Neptunium extraction behaviors

Taylor, R.J., Sinkov, S.I., Choppin, G.R., May, I. 2008. Solvent extraction behavior of neptunium(rV) ions between nitric acid and diluted 30 % tri-butyl phosphate in the presence of simple hydroxamic acids. Solvent Extr. Ion Exch. 26 (1) 41-61. 

The system has been used to effect the isolation and final purification of gram quantities of Np. Interestingly, the only difficulty encountered is in maintaining uranium in the uranium(VI) state, since in this system uranium-(IV) closely resembles neptunium(IV) in its extraction behavior. So after two to three aqueous HCl scrubs to remove contaminants from the neptunium product in the organic phase an oxidation cycle must be inserted to oxidize uranium(IV) to uranium(VI). Under the oxidizing conditions used, neptun-ium(IV) is oxidized to neptunium(VI). But through the action of hydro-quinone, following the oxidation step, neptunium(VI) is rapidly reduced to... 

Gil. Gourisse, D. L oratory Studies of Nitrous Acid and Neptunium Behavior in TBP Extraction Processes, Proceedings of the International Solvent Extraction Confererwe, vol. 1, 1971, p. 781. 

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