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The isotope geochemistry of uranium: Igneous petrology, ore deposits, and groundwater contamination

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Title: The isotope geochemistry of uranium: Igneous petrology, ore deposits, and groundwater contamination
Author(s): Bopp, Charles J., IV
Director of Research: Lundstrom, Craig C.
Doctoral Committee Chair(s): Lundstrom, Craig C.
Doctoral Committee Member(s): Johnson, Thomas M.; Sanford, Robert A.; Marshak, Stephen
Department / Program: Geology
Discipline: Geology
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): uranium uranium isotopes groundwater groundwater contamination groundwater remediation mass spectrometry thermal diffusion thermal migration uranium contamination uranium remediation bioremediation uranium ore roll front uranium mining uranium reduction thermal migration zone refining basalt
Abstract: This study applies high precision 238U/235U measurement techniques two three geologic settings: basalt differentiation, uranium ore genesis, and the remediation of a uranium-contaminated groundwater system. In the latter two cases, 238U/235U is used as a tracer of uranium reduction. 238U preferentially enters the reduced (solid) U phase, thus analysis of U ores can reveal information on the development of an ore body (chapters 2 and 3) while analysis of 238U/235U in contaminated groundwater can be used to monitor the progress of uranium reduction (chapters 4 and 5). 238U/235U measurements are applied in a less orthodox way to the problems of magmatic differentiation, where 235U separates from 238U when a partially-molten basalt is allowed to equilibrate under a temperature gradient. This extends the previous work on the isotopic effects of thermal diffusion into the heavy elements, and presents new research on the mineralogical development of a basalt under a thermal gradient. There are five studies in this work: 238U/235U is first applied to detect the effect of a thermal gradient on a partially molten basalt, with variations of ≈1.0‰ found over ≈150°C. 238U/235U is then applied to the case of sedimentary reduced uranium ore deposits. A general survey of finds a shift of ≈1.0‰ between magmatic-type and sandstone-type uranium ores. A small-scale study of a uranium roll front deposit finds 238U/235U variation in excess of 1.0‰. In both cases, the shift in 238U/235U is attributed to the nuclear field shift effect during uranium reduction. 238U/235U analysis is then applied to a groundwater remediation setting at a biostimulation experiment at the former site of a uranium tailings pile in Rifle, Colorado. 238U/235U analysis of a bioremediation experiment finds a shift of ≈1.0‰ associated with a large (≈90%) decrease in dissolved uranium concentration. This shift is again attributed to the nuclear field shift effect during uranium reduction. Finally, 238U/235U analysis is used to trace the cause of an abnormal change in dissolved uranium concentration during a subsequent biostimulation experiment at the Rifle, Colorado site. By analyzing the sense and timing of shifts in 238U/235U relative to shifts in dissolved uranium concentration I am able to differentiate between uranium reoxidation, uranium desorption, and advection of uranium-bearing groundwater.
Issue Date: 2011-01-14
Rights Information: Copyright 2010 Charles John Bopp IV
Date Available in IDEALS: 2011-01-14
Date Deposited: December 2

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