Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 34 for “"U(VI)"”.
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Interaction of aqueous U(VI) with goethite, montmorillonite, and UO2(s)
<p>Uranium contamination in subsurface environments is a matter of great concern throughout the world. Fate and transport of uranium in the subsurface can be controlled by U(VI) adsorption and reduction onto common iron (oxy)hydroxides and clay minerals. Aqueous U(VI) can also exchange uranium …
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Uranium isotopic fractionation induced by U(VI) adsorption onto common aquifer minerals
… United States. Bioreduction of soluble, mobile U(VI) to U(IV)-bearing solids is a common remediation strategy. Uranium isotopes (238U/235U) have been utilized to track the progress of microbial reduction, with laboratory and field studies finding a ~1‰ isotopic fractionation with the U(IV) product …
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Isotopic fractionation of chromium and uranium during Cr(VI) reduction by ascorbate and U(VI) reduction by sulfide
… conditions which control their chemical behavior in near surface settings. Reduction of hexavalent chromium (Cr(VI)) and uranium (U(VI)) greatly decreases their solubility and mobility, and therefore their toxicity in groundwater. Redox transformations have been shown to induce predictable …
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Isotopic fractionation of chromium and uranium during abiotic and microbial Cr(VI) reduction and microbial U(VI) reduction
Reduction of hexavalent chromium (Cr(VI)) influences the chemical behavior of Cr in a variety of geochemical settings such as ancient and modern oceans, lakes and groundwater and surface water systems. Cr(VI) reduction immobilizes the toxic form of Cr to less toxic and insoluble Cr(III). Several …
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Uranium isotopes as indicators of uranium immobilization and remobilization in contaminated aquifer settings
Tracking U immobilization through U(VI) reduction and mobilization induced by U(IV) oxidation using U concentrations alone is challenging, as groundwater transport, aquifer heterogeneity, and U(VI) adsorption can complicate data interpretation. U isotopes (238U/235U) provide a more direct indicator …
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Geochemical Conditions Affecting Uranium(VI) Fate And Transport In Soil And Groundwater In The Presence Of Phosphate
… with actinides like uranium is a serious environmental concern. Phosphate addition to uranium-contaminated soil and groundwater can potentially provide long-term in-situ U(VI) immobilization by precipitation of low solubility U(VI)-phosphates. Reactions at the iron: oxy)hydroxide-water …
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The effects of bicarbonate and mineral surfaces on uranium immobilization under anaerobic conditions
… sediments and aquifers. In subsurface environments, uranium primarily exists as U(VI) or U(IV), oxidized and reduced species, respectively. U(VI) is highly soluble and toxic, U(IV), while relatively toxic, is insoluble which greatly reduces its exposure pathways. We seek to examine the …
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Sorption of Metals onto Natural Sediments and Engineered Iron Oxide Nanoparticles
<p>Metal contamination of subsurface environments and engineered water systems can be derived from natural processes and anthropogenic activities associated with industrial processes, past weapons production, and mining works. The toxic and carcinogenic effects of uranium and chromium pose a …
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Isotopic study of uranium: determining the isotopic fractionation of uranium during abiotic reduction with iron(II)
… remediation, mobile, hexavalent uranium (U(VI)) can be reduced to immobile, tetravalent uranium (U(IV)) by microbial or abiotic chemical reactions. Unfortunately, due to uranium’s complex geochemistry, measuring concentrations does not reliably give an accurate indicator of the efficiency of …
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Chromium and uranium isotopic exchange kinetics and isotope fractionation during oxidation of tetravalent uranium by dissolved oxygen
… are very powerful new geochemical tools in environmental remediation and paleoredox reconstruction studies. Correctly interpreting Cr and U isotopic compositions in groundwater and sed- imentary rock samples requires thorough understanding of relevant isotope fractionation mechanisms, many of …
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Zum Komplexbildungsverhalten ausgewählter Actiniden (U, Np, Cm) mit mikrobiellen Bioliganden
… sich mit der Wechselwirkung der Actiniden U(VI), Np(V) und Cm(III) mit Modellliganden, die die Funktionalitäten der Pyoverdine simulieren. Für die Metallbindung der Pyoverdine sind die Katecholgruppe des Chromophors und die funktionellen Gruppen der Peptidkette (Hydroxamsäuregruppen und …
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The sorption of uranium(VI) and neptunium(V) onto surfaces of selected metal oxides and alumosilicates studied by in situ vibrational spectroscopy
The migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These …
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Biosorption of uranium and its effect on uranium transport in groundewater
… Then, the partition coefficient between U(VI) and the microbial species Geobacter uraniireducens and Acholeplasma palmae were experimentally determined. The experimentally obtained partition coefficients were used to incorporate biosorption into a thermodynamic model that describes the …
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Ionic liquids and chitinous biomass: materials, synthesis, and applications for uranium sequestration
… the creation of innovative methods that provide waste to volume minimization. Therefore a major objective of this research was to combine the reactivity of chitosan with the toughness and insolubility of chitin by surface modifications with UO22+ selective moieties. Thus the IL platform …
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Origin of Uranium Mineralization at Coles Hill Virginia (USA) and its Natural Attenuation within an Oxidizing Rock-Soil-Ground Water System
… of uranium within an oxidizing, fluid rich environment typical of the eastern US. At the Coles Hill deposit fracture hosted, primary U(IV) bearing mineral assemblages formed during hydrothermal activity associated with Mesozoic faulting. The most abundant ore assemblage consists of coffinite …
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Precipitation and Dissolution of Uranyl Phosphates in a Mircofluidic Pore Structure
The abiotic precipitation of uranium (U(VI)) was evaluated in a microfluidic pore structure (i.e. micromodel) to assess the efficacy of using a phosphate amendment to immobilize uranium in groundwater and mitigate the risk of this contaminant to potential down-gradient receptor sites. U(VI) was …
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The behavior of uranium in the environment : bacterial reduction of an aqueous uranium species
… studies were performed to investigate the behavior of uranium with bacteria in an anaerobic environment. Laboratory studies used Shewanella putrefaciens because of its ability to grow rapidly in aerobic conditions and reduce metals in anaerobic conditions. Under anaerobic conditions, Shewanella …
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Metallo-supramolecular Architectures based on Multifunctional N-Donor Ligands
… and structural properties. This work was divided into three distinct main parts: The bis(2-pyridylimine), the bis(2-hydroxyaryl) imine and the tripodal imine / amine ligand approach. In the first part a series of bis(2-pyridylimine) derivatives having different linking elements were employed …
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Synthesis and evaluation of actinide imprinted resins
Organic resins have previously shown good results with application to actinide separations. Large portions of recent research have been dedicated to the synthesis and evaluation of resins with phenolic-type functional groups. Other recent chemical research with lighter metals has developed a …
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