Uranium

Weigel, F.

doi:10.1007/978-94-009-4077-2_5

Cited by 39 publications

(10 citation statements)

References 365 publications

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“…Work by Vachet and Callahan suggested that the nitrate and acetate anions, within gas-phase transition metal complexes, are primarily bidentate ligands [11]. The acceptance of 3 H 2 O ligands by (UO 2 NO 3 ) ϩ and (UO 2 CH 3 CO 2 ) ϩ is consistent with the formation of gas-phase complexes with pentagonal bipyramidal conformation, with two equatorial coordination sites occupied by O atoms of the anions, reminiscent of the structures of uranyl complexes in solution [1][2][3] and generated computationally [5] To evaluate this possibility, density functional theory (DFT) calculations using the B3LYP-SDD basis set were conducted. The octahedral structure of [(UO 2 OH)(H 2 O) 3 ] ϩ had been recently calculated by Oda and Aoshima [7], and was repeated here to evaluate the approach.…”

Section: Resultsmentioning

confidence: 72%

“…T he speciation and reactivity of uranium is a topic of sustained interest because species dependent chemistry [1] controls processes ranging from nuclear fuel processing [2] to mobility and fate in the geologic subsurface [3,4]. The solution chemistry of uranium is dominated by the uranyl ion, UO 2 2ϩ , for which recent theoretical studies [5][6][7][8] have suggested that strong interactions between the cation and solvent molecules, with significant charge transfer, cause the solvating species to behave like equatorial ligands.…”

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confidence: 99%

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Intrinsic hydration of monopositive uranyl hydroxide, nitrate, and acetate cations

Chien

Anbalagan

Zandler

et al. 2004

J. Am. Soc. Mass Spectrom.

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The intrinsic hydration of three monopositive uranyl-anion complexes (UO 2 A) ϩ (where A ϭ acetate, nitrate, or hydroxide) was investigated using ion-trap mass spectrometry (IT-MS). The relative rates for the formation of the monohydrates [(UO 2 A)(H 2 O)] ϩ , with respect to the anion, followed the trend: Acetate Ն nitrate ӷ hydroxide. This finding was rationalized in terms of the donation of electron density by the strongly basic OH Ϫ to the uranyl metal center, thereby reducing the Lewis acidity of U and its propensity to react with incoming nucleophiles, viz., H 2 O. An alternative explanation is that the more complex acetate and nitrate anions provide increased degrees of freedom that could accommodate excess energy from the hydration reaction. The monohydrates also reacted with water, forming dihydrates and then trihydrates. , for which recent theoretical studies [5][6][7][8] have suggested that strong interactions between the cation and solvent molecules, with significant charge transfer, cause the solvating species to behave like equatorial ligands. Therefore, specific interaction with solvent is likely to influence the physico-chemical behavior of the uranyl ion and its complexes in the environment. Unfortunately, explicit control over the interactions of solvent and non-solvent ligands with the uranyl ion is difficult, which makes the study of species-dependent uranium behavior complicated. To gain a better understanding of the intrinsic interactions between different uranium species and solvent, we have turned to investigations of uranyl-anion complexes in the gas phase. Recent studies have shown that ion-trap mass spectrometry can be used to probe intrinsic metal and metal-complex chemistry by exposing metal species to reagent gases deliberately added to the ion trap [9 -20], or to adventitious H 2 O present in the He bath gas used to collisionally cool ions and improve trapping efficiency [21][22][23][24]. Further motivating the present study is the fact that ion traps will shortly be used to characterize actinide speciation in samples from radioactive waste disposal sites, and a concise understanding of actinide behavior will be critical for correctly interpreting environmental data [25].We recently demonstrated that electrospray ionization (ESI) and multiple stage tandem mass spectrometry (MS) can be used to generate and characterize "solvated", gas-phase complexes featuring the uranyl ion coordinated by hydroxide, nitrate or a series of alkoxides [26]. In the pilot study reported here, ESI was used to produce gas-phase ions from solutions containing uranyl nitrate or uranyl acetate in deionized H 2 O. The dominant species generated by ESI were those having

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Section: Resultsmentioning

confidence: 72%

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confidence: 99%

Intrinsic hydration of monopositive uranyl hydroxide, nitrate, and acetate cations

Chien

Anbalagan

Zandler

et al. 2004

J. Am. Soc. Mass Spectrom.

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“…Solid phase U(VI) can exist as the less common uranate species, which has at least three single U-O bonds and no axial double bonds are known to form (GRIFFITHS and VOLKOVICH, 1999 and references therein). Examples of these are some forms of UO 3 solids and U(VI)-doped perovskites like La 2 MgTiO 6 (AZENHA et al, 1992;KHILLA et al, 1986;WEIGEL, 1986;TANNER et al, 1997). However, these forms have not been identified in the geologic environment (BURNS, 1999 and references therein) and they typically form at high temperature under aqueous and non-aqueous conditions (GRIFFITHS and VOLKOVICH, 1999, and references therein).…”

Section: Introduction-the Geochemical Speciation Of Uranium Influencementioning

confidence: 99%

Uranium co-precipitation with iron oxide minerals

Duff

Coughlin

Hunter

2002

Geochimica et Cosmochimica Acta

425

266

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ABSTRACT-In oxidizing environments, the toxic and radioactive element uranium (U) is most soluble and mobile in the hexavalent oxidation state. Sorption of U(VI) on Fe-oxides minerals [such as hematite (α-Fe 2 O 3 ) and goethite (α-FeOOH)] and occlusion of U(VI) by Feoxide coatings are processes that can retard U transport in environments. In aged Ucontaminated geologic materials, the transport and the biological availability of U toward reduction may be limited by co-precipitation with Fe-oxide minerals. These processes also affect the biological availability of U(VI) species toward reduction and precipitation as the less soluble U(IV) species by metal-reducing bacteria.To examine the dynamics of interactions between U(VI) and Fe oxides during crystallization, indicated that almost all of the Fe in these solids was crystalline and that most of the U was associated with these crystalline Fe oxides. X-ray diffraction and Fourier-transform infrared (FT-IR) spectroscopic studies indicate that hematite formation is preferred over that of goethite when the amount of U in the Fe-oxides exceeds 1 mol % U (~4 wt % U). FT-IR and room temperature continuous wave luminescence spectroscopic studies with unleached U/Fe solids indicate a relationship between the mol % U in the Fe oxide and the intensity or existence of the spectra features that can be assigned to UO 2 2+ species (such as the IR asymmetric υ 3 stretch for O=U=O for uranyl). These spectral features were undetectable in carbonate-or oxalate-leached Molecular modeling studies reveal that U 6+ species could bond with O atoms from distorted Fe octahedra in the hematite structure with an environment that is consistent with the results of the XAFS. The results provide compelling evidence of U incorporation within the hematite structure.

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“…Although it is difficult to measure particle diameter precisely, the expansion is expected to be observed because the molar density of UO 2 F 2 ARTICLE ( UO 2 F 2 ¼ 20;680 mol/m 3 ) is lower than that of UO 2 ( UO 2 ¼ 40;550 mol/m 3 ). 10) In this study, the original model 7,9) is extended to the situation where the particle swells due to the density difference between the intermediate and the particle itself. While the model is dedicated to the fluorination of UO 2 , the extended model is derived for a general gas-solid reaction consisting of a two-step reaction: the formation of a solid intermediate on the core of an unreacted reactant and the consumption of the intermediate.…”

Section: Introductionmentioning

confidence: 99%

Reaction Model for Fluorination of Uranium Dioxide Using Improved Unreacted Shrinking Core Model for Expanding Spherical Particles

Homma

Uoi

Braun

et al. 2008

J. Nucl. Sci. Technol.

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A gas-solid reaction model is developed to represent the fluorination of uranium dioxide (UO 2 ), which consists of a two-step reaction: the formation of a solid intermediate of uranyl fluoride (UO 2 F 2 ) on the core of unreacted UO 2 and the consumption of UO 2 F 2 . The model is an extension of the unreacted shrinking core model with a shrinking spherical particle and takes into account particle expansion resulting from the density difference between UO 2 and UO 2 F 2 . This model successfully represents the initial expansion of the particle by the formation of the low-density UO 2 F 2 intermediate. The accuracy of this model is higher than that of the original model, which does not allow particle expansion.

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Uranium

Cited by 39 publications

References 365 publications

Intrinsic hydration of monopositive uranyl hydroxide, nitrate, and acetate cations

Intrinsic hydration of monopositive uranyl hydroxide, nitrate, and acetate cations

Uranium co-precipitation with iron oxide minerals

Reaction Model for Fluorination of Uranium Dioxide Using Improved Unreacted Shrinking Core Model for Expanding Spherical Particles

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