Solutions Of Uranyl Salts Research Articles

Synthesis and Low Temperature In Situ Sintering of Uranium Oxide Nanoparticles

The recycling and reuse of uranyl salt solutions produced from the acid dissolution of spent nuclear fuels is of particular interest for the reprocessing of nuclear fuels. The ability to utilize these dissolved salts as precursors for bulk UO2 defines a materials pathway for the reduction of nuclear waste destined for long-term repository storage. We present a room temperature (RT) synthesis of uranium dioxide nanoparticles (NPs) in acidic solutions, whose small size and uniform shape allow for dramatic decreases in sintering temperature. Gamma irradiation is a valuable method for the synthesis of a wide range of metal-based NPs. Here it has been successfully used to form (depleted) uranium oxide (d-UO2) NPs. In particular, this study focuses on the reaction dependency of solution pH and reaction dose on the shapes, sizes, yield, and properties of the products. The thermal stability and sintering behavior of the d-UO2 NPs is studied utilizing transmission electron microscopy (TEM) with an in situ heating stage. These d-UO2 NPs exhibit sintering temperatures in the range of 500 °C–600 °C, which is between 700–1000 °C lower than reported bulk UO2 sintering temperatures. Detailed characterization results from UV–vis spectroscopy, TEM, and in situ heating stage TEM are presented for the reaction solutions, the RT NP products, and the sintered NPs.

EPR study of the production of oh radicals in aqueous solutions of uranium irradiated by ultraviolet light

The aim of the study was to establish whether hydroxyl radicals (?OH) were produced in UV-irradiated aqueous solutions of uranyl salts. The production of ?OH was studied in uranyl acetate and nitrate solutions by an EPR spin trap method over a wide pH range, with variation of the uranium concentrations. The production of ?OH in uranyl solutions irradiated with UV was unequivocally demonstrated for the first time using the EPR spin-trapping method. The production of ?OH can be connected to speciation of uranium species in aqueous solutions, showing a complex dependence on the solution pH. When compared with the results of radiative de-excitation of excited uranyl (+22*UO ) by the quenching of its fluorescence, the present results indicate that the generation of hydroxyl radicals plays a major role in the fluorescence decay of + 22 *UO . The role of the presence of carbonates and counter ions pertinent to environmental conditions in biological systems on the production of hydroxyl radicals was also assessed in an attempt to reveal the mechanism of +22*UO de-excitation. Various mechanisms, including ?OH production, are inferred but the main point is that the generation of ?OH in uranium containing solutions must be considered when assessing uranium toxicity.

The photo-oxidation of 2,6-dimethylphenol and monophenylphenols by uranyl ion in aqueous solution

The photo-oxidation of 2,6-dimethylphenol and o-, m- and p-phenylphenols by uranyl ion was investigated in aqueous solution. Steady state and dynamic luminescence quenching studies at pH 0.8 show the rapid dynamic deactivation of excited uranyl ions by the phenols. At the natural pH of uranyl salt solutions (pH 2.3), differences are observed between the steady state and dynamic quenching behaviour, and it is suggested that these differences are due to uranyl hydrolysis. Flash photolysis studies with uranyl ion in the presence of 2,6-dimethylphenol and m- and p-phenylphenols show that the initial photoreaction leads to phenoxyl radical formation. The photolysis products were identified by high performance liquid chromatography (HPLC) and UV absorption spectroscopy. With 2,6-dimethylphenol in aerated solution, both quinone and dimer formation are observed. Kinetic studies show that these processes occur concurrently. In contrast, photolysis of degassed solutions leads to dimer formation only. The quantum yields for these processes are reported. The photo-oxidation of aerated solutions of o-phenylphenol in the presence of uranyl ions leads to the production of two dimers and the quinone, whereas with degassed solutions only the dimers are observed. The photo-oxidation of these substrates by uranyl ion is contrasted with the behaviour of [Co(NH 3) 5N 3] 2+ as photooxidant of the same substrates. With m-phenylphenol, quinone and dimers are observed in aerated solution, whereas only the dimer is observed in deoxygenated solution. With p-phenylphenol, only dimer formation is observed. Possible mechanistic origins of the differences in the selectivity of oxidation by the different metal complexes are discussed.

Improved staining of microfilament bundles in plant cells for high voltage electron microscopy

SUMMARYA post‐polymerization en bloc staining method for high voltage electron microscopy is described. Embedded specimens were initially trimmed to an area close to the point of interest. Trimmed blocks were stained in 5% uranyl acetate/75% ethanol solutions for 36 h at 333 K. This procedure allowed specimens to be stained without the necessity of exposing Formvar films to damaging solutions. After such staining, both the contrast and fine detail of structures such as microfilament bundles were superior to that seen in material stained with aqueous solutions of uranyl salts.

Absorption spectrum, lifetime and photoreactivity towards alcohols of the excited state of the aqueous uranyl ion (UO2+2)

Microsecond flash photolysis of solutions of uranyl salts in water, H3PO4, H2SO4 and other media yields an intense, but short lived transient absorption spectrum in the region of 570 nm which exhibits vibronic structure with an average band separation of 580 cm–1. The decay of the transient in water was determined by laser flash photolysis to be first order with k1= 8.02 × 105 s–1, but with a considerable isotope effect (k1(D2O)= 4.20 × 105 s–1). k1 accords with the lifetime of the luminescence of aqueous UO2+2 ion determined by single photon counting (k1= 3.85 × 105 s–1). Both the 570 nm absorption and the emission (as determined by both single photon counting and conventional fluorimetry) are quenched on addition of various alcohols, the Stern–Volmer quenching constants closely correlating with the absolute quenching constants for the transient determined by laser flash photolysis. Large isotope effects were found for quenching by deuterated methanol, isopropanol and cyclohexanol both of the transient absorption and the emission. We conclude that the same electronic state of UO2+2 is responsible for (i) emission to the ground state, (ii) the absorption at 570 nm to a higher excited state and (iii) the photo-oxidation of aliphatic alcohols, principally by a process of abstraction of an H atom bonded to carbon from a —CH2OH or CHOH group.

Excitation-energy transfer in uranyl-salt solutions to tetravalent uranium and rare-earth-element impurities

Excitation-energy transfer in uranyl-salt solutions to tetravalent uranium and rare-earth-element impurities

Absorption properties and stability of certain uranyl compounds at elevated temperatures

The absorption spectra and acidity of several solutions of uranyl salts and complexes in aqueous, inorganic, and organic solvents were investigated at temperatures higher than room temperature (up to 135°C). Conclusions are drawn concerning the stability of some of the compounds studied at these temperatures. Irreversible chemical processes resulting in the formation of new (probably uranium) compounds were noted.

Relation between the luminescence spectra of uranyl salt solutions in organic solvents and the wavelength of the exciting light

The excitation spectra for various wavelengths of the luminescence from uranyl salt solutions in organic solvents and the relation between the emission spectra and the wavelength of the exciting light were investigated. Two absorption and luminescence centers occur for each solution and a weak interaction exists between them.

Extraction of alkalized solutions of uranyl salts with tributyl phosphate

Extraction of alkalized solutions of uranyl salts with tributyl phosphate

Luminescence spectra of organic solutions of uranyl salts in various stages of damping

Studies have been made of the damping curves and luminescence spectra at various stages of deexcitation of uranyl nitrate and uranyl acetate solutions. Each of the solutions exhibited three luminescence centers, two of which were associated with different uranyl complexes.

Determination of traces of free acid in uranyl salt solutions

A method for the determination of free acid in the presence of uranium(VI) is suggested. It involves the extraction of uranium by TBP from a solution saturated with potassium nitrate or chioride in order to prevent interference from the hydrolysis of uranium. The end-point is detected potentiometrically at pH 3.4. The method is suitable for the determination of 0.1–1.5 millimoles of acid in the presence of as much as 1.0 millimole of uranium.

Configuration of the Uranyl Ion

X-RAY crystallographic data1,2 indicate that in solid uranyl salts and metallic uranates the UO2++ ion is linear, and if this configuration is retained, only one frequency corresponding to the symmetric ν1 vibration should appear in the Raman spectra of uranyl salt solutions. Actual observations3–5, however, have shown at least two fundamental frequencies, at about 860 cm.−1 and 200 cm.−1, which have been assigned to the symmetric ν1 and bending ν2 vibrations respectively. Satyanarayana4 found also a weak line at 909 cm.−1, corresponding to the asymmetric ν3 vibration. These results suggest that the UO2++ ion in solution is bent, a conclusion supported by the infra-red spectral measurements, in which the ν1 frequency, forbidden for a linear model, has always been observed. Both Crandall5 and Satyanarayana have suggested that the ion might be linear in solution, local forces being responsible for the appearance of forbidden frequencies in the spectra. Hitherto, no experimental evidence has been put forward in support of this contention.

The Surface Tension and Viscosity of Solutions of Uranyl Salts

The Surface Tension and Viscosity of Solutions of Uranyl Salts