- INTERACTION BETWEEN URANIUM TETRAFLUORIDE OXIDE AND THE PENTAFLUORIDES OF ARSENIC, NIOBIUM, TANTALUM, AND BISMUTH
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No reaction occurs between UF4O and AsF5 but UF4O*3MF5 (M=Nb and Ta) and UF4O*2BiF5 have been obtained as yellow or orange solids by warming mixtures of UF4O with excess of the appropriate pentafluoride in anhydrous HF or by combination of the oxide tetrafluoride with excess of the pentafluoride as a melt.The solid adducts have been charcterized by their reaction stoicheiometries, chemical analyses, and vibrational spectra.Like UF4O*2SbF5, the adducts are fluorine bridged with some ionic character.The thermal decomposition of the adducts results in the production of uranyl species.
- Holloway, John H.,Laycock, David,Bougon, Roland
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- Oxidation of U(IV) in HNO3 solutions containing urea and Tc(VII)
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The kinetics of U(IV) oxidation with nitric acid in aqueous solutions containing urea, catalyzed with technetium ions, were studied by sampling with subsequent colorimetric determination of the U(IV) concentration. At the constant ionic strength of the solution μ = 2 in the range of the initial concentrations of U(IV) from 2 × 10-3 to 1.28 × 10 -2, Tc(VII) from 5 × 10-5 to 1 × 10 -3, urea from 0.01 to 0.1, and hydrogen ions from 0.4 to 1.96 M, the reaction rate is described by the equation -d[U(IV)]/dt = k 1[U(IV)] [Tc]0.5[CO(NH2)2] × {[H+] 2 + β1[H+] + β2} -1 - k 2[U(IV)]2[H+] 0.4[CO(NH2)2]1.6{ [H +]2 + β1[H+]+ β2}-2, where k 1 = 172 ± 10 mol0.5 l-0.5 min-1 and k 2 = (9.4±1.2)×102 mol l-1 min-1 at 25°C, β1 and β2 are the hydrolysis constants of U4+ ions. The activation energy is 63±2 kJ mol -1. A reaction mechanism is proposed, in which in the slow stages the complex ion U(OH) 2 2+ ?CO(NH2) 2 reacts with TcO2+ and TcO2+ ? CO(NH 2)2 ions. 2005 Pleiades Publishing, Inc.
- Dvoeglazov,Marchenko,Koltunov
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- A study on pyrrolidone derivatives as selective precipitant for uranyl ion in HNO3
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We have found out that N-cyclohexyl-2-pyrrolidone (NCP) can selectively precipitate UO22+ ions in HNO3 solutions. In order to investigate factors of such a specific property of NCP, we have examined reactions of NCP with UO22+ ions in HCl, HClO4, or H2SO4, and the precipitation abilities of pyrrolidone derivatives other than NCP for UO2 2+ in HNO3 solutions. As a result, it was found that UO22+ ions in HCl, HClO4, or H 2SO4 are not precipitated by NCP, that N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP) with lower hydrophobicity than NCP do not precipitate UO22+, and that hydrophobic N-dodecyl-2-pyrrolidone can precipitate UO2 2+. Furthermore, we have investigated the crystal structures of UO2(NO3)2(L)2 (L = NMP, NEP) complexes to compare with that of UO2(NO3) 2(NCP)2. The bond distance between uranium and carbonyl oxygen of NCP in UO2(NO3)2(NCP)2 was found to be shorter than those in UO2(NO3) 2(L)2 (L = NMP, NEP). From these results, it is proposed that the specific property of NCP is ascribed to its relatively high hydrophobicity owing to cyclohexyl group, to its strong coordination ability to UO22+ for forming the symmetrical complex accompanied by two bidentate NO3-, and to the surface of UO 2(NO3)2(NCP)2 which is surrounded by the hydrophobic cyclohexyl groups of coordinated NCP.
- Ikeda, Yasuhisa,Wada, Emiko,Harada, Masayuki,Chikazawa, Takahiro,Kikuchi, Toshiaki,Mineo, Hideaki,Morita, Yasuji,Nogami, Masanobu,Suzuki, Kazunori
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- Redox-switchable carboranes for uranium capture and release
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The uranyl ion (UO2 2+; U(vi) oxidation state) is the most common form of uranium found in terrestrial and aquatic environments and is a central component in nuclear fuel processing and waste remediation efforts. Uranyl capture from either seawater or nuclear waste has been well studied and typically relies on extremely strong chelating/binding affinities to UO2 2+ using chelating polymers1,2, porous inorganic3–5 or carbon-based6,7 materials, as well as homogeneous8 compounds. By contrast, the controlled release of uranyl after capture is less established and can be difficult, expensive or destructive to the initial material2,9. Here we show how harnessing the redox-switchable chelating and donating properties of an ortho-substituted closo-carborane (1,2-(Ph2PO)2-1,2-C2B10H10) cluster molecule can lead to the controlled chemical or electrochemical capture and release of UO2 2+ in monophasic (organic) or biphasic (organic/aqueous) model solvent systems. This is achieved by taking advantage of the increase in the ligand bite angle when the closo-carborane is reduced to the nido-carborane, resulting in C–C bond rupture and cage opening. The use of electrochemical methods for uranyl capture and release may complement existing sorbent and processing systems.
- Keener, Megan,Hunt, Camden,Carroll, Timothy G.,Kampel, Vladimir,Dobrovetsky, Roman,Hayton, Trevor W.,Ménard, Gabriel
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- Formation of Excited Uranyl in Oxidation of U(IV) with Oxygen in HClO4 Aqueous Solutions: II. Catalytic Effect of UO2(2+)
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Strong effect of uranyl ion on the kinetic and chemiluminescence characteristics of U(IV) oxidation with oxygen in weakly acidic HClO4 solutionsis found. For instance, in the presence of 8E-4 M UO2(2+) the reaction rate constant, maximal intensity of the chemiluminescence, and chemilumi nescence efficiency increase by factors of 50, 100, and 8, respectively.The catalytic effect of uranyl ion is probably caused by both formation of the complex UO2(2+)*UO2(1+) (which decreases the rate of disproporti onation of UO2(1+) participating in the chain propagation) and generation of UO2(1+) in the reaction of UO2(2+) with U(IV).
- Lotnik, S. V.,Khamidullina, L. A.,Kazakov, V. P.
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- Oxidation of Uranium Dioxide with Manganates and Permanganates in Carbonate Solutions
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Oxidation and dissolution of uranium dioxide with some alkali and alkaline-earth metal manganates and permanganates in carbonate solution was studied. The kinetics of decomposition of potassium manganate and permanganate in solutions of some carbonates were studied spectrophotometricallyin the range of pH from 7.8 to 13.0. It was found that the stability of MnO4(1-) and MnO4(2-) ions and the pathways of their decomposition are governed by both pH and the nature of salts. The results of similar meas urements in the presence of uranium dioxide showed that throughout the studied range of pH to the higher rate of conversion of KMnO4 to K2MnO4 corresponds the higher rate of oxidation and dissolution of UO2 in carbonate solution.
- Filippov, A. P.
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p. 259 - 264
(2008/10/08)
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- Uranyl-catalyzed chemiluminescent reaction of U4+ oxidation by dioxygen in aqueous HClO4 solution
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Chemiluminescence (CL) accompanying the reaction of U4+ with O2 in 0.0004-0.1 M HClO4 was studied. It was found that the electron-excited uranyl ion (UO22+)* is the CL emitter. The fact that the reaction rate and the CL yield increase as the solution acidity decreases was explained by different reactivities of the U4+aq aquaion and the products of its stepwise hydrolysis, UOH3+ and U(OH)22+, toward O2. Based on the results of analysis of the chain-radical mechanism of the reaction between U4+ and O2, it was concluded that transfer of an electron from the UO2+ ion to the oxidizing agent (a OH radical) is the most plausible elementary step of the reaction of (UO22+)* formation. It was found that the reaction rate, as well as the CL yield, increase substantially in the presence of uranyl ion. Catalytic action of UO22+ was explained by the formation of a UO22+ · UO2+ complex, which reduces the rate of the UO2+ disproportionation reaction (UO2+ is an intermediate of the reaction and is involved in chain propagation), and by regeneration of the active center, UO2+, in the reaction of UO22+ with U4+.
- Lotnik,Khamidullina,Kazakov
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p. 1512 - 1517
(2007/10/03)
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- Kinetics studies on the acid assisted dissociation of some uranium(VI) complexes in solution
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Kinetics of dissociation of the schiff base complexes of uranium(VI), (I) UO2(H2salen)(NO3)2, (II) UO2(H2baen)(NO3)2 and (III) UO2(salgly)(H2O) in acidic ethanol-water solution and of (IV) a 1:1 complex formed by uranium(VI) with chromotropic acid in acidic aqueous medium leading to formation of solvated UO22+ ion have been studied by stopped-flow spectrophotometry.For all the complexes dissociation involves concurrent acid independent and acid dependent paths: kobs = ko + kH+>.Activation parameters corresponding to ko and kH for all the complexes havebeen determined and plausible mechanisms for dissociation have been suggested.
- Basak, Samarendra,Banerjea, Debabrata
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p. 129 - 133
(2007/10/02)
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- Electron-transfer reactions of uranium(V): Kinetics of the uranium(V)-uranium(VI) self-exchange reaction
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Uranium(V) has been prepared photochemically; its UV spectrum shows a peak at 255 nm with an extinction coefficient of 660 L mol-1 cm-1. Conventional UV/visible, stopped-flow, and laser flash photolysis techniques have been used to study the electron-transfer reactions of uranium(V) and uranium(VI) with a range of chromium, ruthenium, and cobalt complexes. Application of Marcus theory to these results suggests a uranium(VI)/uranium(V) self-exchange rate constant in the range 1-15 L mol-1 s-1. Some of the cross-reactions appear to be nonadiabatic, and these are slower than predicted.
- Howes, Kevin R.,Bakac, Andreja,Espenson, James H.
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p. 791 - 794
(2008/10/08)
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- Thermochemistry of uranium compounds. XII. Standard enthalpies of formation of the α and β modifications of uranium pentafluoride. The enthalpy of the β-to-α transition at 298.15 K
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A solution-calorimetric determination of the enthalpies of reaction of the α and β modifications of UF5 with Ce(SO4)2 + H2SO4 is described.Auxiliary measurements were made of the enthalpies of reaction of UO2, γ-UO3, and HF(aq).From these results are calculated the standard enthalpies of formation ΔH0f(298.15 K) of β-UF5, -(2083.0 +/- 6.3) kJ/mol and of α-UF5, -(2075.5 +/- 6.7) kJ/mol.The enthalpy of the (β-to-α) transition is (7.5 +/- 2.1) kJ/mol at 298.15 K.Suggested ΔH0f values are also given for U4F17 and U2F9.
- O'Hare, P. A. G.,Malm, John G.,Eller, P. Gary
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p. 323 - 330
(2007/10/02)
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