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Showing 1 to 20 of 49 for “"Isotopic fractionation"”.
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Modeling effective isotopic fractionation in groundwater aquifers with heterogeneous reaction rates
… into non-toxic forms. Reduction induces isotopic fractionation, which may thus be used to determine the amount of reaction that has occurred. However, when the Rayleigh distillation equation is used to relate the isotope ratio shifts to the amount of reaction, known flaws in this approach …
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Uranium isotopic fractionation induced by U(VI) adsorption onto common aquifer minerals
… with laboratory and field studies finding a ~1‰ isotopic fractionation with the U(IV) product enriched in 238U. However, the isotopic fractionation produced by adsorption may complicate the use of 238U/235U to trace microbial reduction. A previous study found that adsorption of U(VI) onto Mn …
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Oxygen and Hydrogen Isotopic Fractionation Factors Determined in Experimental Clay-Water Systems
Made available in DSpace on 2014-12-14T07:10:54Z (GMT). No. of bitstreams: 1 7915378.pdf: 3168865 bytes, checksum: d709693b3b9b193a5b4f3eac2831364a (MD5) Previous issue date: 1979
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Investigating Controls on Variation in Isotopic Fractionation during Biodegradation of Chlorinated Ethenes and Ethanes
… rate-limiting steps may affect observed isotope fractionation. Two haloalkane dehalogenases catalyzed aerobic 1,2-dichloroethane (1,2-DCA) dechlorination with very different enzyme affinities and turnover rates. However, carbon isotope enrichment factors were the same for both enzymes, reflecting …
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Developing antimony stable isotope methods as a new geochemical redox indicator: computational isotopic fractionation studies
The student, Hannah Shay, submitted this Thesis for approval on 2021-04-21 at 15:54.
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Isotopic study of uranium: determining the isotopic fractionation of uranium during abiotic reduction with iron(II)
… Little work has been done to determine the isotopic fractionation induced by abiotic reduction. This study focuses on determining the isotopic fractionation of uranium during reduction with Fe(II). Time series experiments with aqueous Fe(II) and magnetite (Fe3O4) were conducted with samples …
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An Investigation of Ni and Cu Isotopic Fractionation in Basal Duluth Complex Cu-Ni-PGE Mineralization, Northeastern Minnesota
… Previous studies have demonstrated a notable fractionation of 60Ni and 58Ni in terrestrial materials, including both primary and secondary phases, with a total range of up to 2.1 ‰. Other work has indicated a fractionation of 65Cu and 63Cu, with pronounced differences between primary copper …
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Isotopic fractionation of chromium and uranium during Cr(VI) reduction by ascorbate and U(VI) reduction by sulfide
… concentration based approach. The magnitude of isotopic fractionation has been determined for various abiotic and biotic reduction reactions in the Cr and U systems; other reductants of interest remain to be studied. Using batch reactor experiments, this study quantifies the magnitude of …
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Isotopic fractionation of chromium and uranium during abiotic and microbial Cr(VI) reduction and microbial U(VI) reduction
… used as a redox-indicator. The magnitude of the isotopic fractionation must be determined to connect observed Cr isotope ratios to the extent of reduction. This study determines the Cr isotopic fractionation factors for Cr(VI) reduction by Fe(II) phases (Fe(II-doped goethite, FeS, green rust, …
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Quantitative Models of Fluid Flow, Chemical Reaction, and Stable Isotopic Fractionation and Their Application to Sediment Diagenesis and Hydrothermal Alteration
In this study, I develop a numerical model to predict dissolution and precipitation reactions by groundwater flow through temperature and pressure gradients in sedimentary basins. I incorporate chemical reaction into a transient model of groundwater flow equations that describes heat transfer and …
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Ion Filtration and Stable Oxygen Isotopic Fractionation Resulting From the Passage of Sodium-Calcium-Chloride Brine Through Compacted Smectite Layers at Elevated Temperatures and Pressures
A solution 5.00 molal in NaCl and 0.45 molal in CaCl(,2) was forced through 1.5 cm-thick clay plugs made of sedimented, randomly-oriented one-half to two micron diameter montmorillonite flakes. Two sets of experiments were carried out. In one set the confining pressure on the clay was 5000 pounds …
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Tellurium, antimony, and selenium isotopes as indicators of elemental mobility
… or the oxygenation of early Earth. Stable isotopic fractionation of redox-sensitive elements can be used as a means to identify redox reactions taking place. For example, selenium (Se) isotopes track reductive immobilization of the contaminant Se in groundwater or surface waters. Other …
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Use of uranium decay series for dating an archaeological smelting site
Through the identification of phases and their isotopic composition and variability, an assessment of the applicability of uranium decay series dating to El Manchon slags was made. El Manchon is the only Mesoamerican site to exhibit smelting technology. Uranium series dating is typically used on …
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Antimony isotopes as indicators of redox reactions in aqueous systems: fractionation during Sb(V) reduction by sulfide and isotope exchange kinetics between dissolved Sb(III) and Sb(V)
… of Sb. For other contaminant elements, stable isotopic ratio measurements have been useful for source tracing and detection of environmentally critical chemical reactions (e.g., Wiederhold 2015). We seek to develop Sb isotopic ratios as tools for detecting and quantifying Sb in the environment. …
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Isotopic Tracers as Evidence of Denitrification in the Karlsruhe Aquifer
… the source of the contamination based upon isotopic signatures of specific nitrate sources. </p><p>Periodic sampling was conducted from the fall of 2003 to the spring of 2004 to monitor the relationship between NO₃¯ concentrations and isotopic fractionation. All samples were tested for NO₃¯ …
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The high temperature geochemistry of vanadium: From isotope ratios in ocean island basalt to thermal diffusion processes at the core-mantle boundary
… magmatic processes. Measurements of the V isotopic composition of peridotites, the dominant rock of upper mantle, and primitive meteorites show significant offset with the peridotites heavier by ~0.2 ‰, the largest offsets among all metal stable isotope systems. If primitive meteorites …
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Selenium Stable Isotope Ratios in Wetlands: Insights Into Biogeochemical Cycling and How a Diffusive Barrier Affects the Measured Fractionation Factor
… reduction, sorption, and assimilation. Isotope fractionation studies can potentially distinguish reduction from other removal processes, and possibly quantify the amount of reduction, assuming that the correct isotope fractionation factor, alpha, is applied. Typically, alpha is determined under …
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Deuterium and snow hydrology
… Further studies in the laboratory indicated that isotopic fractionation and vapor transport occurring during depth hoar formation may homogenize the lower part of the snowpack before melt occurs. The homogenization of the HDO content of the snowpack would reduce the problems involved in following …
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The dynamics of ¹³C in several New Zealand lakes
… low enough to affect. photosynthetic carbon isotopic fractionation, and hence plankton 𝜹¹³C values. The enrichment of ¹³C in the dissolved inorganic carbon (DIC) pool during periods of high photosynthetic productivity also affects plankton 𝜹¹³C values. Analysis of diurnal changes in 𝜹¹³C and …
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