A structural and electrochemical investigation of 1-alkyl-3-methylimidazollum salts of the nitratodioxouranate(VI) anions [{UO2(NO3)(2)}(2)(mu(4)-C2O4)](2-), [UO2(NO3)(3)](-), and [UO2(NO3)(4)](2-)

The properties of the 1-butyl-3-methylimidazolium salt of the dinuclear mu(4)-(O,O,O',O'-ethane-1,2-dioato)bis[bis-(nitrato-O,O)dioxouranate(VI)] anion have been investigated using electrochemistry, single-crystal X-ray crystallography, and extended X-ray absorbance fine structure spectroscopy: the anion structures from these last two techniques are in excellent agreement with each other. Electrochemical reduction of the complex leads to the a two-electron metal-centered reduction of U(VI) to U(IV), and the production Of UO2, or a complex containing UO2. Under normal conditions, this leads to the coating of the electrode with a passivating film. The presence of volatile organic compounds in the ionic liquids 1-alkyl-3-methylimidazolium nitrate (where the 1-alkyl chain was methyl, ethyl, propyl, butyl, pentyl, hexyl, dodecyl, hexadecyl, or octadecyl) during the oxidative dissolution of uranium(IV) oxide led to the formation of a yellow precipitate. To understand the effect of the cation upon the composition and structure of the precipitates, 1-alkyl-3-methylimidazolium salts of a number of nitratodioxouranate(VI) complexes were synthesized and then analyzed using X-ray crystallography. It was demonstrated that the length of the 1-alkyl chain played an important role, not only in the composition of the complex salt, but also in the synthesis of dinuclear anions containing the bridging mu(4)-(O,O,O',O'-ethane-1,2-dioato), or oxalato, ligand, by protecting it from further oxidation.

An EXAFS, X-ray diffraction, and electrochemical investigation of 1-alkyl-3-methylimidazolium salts of [{UO2(NO3)(2)}(2)(mu(4)-C2O4)](2-)

The structure of the 1-alkyl-3-methylimidazolium salts of the dinuclear mu(4)-(O,O,O',O'-ethane-1,2-dioato)-bis[bis(nitrato-O,O)dioxouranate(VI)] anion have been investigated using single crystal X-ray crystallography. In addition, EXAFS and electrochemical studies have been performed on the [C(4)mim](+) salt which is formed following the oxidative dissolution of uranium(IV) oxide in [C(4)mim][NO3]. EXAFS analysis of the solution following UO2 dissolution indicates a mixture of uranyl nitrate and mu(4)-(O,O,O',O'-ethane-1,2-dioato)-bis[bis(nitrato-O,O)dioxouranate(VI)] anions are formed.

Performance evaluation of a zerovalent iron reactive barrier: Mineralogical characteristics

There is a limited amount of information about the effects of mineral precipitates and corrosion on the lifespan and long-term performance of in situ Fe° reactive barriers. The objectives of this paper are (1) to investigate mineral precipitates through an in situ permeable Fe° reactive barrier and (2) to examine the cementation and corrosion of Fe° filings in order to estimate the lifespan of this barrier. This field scale barrier (225' long x 2' wide x 31' deep) has been installed in order to remove uranium from contaminated groundwater at the Y-12 plant site, Oak Ridge, TN. According to XRD and SEM-EDX analysis of core samples recovered from the Fe° portion of the barrier, iron oxyhydroxides were found throughout, while aragonite, siderite, and FeS occurred predominantly in the shallow portion. Additionally, aragonite and FeS were present in up-gradient deeper zone where groundwater first enters the Fe° section of the barrier. After 15 months in the barrier, most of the Fe° filings in the core samples were loose, and a little corrosion of Fe° filings was observed in most of the barrier. However, larger amounts of corrosion (~10-150 µm thick corrosion rinds) occurred on cemented iron particles where groundwater first enters the barrier. Bicarbonate/ carbonate concentrations were high in this section of the barrier. Byproducts of this corrosion, iron oxyhydroxides, were the primary binding material in the cementation. Also, aragonite acted as a binding material to a lesser extent, while amorphous FeS occurred as coatings and infilings. Thin corrosion rinds (2-50 µm thick) were also found on the uncemented individual Fe° filings in the same area of the cementation. If corrosion continues, the estimated lifespan of Fe° filings in the more corroded sections is 5 to 10 years, while the Fe° filings in the rest of the barrier perhaps would last longer than 15 years. The mineral precipitates on the Fe° filing surfaces may hinder this corrosion but they may also decrease reactive surfaces. This research shows that precipitation will vary across a single reactive barrier and that greater corrosion and subsequent cementation of the filings may occur where groundwater first enters the Fe° section of the barrier.

Ionic liquids for the nuclear industry: A radiochemical, structural, and electrochemical investigation

The applicability of ionic liquids within the nuclear industry has been investigated. The radiation stability of ionic liquids containing dialkylimidazolium cations has been tested through with alpha, beta and gamma irradiation. The results of these tests suggest that imidazolium salts have stabilities similar to alkylbenzenes and greater than tetrabutylphosphate / odorless kerosene (TBP/OK) mixtures. The oxidative dissolution of uranium dioxide and the anodic dissolution of uranium metal and plutonium metal have been carried out in various ionic liquid media (C) 2002 American Chemical Society.

Pyrrolidinium Ionic Liquid Crystals

N-Alkyl-N-methylpyrrolidinium cations have been used for the design of ionic liquid crystals, including a new type of uranium-containing metallomesogen. Pyrrolidinium salts with bromide, bis(trifluoromethylsulfonyl)-imide, tetrafluoroborate, hexafluorophosphate, thiocyanate, tetrakis(2-thenoyltrifluoroacetonato)europate(III) and tetrabromouranyl] counteranions were prepared. For the bromide salts and tetrabromouranyl compounds, the chain length of the alkyl group CnH2n+1 was varied from eight to twenty carbon atoms (n =8. 10-20). The compounds show rich mesomorphic behaviour: highly ordered smectic phases (the crystal smectic E phase and the uncommon crystal smectic T phase), smectic A phases, and hexagonal. columnar phases were observed, depending on chain length and anion. This work gives better insight into the nature and formation of the crystal smectic T phase, and the Molecular requirements for the appearance of this highly ordered phase. This uncommon tetragonal mesophase is thoroughly discussed on the basis of detailed powder X-ray diffraction experiments and in relation to the existing literature. Structural models are proposed for self-assembly of the molecules within the smectic layers. In addition, the photophysical properties of the compounds containing a metal complex anion were investigated. For the uranium-containing mesogens, luminescence can be induced by dissolving them in an ionic: liquid matrix. The europium-containing compound shows intense red photoluminescence with high colour Purity.

Task-specific ionic liquid for solubilizing metal oxides

Protonated betaine bis(trifluoromethylsulfonyl) imide is an ionic liquid with the ability to dissolve large quantities of metal oxides. This metal-solubilizing power is selective. Soluble are oxides of the trivalent rare earths, uranium(VI) oxide, zinc(II) oxide, cadmium( II) oxide, mercury( II) oxide, nickel( II) oxide, copper(II) oxide, palladium(II) oxide, lead(II) oxide, manganese( II) oxide, and silver( I) oxide. Insoluble or very poorly soluble are iron(III), manganese(IV), and cobalt oxides, as well as aluminum oxide and silicon dioxide. The metals can be stripped from the ionic liquid by treatment of the ionic liquid with an acidic aqueous solution. After transfer of the metal ions to the aqueous phase, the ionic liquid can be recycled for reuse. Betainium bis( trifluoromethylsulfonyl) imide forms one phase with water at high temperatures, whereas phase separation occurs below 55.5 degrees C ( temperature switch behavior). The mixtures of the ionic liquid with water also show a pH-dependent phase behavior: two phases occur at low pH, whereas one phase is present under neutral or alkaline conditions. The structures, the energetics, and the charge distribution of the betaine cation and the bis( trifluoromethylsulfonyl) imide anion, as well as the cation-anion pairs, were studied by density functional theory calculations.

Uranyl Complexes of Carboxyl-Functionalized Ionic Liquids

Uranium(VI) oxide has been dissolved in three different ionic liquids functionalized with a carboxyl group: betainium bis[trifluoromethyl)sulfonyl]imide, 1-(carboxymethyl)-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, and N-(carboxymethyl)-N-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide. The dissolution process results in the formation of uranyl complexes with zwitterionic carboxylate ligands and bis[trifluoromethyl)sulfonyl]imide (bistriflimide) counterions. An X-ray diffraction study on single crystals of the uranyl complexes revealed that the crystal structure strongly depends on the cationic core appended to the carboxylate groups. The betainium ionic liquid gives a dimeric uranyl complex, the imidazolium ionic liquid a monomeric complex, and the pyrrolidinium ionic liquid a one-dimensional polymeric uranyl complex, Extended X-ray absorption fine structure measurements have been performed on the betainium uranyl complex. The absorption and luminescence spectra of the uranyl betainium complex have been studied in the solid state and dissolved in water, in acetonitrile, and in the ionic liquid betainium bistriflimide. The carboxylate groups remain coordinated to uranyl in acetonitrile and in betainium bistriflimide but not in water.

CHARACTERIZATION OF A LASER-PRODUCED PLASMA USING THE TECHNIQUE OF POINT-PROJECTION ABSORPTION-SPECTROSCOPY

The technique of point-projection spectroscopy has been shown to be applicable to the study of expanding aluminum plasmas generated by approximately 80 ps laser pulses incident on massive, aluminum stripe targets of approximately 125-mu-m width. Targets were irradiated at an intensity of 2.5 +/- 0.5 x 10(13) W/cm2 in a line focus geometry and under conditions similar to those of interest in x-ray laser schemes. Hydrogenic and heliumlike aluminum resonance lines were observed in absorption using a quasicontinuous uranium back-lighter plasma. Using a pentaerythrital Bragg crystal as the dispersive element, a resolving power of approximately 3500 was achieved with spatial resolution at the 5-mu-m level in frame times of the order of 100 ps. Reduction of the data for times up to 150 ps after the peak of the incident laser pulse produced estimates of the temperature and ion densities present, as a function of space and time. The one-dimensional Lagrangian hydrodynamic code MEDUSA coupled to the atomic physics non-local-thermodynamic-equilibrium ionized material package was used to simulate the experiment in planar geometry and has been shown to be consistent with the measurements.

Angular correlations in radiative cascades following resonant electron capture by highly charged ions

We investigate the angular correlations between the photons emitted in the dielectronic recombination (DR) of initially hydrogenlike heavy ions. The theoretical analysis is performed based on a density-matrix approach and Dirac's relativistic theory. Special emphasis has been placed upon the effects of the higher-order, nondipole terms in the expansion of the electron-photon interaction. To illustrate these effects, we present and discuss detailed calculations for K-LL DR of initially hydrogenlike xenon, gold, and uranium. These computations show that the angular correlations are significantly affected by interference between the leading electric-dipole (E1) and the magnetic-quadrupole (M2) transitions.

Dioxouranium(VI) extraction in microchannels using ionic liquids

The extraction of uranium(VI) from aqueous nitric acid solutions by tributylphosphate {TBP; 30%(v/v)} dissolved in the ionic liquid 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide was investigated. The experiments were performed in a Teflon microchannel of 0.5 mm internal diameter, while the dioxouranium(VI) concentrations in the aqueous and the ionic liquid phases were determined by UV-Vis spectroscopy. The effects of initial nitric acid concentration (0.01-3 M), residence time, and phase flow rate ratio were studied. It was found that, with increasing nitric acid concentration, the percentage of dioxouranium(VI) extracted decreased and then increased again, while the extraction efficiency followed a slightly different trend. Overall mass transfer coefficients varied between 0.049 s and 0.312 s . © 2012 Elsevier B.V. All rights reserved.

Investigating local relationships between trace elements in soils and cancer data

Medical geology research has recognised a number of potentially toxic elements (PTEs), such as arsenic, cobalt, chromium, copper, nickel, lead, vanadium, uranium and zinc, known to influence human disease by their respective deficiency or toxicity. As the impact of infectious diseases has decreased and the population ages, so cancer has become the most common cause of death in developed countries including Northern Ireland. This research explores the relationship between environmental exposure to potentially toxic elements in soil and cancer disease data across Northern Ireland. The incidence of twelve different cancer types (lung, stomach, leukaemia, oesophagus, colorectal, bladder, kidney, breast, mesothelioma, melanoma and non melanoma(NM) both basal and squamous, were examined in the form of twenty-five coded datasets comprising aggregates over the 12 year period from 1993 to 2006. A local modelling technique,geographically weighted regression (GWR) is usedto explore the relationship between environmental exposure and cancer disease data. The results show comparisons of the geographical incidence of certain cancers (stomach and NM squamous skin cancer) in relation to concentrations of certain PTEs (arsenic levels in soils and radon were identified). Findings from the research have implications for regional human health risk assessments.

Hydrobiogeochemical Interactions along “Flow Tubes” Controls: Watershed Scale Contaminant Flow and Transformation at the Oak Ridge IFRC

Geochemical,spectrographic, microbiological and hydrogeologic studies at the ORIFRC site indicate that groundwater transport in structured media may behave as a system of parallel flow tubes. These tubes are preferred flowpaths that enable contaminant transport parallel to bedding planes (strike) over distances of 1000s of meters. A significant flux of groundwater is focused within an interval defined by the interface between the competent bedrock and overlying highly-weathered saprolite, commonly referred to as the"transition zone." Characteristics of this transition zone are dense fractures and the relative absence of weathering products (e.g. clays)results in a significantly higher permeability compared to both the overlying clay-saprolite and underlying bedrock. Several stratabound low seismic velocity zones located below the transition zone were identified during geophysics studies and were also determined to be fractured high permeability preferred contaminant transport pathways during subsequent drilling activities. XANES analysis of precipitates collected from these deeper flow zones indicate 95% or more of the U deposited is U(VI). Linear combination fitting of the EXAFS data shows that precipitates are ~51±5% U(VI)-carbonate-like phase (e.g., liebigite) and ~49±5% U(VI) associated with an iron oxide phase; inclusion of a third component in the fit suggests that up to 15% of the U(VI) may be associated with a phosphate phase or OH- phase (e.g.,schoepite). Although precipitates with similar U(VI)-carbonate and/or phosphate associations were identified in the transition zone pathways,there were also U(VI) complexes adsorbed to mineral surfaces that would tend to be more readily mobilized. Groundwater in the different flow tubes has been determined to consist of different water quality types that vary with the solid phase encountered (e.g., clays, carbonates, clastics) as contaminants migrate along the flow paths. This lateral and vertical variability in geochemistry, particularly pH, has a significant impact on microbiological community composition and activity. Ribosomal RNA gene analyses coupled with physiological and genomic analyses suggest that bacteria from the genus Rhodanobacter(a diverse population of denitrifiers that are moderately acid tolerant) have a high relative abundance in the acidic source zone at the ORIFRC site.Watershed-scale analysis across different flow paths/tubes revealed strong negative correlation between pH and the absolute and relative abundance of Rhodanobacter. Recent studies also confirmed that the ORIFRC site hosts a diverse fungal community, with significant differences observed between acidic (pH <5) and circumneutral (>5) wells. The lack of nitrous oxide reduction capability in fungi, and the detection of denitrification potential in slurry microcosms suggest that fungi may have aheretofore under appreciated role in biogeochemical transformations, with implications forsite remediation and greenhouse gas emissions. Further research is needed to determine if these organisms can influence U(VI) mobility either directly through immobilization or indirectly through the depletion of nitrate.In conclusion, additional studies are required to quantify the processes (e.g., solid phase reactions, recharge, diffusion, microbial interactions) that are occurring along the groundwater flow tubes identified at the ORIFRC so predictive models can be parameterized and used to assess long-term contaminant fate and transport and remedial options.

A geochronologic framework for the Ziegler Reservoir fossil site, Snowmass Village, Colorado

The Ziegler Reservoir fossil site near Snowmass Village, Colorado, provides a unique opportunity to reconstruct high-altitude paleoenvironmental conditions in the Rocky Mountains during the last interglacial period. We used four different techniques to establish a chronological framework for the site. Radiocarbon dating of lake organics, bone collagen, and shell carbonate, and in situ cosmogenic Be and Al ages on a boulder on the crest of a moraine that impounded the lake suggest that the ages of the sediments that hosted the fossils are between ~ 140 ka and > 45 ka. Uranium-series ages of vertebrate remains generally fall within these bounds, but extremely low uranium concentrations and evidence of open-system behavior limit their utility. Optically stimulated luminescence (OSL) ages (n = 18) obtained from fine-grained quartz maintain stratigraphic order, were replicable, and provide reliable ages for the lake sediments. Analysis of the equivalent dose (D) dispersion of the OSL samples showed that the sediments were fully bleached prior to deposition and low scatter suggests that eolian processes were likely the dominant transport mechanism for fine-grained sediments into the lake. The resulting ages show that the fossil-bearing sediments span the latest part of marine isotope stage (MIS) 6, all of MIS 5 and MIS 4, and the earliest part of MIS 3.