Neptunium acid solutions

Actinide Peroxides. Many peroxo compounds of thorium, protactinium, uranium, neptunium, plutonium, and americium are known (82,89). The crystal stmctures of a number of these have been deterrnined. Perhaps the best known are uranium peroxide dihydrate [1344-60-1/, UO 2H20, and, the uranium peroxide tetrahydrate [15737-4-5] UO 4H2O, which are formed when hydrogen peroxide is added to an acid solution of a uranyl salt. 

Because of the ease of oxidation of protactinium(IV) and uranium(IV), peroxides and peroxo complexes are limited to their higher oxidation states. The compounds M04"JcH20 precipitated from dilute acid solutions of neptunium(IV) and plutonium(IV) by hydrogen peroxide appear to be actinide(IV) compounds. Soluble intermediates of the type [Pu( U-02)2Pu]4+ are formed at low hydrogen peroxide concentrations. 

Nagasaki, S., Wisnubroto, D.S., Enokida, Y., Suzuki, A. 1994. Neptunium separation from nitric acid solutions with CMPO. 4th Int. Conf. Nuclear Fuel Reprocessing and Waste Management, RECOD 94 Proceedings Vol. 3, London, UK, April 24-28. 

An alternative procedure for the study of neptunium oxidation states at trace concentrations has been described by Inoue and Tochiyama (1977). They showed that, in the pH range 6-7, Nplv may be quantitatively absorbed on silica gel whilst Npv remains in solution. In acid solution, however, a precipitate of barium sulfate selectively absorbs Nplv leaving the higher oxidation states in solution. The authors gave no environmental data for neptunium in their publication but Nelson and Orlandini (1979) subsequendy adapted the procedure to demonstrate that the dominant oxidised plutonium species in natural waters is Puv and not Puvl. 

Co-extraction of Np and Pu The waste from the uranium extraction battery is adjusted to 5 M LiNO and then passed through an IRA-400 column at a high flow rate (30 L/h). The americium is not sorbed. Neptunium and plutonium are stripped by a dilute nitric acid solution and precipitated as a hydroxide, and calcined to yield mixture of oxides. 

The procedure involves the coprecipitation of the transuranic nuclides on calcium fluoride from acid solution after reduction of the plutonium and neptunium with bisulfite. The calcium fluoride precipitate is dissolved in aluminum nitrate-nitric acid solution and the plutonium and neptunium separated on an ion-exchange resin column. The column... 

Neptunium (V) Anionic Exchange in Sulfate-Sulfuric Acid Solutions... 

Each mixture of resin and neptunium sulfate solution was mixed by mechanical shaking and was allowed to equilibrate overnight. This time interval is long, compared to the duration of an analytical procedure. The liquid was then filtered away from the resin, and the residual radioactivity of a measured aliquot of the liquid was compared to an identical solution that had not been added to any anion exchange resin. The radioactivity measurements were performed in an end-window Nal crystal counter shielded with lead. The acidity of each solution was measured by titration with a standard base. 

Since 1958, more than 20 nuclides of actinides ranging from neptunium to einsteinium were identified and prepared for tracer studies. From neutron-irradiated uranium samples 2 9Np was adjusted to the pentavalent state and separated by TBP extraction from perchloric acid media. Plutonium-239 was separated by TBP extraction from nitric acid solution followed by anion exchange in a system of Dowex-1 resin and nitric acid. Neptunium-237 was separated from a spent fuel solution of JRR-1 (Japan Research Reactor -1) using anion exchange and TBP extraction. The TBP extraction in the hydrochloric acid medium is a simple and effective technique to purify neptunium from plutonium contamination. On the other hand, both anion exchange and solvent extraction with HDEHP could be used to separate tracer scale plutonium from irradiated neptunium targets. 

For the mutual separation of plutonium and neptunium, both of those are adsorbed on an anion-exchange resin column and the resin converted to chloride form by washing with concentrated hydrochloric acid. Then the plutonium is reduced to the trivalent state and eluted with 9 H hydrochloric acid solution containing 0.1 M hydro-iodic acid. 

Swanson, J. L Oxidation of Neptunium(V) in Nitric Acid Solution—Laboratory Study of Rate Accelerating Materials (RAM), Report BNWL-1017, Apr. 1969. 

The neptunium(vii) species has been prepared electrolytically in molar sodium hydroxide. In dilute perchloric acid solutions, the ion oxidises water with rapid disappearance of the characteristic green colour. The reaction proceeds via two paths, one of which is first-order, the other second-order in neptunium(vii) with no direct evidence for participation of perchlorate in... 

Neptunium can easily be separated quantitatively from plutonium with the aid of anion exchangers. If both ions are in a concentrated hydrochloric acid solution, iodide ions are added to reduce plutonium to Pu(III) and neptunium to Np(IV). The solution then passes through a column filled with Dowex-1 anion exchanger. Plutonium is thus quantitatively eluted with concentrated hydrochloric acid, and neptunium can be desorbed with 0.5 mol 1 HCl. 

Extractions involving the chelating agent thenoyltrifluoroacetone (TTA) in an organic solvent are particularly useful in the isolation of uranium, neptunium, and plutonium from nitric acid solutions some of the radiochemical milking experiments used to determine the... 

Sevost yanova EP (1983) Stability of neptunium(IV, V and VI) in citric acid solutions. Radiokhim 25 340-345... 

As mentioned in the Introduction, the actinyl ions are not stable under all chemical conditions. Plutonium can coexist in solution in several oxidation states, the stability of which often depends strongly on acidity (26). As a result, great care must be taken to obtain pure solutions of PuOl(27). On the other hand, the neptunyl ion NpO is the most stable form of neptunium in aqueous solution. It is noteworthy that the exchange between the oxygen atoms of PuO and H20 is very slow (ti/2 > 10 h) (25), whereas it is quite fast (h/2 2.2 s) in the case of NpO. ... 

Neptunium has been characterized from the +3 to +7 oxidation states in aqueous solution. The standard potentials for various Np ions have been determined from measured formal potentials of the various redox couples. These data have been thoroughly reviewed by Martinet [94] and Fahey [95]. Recently the standard potentials for the redox couples Np02 /Np02, Np +/Np +, and Np02 /Np" in acidic aqueous solution have been reevaluated with more detailed consideration of activity coefficients [49,50]. The standard potential accepted here for the Np02 /Np02 couple is 1.161 0.011 V as determined from... 

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