Multinuclear NMR, Raman, EXAFS, and X-ray diffraction studies of uranyl carbonate complexes in near-neutral aqueous solution. X-ray structure of [C(NH2)3]6[(UO2)3(CO3)6].cntdot.6.5H2O

Allen, P. G.; Bucher, J. J.; Clark, David L.; Edelstein, Norman M.; Ekberg, Scott A.; Gohdes, Joel W.; Hudson, Eric A.; Kaltsoyannis, Nikolas; Lukens, Wayne W.; Neu, Mary P.; Palmer, Phillip D.; Reich, Tobias; Shuh, David K.; Tait, C. Drew; Zwick, Bill D.

doi:10.1021/ic00123a013

Cited by 195 publications

(174 citation statements)

References 32 publications

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“…A coincidence of these two vibrations with the 2 CO 3 2 bending vibration is expected. 48 49 The obtained U-O bond lengths, 1.777 and 1.785Å, respectively, are in good agreement with the values inferred by Burns and coworkers 50 -52 for hexagonal dipyramidal uranyl coordination polyhedra, close to uranyl tricarbonate minerals and their synthetic analogs, and 1.781(5)Å inferred from EXAFS spectrum for zellerite by Catalano and Brown. 15 The Raman band at 233 cm 1 is assigned to the 2 υ UO 2 2C bending vibration, while the bands at 363 cm 1 (Raman) and 565 and 594 cm 1 (infrared) may be attributed to the U-O ligand vibrations.…”

Section: Raman and Infrared Uranyl (Uo 2 ) 2+ Vibrationssupporting

confidence: 89%

Raman spectroscopic study of the uranyl carbonate mineral zellerite

Frost

Dickfos

Čejka

2008

J Raman Spectroscopy

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Raman and infrared spectra of the uranyl mineral zellerite, Ca[(UO 2 )(CO 3 ) 2 (H 2 O) 2 ]·3H 2 O, were measured and tentatively interpreted. U-O bond in uranyl and O-H· · ·O hydrogen bonds were calculated from the vibrational spectra. The presence of structurally nonequivalent water molecules in the crystal structure of zellerite was inferred. A proposed chemical formula of zellerite is supported. Raman bands at 3514, 3375 and 2945 cm −1 and broad infrared bands at 3513, 3396 and 3326 cm −1 are related to the n OH stretching vibrations of hydrogen-bonded water molecules. Observed wavenumbers of these vibrations prove that in fact hydrogen bonds participate in the crystal structure of zellerite. The presence of two bands at 1618 and 1681 cm −1 proves structurally distinct and nonequivalent water molecules in the crystal structure of zellerite.

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Section: Raman and Infrared Uranyl (Uo 2 ) 2+ Vibrationssupporting

confidence: 89%

Raman spectroscopic study of the uranyl carbonate mineral zellerite

Frost

Dickfos

Čejka

2008

J Raman Spectroscopy

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“…In aqueous solutions, a hydration number of 5 is reported for the (U02)2+ ion [40] although a coordination number of 6 is expected for carbonate or other bidentate ligands [23,37]. The coordination geometry observed for the uranyl ion in the clay samples examined here is consistent with that observed in the aqueous phase, and in other studies of uranyl-clay complexes.…”

Section: Powder X-ray Diffractionsupporting

confidence: 84%

“…Comparisons of the radial distribution functions of k2-and k3-weighted EXAFS do not show evidence of U-U backscattering, a fact which is more consistent with the 3,5 hydrolysis product. The reported structure of the 3,5 trimer E421 is similar to that of the tri-uranyl carbonate anion, [(~02)3(co3)6]6- [37]. Our EXAFS spectrum of the C18SiC13-Coated, hydrothermally treated system shows qualitative similarities to that of the carbonate compound.…”

Section: Powder X-ray Diffractionsupporting

confidence: 59%

Speciation of uranium in surface-modified, hydrothermally treated, (UO{sub 2}){sup 2+}-exchanged smectite clays

Giaquinta¹,

Soderholm²,

Yuchs³

et al. 1997

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I .--X-ray absorption spectroscopy (XAS) is used to determine the uranium speciation in exchanged and surface-modified clays. The XAS data from uranyl-loaded bentonite clay are compared with those obtained after the particle surfaces have been coated with alkylsilanes. These silane films, which render the surface of the clay hydrophobic, are added in order to minimize the ability of external water to exchange with the water in the clay interlayer, thereby decreasing the release rate of the exchangeduranium species. Mild hydrothermal conditions are used in an effort to mimic potential geologic conditions that may occur during long-term radioactive waste storage. The XAS spectra indicate that the uranyl monomer species remain unchanged in most samples, except in those samples that were both coated with an alkylsilane and hydrothermally treated. When the clay was coated with an organic film, formed by the acidic deposition of octadecyltrimethoxysilane, hydrothermal treatment results in the formation of aggregated uranium species in which the .. , 2 uranium is reduced from UvI to UIV. The implications of this reduction to efforts in environmental remediation are discussed.

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“…X-ray absorption fine structure spectroscopy (XAFSS) and X-ray photoelectron spectroscopy (XPS) have been used to provide information on the U oxidation state and the coordination environment of UO 2 2+ in solids (e.g., sediments) and at the solid-water interface (Table 1) [53,54,55]. Both in water and at the solid-water interface, the formation of multinuclear uranyl complexes may be detected as precursors to solid phase formation [56,57]. Fluorescent XAFSS is used for solids containing lower U concentrations, because of its higher sensitivity to U. Photothermal (photoacoustic) spectrometry (Table 1) has been used to effectively characterize the speciation of UO 2 2+ in solids, particularly amorphous phases [58].…”

Section: Sedimentmentioning

confidence: 99%

Uranium Speciation and Bioavailability in Aquatic Systems: An Overview

Markich

2002

The Scientific World JOURNAL

201

142

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The speciation of uranium (U) in relation to its bioavailability is reviewed for surface waters (fresh-and seawater) and their sediments. A summary of available analytical and modeling techniques for determining U speciation is also presented. U(VI) is the major form of U in oxic surface waters, while U(IV) is the major form in anoxic waters. The bioavailability of U (i.e., its ability to bind to or traverse the cell surface of an organism) is dependent on its speciation, or physicochemical form. U occurs in surface waters in a variety of physicochemical forms, including the free metal ion (U 4+ or UO 2 2+ ) and complexes with inorganic ligands (e.g., uranyl carbonate or uranyl phosphate), and humic substances (HS) (e.g., uranyl fulvate) in dissolved, colloidal, and/or particulate forms. Although the relationship between U speciation and bioavailability is complex, there is reasonable evidence to indicate that UO 2 2+ and UO 2 OH + are the major forms of U(VI) available to organisms, rather than U in strong complexes (e.g., uranyl fulvate) or adsorbed to colloidal and/or particulate matter. U(VI) complexes with inorganic ligands (e.g., carbonate or phosphate) and HS apparently reduce the bioavailability of U by reducing the activity of UO 2 2+ and UO 2 OH + . The majority of studies have used the results from thermodynamic speciation modeling to support these conclusions. Time-resolved laser-induced fluorescence spectroscopy is the only analytical technique able to directly determine specific U species, but is limited in use to freshwaters of low pH and ionic strength. Nearly all of the available information relating the speciation of U to its bioavailability has been derived using simple, chemically defined experimental freshwaters, rather than natural waters. No data are available for estuarine or seawater. Furthermore, there are no available data on the relationship between U speciation and bioavailability in sediments. An understanding of this relationship has been hindered due to the lack of direct quantitative U speciation techniques for particulate phases. More robust analytical techniques for determining the speciation of U in natural surface waters are needed before the relationship between U speciation and bioavailability can be clarified.

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Multinuclear NMR, Raman, EXAFS, and X-ray diffraction studies of uranyl carbonate complexes in near-neutral aqueous solution. X-ray structure of [C(NH2)3]6[(UO2)3(CO3)6].cntdot.6.5H2O

Cited by 195 publications

References 32 publications

Raman spectroscopic study of the uranyl carbonate mineral zellerite

Raman spectroscopic study of the uranyl carbonate mineral zellerite

Speciation of uranium in surface-modified, hydrothermally treated, (UO{sub 2}){sup 2+}-exchanged smectite clays

Uranium Speciation and Bioavailability in Aquatic Systems: An Overview

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