Neptunium isolation

Kilogram amounts of neptunium ( Np) have been isolated as a by-product of the large-scale synthesis of plutonium in nuclear reactors that utilise 235u and 238u as fuel. The following transmutations occur ... 

The wastes from uranium and plutonium processing of the reactor fuel usually contain the neptunium. Precipitation, solvent extraction, ion exchange, and volatihty procedures (see Diffusion separation methods) can be used to isolate and purify the neptunium. 

That magnetic measurements often raise more problems than they solve, is demonstrated for the indicated compound. We prepared a series of [ (C2H5N] i,An(NSC) e compounds (An = Th, U, Np, Pu) with cubic coordination of the actinide ion. We derived a consistent interpretation of the magnetic and optical properties of the uranium and the neptunium compounds (6 ). In the case of Pu we expect an isolated T1 ground state and a first excited state at about 728 cm-1. To our surprise we found a magnetic ground state much more pronounced than in the case of the hexachloro-complex, Fig. 4. 

For instance, observation of identical phases for zirconium and plutonium indicate that the zirconium compound would serve as a suitable matrix in which to isolate plutonium. Similarly, the appearance of identical phases for Th, U and Np makes possible the doping of uranium or neptunium into a thorium matrix. 

Holm et al. [74] used a spectrometry for the determination of 237neptunium in seawater. The actinides are preconcentrated from a large seawater sample by hydroxide precipitation. The neptunium was isolated by ion exchange, fluoride precipitation, and extraction with TTA. 238Neptunium or 235neptunium was used to determine the radiochemical yield. 

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. 

A radiochemist isolates 8.6 /ng of a chloride of neptunium (atomic weight = 237 g/mole), which she proves has the formula NpCl3. in trying to find the possible valence states of Np, she finds that titration of the 8.6 /xg sample requires 37.5. 1 of 0.00200 N KMn04 solution. To what electrical charge must the Np have been oxidized ... 

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. 

Novak C. F., Nitsche H., Silber H. B., Roberts K., Torretto P. C., Prussin T., Becraft K., Carpenter S. A., Hobart D. E., and AlMahamid 1. (1996) Neptunium(V) and neptunium(Vl) solubilities in synthetic brines of interest to the Waste Isolation Pilot Plant (WIPP). Radiochim. Acta 74, 31-36. 

Heptavalent neptunium and plutonium can be prepared in highly alkaline aqueous media via electrochemical or chemical oxidation of An, Arr, or An species, with Np being more easily obtained and isolated than Pu. The complexes formed have been characterized in solution primarily by optical absorbance and vibrational spectroscopy, and more recently by NMR and EXAFS, and in the solid state by EXAFS and X-ray diffraction. Most research in this area was conducted at the Russian Academy of Sciences. 

The actinides are base metals which require the reduction of a chloride or fluoride with sodium or barium for their isolation. Neptunium, for example, has been made by reducing its trifluoride with barium vapour at 1200°. The need for such drastic methods is understandable because the heats of formation of the ions are as much as three times greater than that of the Pt ion. The metals are silvery white and, except thorium and americium, have high densities. 

Lithium naphthalide and uranocene in thf give the monoanion [U(r/-cot)2], isolated as a solvated lithium salt (405) neutral (406) and anionic (407) neptunium and plutonium analogs have also been prepared. 

The terrestrial occurrence of Ac, Pa, U, and Th is due to the half-lives of the isotopes 235U, 238U and 232Th which are sufficiently long to have enabled the species to persist since genesis. They are the sources of actinium and protactinium formed in the decay series and found in uranium and thorium ores. The half-lives of the most stable isotopes of the trans-uranium elements are such that any primordial amounts of these elements appear to have disappeared long ago. However, neptunium and plutonium have been isolated in traces from uranium13 minerals in which they are formed continuously by neutron reactions such as... 

Lanthanum fluoride cycle. This classical procedure was first developed by McMillan and Abelson for the isolation of neptunium, but it is applicable elsewhere and is of great utility. For the U-Pu separation again, we have Scheme 28-3. The cycle shown is repeated with progressively smaller amounts of lanthanum carrier and smaller volumes of solution until plutonium... 

Neptunium, plutonium and americium metals have been isolated by reduction of their fluorides with barium at 1200° C. Like uranium they are base metals and do not resemble the platinum group. The metal curium has not yet been described. 

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