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 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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Geology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2019

Author dc:creator

• Jemison, Noah

Contributors dc:contributor

• Johnson, Thomas M.
• Druhan, Jennifer L
• Lundstrom, Craig C.
• Sanford, Robert A.

• 238U/235U, U(VI) reduction, U(IV) oxidation

Statement dc:rights

• Copyright 2018 Noah Jemison

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/102885

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/102885