation in the absence of air than the corresponding uranium(Ill) solutions. The electronic spectra of uranium(III) and neptunium(III) in different chemical environments are discussed in terms of partial covalency of the metal-ligand bonds. Uranium(III), uranium(IV) and neptunium(IV) species have been extracted from aqueous thiocyanate solution using tri-n-butylphosphate in hexane solutions. The tetravalent species, M(NCS)[4], are associated with four molecules of the extracting agent in the organic phase in each case. The extraction of neptunium(III) from aqueous thiocyanate solution and dilute mineral acid solution has been attempted