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Separation of Uranium and Thorium for 230Th-U Dating of Submarine Hydrothermal Sulfides
Published on: May 20, 2019
Uranium isotope fractionation during adsorption to Mn-oxyhydroxides
Gregory A Brennecka1, Laura E Wasylenki, John R Bargar
1School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
Environmental Science & Technology
|January 22, 2011
Summary
Uranium (U) isotope fractionation occurs during adsorption to ferromanganese oxides. This study reveals differences in uranium coordination environments, explaining observed isotope variations and enabling new paleoredox proxy applications.
Area of Science:
- Geochemistry
- Environmental Science
- Nuclear Chemistry
Background:
- Uranium (U) isotope fractionation between natural ferromanganese crusts and seawater is documented.
- Understanding the mechanism of (238)U/(235)U fractionation during adsorption is crucial for its application as a tracer and paleoredox proxy.
Purpose of the Study:
- To investigate the mechanism of uranium isotope fractionation during adsorption to K-birnessite.
- To determine the role of coordination environment changes in U isotope fractionation.
Main Methods:
- Conducted U adsorption experiments using synthetic K-birnessite and U-bearing solutions.
- Analyzed adsorbed U using extended X-ray absorption fine structure (EXAFS) spectroscopy.
- Compared coordination environments of dissolved and adsorbed U species.
Main Results:
- Adsorbed U was isotopically lighter by approximately 0.2‰ (δ(238/235)U) than dissolved U, matching natural observations.
- Uranium redox state remained unchanged during adsorption.
- EXAFS spectroscopy revealed subtle differences in the U-O coordination shell between dissolved and adsorbed U.
Conclusions:
- Differences in the coordination environment between dissolved and adsorbed U are likely responsible for the observed isotope fractionation.
- This mechanism explains U isotope variations in natural samples and supports the use of U isotopes as tracers and paleoredox proxies.
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