Showing papers on "Uranyl published in 1982"

Specimen preparation for electron microscopy using low temperature embedding resins

Abstract: SUMMARY Studies using polar and non-polar methacrylate-based resins (Lowicryl® K4M and HM20) suitable for low temperature embedding are described. We present the first applications of the system to various membrane structures in glutaraldehyde-fixed, uranyl acetate-stained thin sections of bacteria, mitochondria and cell-cell contact regions.

X-ray dichroism and polarized anomalous scattering of the uranyl ion

Abstract: Dichroism is observed near the L1 and L3 edges of uranium in X-ray absorption spectra of single-crystal rubidium uranyl nitrate, Rb.UO2.3NO3, recorded with linearly polarized synchrotron radiation. The anomalous X-ray scattering terms f′ and f′′ calculated from these spectra are anisotropic functions of polarization direction at these wavelengths, adding new complexity to diffraction optics. These terms are measured independently in diffraction experiments with sodium uranyl acetate at five wavelengths near L3. The cubic symmetry permits the diffraction effects to be observed without the complications of macroscopic dichroism and birefringence. Both f′ and f′′ change with polarization direction by as much as 2 electrons atom-l. These values agree with those derived from the absorption experiments.

The Behaviour of Uranium-233 Oxide and Uranyl-233 Nitrate in Rats

Abstract: 233UO2 and 233UO2(NO3)2 in aqueous suspension have been administered to rats by pulmonary intubation. The 233U associated with the fraction of the 233UO2 less than 4 nm in diameter translocates from lungs to blood at the same rapid rate as 233U from 233UO2(NO3)2. Identical reactions with blood plasma and lung fluid were observed whether the 233U was administered as less than 4 nm 233UO2 particles or 233UO2(NO3)2. It is suggested that oxidation of UO2 to UO3 occurs followed by the formation of uranyl ion. In blood plasma, approximately 50 per cent of the 233U is bound to transferrin, 25 per cent to citrate and 25 per cent on bicarbonate.

Thermodynamic properties of selected uranium compounds and aqueous species at 298.15 K and 1 bar and at higher temperatures; preliminary models for the origin of coffinite deposits

Abstract: Thermodynamic values for 110 uranium-bearing phases and 28 aqueous uranium solution species (298.15 K and 1 bar) are tabulated based upon evaluated experimental data (largely from calorimetric experiments) and estimated values. Molar volume data are given for most of the solid phases. Thermodynamic values for 16 uranium-bearing phases are presented for higher temperatures in the form of and as a supplement to U.S. Geological Survey Bulletin 1452 (Robie et al., 1979). The internal consistency of the thermodynamic values reported herein is dependent upon the reliability of the experimental results for several uranium phases that have been used as secondary calorimetric reference phases. The data for the reference phases and for those phases evaluated with respect to the secondary reference phases are discussed. A preliminary model for coffinite formation has been proposed together with an estimate of the free energy of formation of coffinite. Free energy values are estimated for several other uranium-bearing silicate phases that have been reported as secondary uranium phases associated with uranium ore deposits and that could be expected to develop wherever uranium is leached by groundwaters. I: Evaluation of experimental and estimated thermodynamic data, and properties at 298.15 K and 1 bar (10 5 Pascals). Preliminary models for the origin of coffinite deposits. Introduction Several reviews of the thermodynamic properties of uranium bearing phases and aqueous species have been published recently (e.g., Wagman, et al., 1981; Lemire and Tremaine, 1980; Langmuir, 1978; and Cordfunke and O'Hare, 1978). These reviews draw upon the same experimental data and, in general, the same interpretation of the experimental data for those phases evaluated in two or more of these studies. Although there has been moderate experimental activity on phases bearing uranium in the last twenty years, many of the naturally occurring phases have not been studied. Where data are lacking it has been necessary to estimate thermodynamic properties and where the experimental data is sparse or poorly defined, it has been necessary to make simplifying assumptions in order to calculate thermodynamic values. This report contains a review of some of the experimental data and interpretations for uranium phases and aqueous species that may be of importance in evaluating the origin of uranium ore bodies or the evolution of such ore bodies, in developing programs for the solution mining of low grade uranium deposits or mine dumps, in the study of radioactive waste and in the containment of such waste, and finally, that may be of importance in reactions within breeder reactors. The thermodynamic data listed in Tables 1 and 2 represent, to the extent possible, an internally consistent data set that has been evaluated and developed by the stepwise or sequential method. The majority of data are tied to the enthalpy of formation of 1)303 as given by Huber and Holley (1969) or to secondary standards such as -U03, U02Cl2» UC14, and U02. Consequently, few cross links are available within the system that would allow the use of the simultaneous regression approach of Haas and Fisher (1976) to identify erroneous data. Where a reaction involving a reference phase is found to be in error, all thermodynamic data based upon that reaction must be corrected. In order to facilitate that process, a brief description of the reaction scheme for each phase is provided in this study along with a reference to the experimental study that contains a detailed description of the thermochemical cycle. Ancillary thermodynamic values required in the thermochemical cycles cited in this study are from Robie et al. (1979) unless otherwise stated. The atomic weights and physical constants are also taken from Robie et al. Triuranium octaoxide is the primary reference compound in this network. Selection of this material was predicated by its use as the reference phase for 7-1103 and U02Cl2» the two phases to which most other Table 1. Thermodynamic properties of selected uranium bearing phases at 298.15 K and 1 bar. Estimated values are enclosed in parentheses Uncertainties are listed below values Name ^ formula and (references) J/(mol-K) Molar volume 3 cm Enthalpy of formation kJ/mol Gibbs free energy of formation kJ/mol Oxides, hydroxides and multiple oxides Uraninite: U0 2 (133;133;133) Triuranium heptaoxide (alpha): U 3 0 ? (158;74;) Triuranium heptaoxide (beta): U 3 0 ? (158;74;49) Tetrauranium ennanoxide: U 4 0 9 (120;116;49) Triuranium octaoxide: U 3 0 g (157;45;23) Hydrated uranium dioxide: UO '2H 0 (crystals) (;;166) UO -2H 0 (amorphous) (;;166) Uranium peroxide dihydrate: UO -2H 0 (;152;30) Studite: U0 4 '4H 2 0 (;152;30) Uranyl trioxide (gamma): U0 3 (156;133;23) Uranyl trioxide (beta): U0 3 (156;45;34) Uranyl trioxide (alpha): U0 3 (156;45;25) Uranyl trioxide (delta): UO( ; ; 25 ) 77.03 0.24 247.65 0.75

Chemical Forms of Uranium in Artificial Seawater

Abstract: The chemical forms of uranium in an artificial seawater are determined by use of the ion-association model. The data on the stoichiometric association constants of the ion pairs are used in calculation to evaluate the distribution of the major ionic species. Also, the more accurate values of the thermodynamic stability constants are used for the uranyl complexes. The calculation indicates that a dominant species of uranium is UO2(CO3)4- 3in artificial seawater at 25°C.

Hydrolysis and carbonate complexation of dioxouranium(VI) in the neutral-pH range at 25.degree.C

Abstract: The study was performed in an attempt to clarify the nature of the uranyl species formed in the neutral pH range at relatively CO/sub 2/ partial pressures of 10/sup -35/ to 10/sup -25/ atm. The existence of a hydroxocarbonato species having a uranium/CO/sub 3/ mole ratio of 2.0 has been demonstrated by analytical, spectroscopic, and electrochemical methods. The stoichiometry of the reactions leading to its formation from either UO/sup 2 +/ or UO/sub 2/(CO/sub 3/)/sub 3//sup 4 -/ and the data analysis of the potentiometric titrations indicate that this species is apparently (UO/sub 2/)/sub 2//sup -/CO/sub 3/(OH)/sub 3//sup -/. Equilibrium constants derived from the fit of the data are in agreement with literature values. An integrated view of the carbonate complexation and hydrolysis of the uranyl ion as a function of pH and P/sub CO//sub 2/ has been obtained. 4 figures, 2 tables.

Kinetics of uranous ion and ferrous iron oxidation byThiobacillus ferrooxidans

Abstract: Kinetic constants for the oxidation of uranous and ferrous ions byThiobacillus ferrooxidans were estimated. The kinetics indicate a direct biological mechanism for uranium oxidation. The complex interrelations of ferric, uranyl and uranous ion inhibition are considered.

Electronic structure of uranium halides and oxyhalides in the solid state. An X-ray photoelectron spectral study of bonding ionicity

Abstract: Core and valence X-ray photoelectron spectra of 18 uranium halides (U/sup 3 +/ to U/sup 5 +/) and oxyhalides (U/sup 3 +/ to U/sup 6 +/) (fluorides, chlorides, and bromides) are described. The results are discussed, as a function of halogen nature and compounds stoichiometry, in terms of ionicity of the bonds, of U 5f participation in bonding, and effect of oxygen. Evidence is produced that UF/sub 3/ has an unexpectedly strong covalent character. The experimental study of uranium halides (F, Cl, Br) and oxyhalides has brought to light some important information about the nature of chemical bonding in these compounds: (a) The combined examination of valence photoelectron peaks (particularly U 5f), core levels, and U 4f shake-up satellites is a powerful tool in the determination of the ionicity of the solid. Only core level chemical shifts are not sufficient by themselves. (b) There is evidence for U 5f participation in chemical bonding; this contribution increases when the compound becomes more covalent. (c) Ionicity is largest for the higher halides (higher uranium oxidation state) and with the more electronegative halogens; and exception to this rule is UF/sub 3/, which is more covalent than UCl/sub 3/. (d) The oxygen in oxyhalidesmore » shows a growing tendency to form uranyl groups, as the uranium oxidation state goes up. These uranyl groups have covalent bonding and behave as a single species vs. the halogen.« less

Uranyl selective electrode based on organophosphorus compounds

Abstract: A comparative study on the potential functions of different membrane components showed that the combination of tri-n-butyl phosphate, tri-n-octylphosphine oxide, and sodium tetraphenylborate in the PVC matrix gave the best full Nernstian response (59 mV/decade) and it gave nearly the same potential behavior among uranyl chloride, nitrate, and sulfate bathing solutions. Due to the high affinity with uranyl ions, the membrane containing tri-n-octylphosphine oxide can be responsive to both cations and anions depending on the concentrations of the bathing solutions. Incorporation of sodium tetraphenylborate was found necessary for obtaining permselectivity of the cations. Monovalent cations were regarded as permeating species for the membrane. 3 figures, 3 tables.

Actinide structural studies. Part 3. The crystal and molecular structures of UO2SO4·H2SO4·5H2O and 2NpO2SO4·H2SO4·4H2O

Abstract: The crystal structures of the title compounds, (1) and (2) respectively, have been determined using X-ray diffraction methods. Complex (1) is monoclinic, space group C2/c, with pentagonal-bipyramidal co-ordination involving four bidentate sulphate ions and a water molecule around the uranyl(VI) ion. Complex (2) is orthorhombic, space group P21212, with pentagonal-bipyramidal co-ordination about the neptunium atom involving two quadridentate and three tridentate sulphate ions. In both (1) and (2) the sulphato-ligands are bridging between the MO22+ groups giving infinite polymeric networks. The metal–ligand oxygen distances in (1) and (2) fall in the range 2.36–2.46 A and the M–O(MO22+) distances are 1.776(9)A in (1) and 1.741(12), 1.742(12)A in (2). Crystal data: (1), a= 15.619(3), b= 8.242(2), c= 11.008(2)A, β= 113.71(1)°, Z= 4; (2), a= 9.474(2), b= 10.065(2), c= 8.409(2)A, and Z= 2. The structures of (1) and (2) have been refined to R values of 0.037 and 0.038 respectively, using 985 and 1 007 observed, diffractometer-measured intensities.

The crystal structure of meta-uranocircite II, Ba(UO 2 ) 2 (PO 4 ) 2 ·6H 2 O

Abstract: The crystal structure of meta-uranocircite II, Ba(UO2)2(PO4)2·6H2O, has been determined with a synthetic crystal using three-dimensional X-ray techniques.R=0.071 andR w =0.064 were obtained for 1743 observed reflections. Ba(UO2)2(PO4)2·6H2O is monoclinic, space groupP1121/a, a=9.789,b=9.822,c=16.868 A, γ=89.95° andZ=4. The structure consists of slightly corrugated UO2PO4 layers parallel (001). The layers are connected by Ba atoms and H2O molecules. Uranium exhibits a (2+4)-coordination with mean U-O bond lengths of 1.78 A for the uranyl oxygens and 2.28 A for the phosphate oxygens. The average P-O bond length is 1.52 A. Barium is coordinated by two uranyl oxygens. two phosphate oxygens and five water molecules. The Ba−O bond lengths vary from 2.74 to 3.11 A. Two of the six water molecules of the formula are not bonded to barium.

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

Abstract: The structure of LiUO2AsO4.4D2 ° has been determined in space group P4/n with a = 7.0969 (1), c = 9.1903 (2)A and Z = 2 from a powder neutron 0567-7408/82/041108-05501.00 diffraction study at 294 K. 258 reflections were refined to an R factor on intensities of 3.8%. The water molecules are arranged in a two-dimensional array alternating with UO~ ÷ and AsO~ions. The Li ÷ ions are tetrahedrally coordinated to the O atoms of the © 1982 International Union of Crystallography A. N. FITCH, B. E. F. FENDER AND A. F. WRIGHT 1109 water molecules and play an important role in binding the layers together. The structural relationship with related compounds is discussed.

Uranium from seawater

Abstract: A novel process for recovering uranium from seawater is proposed and some of the critical technical parameters are evaluated. The process, in summary, consists of two different options for contacting adsorbant pellets with seawater without pumping the seawater. It is expected that this will reduce the mass handling requirements, compared to pumped seawater systems, by a factor of approximately 10/sup 5/, which should also result in a large reduction in initial capital investment. Activated carbon, possibly in combination with a small amount of dissolved titanium hydroxide, is expected to be the preferred adsorbant material instead of the commonly assumed titanium hydroxide alone. The activated carbon, after exposure to seawater, can be stripped of uranium with an appropriate eluant (probably an acid) or can be burned for its heating value (possible in a power plant) leaving the uranium further enriched in its ash. The uranium, representing about 1% of the ash, is then a rich ore and would be recovered in a conventional manner. Experimental results have indicated that activated carbon, acting alone, is not adequately effective in adsorbing the uranium from seawater. We measured partition coefficients (concentration ratios) of approximately 10/sup 3/ in seawater instead of the reported values ofmore » 10/sup 5/. However, preliminary tests carried out in fresh water show considerable promise for an extraction system that uses a combination of dissolved titanium hydroxide (in minute amounts) which forms an insoluble compound with the uranyl ion, and the insoluble compound then being sorbed out on activated carbon. Such a system showed partition coefficients in excess of 10/sup 5/ in fresh water. However, the system was not tested in seawater.« less

The correlation between bismuth and uranyl staining and phosphorus content of intracellular structures as determined by electron spectroscopic imaging

Abstract: Four groups of intracellular structures can be recognized according to bismuth and uranyl staining and phosphorus content. (1) Those which contain phosphorus and stain strongly with uranyl acetate but not with bismuth (ribosomes, heterochromatin and mature ribosomal precursor granules), presumably because of their nucleic acid content. (2) Those which contain phosphorus and stain with uranyl acetate and bismuth (interchromatin granules, immature ribosomal precursor granules and mitochondrial granules), presumably because at least some of their phosphate is available to react with bismuth. (3) Those which contain little phosphorus but which stain strongly with bismuth and weakly with uranyl acetate (Golgi complex beads), perhaps because some ligand in addition to phosphate reacts with bismuth, and (4) those which do not contain phosphorus and stain with neither uranyl acetate nor bismuth (portasomes). Uranyl staining correlates strongly with the phosphorus content of nucleic acids, proteins and inorganic deposits. Bismuth will stain some phosphorylated molecules but not all. Thus only some phosphates stain with bismuth.

Margaritasite: a new mineral of hydrothermal origin from the Pena Blanca uranium district, Mexico.

Abstract: Margaritasite, a Cs-rich analogue of carnotite, is newly discovered. It occurs as disseminated pore fillings and relict phenocryst linings within a rhyodacitic tuff breccia of the lower Escuadra Formation (Oligocene) and provides significant reserves of both uranium and cesium. It is a fine-grained yellow mineral and, with the possible exception of the index of refraction, is optically indistinguishable from carnotite. Margaritasite is most easily recognized by X-ray diffraction through a shift in the (001) reflection representing an increase, relative to carnotite, in the c dimension. This increase is due to the large Cs atom in sites normally occupied by K in the carnotite structure. This Cs-K uranyl vanadate, with Cs:K about 5, is the natural equivalent of the compound Cs 2 (UO 2 ) 2 V 2 O 8 synthesized by fusion (Barton, 1958). Formula (Cs (sub 1.38) (H 3 O) (sub 0.35) K (sub 0.29) ) (sub Sigma 2.02) (UO 2 ) (sub 1.99) (V 2 O 8 ) (sub 1.00) .1.07H 2 O corresponding to the generalized formula (Cs,K,H 3 O) 2 (UO 2 ) 2 V 2 O 8 .nH 2 O where Cs>K,H 3 O and n nearly equal l. Unit cell parameters are a = 10.514, b = 8.425, and c = 7.25Aa,beta = 106.01 degrees (P2 1 /a,Z = 2). Microprobe analyses of margaritasite and Cs-enriched carnotites suggest a solid solution, but X-ray powder patterns reveal that two discrete c dimensions exist with no intermediate value between them. The margaritasite has a (001) reflection at 12.7 degrees (2theta ) while that of carnotite lies at 13.8 degrees (2theta ); these peaks do not shift. It is likely that there are two distinct phases, perhaps as interlayered lamellae which are intergrown on a smaller scale than can be resolved by the electron microprobe beam. Local hydrothermal or pneumatolitic activity during or after uranium mineralization. High Cs:total alkali element ratios required to produce Cs-rich minerals can be generated and sustained only in high temperature environments. Synthesis experiments show that margaritasite can form by reaction of Cs-rich solutions with natural carnotite at 200 degrees C, but the same reaction does not occur or is too slow to be observed in 61 days at 80 degrees C. Unlikely that margaritasite is part of the ore in any Colorado Plateau-type uranium deposit. Reported "carnotite" occurrences from uranium deposits of probable hydrothermal origin are likely sites for new discoveries of margaritasite.--Modified journal abstract.

Normal coordinate analysis and mean amplitudes of bis(2,2,6,6-tetramethylheptane-3,5-dionato)uranyl

Abstract: A normal coordinate analysis has been performed for bis(2,2,6,6-tetramethylheptane-3,5-dionato)uranyl according to two simplified models: (i) a 35-atom model consisting of one tetramethylheptanedionate ligand attached to uranyl; symmetry C 2 V and (ii) a 31-particle model of the whole complex, where the methyl groups are taken as point masses; symmetry D 2h . The construction of independent symmetry coordinates by the “method of fragments” is described. Calculated vibrational frequencies are reported along with mean amplitudes ( l - values) and perpendicular amplitude coefficients ( K - values) for selected interatomic distances.