Uranyl Oxyhydroxide Research Articles

Correlative morphological, elemental and chemical phase analyses at the micrometric scale of powdered materials: Application to nuclear forensics

To characterize a mixture of powders using several analytical techniques, it is necessary that successive analyses be carried out on well-identified and localized particles, so that each characterization corresponds to a given powder. In this publication, powdered nuclear materials are characterized at the morphological and elemental levels with a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and at the chemical level with a micro-Raman spectrometer (MRS). However, to avoid a time-consuming and insufficiently accurate microparticle relocation process between SEM/EDS and MRS, micro-Raman analyses are carried out inside the SEM using a coupling device. In this way, all three pieces of information are obtained for exactly the same micrometric spot, without moving the sample or relocating the microparticles analyzed. The information can therefore be combined to characterize each component of the mixture. In this article, we describe in detail the methodology we have developed and optimized for morphological, elemental and chemical analysis of microparticles using a combined SEM/EDS and SRM. This methodology has been applied to powdered nuclear materials in two international nuclear forensics exercises. In the first exercise, named CMX-6, the combined use of the two instruments identified the presence of PuO2 microparticles and several uranium compounds (UO2, U3O8, UO2F2) in both materials. In the second exercise, called CMX-7, the methodology developed enabled us to distinguish two chemical phases of uranium, a uranyl oxy-hydroxide and a uranyl nitrate, each characterized by specific morphologies and the detection or non-detection of a minor elemental constituent (calcium).

Synthetic metaschoepite mineral film on silicon: An analog surface for weathered spent nuclear fuel

Incorporation of fission products in spent nuclear fuel is of interest in the frame of safe storage of high-level nuclear waste in a deep geological repository. Uranyl oxyhydroxide films were grown on silicon wafer to represent the corrosion product formed on the surfaces of the fuel. Films were obtained by hydrolysis of uranyl ions (9 mM) in mild conditions (≤60 °C) using either Mg(OH)2, raw brucite, La(OH)3, or NH4OH to control the solution pH to ≈ 5.0. To identify the mineral phases we used the grazing-incidence X-ray technique. Atomic force microscopy data indicated that the surfaces of metaschoepite films prepared using either Mg(OH)2 or brucite at 50 °C for 3 h were self-affine fractal (Df = 2.5). The concentration (wt.%) of reactant ions detected in a metaschoepite film after reaction at 70 °C for three days as determined by X-ray fluorescence was: La (8.90) > Nd (5.6) > Ce (3.2) > Eu (2.5) > Pb (0.7) > Sr (0.14). Metaschoepite and sodium uranate hydrate were identified in a film formed in Cl-SO4-Na type groundwater from the Beishan area (China), the preselected area of a radioactive waste disposal repository.

Characterization of vandenbrandeite: A potential alteration product of spent nuclear fuel

AbstractThe use of copper canisters in the Swedish KBS-3 concept for spent nuclear fuel disposal could result in the formation of copper-bearing uranyl phases should a canister suffer from defects or if the containment were to fail before reducing conditions are established in the repository. Most uranyl species would be expected to display higher solubility than the original uranium(IV) dioxide fuel, leading to enhanced release, though this would depend on the phase and prevailing groundwater conditions. Secondary alteration products may also be poorly crystalline or even amorphous, making characterization difficult during the pre-closure period owing to the high radiation field close to the canister. Vandenbrandeite, [CuUO2(OH)4], is a rare mineral in nature but known to form by alteration of primary uraninite through interaction with oxidizing groundwater containing dissolved copper. Consequently, an attempt has been made to characterize two vandenbrandeite specimens of varying crystallinity by luminescence and multiple-laser Raman spectroscopy; techniques amenable to remote, robotic deployment and which have proved useful in discriminating other uranyl oxy-hydroxides, silicates, and phosphates. The first reported luminescence emission and excitation spectra for vandenbrandeite revealed near-negligible luminescence, with a slightly enhanced signal for the specimen displaying poorer crystallinity. This observation agrees well with density functional theory calculations. The simulated projected density of state and band structure show an unlikely transition from the U f-orbitals to Cu d-orbitals, or O states, would be required for luminescence to be detectable; this probably improves for poorly crystalline specimens as the spatial overlap between the orbitals increases. Furthermore, negligible differences in the number of peaks and peak positions were detected in the laser wavelength-dependent Raman spectra although again, variation in background noise and peak shape was observed based on the degree of crystallinity. Good agreement was obtained between experimental and simulated Raman spectra, particularly with the environmentally sensitive axial uranyl stretching modes, validating the crystal system derived in this study. The findings of this study suggest luminescence spectroscopy, when combined with Raman spectroscopy, may be able to both identify vandenbrandeite and distinguish between crystalline and amorphous forms based on their relative luminescence intensity.

From EXAFS of reference compounds to U(VI) speciation in contaminated environments.

Understanding the speciation of technogenic uranium in natural systems is crucial for estimating U migration and bioavailability and for developing remediation strategies for contaminated territories. Reference EXAFS data of model laboratory-prepared uranium compounds (`standards') are necessary to analyze U-contaminated samples from nuclear legacy sites. To minimize errors associated with measurements on different synchrotrons, it is important not only to compare data obtained on environmentally contaminated samples with the literature but also with `standards' collected at the same beamline. Before recording the EXAFS spectra, all reference compounds were thoroughly characterized by Raman spectroscopy and powder X-ray diffraction. The U(VI) local molecular environments in the reference compounds, i.e. uranyl oxyhydroxides, phosphates, carbonates and uranates, were examined using XAFS. Based on the EXAFS fitting results obtained, including the nature of the bonding, interatomic distances and coordination numbers, parameters that are typical for a particular U compound were differentiated. Using data for `standards', U speciation in the sample of radioactively contaminated soil was determined to be a mixture of U oxyhydroxide and carbonate phases.

Spectroscopic evaluation of UVI-cement mineral interactions: ettringite and hydrotalcite.

Portland cement based grouts used for radioactive waste immobilization contain high replacement levels of supplementary cementitious materials, including blast-furnace slag and fly ash. The minerals formed upon hydration of these cements may have capacity for binding actinide elements present in radioactive waste. In this work, the minerals ettringite (Ca6Al2(SO4)3(OH)12·26H2O) and hydrotalcite (Mg6Al2(OH)16CO3·4H2O) were selected to investigate the importance of minor cement hydrate phases in sequestering and immobilizing UVI from radioactive waste streams. U LIII-edge X-ray absorption spectroscopy (XAS) was used to probe the UVI coordination environment in contact with these minerals. For the first time, solid-state 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was applied to probe the Al coordination environment in these UVI-contacted minerals and make inferences on the UVI coordination, in conjunction with the X-ray spectroscopy analyses. The U LIII-edge XAS analysis of the UVI-contacted ettringite phases found them to be similar (>∼70%) to the uranyl oxyhydroxides present in a mixed becquerelite/metaschoepite mineral. Fitting of the EXAFS region, in combination with 27Al NMR analysis, indicated that a disordered Ca- or Al-bearing UVI secondary phase also formed. For the UVI-contacted hydrotalcite phases, the XAS and 27Al NMR data were interpreted as being similar to uranyl carbonate, that was likely Mg-containing.

Insights into sorption speciation of uranium on phlogopite: Evidence from TRLFS and DFT calculation

Knowledge of the sorption speciation of uranium at mineral/water interface is essential to construct reliable retention and migration models. In this work, the sorption speciation of U(VI) at the phlogopite/water interface was studied at trace concentrations by combining batch sorption, time-resolved luminescence spectroscopy, and theoretical calculation. Batch experiments showed that the sorption of U(VI) on phlogopite was strongly dependent on pH but weakly affected by ionic strength, implying that the inner-sphere surface complexation was mainly responsible for U(VI) sorption on phlogopite. The diverse luminescence spectral characteristics indicated the formation of multiple inner-sphere surface species at the phlogopite/water interface, whose abundances varied as a function of pH. A portion of U(VI) precipitated as uranyl oxyhydroxides such as metaschoepite and becquerelite at high pH. Density functional theory calculation revealed that the bidentate complex at the edge of phlogopite (≡AlO-MgO-UO2(H2O)3) was the most favorable sorption configuration for U(VI) at acidic condition. The increasing temperature enhanced the sorption of U(VI) on phlogopite without altering the sorption species, and such enhancement in U(VI) sorption was withdrawn once the temperature decreased. These findings are essential for understanding the immobilization mechanism of U(VI) in mica-rich granitic terrains at a molecular scale and building a reliable retention model.

The use of Raman and TRLF spectroscopy for differentiating early stage alteration products of spent nuclear fuel

Non-invasive techniques capable of distinguishing the alteration products of spent nuclear fuel during prolonged storage would be of great benefit when assessing the potential mobility of uranium from the fuel matrix. Two potential alteration products, becquerelite (Ca(UO2)6O4(OH)6·8(H2O)) and vandendriesscheite (Pb1.5(UO2)10O6(OH)11·11(H2O)), were characterised by multiple laser-wavelength Raman and time-resolved laser fluorescence spectroscopy (TRLFS). Chemical composition was confirmed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Well-defined Raman features were obtained, particularly with a 785 nm laser, allowing subtle differences between the two minerals to be observed. Differences were also found in the Raman spectra using lasers at 457, 532 and 633 nm, with the degree of luminescence depending on the metal cation present. Chemical quenching of luminescence in Raman data correlated with luminescence excitation and emission spectra results. Five and seven luminescence emission peaks were resolved for becquerelite and vandendriesscheite, respectively. The first reported luminescence excitation spectra were collected for each mineral but not all of the spectral ranges could be resolved into individual peaks. A luminescence decay lifetime of 5.5 ± 0.9 μs was obtained for vandendriesscheite. This study demonstrates that Raman spectroscopy and TRLFS are potentially valuable techniques for characterising uranyl oxy-hydroxides and could be used in conjunction with other methods, such as laser induced breakdown spectroscopy (LIBS), as part of a remote analysis package in nuclear waste management.

Periodic density functional theory study of the Raman spectrum of the hydrated uranyl oxyhydroxide mineral becquerelite

Raman spectroscopy is one of the main analytic techniques used to identify uranyl-containing minerals. However, the assignment of the Raman spectra of these minerals is usually performed by using empirical arguments leading to unreliable assignments. In this paper, the Raman spectrum of the hydrated uranyl oxyhydroxide mineral becquerelite, $${\text{Ca}}\left( {{\text{UO}}_{2} } \right)_{6} {\text{O}}_{4} \left( {\text{OH}} \right)_{6} \cdot 8{\text{H}}_{2} {\text{O}}$$ , was studied by means of rigorous theoretical solid-state calculations. The computations were carried out using periodic density functional theory with plane waves and pseudopotentials. The theoretical determination of this Raman spectrum was possible due to the previous development of a high-quality norm-conserving relativistic pseudopotential specific for the uranium atom and the recent optimization of the full crystal structure of this mineral, including the position of all hydrogen atoms in the corresponding unit cell. These two pieces of knowledge were formerly used in order to study the structural, mechanical, and thermodynamic properties of this mineral, but due to the very large size of the unit cell, the determination of the vibrational spectra was not possible. The corresponding results for the Raman spectrum, resulting from an intensive computational work, are reported here. The calculated Raman spectrum was compared with the experimental spectrum, and the results were found to be in very good agreement. Therefore, a normal mode analysis of the theoretical spectra was performed to assign the main bands of the Raman spectrum. This assignment improved significantly the current empirical assignment of the bands of the Raman spectrum of becquerelite mineral.

Three Different Modes of Association between Metal Cations in Heterometallic Uranyl–CoIII and Uranyl–MnII Species

Three heterometallic complexes including uranyl and either CoIII or MnII cations were crystallized under hydrothermal conditions. Complexes [Co(bipy)3]2[UO2(NO3)4]2[(UO2)2(NO3)4(OH)2] (1) and [UO2(NO3)2Co(bipy)2(OH)2]·NO3·H2O (2) (bipy = 2,2′‐bipyridine) were obtained from the same solution. UO22+ and CoIII are part of separate anions and cations, respectively, in complex 1, the uranyl ion being present in both a mononuclear dianion with two chelating and two monodentate nitrates in cis positions, and in a dinuclear, bis‐hydroxo‐bridged dianion. In contrast, both metal cations are part of a monocationic heterometallic bis‐hydroxo‐bridged complex in 2, UO22+ retaining two nitrate and CoIII two bipy ligands. This is the third example only of a hydroxo‐bridged heterometallic uranyl complex, and the first to involve CoIII. The complex [(UO2)6Mn(O)4(OH)6(H2O)4]·5H2O (3), synthesized in the absence of any added ligand, crystallizes as a three‐dimensional framework in which anionic uranyl oxyhydroxide layers with the α‐U3O8‐type polyhedral arrangement are connected to one another by Mn(H2O)42+ cations axially bound to two uranyl oxo atoms. These very simple systems thus display a large range of possible intermetallic associations, that involving bis‐oxo‐bonding to uranyl enabling formation of a framework through pillaring of sheets.

Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

Uranyl oxyhydroxide minerals are important weathering products in uranium-contaminated surface and subsurface environments that regulate dissolved uranium (U) concentrations. However, dissolution rates for this class of minerals and associated dissolution mechanisms have not been previously reported for circumneutral pH conditions, particularly for the case of flow through porous media. In this work, the dissolution rates of K- and Na-compreignacite (K2(UO2)6O4(OH)6·8H2O and Na2(UO2)6O4(OH)6·8H2O, respectively) were measured using flow-through columns reacted with two simulated background porewater (BPW) solutions of low and high dissolved carbonate concentration (ca. 0.2 and 2.8mmolL−1). Column materials were characterized before and after reaction with electron microscopy, bulk chemistry, and EXAFS to identify structural and chemical changes during dissolution and to obtain insight into molecular-scale processes. The reactive transport code CrunchFlow was used to calculate overall dissolution rates while accounting for fluid transport and changes in mineral volume and reactive surface area, and results were compared to steady-state dissolution rate calculations. In low carbonate BPW systems, interlayer K and Na were initially leached from both minerals, and in Na-compreignacite, K and minor divalent cations from the input solution were incorporated into the mineral structure. Results of characterization analyses suggested that after reaction both K- and Na-compreignacite resembled a disordered K-compreignacite with altered surfaces. A 10-fold increase in dissolved carbonate concentration and corresponding increase in pH (from 6.65 to 8.40) resulted in a net removal of 58–87% of total U mass from the columns, compared to <1% net loss in low carbonate BPW systems. Steady-state release of dissolved U was not observed with high carbonate solutions and post-reaction characterizations indicated a lack of development of leached or altered surfaces. Dissolution rates (normalized to specific surface area) were 2.5–3 orders-of-magnitude faster in high versus low carbonate BPW systems, with Na-compreignacite dissolving more rapidly than K-compreignacite under both BPW conditions, possibly due to greater ion exchange (1.57·10−10 vs. 1.28·10−13molm−2s−1 [logR=−9.81 and −12.89] and 5.79·10−10 vs. 3.71·10−13molm−2s−1 [logR=−9.24 and −12.43] for K- and Na-compreignacite, respectively). Experimental and spectroscopic results suggest that the dissolution rate is controlled by bond breaking of a uranyl group and detachment from polyhedral layers of the mineral structure. With higher dissolved carbonate concentrations, this rate-determining step is accelerated by the formation of Ca-uranyl carbonate complexes (dominant species under these conditions), which resulted in an increase of the dissolution rates. Optimization of both dissolution rate and mineral volume fraction in the reactive transport model to account for U mass removal during dissolution more accurately reproduced effluent data in high carbonate systems, and resulted in faster overall rates compared with a steady-state dissolution assumption. This study highlights the importance of coupling reaction and transport processes during the quantification of mineral dissolution rates to accurately predict the fate of contaminants such as U in porous geomedia.

Effects of calcium and phosphate on uranium(IV) oxidation: Comparison between nanoparticulate uraninite and amorphous UIV–phosphate

The mobility of uranium in subsurface environments depends strongly on its redox state, with UIV phases being significantly less soluble than UVI minerals. This study compares the oxidation kinetics and mechanisms of two potential products of UVI reduction in natural systems, a nanoparticulate UO2 phase and an amorphous UIV–Ca–PO4 analog to ningyoite (CaUIV(PO4)2·1–2H2O). The valence of U was tracked by X-ray absorption near-edge spectroscopy (XANES), showing similar oxidation rate constants for UIVO2 and UIV–phosphate in solutions equilibrated with atmospheric O2 and CO2 at pH 7.0 (kobs,UO2=0.17±0.075h−1 vs. kobs,UIVPO4=0.30±0.25h−1). Addition of up to 400μM Ca and PO4 decreased the oxidation rate constant by an order of magnitude for both UO2 and UIV–phosphate. The intermediates and products of oxidation were tracked by electron microscopy, powder X-ray diffraction (pXRD), and extended X-ray absorption fine-structure spectroscopy (EXAFS). In the absence of Ca or PO4, the product of UO2 oxidation is Na–uranyl oxyhydroxide (under environmentally relevant concentrations of sodium, 15mM NaClO4 and low carbonate concentration), resulting in low concentrations of dissolved UVI (<2.5×10−7M). Oxidation of UIV–phosphate produced a Na-autunite phase (Na2(UO2)PO4·xH2O), resulting in similarly low dissolved U concentrations (<7.3×10−8M). When Ca and PO4 are present in the solution, the EXAFS data and the solubility of the UVI phase resulting from oxidation of UO2 and UIV–phosphate are consistent with the precipitation of Na-autunite. Bicarbonate extractions and Ca K-edge X-ray absorption spectroscopy of oxidized solids indicate the formation of a Ca–UVI–PO4 layer on the UO2 surface and suggest a passivation layer mechanism for the decreased rate of UO2 oxidation in the presence of Ca and PO4. Interestingly, the extractions were unable to remove all of the oxidized U from partially oxidized UO2 solids, suggesting that oxidized U is distributed between the interior of the UO2 nanoparticles and the labile surface layer. Accounting for the entire pool of oxidized U by XANES is the likely reason for the higher UO2 oxidation rate constants determined here relative to prior studies. Our results suggest that the natural presence or addition of Ca and PO4 in groundwater could slow the rates of UIV oxidation, but that the rates are still fast enough to cause complete oxidation of UIV within days under fully oxygenated conditions.

U(VI) behaviour in hyperalkaline calcite systems

The behaviour of U(VI) in hyperalkaline fluid/calcite systems was studied over a range of U(VI) concentrations (5.27×10−5μM to 42.0μM) and in two high pH systems, young and old synthetic cement leachate in batch sorption experiments. These systems were selected to be representative of young- (pH 13.3) and old-stage (pH 10.5) leachate evolution within a cementitious geological disposal facility. Batch sorption experiments, modelling, extended X-ray absorption fine structure spectroscopy, electron microscopy, small angle X-ray scattering and luminescence spectroscopy were used to define the speciation of U(VI) across the systems of study. At the lowest concentrations (5.27×10−5μM 232U(VI)) significant U removal was observed for both old and young cement leachates, and this was successfully modelled using a first order kinetic adsorption modelling approach. At higher concentrations (>4.20μM) in the young cement leachate, U(VI) showed no interaction with the calcite surface over an 18month period. Small angle X-ray scattering techniques indicated that at high U concentrations (42.0μM) and after 18months, the U(VI) was present in a colloidal form which had little interaction with the calcite surface and consisted of both primary and aggregated particles with a radius of 7.6±1.1 and 217±24Å, respectively. In the old cement leachate, luminescence spectroscopy identified two surface binding sites for U(VI) on calcite: in the system with 0.21μM U(VI), a liebigite-like Ca2UO2(CO3)3 surface complex was identified; at higher U(VI) concentrations (0.42μM), a second binding site of undetermined coordination was identified. At elevated U(VI) concentrations (>2.10μM) in old cement leachate, both geochemical data and luminescence spectroscopy suggested that surface mediated precipitation was controlling U(VI) behaviour. A focused ion beam mill was used to create a section across the U(VI) precipitate–calcite interface. Transmission electron microscope images of the section revealed that the calcite surface was coated with a nano crystalline, U containing phase. Selected area electron diffraction images of the U precipitate which was formed at a U(VI) concentration of 4.20μM were consistent with the formation of calcium uranate. XAS spectroscopy at higher concentrations (⩾21.0μM) suggested the formation of a second U(VI) phase, possibly a uranyl oxyhydroxide phase.These results indicated that in the young cement leachate, U(VI) did not react with the calcite surface unless U(VI) concentrations were very low (5.27×10−5μM). At higher concentrations, speciation calculations suggested that U(VI) was significantly oversaturated and experimental observations confirmed it existed in a colloidal form that interacted with the mineral surface only weakly. In the old cement leachate systems at low concentrations batch sorption and luminescence data suggested that U(VI) removal was being driven by a surface complexation mechanism. However, at higher concentrations, spectroscopic methods suggest a combination of both surface complexation and surface mediated precipitation was responsible for the observed removal. Overall, U(VI) behaviour in hyperalkaline calcite systems is distinct from that at circumneutral pH conditions: at high pH and anything but low U(VI) concentrations, a surface mediated precipitation mechanism occurs; this is in contrast to circumneutral pH conditions where U(VI) surface complexation reactions tend to dominate.

ChemInform Abstract: Mixed‐Valence Uranium(V,VI) and Uranyl Oxyhydroxides Synthesized under High‐Temperature, High‐Pressure Hydrothermal Conditions: Na5[U5O16(OH)2] and Na5[U5O17(OH)

AbstractThe mixed‐valence uranium(V,VI) oxyhydroxide Na5[U5O16(OH)2] is prepared via reduction of UO22+ under hydrothermal conditions using UO3, NaOH, Na2MoO4 (mineralizer), and Zn as reductant (autoclave, gold ampoule, 570 °C and 150 MPa, 2 d, 50% yield).

Mixed-Valence Uranium(V,VI) and Uranyl Oxyhydroxides Synthesized under High-Temperature, High-Pressure Hydrothermal Conditions: Na5[U5O16(OH)2] and Na5[U5O17(OH)

An unusaul mixed-valence uranium(V,VI) oxyhydroxide, Na5[U5O16(OH)2], was synthesized via reduction of UO2(2+) with zinc under hydrothermal conditions at 570 °C and 150 MPa. Its structure consists of extended sheets of edge-sharing U(VI) pentagonal bipyramids and U(V) square bipyramids. The overall anion topology is the same as that of the uranyl mineral sayrite, but the squares are populated by U(V)(OH)2(3+) ions. The valence state of uranium was confirmed by X-ray photoelectron spectroscopy. A hydrothermal reaction without zinc under the same reaction conditions yielded a uranyl oxyhydroxide, Na5[U5O17(OH)], with a new sheet structure. The sheet anion topology, which is closely related to that of the mixed-valence compound, contains chains of edge-sharing pentagons as well as dimers of corner-sharing squares.

Raman spectroscopic study of the uranyl titanate mineral brannerite (U,Ca,Y,Ce)2(Ti,Fe)2O6:effect of metamictisation

AbstractRaman spectra of the uranyl titanate mineral brannerite were analysed and related to the mineral structure. A comparison is made with the Raman spectra of uranyl oxyhydroxide hydrates. The observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, UOH bending vibrations, as well as H2O and (OH)− stretching, bending and libration modes. UO bond lengths in uranyls and OH···O bond lengths were calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of brannerite are in harmony with those of the uranyl oxyhydroxides. The mineral brannerite is metamict, as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader. Copyright © 2010 John Wiley &amp; Sons, Ltd.

The effect of metamictization on the Raman spectroscopy of the uranyl titanate mineral davidite (La,Ce)(Y,U,Fe2+)(Ti,Fe3+)20(O,OH)38

Raman spectra of the uranyl titanate mineral davidite-(La), (La,Ce)(Y,U,Fe2+)(Ti,Fe3+)20(O,OH)38, were analyzed and related to the mineral structure. Observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, U–OH bending vibrations, H2O and (OH)− stretching, bending and libration modes. U–O bond lengths in uranyls and O-H ··· O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of davidite-(La) are in harmony with those of the uranyl oxyhydroxides. The mineral davidite-(La) is metamict, as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader.

Raman spectroscopic study of the uranyl titanate mineral euxenite (Y,Ca,U,Ce,Th) (Nb,Ta,Ti)2O6

AbstractRaman spectra of the uranyl titanate mineral euxenite were analysed and related to the mineral structure. A comparison is made with the Raman spectra of uranyl oxyhydroxide hydrates. The observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, as well as lattice vibrations of rare‐earth ions. The Raman bands of euxenite are in harmony with those of the uranyl oxyhydroxides. The mineral euxenite is metamict as is evidenced by the intensity of the UO stretching and bending modes, which are of lower intensity than expected, and with bands that are significantly broader. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Raman spectroscopic study of the uranyl titanate mineral betafite (Ca,U)2(Ti,Nb)2O6(OH): effect of metamictization

Raman spectra of the uranyl titanate mineral betafite were obtained and related to the mineral structure. A comparison is made with the spectra of uranyl oxyhydroxide hydrates. Observed bands are attributed to the (UO2)2+ stretching and bending vibrations, U–OH bending vibrations and H2O and (OH)− stretching, bending and libration modes. U–O bond lengths in uranyls and O−H···O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of betafite are comparable with those of the uranyl oxyhydroxides. The mineral betafite is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and by bands that are significantly broader.

Vibrational spectroscopic study of hydrated uranyl oxide: Curite

Raman and infrared spectra of the uranyl oxyhydroxide hydrate: curite is reported. Observed bands are attributed to the (UO 2) 2+ stretching and bending vibrations, U–OH bending vibrations, H 2O and (OH) − stretching, bending and librational modes. U–O bond lengths in uranyls and O–H…O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. These bond lengths are close to the values inferred and/or predicted from the X-ray single crystal structure. The complex hydrogen-bonding network arrangement was proved in the structures of the curite minerals. This hydrogen bonding contributes to the stability of these uranyl minerals.

Raman spectroscopic study of the uranyl oxyhydroxide hydrates: becquerelite, billietite, curite, schoepite and vandendriesscheite

AbstractRaman and infrared spectra of five uranyl oxyhydroxide hydrates, becquerelite, billietite, curite, schoepite and vandendriesscheite, are reported. The observed bands are attributed to the (UO2)2+ stretching and bending vibrations, UOH bending vibrations and H2O and (OH)− stretching, bending and libration modes. The UO bond lengths in uranyls and the OH···O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. They are close to the values inferred and/or predicted from the X‐ray single‐crystal structure. The complex hydrogen‐bonding network arrangement was proved in the structures of all the minerals studied. This hydrogen bonding contributes to the stability of these uranyl minerals. Copyright © 2006 John Wiley &amp; Sons, Ltd. John Wiley &amp; Sons, Ltd.