Uranium isotopic fractionation induced by U(VI) adsorption onto common aquifer minerals

Jemison, Noah Edward

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https://hdl.handle.net/2142/88079 Copy

Description

Title

Uranium isotopic fractionation induced by U(VI) adsorption onto common aquifer minerals

Author(s)

Jemison, Noah Edward

Issue Date

2015-07-17

Director of Research (if dissertation) or Advisor (if thesis)

Johnson, Thomas M.

Department of Study

Geology

Discipline

Geology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• U(VI) adsorption
• isotopic fractionation

Abstract

Uranium groundwater contamination due to mining and processing affects numerous sites in the western 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 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 oxides produced a -0.2‰ fractionation with the adsorbed U(VI) depleted in 238U (Brennecka et. al. 2011b). The aqueous speciation of U(VI), and the characteristics of the sorbent surfaces may both produce variations in isotopic fractionation induced by adsorption. This study determined U isotopic fractionation induced by U(VI) adsorption onto goethite, birnessite, illite, quartz, and complex aquifer materials. The influence of U(VI) speciation on fractionation was also examined by measuring differences between fractionation factors accompanying the adsorption of uranyl, uranyl hydroxyl, uranyl carbonato, and calcium uranyl carbonato ions. To increase our ability to resolve fractionation, experiments were carried out with a multi-stage, batch approach, in which a U(VI)-bearing solution was exposed to three stages of adsorption. The dissolved U(VI) was analyzed by a double-spike MC-ICP-MS method. Adsorption to the studied solid phases induces an average isotopic fractionation of -0.17‰ with the adsorbed U(VI) isotopically lighter. U(VI) speciation can affect the magnitude of isotopic fractionation with uranyl carbonato and calcium uranyl carbonato complexes producing a greater isotopic fractionation than uranyl hydroxyl species. Studies using U isotope data to assess U(VI) reduction must consider adsorption as a lesser, but significant isotope-fractionating process.

Graduation Semester

2015-8

Type of Resource

text

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http://hdl.handle.net/2142/88079

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Copyright 2015 Noah Jemison

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