Uranyl Arsenate Research Articles

Spectroscopic properties of uranium(VI) minerals studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

We studied the fluorescence properties of 120 uranium minerals in order to provide a data base of potential secondary solids that may form in the flooding process of defunct uranium mines. This data base may provide a link of the fluorescence spectra of the minerals to solution spectra containing so far unknown tertiary and quaternary solution complexes in environmental uranium(VI)-containing waters. In our initial effort to establish the data base, we are focusing on phosphate- and arsenate-containing uranium(VI) minerals. Except for chernikovite [(H3O)2(UO2)2(PO4)2 · 6H2O], these minerals show intensive fluorescence emissions bands with a bathochromic shift of up to 18 nm compared to the fluorescence of the uranyl ion in solution. We found hypsochromic shifts of the fluorescence emission for the uranyl phosphates and bathochromic shifts for the uranyl arsenates. The band spacing of the fluorescence emissions from the 20502 cm-1 level are comparable to the vibrational frequency available from IR-data. Using these data we estimated the axial U-O bond lengths. The decrease of the vibration frequency from 813 cm-1 (saleiite, [Mg(UO2)2(PO4)2 · 10(H2O)]) to 794 cm-1 (uranocircite, [Ba(UO2)2(PO4)2 · 12(H2O)]) is related to a slight increase of the U-O bond length by 3 pm. In both series, the fluorescence lifetime decreases with decreasing crystal water. This is different compared to solution spectra where the lifetime increases as water is displaced from the inner coordination shell. Comparing the fluorescence data of the mineral troegerite [H2(UO2)2(AsO4)2 · 8(H2O)] with the fluorescence spectra of uranyl arsenate solutions, we identified one of the three uranyl arsenate complexes in solution as HUO2(AsO4)(aq.).

Crystallographic Aspects of Solid Electrolytes

Abstract The electrical conductivities of many solid electrolytes are discussed in relation to their crystal structures: especially the alumina and fluorite structures, and the hydrogen uranyl arsenate (HUAs) and phosphate (HUP) structures. Electrolytes which operate at low (-40°C to 100°C), medium (100°C to 400°C) and high (400°C to 1200°C) temperatures are reviewed. Conductivity is by ions of copper, fluorine, lithium, oxygen and silver, as well as by protons. Applications of these electrolytes include solid state batteries for powering small and large devices (such as cardiac pacemakers and electric vehicles,), coulometers, electrochromic displays and gas sensors.

ChemInform Abstract: Structural and Optical Properties of Hydrated Lanthanoid Uranyl Arsenates.

AbstractCompounds of approximate composition Ln(UO2AsO4)3·xH2O (Ln: La, Ce‐Lu; x = 13‐16) are prepared by intercalation of Ln3+ into either HUO2AsO4·4 H2O or n‐butylammonium uranyl arsenate.

Structural and optical properties of hydrated lanthanon uranyl arsenates

An investigation of the structural and optical properties of the lamellar lanthanon derivatives of hydrogen uranyl arsenate (HUO 2AsO 4 · 4H 2O (HUAs)) is reported. The hydrated lanthanon uranyl arsenate compounds have the approximate composition Ln( UO 2 AsO 4) 3 · xH 2 O (LnUAs) ( Ln ≡ La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, x ≈ 13–16) and are prepared by intercalation of the lanthanon ions into either HUAs or n-butylammonium uranyl arsenate. Upon intercalation of the tripositive guest ions, the lattice symmetry and crystallinity are reduced, as observed by X-ray powder diffraction. The LnUAs samples exhibit emission characteristic of the UO 2 2+ moiety. Those samples having Ln ≡ Ce, Pr, Nd, Sm, Ho and Er are very weakly emissive, whereas the remaining solids (with Ln ≡ La, Eu, Gd, Tb, Dy, Tm, Yb and Lu) emit strongly at 298 K when excited with near-UV light. The emissive LnUAs samples have photoluminescence (PL) decay curves that are exponential and yield lifetimes for the strongly emissive samples in the approximate range of 8–100 μs with quantum yields of about 0.02–0.09. From these data, unimolecular radiative and non-radiative rate constants have been calculated for uranyl PL, yielding values of about (5–30) × 10 2 s −1 and about (1–10) × 10 4 s −1 respectively. For EuUAs there is extensive host-to-guest energy transfer, resulting in long-lived emission from the europium guest species. Electronic absorption and PL properties of the LnUAs samples are similar to those of their Ln( UO 2 PO 4) 3 · xH 2 O counterparts

Two families of lamellar, luminescent solid solutions: The intercalative conversion of hydrogen uranyl phosphate arsenates to uranyl phosphate arsenates

Hydrogen uranyl phosphate (HUP) and hydrogen uranyl arsenate (HUAs) form solid solutions of composition HUO 2(PO 4) 1− x (AsO 4) x ·4H 2O (HUPAs;0⩽ x⩽1), representing a family of lamellar, luminescent solids that can serve as hosts for intercalation chemistry; structural and spectroscopic data are all consistent with the formation of single-phase solid solutions from aqueous co-precipitation reactions of UO 2+ 2 with mixtures of PO 3- 4 and AsO 3- 4. Hydrated, lamellar uranyl phosphate arsenates, (UO 2) 3(PO 4) 2−2 x (AsO 4) 2 x (UPAs;0⩽ x⩽1), can be prepared form the corresponding HUPAs solids by either of two routes: (1) intercalative exchange of UO 2+ 2 ions into the HUPAs solids; and (2) thermal decomposition of HUPAs solids in aqueous slurries. Power X-ray diffraction of the UPAs solids reveals them to be single phases, whose lattice constants increase monotonically with x; the interlamellar spacings increase by about 2.5 Å (to ≈ 11 Å) compared to the HUPAs starting material. Samples of UPAs slowly revert to their corresponding HUPAs precursors upon cooling to room temperature in appropriate aqueous media. Unlike the highly emissive HUPAs solids (radiative quantum yields ø r>0.2; lifetimes τ> 100 μs), the UPAs solids are only weakly emissive at 295 K (ø r≈0.003; τ<10 microm). Since both families of solids have similar radiative rate constants for unimolecular decay (≈1×10 3 s −1), the difference in photophysical properties arises from an ≈ 100-fold increasein the nonradiative rate constant caused by the introduction of the interlamellar UO 2+ 2 ions. Rates for the intercalation and thermal conversion reactions have been measured for HUP and HUAs as a function of temperature (0−27°C for intercalation; 40–80°C for thermal decomposition), using the structural and optical changes accompanying the conversions.

ChemInform Abstract: Solid Solutions of Hydrogen Uranyl Phosphate and Hydrogen Uranyl Arsenate. A Family of Luminescent, Lamellar Hosts.

AbstractIt is shown that HUO2PO4·4 H2O and HUO2AsO4·4 H2O are miscible, yielding solid solutions of type (IV).

Thermochemical properties of uranyl arsenates: II. Derivations of standard entropies

Standard entropies of uranyl arsenates have been derived by combining their standard enthalpies of formation and high-temperature data. As a result the high-temperature molar thermodynamic values of these compounds have been calculated.

Solid solutions of hydrogen uranyl phosphate and hydrogen uranyl arsenate. A family of luminescent, lamellar hosts

Hydrogen uranyl phosphate, HUO/sub 2/PO/sub 4/ /times/ 4H/sub 2/O (HUP), and hydrogen uranyl arsenate, HUO/sub 2/AsO/sub 4/ /times/ 4H/sub 2/O (HUAs), form solid solutions of composition HUO/sub 2/(PO/sub 4/)/sub 1-x/(AsO/sub 4/)x (HUPAs), representing a family of lamellar, luminescent solids that can serve as hosts for intercalation chemistry. The solids are prepared by aqueous precipitation reactions from uranyl nitrate and mixtures of phosphoric and arsenic acids; thermogravimetric analysis indicates that the phases are tetrahydrates, like HUP and HUAs. Powder x-ray diffraction data reveal the HUPAs solids to be single phases whose lattice constants increase with X, in rough accord with Vegard's law Spectral shifts observed for the HUPAs samples. Emission from the solids is efficient (quantum yields of /approximately/ 0.2) and long-lived (lifetimes of /approximately/ 150 /mu/s), although the measured values are uniformly smaller than those of HUP and HUAs; unimolecular radiative and nonradiative rate constants for excited-state decay of /approximately/ 1500 and 5000 s/sup /minus/1/, respectively, have been calculated for the compounds. 18 refs., 5 figs., 2 tabs.

Thermochemical properties of uranyl arsenates. I. Arsenic oxide dissociation pressures

A transportation method has been used to measure the arsenic oxide pressure of uranyl arsenates at various oxygen pressures. It is concluded that at 1 atm oxygen the vaporization reactions lead, stepwise, from meta, pyro, and orthoarsenate to U 3O 8, whilst gaseous As 4O 10 is evolved. The free energy functions of the evaporation reactions have been calculated from the pressure functions.

Hydrogen uranyl arsenate hydrate single crystals: H 2(UO 2) 2(AsO 4) 2·8H 2O; gel growth and characterization

Single crystals of hydrogen uranyl arsenate hydrate (HUAsH) were grown in tetramethoxysilane gels at different temperatures, below and above the paraelastic-ferroelastic transition temperature, T 0. The crystals were characterized by X-ray diffraction, chemical etching, scanning electron microscopy and optical microscopy. The habit of the gel grown crystals allowed the three-dimensional features of the domain structure to be studied for the first time. A correlation was made between crystal perfection, domain structure and growth history.

ChemInform Abstract: STANDARD ENTHALPIES OF FORMATION OF URANIUM COMPOUNDS. IX. ANHYDROUS URANYL ARSENATES

Chemischer InformationsdienstVolume 13, Issue 51 Physical Inorganic Chemistry ChemInform Abstract: STANDARD ENTHALPIES OF FORMATION OF URANIUM COMPOUNDS. IX. ANHYDROUS URANYL ARSENATES E. H. P. CORDFUNKE, E. H. P. CORDFUNKESearch for more papers by this authorW. OUWELTJES, W. OUWELTJESSearch for more papers by this authorH. BARTEN, H. BARTENSearch for more papers by this author E. H. P. CORDFUNKE, E. H. P. CORDFUNKESearch for more papers by this authorW. OUWELTJES, W. OUWELTJESSearch for more papers by this authorH. BARTEN, H. BARTENSearch for more papers by this author First published: December 21, 1982 https://doi.org/10.1002/chin.198251013AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue51December 21, 1982 RelatedInformation

Standard enthalpies of formation of uranium compounds IX. Anhydrous uranyl arsenates

The enthalpies of solution of (UO 2) 3(AsO 4) 2, (UO 2) 2As 2O 7, and UO 2(AsO 3) 2 in 1.505 mol·dm −3 H 2SO 4 solution have been measured calorimetrically. In combination with the enthalpies of solution of γ-UO 3(s) and As 2O 5 · 5 3 H 2O(s) in this solvent. the standard enthalpies of formation of the uranyl arsenates have been derived. The results are: ΔH f o(s. 298.15 K)/(kJ · mol −1): (UO 2) 3(AsO 4) 2, −(4689.4 ± 2.8); (UO 2) 2As 2O 7, −(3426.0 ± 2.1); UO 2(AsO 3) 2, −(2156.6 ± 1.3).

The structure of deuterated lithium uranyl arsenate tetrahydrate LiUO2AsO4.4D2O by powder neutron diffraction

The structure of deuterated lithium uranyl arsenate tetrahydrate LiUO₂AsO₄.4D₂O by powder neutron diffraction

The formation and stability of hydrated and anhydrous uranyl arsenates

Three hydrated uranyl arsenates, (UO 2) 3(AsO 4) 2 · 11 H 2O, UO 2HAsO 4 · 4 H 2O, and UO 2(H 2AsO 4) 2 · 1 H 2O, have been prepared. The dehydration of these compounds has been studied by thermal analysis. Three crystalline anhydrous uranyl arsenates, (UO 2) 3(AsO 4) 2, (UO 2(AsO 3) 2, have been found. These show melting phenomena and lose arsenic oxide vapour at high temperatures to result, finally, in U 3O 8 at 1500°C in air. The anhydrous compounds have been prepared under isothermal conditions and the strongest X-ray reflections are given. A tentative phase diagram in the composition range UO 3 to As 2O 5 has been constructed.

Studies of layered uranium(VI) compounds. IV. Proton conductivity in single-crystal hydrogen uranyl phosphate tetrahydrate (HUP) and in polycrystalline hydrogen uranyl arsenate tetrahydrate (HUAs)

Single-crystal measurements on hydrogen uranyl phosphate tetrahydrate, HUO 2PO 4·4H 2O (HUP), have confirmed that the high proton conductivity is a bulk characteristic. The conductivity values were in substantial agreement with those previously reported for polycrystalline disks. A conductivity of 0.6 ohm −1 m −1 at 290°K and an activation energy of 30 ± 1 kJ mole −1 were measured parallel to the structural layers of the crystal. The conductivity was at least 100 times lower when measured in the perpendicular direction. A reasonable attempt frequency ω 0 of approximately 10 15 Hz could be derived from the parallel conductivity on the assumption that the charge carrier concentration was equal to that of the H 3O + ions. This implies a low proton mobility, of the order of 10 −9 m 2 V −1 sec −1 at 290°K, in support of previous estimates. We have also shown that polycrystalline hydrogen uranyl arsenate tetrahydrate, HUO 2AsO 4·4H 2O (HUAs), has a high conductivity of 0.6 ohm −1 cm −1 at 310°K, with an activation energy of 31 ± 2 kJ mole −1. Below the respective dielectric ordering transition temperatures of HUP and HUAs of 274 and 301°K, the lower conductivity values show a marked frequency dependence, which may be due to dispersion effects caused by water reorientations.

Studies of layered uranium (VI) compounds. IV. Proton conductivity in single-crystal hydrogen uranyl phosphate tetrahydrate (HUP) and in polycrystalline hydrogen uranyl arsenate tetrahydrate (HUAs): Arthur T. Howe and Mark G. Shilton. Department of Inorganic and Structural Chemistry, University of Leeds, Leeds LS2 9JT, England

Studies of layered uranium (VI) compounds. IV. Proton conductivity in single-crystal hydrogen uranyl phosphate tetrahydrate (HUP) and in polycrystalline hydrogen uranyl arsenate tetrahydrate (HUAs): Arthur T. Howe and Mark G. Shilton. Department of Inorganic and Structural Chemistry, University of Leeds, Leeds LS2 9JT, England

Hydrogen-bond ordering in the proton conductors hydrogen uranyl phosphate and arsenate tetrahydrates

An H-bond ordering scheme is proposed for hydrogen uranyl arsenate HUO2AsO4·4H2O which explains the observed transition from high to low values of conductivity, the antiferroelectric ordering, and the twinning behaviour, and is consistent with recent X-ray and i.r. data; evidence implies that HUO2PO4·4H2O also orders in the same way.

N.M.R. study of hydrogen motion in hydrogen uranyl phosphate (HUP) and hydrogen uranyl arsenate (HUAs)

Pulsed 1H n.m.r. measurements have been made of relaxation times in hydrogen uranyl phosphate and arsenate, which are fast proton conductors. Both compounds were found to undergo a phase transition resulting in discontinuities in T 1 and T 2 and a DTA peak. This transition occurs around 274 K in HUP and around 302 K in HUAs. Above the transition the n.m.r. behaviour of the two compounds is very similar, with an activation energy for T 1 and T 2 of 20 ± 1 kJ mol −1. The T 1 values are almost equal to T 2 values, and this can best be explained by the rapid diffusion of hydrogen. Possible mechanisms for hydrogen self-diffusion and charge transport are discussed that can account for the higher activation energies reported for the conductivities compared to those for n.m.r. relaxation.

Determination of arsenic by the uranyl salt method. II. The radiometric determination of microgram amounts of arsenic by a filter-spot technique.

A development of the uranyl salt method for the gravimetric determination of arsenic is described. Gravimetric manipulations are conducted on a filter-paper base and the arsenic content of the ammonium uranyl arsenate precipitate is determined indirectly by measuring the alpha countrate of the associated uranium.The method has been demonstrated to be applicable in the range 1 to 8 µg of arsenic.

Application of the uranyl salt method to the determination of arsenic by the oxygen flask technique

A modified oxygen flask technique is described for determining As in organic compounds, the conventional Pt supports being replaced by Al spirals or steel gauzes, which resist attack by As during the vigorous combustion. A favorable gravimetric factor is ensured by the quantitative precipitation of the As as ammonium uranyl arsenate and subsequent ignition, under controlled conditions, to the black triuranium octaoxide, U/sub 3/O/sub 8/. Phosphate and vanadate form similar insoluble ammonium uranyl salts, and the method is not directly applicable to organic compounds containing these elements without prior separation. (auth)