Showing papers on "Uranyl published in 1980"

Improved planar solar converter based on uranyl neodymium and holmium glasses

Abstract: The use of uranyl doped glasses for solar energy conversion and concentration was discussed by Reisfeld and Neuman1. While the UO2+2 ion is an efficient energy converter, its maximum emission peaking around 500 nm does not coincide with the maximum sensitivity of the existing solar cells which is around 700–1,000 nm. The use of Nd3+ doped glasses for solar energy collectors was described by Levitt and Weber2. While the emission of Nd3+ peaking at 880 nm (4F3/2→4I9/2) and at 1.06 µm (4F3/2→4I11/2) is ideal for matching with the maximum sensitivity of solar cells, its absorbance arising from the forbidden transition 4f–4f is low and the overlap of the absorption spectrum of Nd3+ with the solar spectrum is rather weak. To increase the operational efficiency of solar collectors, a maximum overlap between the absorption spectrum of the collector and the solar spectrum is required3. In this report we suggest that glasses doped by uranyl and neodymium and uranyl and holmium increase the response to the solar spectrum, thus increasing the collection efficiency, and convert the absorbed light in the wide spectral range into the narrow fluorescence band at 1.06 µm and 880 nm in uranyl–neodymium glasses and 660 nm (5F5→5I8) and 750 nm (5F4, 5S2→5I7) in the uranyl-holmium co-doped glasses.

Macrocyclic hexacarboxylic acid. A highly selective host for uranyl ion

Abstract: Previously a macrocyclic hexaketone which effectively bound uranyl ion was prepared succesfully. Recently, two types of ligand of macrocyclic hexacarboxylic acid were prepared by symmetrically arranging six carboxylates on a macrocyclic skeleton in which the ring size was adjusted to give a cavity to accommodate uranyl ion comfortably. Three of six carboxylates seem to compose a binding site. One of the three additional carboxylic acid units in both ligands is amenable to attachment to a suitable polymer support. The other two probably act to make the microscopic environment around the metal binding site more hydrophilic as well as to decrease the entropy loss involved in the complexation. Compared with the previous hexaketone, the new macrocycle hexacarboxylic acids are capable of much more facile preparation in reasonable overall yields and are far more effective and selective for the binding of the uranyl ion. The preparation is a straightforward reaction between tetraethyl n-decane-1,1,-10,10-tetracarboxylate and diethyl ..cap alpha.., ..cap alpha..-bis(8-iodooctyl)malonate. The cyclization was achieved under high-dilution conditions, and the hexaethyl ester of macrocyclic hexacarboxylic acid was isolated through silica gel column chromatography. Alkaline hydrolysis yielded the hexacarboxylic acid. Similar procedures gave a hexacarboxylic acid containing an ether bridge. Uranyl ion is known tomore » form a stable complex with carbonate (CO/sub 3//sup 2 -/). High selectivity of these ligands to uranyl was ascertained also by competition with other metal cations such as: Na/sup +/, Mg/sup 2 +/, Ni/sup 2 +/, and Zn/sup 2 +/. These results indicate that uranyl ions can be extracted efficiently from sea water using these hexacarboxylic acid ligands which are attached to a polymer completely insoluble in water.« less

Uranium Isotope Enrichment by Chemical Method

Abstract: Through basic research on the separation of uranium isotopes by the isotopic equilibrium reaction of uranus and uranyl ions, a novel redox chromatography in adsorption columns has been discovered, which is most efficient for the enrichment of /sup 235/U. Further studies of kinetics and multicomplexes have led to the formation of two very important equations that satisfactorily predict the degree of separation of uranium isotopes. Some results from extensive single- and multicolumn experiments and a model plant currently under design for recovery of 3% enriched uranium are also described. 8 refs.

Influence of ion exchanger and diluent structure on uranyl ion selective electrode response

Abstract: A series of uranyl complexes were tested as the active substance in the membranes of uranyl ion selective electrodes, ISEs. Complexes with phosphites as ligands, ion exchangers, give better electrodes than those with phosphates and phosphonates. This observation seems to be related to the fact that phosphites are weaker ligands and therefore more labile ligands for uranyl. A simple technique for the preparation of PVC-based membranes for ISEs is described. 7 figures, 3 tables.

Uranium in secondary silica; a possible exploration guide

Abstract: Study of uraniferous silica precipitates in the Shirley Basin, Wyoming, identified areas where ancient uraniferous ground water once ponded. Chalcedony collected from and directly beneath thick accumulations of rhyolite ash contain as much as 250 ppm uranium in a pre-ash topographic low and lesser concentrations (10 to 160 ppm) elsewhere. Differences in the U concentration of chalcedony collected from approximately the same stratigraphic horizon reflect the enrichment of uranium in ground water as it percolated downward and basinward through the overlying rhyolite ash. Uranium is homogeneously distributed as a uranyl species within the chalcedony and reflects coprecipitation of dissolved uranium and colloidal silica in a uraniferous silica-gel. Laboratory measurements of the partitioning of uranium between various solutions and silica-gel precipitates indicate that, for ranges of pH and dissolved carbonate typical of ground water, dried silica-gel contains about 400 to 1,000 times the uranium concentration of the solution from which it forms. Uranium is postulated to be incorporated as an adsorbed uranyl-silica-hydroxyl complex. A 20-m.y.-minimum apparent age for uraniferous chalcedony was obtained by U-Pb isotope dating. Reported minimum ages for nearby sedimentary uranium deposits generally lie between this age and the age of rhyolite which hosts the silica (32.4 + or - 2.6 m.y.). Leaching of uranium from ash during the period 20 to 32 m.y. is therefore compatible with a volcanic source-rock hypothesis.

Photochemistry and exciplex of the uranyl ion in aqueous solution

Abstract: The effects of acidity, temperature, self-quenching and H-donor concentration on the luminescent state of the aqua-uranyl (VI) ion have been studied in aqueous acidic nitrate and perchlorate solution. The detailed results cannot be explained by any single simple mechanism such as radiative, nonradiative or spontaneous collisional quenching, or irreversible hydrogen abstraction from water. Quantitative analysis of the results shows a far more complex mechanism, involving the adiabatic formation of the species UO2H2+ and U2O4H4+, as already proposed by the author. This mechanism is supported by state and m.o. correlations. The abstraction of hydrogen from water is shown to take place by H atom transfer in a uranyl–water complex intermediate, rather than by attack of H+ on the fully occupied πu orbitals of uranium (V) in a well-defined uranyl water complex with strong charge transfer character. A qualitative description of the exciplex U2O4H4+ is shown to be possible in a v.b. formalism and the origin of its radiative properties is discussed on this basis.

Reactivity of uranyl ion with quinquedentate chelating hydrazine derivatives. Part 1. 2,6-Diacetylpyridine bis(2′-pyridylhydrazone)

Abstract: Uranyl nitrate reacts with 2,6-diacetylpyridine bis(2′-pyridylhydrazone)(H2dapp) to give [UO2(H2dapp)(NO3)]2–[UO2(NO3)4](1) or a mixture (2) of ionic mononuclear species, in each of which H2dapp acts as a quinquedentate chelating ligand, depending on the experimental conditions. The complexes have been characterized by a number of physicochemical measurements including the X-ray analysis of (1). Crystals of (1) are triclinic with a= 14.071(9), b= 10.801(7), c= 10.122(6)A, α= 63.86(7), β= 75.65(9), γ= 78.86(9)°, space group P[graphic ommitted], and Z= 1. The structure has been solved by conventional techniques, and refined to a final R of 0.07. The unit cell contains two very highly distorted eight-co-ordinated cations [UO2(H2dapp)(NO3)]+, related by a centre of symmetry and with the N5O donor set in a symmetrically twisted ‘equatorial plane’[U–N (mean) 2.62 A, N–U–N (mean) 59.5°, and U–O 2.48 A for the unidentate nitrate group], and an uranyl tetranitrate counter anion [UO2(NO3)4]2–[two bidentate nitrates (U–O 2.53 A) and two unidentate (U–O 2.45 A)], at the centre of symmetry, in a hexagonal bipyramidal arrangement. The nature of the solvent(s), the high stabilizing effect of the 5,5,5,5 chelation mode, and reactivity tests, which allow the isolation of [UO2(H2dapp)(NO3)][BPh4](3) and [UO2(H2dapp)][ClO4]2(4), are discussed. Owing to the deprotonation of the diazapropenic sequences CN–NH–, the neutral complex [UO2(dapp)](6), containing U–N covalent bonds, can be obtained by the action of non-hydroxylated bases on (1)–(4). Like uranyl amides, compound (6) reacts with alcohols to give alkoxy-derivatives. Polymeric [{(UO2)2(H2dapp)(OCH3)4·xCH3OH}n](7) has been isolated.

Interactions of uranyl ions with lipid bilayer membranes.

Abstract: Uranyl ions (UO2(2+)), once bound to the phosphate moieties of phospholipid head groups, stabilize bimolecular lipid membranes (BLMs) as well as decrease the nonactin-induced membrane conductance. UO2(2+) bind to a phosphatidyl choline-cholesterol (2:1, molar ratio) BLM surface with a dissociation constant of 2.3 microM and a maximum change in surface potential of 88 mV, which corresponds approximately to one uranyl ion per 31 nm2 surface area. Furthermore, uranyl ions can penetrate the lipid bilayers as neutral complexes such as uranyl acetate.

Study of the retention mechanism of uranium on titanium oxide

Abstract: We have studied the phenomenon of retention of uranium, as a carbonato complex UO2(CO3)34− on titanium oxide. We first proposed a method for preparing titanium oxide whose ion-exchange capacities (2.9 meq Na+/g, 0.11 meq UO22+/g) and physical properties (mechanical resistance and granulometry) make it quite suitable for liquid chromatography and particularly for the extraction process of uranium from sea-water. We prepared the sodium tricarbonatouranate, the major form of uranium in sea-water. We studied the retention of this compound on titanium oxide. From a thermodynamic study of the retention equilibrium we proposed a retention mechanism of the ligang-exchange type: uranyl is retained on titanium oxide, surrounded with two CO32− ligands and two ≥TiO− ligands. We shown that 2/3 of the exchanged hydroxyl groups have pKH1=4.9 and 1/3 of them have pKH2=9.3.

Preparation and characterization of a volatile uranyl compound, Bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)dioxouranium-tetrahydrofuran

Abstract: A volatile uranyl compound UO/sub 2/((CF/sub 3/CO)/sub 2/CH)/sub 2/.THF with a vapor pressure of 0.7 torr at 100/sup 0/C has been prepared. The compound has high thermal stability and is suitable for studies of laser-induced isotope separation. The compound has been characterized by its IR, UV, NMR, fluorescence, and mass spectra and other physical and chemical properties including an X-ray structural determination. The molecule contains a linear uranyl ion equatorially surrounded by a pentagon of oxygen atoms. The chelating anions are tilted slightly in a boatlike configuration from this plane. The crystals are monoclinic,P2/sub 1/c, with a = 8.540 (3) A, b = 9.110 (4) A, c = 28.884 (11) A, ..beta.. = 94.26 (3)/sup 0/, and Z = 4.

Luminescence spectra of the uranyl ion in two geometrically similar coordination environments. Uranyl nitrate hexahydrate and di-. mu. -aquo-bis(dioxobis(nitrato)uranium(VI)) diimidazole

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Organic geochemistry and uranium in Grants mineral belt

Abstract: Organic material is intimately associated with the primary uranium deposits of the Grants mineral belt. This organic material is now insoluble and nonvolatile, and most of it lacks cellular structure. The relationship of organic matter and uranium can be shown physically, chemically, and statistically. Pyrolysis-gas chromatography, mass spectrometry, and elemental analysis have been used to examine the organic matter from several ore deposits. The results show carbon-rich materials that have been severely degraded by radiation from uranium and daughter products. The organic material now resembles amorphous carbon, having lost most of its hydrogen and oxygen. From the uranium content and approximate age the radiation dose is calculatd to be 10/sup 11/ rads. The radiation damage has also produced an interesting new carbon-isotope fractionation effect, by which the carbon associated with ore is enriched in carbon-13 (C/sup 13/) relative to the non-ore carbon. From model experiments and laboratory work on samples from the Grants district, the following hypotheses are made: first, the soluble organic matter (of unknown origin) coated or precipitated on the mineral grains; subsequently, the uranium (probably as uranyl cation or carbonate anio complex) was concentrated in and on this organic matter by ion exchange and chelation with functionalmore » groups. This cycle of organic coating and uranium concentration could have been episodic or continuous but must have lasted at least 10/sup 6/ years, based on calculations using assumed porosity, permeability, hydraulic gradient, uranium content of water, and organic concentration factors. Finally, after 10/sup 8/ years, the radiation damage has created an amorphous carbon material that is deficient in hydrogen and oxygen; this material helps to protect the ore from mobilization because it is chemically inert.« less

Metal-catalysed organic photoreactions. Evidence for the long-range electron-transfer mechanism in the uranyl- or iron(III)-catalysed photoreactions of olefins

Abstract: A scheme involving interligand electron transfer from the electron-donating ligand (OH– or Cl–) to molecular oxygenn through the metal ion and olefin molecule is proposed for the metal-catalysed photo-oxidation of olefins. The scheme is verified for the uranyl-catalysed photochemical formation of bromohydrins from olefins and various polyhalogenated compounds by correlation of the reactivities and product ratios with the half-wave reduction potentials of the polyhalogenated compounds.

Crystal structure of tetra(glycolato)uranium(IV) dihydrate a photoreduction product of uranyl ions in the presence of glycolic acid

Abstract: The crystal structure of the title compound has been determined as the first example of a monomeric carboxylatocomplex of UIV. The crystals are monoclinic, P21/a, with a= 6.555(6), b= 17.652(13), c= 8.008(2), β= 128.52(4), and Z= 2. The structure has been solved by the heavy-atom method and refined to R= 0.057 for 1 031 observed reflections. The uranium atoms are ten-co-ordinate, with bicapped square-antiprismatic geometry [U–O 2.38(2)–2.55(1)A], and the glycolate anions are planar, 1 : 4 co-ordinated.

The longitudinal spin lattice relaxation time of the uranyl phenanthraquinone radical ion complex

Abstract: The longitudinal spin lattice relaxation time T1 for the uranyl phenanthraquinone radical complex ion (UO2PQ)+. is much less than that for the phenanthraquinone radical anion PQ−.. A qualitative understanding of the effect is achieved by recognizing that the U atom has an enormous spin–orbit coupling. A calculation which includes the U 5f±2 (5fz,x2−y2 and 5fzxy) orbitals in the π system provides a semiquantitative understanding but the formal charge of U is closer to +1 than to +2. The state of the odd electron is described by a Huckel approach and the description of T1 includes G tensor modulation and spin–rotation interaction.

Structure of tris(urea)dioxouranium(VI) sulfate, UO2(OC(NH2)2)3SO4

Abstract: As part of a study of structures of uranium complexes the crystal structure of tris(urea)uranyl sulfate was determined by single-crystal x-ray diffraction methods. The uranyl ion is coordinated to oxygen atoms from the three urea molecules and from the sulfate ions in a pentagonal-bipyramid arrangement in which the pentagonal bipyramids are bridged by the sulfate ions to form an infinite chain. This result is in contrast to the structure of pentakis(urea)dioxouranium(VI) dinitrate in which the oxygen atoms of the five urea molecules are coordinated to the uranyl ion to form discrete complexes with the same pentagonal-bipyramidal geometry; the nitrate ions are not coordinated to the uranyl ion. 1 figure, 4 tables. (DP)

UV-visible and infrared spectra of volatile uranyl complexes in the gas phase

Abstract: The gas-phase UV-visible and infrared spectra of bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)dioxouranium(VI) (UO/sub 2/(HFA)/sub 2/) were found to exhibit a marked pressure and temperature dependence which appears consistent with the monomer-dimer equilibrium previously established for this compound. The visible spectra obtained for both the monomeric and dimeric species are unusual because the vibrational structure characteristic of the spectra of many uranyl compounds is completely absent. The IR spectra, which were in part obtained with a CW N/sub 2/O/CO/sub 2/ laser spectrometer, showed three bands attributable to the asymmetric stretch (..nu../sub 3/) of the uranyl group. A study of the pressure and temperature dependence of the intensity of these bands indicated that two could be assigned to the dimeric form and the third to the monomeric form. These observations permit the assignment of a probable structure to the dimeric form of UO/sub 2/(HFA)/sub 2/. Some preliminary observations on the spectra of the trimethylphosphate derivative (UO/sub 2/(HFA)/sub 2/TMP) of UO/sub 2/(HFA)/sub 2/ are also described.

A Microcalorimetric Study of U(IV)-Oxidation by Thiobacillus Ferrooxidans and Ferric-Iron

Abstract: Uranium commonly occurs in the tetravalent form [U(IV)] in uranium-bearing rocks and the solubilization involves its oxidation to the hexavalent uranyl ion.

Laser Raman Spectra and Normal Coordinate Analysis of Some Uranyl Tetrachloride Complexes

Abstract: Laser Raman spectra of uranyl tetrachloride complexes [K2UO2Cl4, Rb2UO2Cl4, (Cs2UO2Cl4, (NH4)2UO2Cl4] have been measured in the region from 3500 to 10 cm−1. Vibrational assignments as well as normal coordinate analyses have been carried out with the assumption that all the complexes contain discrete (UO2Cl4)2- ions belonging to a point group D4h. To understand the nature of the uranyl bonds in the complexes, approximate π-bonding energies of such bonds have been estimated from the U—O stretching force constants. The reliability of the values obtained are discussed in detail on the basis of Mulliken's magic formula.

Reactions of uranyl(VI) complexes of acid dihydrazides with β-diketones

Abstract: Uranyl(VI) complexes of malonic acid dihydrazide (MDH2) and phthalic acid dihydrazide (PDH2) and the products of their reactions with four β-diketones have been characterised by elemental analysis and by electrical conductance, and spectral (i.r. and electronic) measurements. The MDH2 and PDH2 complexes UO2(L)2(H2O)2 are eight coordinate whereas the macrocyclic UO2(L′)(H2O)2 complexes are six coordinate. In each complex MDH2 and PDH2 act as bidentate liglands having the coordination sites at secondary amide-nitrogen atoms.