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Title:Uranium isotopes as indicators of uranium immobilization and remobilization in contaminated aquifer settings
Author(s):Jemison, Noah
Director of Research:Johnson, Thomas M.
Doctoral Committee Chair(s):Johnson, Thomas M.
Doctoral Committee Member(s):Druhan, Jennifer L; Lundstrom, Craig C.; Sanford, Robert A.
Department / Program:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):238U/235U, U(VI) reduction, U(IV) oxidation
Abstract: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 of these geochemical reactions controlling U mobility. U(VI) reduction induces a strong fractionation of U isotopes, shifting the U isotopes of the remaining U(VI) and producing U(IV) with a distinct isotopic composition. Our published laboratory studies imply that U(VI) adsorption, while impacting U concentrations, has only a minor, consistent effect on U isotopes. Adsorption to various aquifer minerals induces an average isotopic fractionation of -0.15‰ with the adsorbed U(VI) isotopically lighter than coexisting aqueous U(VI). Studies using U isotope data to assess U(VI) reduction and U(IV) oxidation must consider adsorption as a lesser, but significant, isotope fractionation process. Published field studies demonstrate that U(IV) oxidation can be detected via observation of changes in U isotopes. The incorporation of remobilized U(IV) with a high 238U/235U ratio into the aqueous U(VI) pool produces an increase in 238U/235U of aqueous U(VI). However, microbial, geochemical, and hydrologic complexities can complicate the use of 238U/235U in tracking U(IV) oxidation and U(VI) reduction. Through inclusion of 238U/235U into a multicomponent reactive transport modeling framework, we track U removal during both natural and biostimulated U(VI) reduction and U remobilization during U(IV) oxidation to develop 238U/235U as a simple, reliable tool for analyzing U geochemical behavior.
Issue Date:2018-08-27
Rights Information:Copyright 2018 Noah Jemison
Date Available in IDEALS:2019-02-08
Date Deposited:2018-12

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