Uranium neptunium and

Spectra of Uranium, Neptunium and Curium. Report UCRL-3940. J. chem. Phys. 27, 1416 (1957). 

Subsequently, solvent extraction was applied to recover the fission product technetium from the residue remaining after the fluorination of irradiated uranium fuel elements . The residue was leached with concentrated aluminum nitrate solution, which was extracted by 0.3 M trilaurylamine in a hydrocarbon diluent. After separation of uranium, neptunium, and aluminum nitrate, technetium was back extracted into a 4 N sodium hydroxide solution. 

If an actinide metal is available in sufficient quantity to form a rod or an electrode, very efficient methods of purification are applicable electrorefining, zone melting, and electrotransport. Thorium, uranium, neptunium, and plutonium metals have been refined by electrolysis in molten salts (84). An electrode of impure metal is dissolved anodically in a molten salt bath (e.g., in LiCl/KCl eutectic) the metal is deposited electrochemically on the cathode as a solid or a liquid (19, 24). To date, the purest Np and Pu metals have been produced by this technique. 

Astatine is one of the rarest elements in nature. Extremely small amounts of short-lived isotopes At-215, At-217, At-218 and At-219 are naturally found occurring in equilibrium with uranium, neptunium and thorium isotopes. The element was named hy Corson, MacKenzie and Segre who produced the first of its isotope At-211 in 1940 hy homharding bismuth with alpha particles. Since then many isotopes in the mass range 200 to 219 have been synthesized. All isotopes, however, are unstable, their half-lives ranging between a few microseconds to less than ten hours. The most stable ones are At-210, At-211 and At-209. No use of this element is known so far. 

Heavier isotopes Es-253, Es-254 and Es-255 can be produced in a nuclear reactor by multiple neutron capture reactions that may occur when uranium, neptunium and plutonium isotopes are irradiated under intense neutron flux. These and other isotopes also are produced during thermonuclear explosions. 

Fluorine is used in the separation of uranium, neptunium and plutonium isotopes by converting them into hexafluorides followed by gaseous diffusion then recovering these elements from nuclear reactors. It is used also as an oxidizer in rocket-fuel mixtures. Other applications are production of many fluo-ro compounds of commercial importance, such as sulfur hexafluoride, chlorine trifluoride and various fluorocarbons. 

The remaining exceptions concern the lanthanide series, where samarium at room temperature has a particular hexagonal structure and especially the lower actinides uranium, neptunium, and plutonium. Here the departure from simple symmetry is particularly pronounced. Comparing these three elements with other metals having partly filled inner shells (transition elements and lanthanides), U, Pu, Np have the lowest symmetry at room temperature, normal pressure. This particular crystallographic character is the reason why Pearson did not succeed to fit the alpha forms of U, Pu, and Np, as well as gamma-Pu into his comprehensive classification of metallic structures and treated them as idiosyncratic structures . Recent theoretical considerations reveal that the appearance of low symmetries in the actinide series is intimately linked to the behaviour of the 5f electrons. 

In 1970, Hill pointed out that one may classify uranium, neptunium and plutonium compounds into a magnetic and non magnetic group depending on interactinide distance dAn-An (sce Chap. A) with a critical value of about 3.4 A. This systematics clearly evidences a localization process related to direct 5 f-5 f overlap. As we said at the beginning of this section, the critical distance may be viewed from the 2 different points of view... 

Since this is so, it was inevitable that as soon as Seaborg and his collaborators had clearly established the identity and properties of neptunium and plutonium, they would look for the next higher elements, numbers 95 and 96. The general similarity in chemical properties of uranium, neptunium, and plutonium led Seaborg to believe that these new elements could be isolated by methods similar to those already used. 

Allard, B., Kipatsi, H. and Liljenzin, J. 0., "Calculated Species of Uranium, Neptunium and Plutonium in Neutral Aqueous Solution", subm. to Radiochem. Radioanal. Lett. 

The most widely used neutral extractants, however, are the organophosphoms compounds, of which the ester, TBP, is the most important. TBP forms complexes with the actinide elements thorium, uranium, neptunium, and plutonium by bonding to the central metal atom via the phosphoryl oxygen in the structure... 

Anyun, Z., Jingxin, H., Xianye, Z., Fangding, W. 2001. Hydroxylamine derivatives in PUREX process, VI. Study on the partitioning of uranium/neptunium and uranium/ plutonium with N,N-diethylhydroxylamine in the purification cycle of uranium contactor. Solvent Extr. IonExch. 19 (6) 965-979. 

A mixture of uranium, neptunium, and plutonium to fabricate new mixed actinide-fuels (either metallic or oxides)... 

Bergeonneau, P., C. Jaonen, M. Germain, and A. Bathellier. 1979. Uranium, Neptunium, and Plutonium Kinetics of Extraction by Tributylphosphate and Trilaurylamine in a Centrifugal Contactor. Proceedings of International Solvent Extraction Conference (ISEC 77), September 9-16, 1977, Toronto, Canada, vol. 2, 612-619. 

Tin and americium were so extensively sorbed under all conditions that isotherm data could not be obtained. These elements are not significantly mobile in the Mabton Interbed aquifer. Values of Freundlich constants for technetium, radium, uranium, neptunium, and plutonium are given in Table IV. The Freundlich equation did not fit the selenium sorption data very well probably because of slow sorption kinetics or precipitation. Precipitation was also observed for technetium at 23°C for concentrations above 10 7M. This is about the same solubility observed for technetium in the sandstone isotherm measurements. Linear isotherms were observed only in the case of radium sorption. In general, sorption on the Mabton Interbed was greater than on the Rattlesnake Ridge sandstone. This is probably due to the greater clay content of the Mabton standard. 

Foti, S. C. Freiling, E. C., "The Determination of the Oxidation States of Tracer Uranium, Neptunium, and Plutonium in Aqueous Media." Talanta 1964 11, 384-392. 

Allard, B. Kipatsi, H. LiTjinzin, J. O. "Expected Species of Uranium, Neptunium, and Plutonium in Neutral Aqueous Solutions, J. Inorg. and Nuclear Chemistry 1982,42,1015-1027. 

Especially interesting in a discussion of radionuclide speciation is the behaviour of the transuranium elements neptunium, plutonium, americium and curium. These form part of the actinide series of elements which resemble the lanthanides in that electrons are progressively added to the 5f instead of the 4f orbital electron shell. The effective shielding of these 5f electrons is less than for the 4f electrons of the lanthanides and the differences in energy between adjacent shells is also smaller, with the result that the actinide elements tend to display more complex chemical properties than the lanthanides, especially in relation to their oxidation-reduction behaviour (Bagnall, 1972). The effect is especially noticeable in the case of uranium, neptunium and plutonium, the last of which has the unique feature that four oxidation states Pum, Pu, Puv and Pu are... 

Foti, S.C. and Freiling, E.C. (1964) The determination of the oxidation states of tracer uranium, neptunium and plutonium in aqueous media. Talanta, 11, 385-392. 

Analysis of the Crystal-Field Spectra of the Actinide Tetrafluorides. I. Uranium, Neptunium, and Plutonium Tetrafluorides (UF4, NpF4, and PUF4), W.T. Camall, G.K. Liu, C.W. Williams, andM.F. Reid../. Chem. Phys. 95, 7194-7203 (1991). 

X-Ray Photoemission Spectroscopy (XPS) Study of Uranium, Neptunium, and Plutonium Oxides in Silicate-Based Glasses... 

For the larger chloride ion, the final member in the series is the tetrachloride, An02CLi A The uranium, neptunium, and plutonium tetrachloride dianions have been isolated with a number of different cations, for example, Na+, NH4+, K+, Cs+, K+18-crown-6, and so on. The An=0 distances were found to be 1.768, 1.751, and 1.737A for An = U, Np, and Pu, respectively. The An-Cl distances in these complexes is virtually unchanged 2.675 A (U), 2.659 A (Np), and 2.656 A (Pu). These stmctural data suggest that the chloride hgands are bound in essentially a purely ionic manner while the covalent nature of the An=0 bond is preserved. 

Intermolecular electron-transfer rates have been studied for uranocene and substituted derivatives of uranium, neptunium, and plutonium by examining the variable-temperature NMR spectra of mixtures of (CgH8)2An and [(C8Hg)2An]. In all cases, electron-transfer rates are rapid. Specific rates could not be derived for uranium and plutonium derivatives owing to the small chemical shift differences between analogous An(fV) and An(III) compounds, but in the case of (f-BuC8H7)2Np, the rate has been estimated to be of the same order of magnitude as comparable lanthanide cyclooctatetraene compounds ( 10 s ). ... 

Most of the compounds of tetravalent to hexavalent americium described here were obtained for uranium, neptunium, and plutonium (Table III). The decomposition temperatures of the americium compounds are considerably below (200°-300°C.) those of the corresponding temperatures of the analogous neptunates and plutonates (4, 25). 

Investigations of the solid-state chemistry of the americium oxides have shown that americium has properties typical of the preceding elements uranium, neptunium, and plutonium as well as properties to be expected of a typical actinide element (preferred stability of the valence state 3-j-). As the production of ternary oxides of trivalent plutonium entails considerable difficulties, it may be justified to speak of a discontinuity in the solid-state chemical behavior in the transition from plutonium to americium. A similar discontinuous change in the solid-state chemical behavior is certainly expected in the transition Am Cm. Americium must be attributed an intermediate position among the neighboring elements which is much more pronounced in the reactions of the oxides than in those of the halides or the behavior in aqueous solution. 

Oxidation state. Differences among the potentials of the redox couples of the actinides account for much of the differences in their speciation and environmental transport. Detailed information about the redox potentials for these couples can be found in numerous references (e.g., Hobart, 1990 Silva and Nitsche, 1995 Runde, 2002). This information is not repeated here, but a few general points should be made. Important oxidation states for the actinides under environmental conditions are described in Table 4. Depending on the actinide, the potentials of the III/IV, IV/V, V/VI, and/or IV/VI redox couples can be important under near-surface environmental conditions. When the redox potentials between oxidation states are sufficiently different, then one or two redox states will predominate this is the case for uranium, neptunium, and americium (Runde, 2002). The behavior of uranium is controlled by the predominance of U(VI) species under... 

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