Showing papers on "Uranyl published in 1985"

The role of sulfate‐reducing bacteria in the deposition of sedimentary uranium ores

Abstract: The formation of many important sediment‐hosted uranium ore deposits is thought to have resulted from the reduction of relatively soluble uranyl ion—U(VI)—to insoluble uranium (IV) oxides and silicates by aqueous sulfide species. This study focused on the influence that the sulfate‐reducing bacteria Desulfovibrio desulfuricans (ATCC 7757) has on this process. Preliminary studies showed that bacterial growth was not inhibited by concentrations of uranyl ion up to 100 mg U per liter. More detailed studies showed that sulfate‐reducing bacteria have an influence on uranyl ion removal beyond the simple production of the aqueous sulfide reductant. Comparative studies of bacterial cultures containing high densities of the sulfate reducers with bacterial cell‐free but otherwise identical media showed that the bacteria themselves enhance uranium removal from solution. At pH 8.0, no reaction was observed in H2S‐bearing cell‐free media, whereas at the same H2S concentration, the uranyl ion decreased markedl...

The sorption of uranyl species on a hematite sol

Abstract: The sorption of uranyl species on a hematite sol of narrow size distribution has been studied as a function of uranium concentration and solution pH. The adsorption increases with increasing uranium content in the solution. Raising the pH from 5 to about 6.2 markedly enhances the uptake of uranium. The enhanced uptake coincides with a proportional increase of . The sudden increase in adsorption around this pH region does not appear to be due to changes in surface charge of the hematite particles. It may be due to specific interactions between and the hematite particles. Results of desorption experiments show that different binding sites may exist on the hematite surface.

Synthesis of 1,3-Diphenyl-4,5-bis(hydroxyimino)imidazolidine and Its Complexes with Nickel(II), Cobalt(II), Copper(II), Palladium(II), and Uranyl(VI)

Abstract: 1, 3-Dipheny1-4, 5-bis(hydroxyimino)imidazolidine (LH2) has been prepared from anti-dichloroglyoxime, N,N′-diphenylmethylenediamine, and sodium bicarbonate in ethanol. Complexes of Cu(II), Ni(II), Co(II), Pd(II), and UO2(VI) and LH2 give a metal-ligand ratio of 1:2. A tetrahedral complex is obtained for the Ni(II) complex by coordination through N and O atoms. The (LH2)Co. H2O complex is squarepyramidal while the Cu(II), Pd(II) and UO2(VI) complexes are square-planar. The structures of the ligand and complexes are proposed based on elemental analysis, mass spectral, 1H-n.m.r., i.r., u. v. -visible, and magnetic data.

Uranium accumulation in the lichen Cladonia rangiferina. Part II. Toxic effects of cationic, neutral, and anionic forms of the uranyl ion

Abstract: The toxicity of the uranyl ion to the lichen Cladonia rangiferina (L.) Wigg. was shown to be strongly dependent on chemical speciation. Photosynthetic measurements indicated that the anionic complex of oxalate was more toxic than the uncomplexed cation . No detrimental response could be assigned to the neutral phthalate complex (UO2L). Toxicity was also affected by the physiological condition of the lichen material. Samples exhibiting low photosynthetic levels typical for winter-collected material were damaged to a greater degree. Neither the cationic nor anionic species induced K+ loss from the lichen and the small release induced by the neutral species of the uranyl ion in phthalate buffer reflects a reduction in membrane integrity resulting from Ca2+ depletion. The effects of the uranyl ion and of the buffers used on Ca2+ displacement from lichen samples are discussed. Uranium uptake induced a reduction in total 14C fixation rates, a decrease in the proportion of radioactivity in the ethanol-soluble fr...

Uranyl clay photocatalysts

Abstract: Uranyl-exchanged clay photocatalysts have been used to photooxidize alcohols to ketones. Luminescence excitation, emission, and lifetime studies have been used to characterize these materials before, during, and after reaction. The absorption maxima for most of the uranyl-exchanged clays shift to higher wavelengths with respect to those for other aluminosilicate catalysts. Lifetime results indicate that several sites exist on these catalysts. Saturation of alcohol/clay slurries with oxygen leads to increasing rates of ketone formation. These uranyl-sensitized photoautoxidation reactions also produce coupled products as well as aldehydes, such as acetaldehyde, as identified by gas chromatography/mass spectrometry techniques. Different clays yield different amounts of product and rates of product formation. Hectorite exchange with uranyl ions is the most active catalyst of all aluminosilicate materials we have studied over short photolysis mass. 22 references, 6 figures, 6 tables.

The Synthesis and Complex Formation of N-(2-Methylpyridyl)-aminoglyoxime

Abstract: N-(2-Methylpyridyl)aminoglyoxime (LH2) has been prepared from 2-(aminomethyl)pyridine and anti-chloroglyoxime in a mixture of chloroform and diethyl ether at -15°C with triethanolamine as the base. The structure of this ligand has been determined according to 1H n.m.r. and i.r. spectral data. LH2 gives a planar (LH2)Ni complex with slight octahedral distortion. In the Cu(II) complex, [(LH)ClCu], the N atom of the pyridyl group is also taking part in complex formation, the Cd(II) complex is binuclear, [(LH)Cl3(OH2Cd2] and the Zn(II) complex is ionic, [(LH2)ClZn]Cl. The uranyl complex is binuclear with hydroxo-bridges, [(LH)(UO2)(OH)2(UO2)(LH)]. The structures of the complexes have been proposed according to elemental analysis, magnetic measurements, i.r., and 1H n.m.r. data.

Synergistic extraction of uranyl ion with 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (HPMBP) and diphenyl sulfoxide (DPSO), TRI-n-butyl phosphate (TBP) or tri-n-octylphosphine oxide (TOPO)

Abstract: Synergistic extraction of uranyl ion with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP) and oxo donors with widely varying basicity, viz. diphenyl sulfoxide (DPSO), tri-n-butyl phosphate (TBP) and tri-n-octylphosphine-oxide (TOPO) has been studied at various fixed temperatures. Results indicate that the equilibrium constants in the organic phase for addition reactions (KS) with these donors follow their order of basicity (KH) viz. DPSO (0.033)

Determination of Uranium by Reversed-Phase High-Performance Liquid Chromatography

Abstract: In spite of the large number of methods already reported, the determination of the uranyl ion is still a relevant analytical problem because the usual techniques of atomic absorption and emission spectroscopy are not suitable for the trace analysis of UO/sub 2//sup 2 +/, owing to their high detection limits. In this paper a new chromatographic procedure is proposed; this procedure is based on the separation and determination of UO/sub 2//sup 2 +/ as a neutral complex, using reversed-phase chromatography and spectrophotometric detection. In this work the ligand 2,6-diacetylpyridine bis(benzoyl-hydrazone) was used for the solvent extraction and chromatographic determination of uranium. The compounds of this class of bis(aroylhydrazone) derivatives are potential pentadentate chelating agents which can behave as neutral or bisdeprotonated ligands. Because of its steric and electronic features, H/sub 2/DIB is particularly suitable for complexing the uranyl ion. High extraction yields of UO/sub 2//sup 2 +/ from aqueous to dichloromethane solutions have been obtained, copper being the only metal with comparable extraction yield. The behavior of this ligand in the extraction of the uranyl ion, in addition to the high molar absorption of the complex in the UV region, suggested its use for the chromatographic determination of uranium, usingmore » a commercial apparatus with spectrophotometric detection.« less

Discussion on the complexing ability of the uranyl ion with several crown ethers and cryptands in water and in propylene carbonate

Abstract: Interactions of the uranyl ion (UO/sub 2//sup 2 +/) with some common crown ethers (12C4, 15C5, 18C6, DB-18C6) and cryptands (22,222) are investigated in aqueous and propylene carbonate (PC) solutions, I = 0.1 M ((TEA)ClO/sub 4/). Stability constants of the complexes formed are determined by potentiometric and spectrophotometric measurements. Discussions on the stability constants of the complexes allow us to postulate whether or not direct uranyl-macrocycle bonds are obtained. In PC solution, uranyl inner-sphere complexes with 18C6, DB-18C6, 22, and 222 are formed with the uranyl ion probably inside or partially enclosed in the ligand cavity. In aqueous media, complexation occurs only with crown ethers by formation of hydrogen bonds between hydrogen of water molecules of the hydrate shell of the uranyl ion and oxygen atoms of the crown ether (UO/sub 2//sup 2 +/ outer-sphere complexes). 31 references, 5 figures, 3 tables.

Kinetics and mechanisms of complex formation of uranyl ion with 18-crown-6 and diaza-18-crown-6 ligands in propylene carbonate

Abstract: Formation des complexes UO 2 -18C6 2+ et UO 2 (diaza-18C6) 2 2+ . Observation de 3 etapes avec 18C6 et de 4 etapes avec diaza-18C6

Water Soluble Pyridylazoaminophenols and Pyridylazoaminobenzoic Acids as Highly Sensitive Photometric Reagents for Zinc, Uranium, Cobalt and Nickel

Abstract: A series of water-soluble derivatives of pyridylazoaminophenol and pyridylazoaminobenzoic acid have been synthesized; they were evaluated as highly sensitive chromogenic reagents for metals. 2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (5-Br-PAPS) and 2-(3, 5-dibromo-2-pyridylazo)-5-(N-ethyl-N-sulfopropylamino) benzoic acid (DSAB) were found to be highly sensitive reagents, the former for zinc(e=13.3×104 at 552nm) and uranyl (e=6.6×104 at 578nm), and the latter for cobalt(III) (e=15.2×104 at 670nm)and nickel (e=13.7×104at 620nm).

Oxygen-17 NMR Study of the Uranyl Ion. II. Correlation between 17O NMR Chemical Shifts and Wavelengths of UV-Visible Absorption Bands of Uranyl Complexes

Abstract: 17O NMR chemical shifts, UV-visible and IR spectra of a series of [UO2Ln](ClO4)2 (L=unidentate oxygen-donor ligand; n=coordination number) complexes in nonaqueous solvents have been measured. The electronic transition bands of the UO22+ entity shift toward lower energies with the increase in base strength of ligands in the equatorial plane. The asymmetric stretching frequencies of U=O bands are also affected by the base strength of equatorial ligands and correlated with the lowest electronic transition energies of uranyl complexes with the same geometry. The 17O chemical shifts are shown to be related to the lowest electronic transition energies of uranyl complexes. It appears that oxygen isotope shifts in 17O NMR spectra of the uranyl ion are predominantly attributed to the increase in the lowest electronic transition energies.

Photophysics of the excited uranyl ion in aqueous solutions. Part 4.—Quenching by metal ions

Abstract: The quenching of the excited state of the uranyl ion by metal ions in aqueous solutions has been studied under conditions where (UO2+2)* decay is biexponential. The effect of metal ions always follows Stern–Volmer behaviour both for real quenching and for the second process, which is suggested to involve reversible crossing via solvent exchange between two energetically close excited states. With Tl+, Ag+, Fe2+, Pb2+, Mn2+, Ce3+ and Ni2+ quenching is suggested to occur by electron transfer. Theoretical calculations using a quantum-mechanical tunnelling model support a mechanism involving an inner-sphere exciplex. With Eu3+ preferential quenching of the emitting U* state is suggested to involve enhanced hydrogen-atom abstraction by (UO2+2)* following complexing and overlap of europium and uranyl orbitals. Initial fluorescence enhancement by metal ions in the uranyl system is observed in both dynamic and static studies. In cases where there is no complexing in the ground state with UO2+2, this initial enhancement is interpreted in terms of an effect of the metal ion on the initial relaxation of the emitting (UO2+2)* state.The time-resolved fluorescence spectra of UO2+2, together with other data on the photophysics of (UO2+2)*, suggest that the UO2+2 ground state and the lowest excited state, X*, have a slightly bent geometry (ca. 176°), whereas the second excited state, U*, is linear.

Synthesis of a new chelate resin for uranium adsorption from seawater: polystyrene resin containing two amide oxime functions in the repeating unit

Abstract: Dicyanoethylated polystyrene, poly{1-[4-(2,2-dicyanoethyl)phenyl]ethylene} (2), which was obtained from the reaction of chloromethylated polystyrene, poly[1-(4-chloromethylphenyl)-ethylene] (1) with malononitrile under phase transfer reaction conditions, was treated with hydroxylamine in methanol to afford a polystyrene resin 3 with two amide oxime functions in the repeating unit. Resins 3 exhibit a higher adsorptivity of uranium in seawater than a corresponding resin 5 with one amide oxime function in the repeating unit. The effective adsorption of uranyl ions by resins 3 is attributed to the close proximity of the two amide oxime functions in the styrene monomeric unit, which can effectively coordinate to a uranyl ion.

Glycine complexation with uranyl ion: absorptiometric, luminescence and X-ray structural studies of tetrakis(glycine) dioxouranium(VI) nitrate

Abstract: Addition of glycine to uranyl nitrate in aqueous acidic solution induces shifts in both the highly structured absorption and emission bands in the visible region. An analysis by Job's method indicates the formation of a complex of stoicheiometry uranyl ion: glycine of 1 : 4. The structure determination of a single crystal of the complex [UO2(O2CCH2NH3)4][NO3]2 by X-ray diffraction methods confirms this formulation. The structure has been refined to an R factor of 0.026 using 2 281 ‘observed’ measured intensities. The complex is triclinic, space group P, with hexagonal bipyramidal co-ordination about the uranium atom. All the glycine ligands are in the zwitterionic form, NH3+CH2CO2– and act as O-donors; two are bidentate [U–O = 2.562(5)–2.489(6)A], and two unidentate [mean U–O = 2.437(4)A]. The uranyl UO distance is 1.771(5)A(mean).

Characterization of silica-supported uranium-molybdenum oxide catalysts

Abstract: The techniques of X-ray diffraction, infrared and electron spin resonance spectroscopies, kinetics of reduction by H2, and XPS were used to investigate the chemical species present at the interface in silica-supported uranium–molybdenum oxide catalysts. In this catalyst series, with constant MoO3 loading (16.7 wt%) and Mo/(Mo + U) atomic ratios ranging between 1 and 0, it was found that the oxidic forms of Mo and U were not well dispersed, MoO3 crystallites being detected on the catalysts with a high Mo/(Mo + U) atomic ratio. In the less-uranium-rich catalysts [Mo/(Mo + U) = 0.89] both MoO3 crystallites and a crystalline ‘uranyl molybdate’ phase were present. This catalyst exhibited the highest reduction degree by H2 and the highest ESR signal intensity of Mo5+ ions when reduced under very mild conditions. The information obtained with these techniques was used to explain the promotional effect of U on the MoO3/SiO2 base catalyst for the selective oxidation of isobutene.

Kinetic molecular design of uranophile. Linear tris(dithiocarbamate) as a strong and rapid extracting reagent for uranyl ion from dilute carbonate solution

Abstract: Preparation au tri(acidedithiocarbamique)(4) dont on etudie la structure par RMN de 1 H et 13 C, IR, UV Formation de complexes 1:1 avec l'ion uranyle en solution aqueuse On compare les resultats avec ceux du macrocycle derivant de (4)

Photophysics of the excited uranyl ion in aqueous solutions. Part 5.—Fluorescence quenching by micellar solutions of triton X-100

Abstract: The effect of the micelles of Triton X-100 on the biexponential decay of (UO2+2)* has been investigated. Data are analysed in terms of a reversible crossing mechanism for the decay. Azulene fluorescence quenching and 13C n.m.r. studies strongly suggest that uranyl ions are able to penetrate deep inside the micelle core. Micelle quenching for the reversible decay of (UO2+2)* occurs in the interior (kq= 3 × 1010 dm3 mol–1 s–1) and at the surface (kq= 1.5 × 109 mol–1 dm3 s–1) of the micelles. The latter process has a rate virtually identical to that for the free surfactant molecules. Penetration of (UO2+2)* inside the non-polar regions of the micelle core increases solvent exchange rates by ca. two orders of magnitude. Uranyl-ion excimers are formed in occupied micelles. The quenching processes decrease strongly for these species because excimers do not penetrate the micelles.

Molecular Design of Specific Uranophiles

Abstract: Molecular design of uranyl specific ligands is reviewed. Basic principles to characterise the unique nature of uranyl complexes are scrutinized from ligand field caluclations, crystallographic analyses and stability constants of various complexes. The most typical characteristic of uranyl coordination is a planar hexacoordiantion by anionic ligands giving rise to the formation of the “ate-complex.” Several macrocycles were synthesized by the appropriate combination of these principles. Approaches to recovery of uranium from sea water are briefly reviewed. Organic chelating resins are the most promising candidates for the practical adsorbent.