Details
| Original language | English |
|---|---|
| Pages (from-to) | 1753-1762 |
| Number of pages | 10 |
| Journal | Environmental Science and Technology |
| Volume | 56 |
| Issue number | 3 |
| Early online date | 21 Jan 2022 |
| Publication status | Published - 1 Feb 2022 |
Abstract
Uranium isotopic signatures can be harnessed to monitor the reductive remediation of subsurface contamination or to reconstruct paleo-redox environments. However, the mechanistic underpinnings of the isotope fractionation associated with U reduction remain poorly understood. Here, we present a coprecipitation study, in which hexavalent U (U(VI)) was reduced during the synthesis of magnetite and pentavalent U (U(V)) was the dominant species. The measured δ238U values for unreduced U(VI) (∼−1.0‰), incorporated U (96 ± 2% U(V), ∼−0.1‰), and extracted surface U (mostly U(IV), ∼0.3‰) suggested the preferential accumulation of the heavy isotope in reduced species. Upon exposure of the U-magnetite coprecipitate to air, U(V) was partially reoxidized to U(VI) with no significant change in the δ238U value. In contrast, anoxic amendment of a heavy isotope-doped U(VI) solution resulted in an increase in the δ238U of the incorporated U species over time, suggesting an exchange between incorporated and surface/aqueous U. Overall, the results support the presence of persistent U(V) with a light isotope signature and suggest that the mineral dynamics of iron oxides may allow overprinting of the isotopic signature of incorporated U species. This work furthers the understanding of the isotope fractionation of U associated with iron oxides in both modern and paleo-environments.
Keywords
- isotope fractionation, pentavalent uranium, redox tracer, uranium remediation
ASJC Scopus subject areas
- Chemistry(all)
- Environmental Science(all)
- Environmental Chemistry
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In: Environmental Science and Technology, Vol. 56, No. 3, 01.02.2022, p. 1753-1762.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Persistence of the Isotopic Signature of Pentavalent Uranium in Magnetite
AU - Pan, Zezhen
AU - Roebbert, Yvonne
AU - Beck, Aaron
AU - Bartova, Barbora
AU - Vitova, Tonya
AU - Weyer, Stefan
AU - Bernier-Latmani, Rizlan
N1 - Funding Information: The work at EPFL was supported by the Swiss National Science Foundation Grant 200021E-164209 and the European Research Council Consolidator Grant 725675 (UNEARTH). We thank Luca Loreggian and Ashley Brown at EPFL for helpful instructions and discussions. We thank the Institute for Beam Physics and Technology for the operation of the storage ring of the KIT synchrotron radiation facility, the Karlsruhe Research Accelerator (KARA). We acknowledge Dr. Jo?rg Rothe, Dr. Kathy Dardenne, Jurij Galanzew, and Bianca Schacherl for help with the organization and running of synchrotron experiments. We acknowledge the Diamond Light Source for time on Beamline I20-Scanning (L3-edge EXAFS measurements) under proposal SP17472 and thank the beamline scientist Shu Hayama for beamtime assistance. We appreciate the comments of Associate Editor David Waite and three anonymous reviewers that helped us improve the presentation and interpretation of our study.
PY - 2022/2/1
Y1 - 2022/2/1
N2 - Uranium isotopic signatures can be harnessed to monitor the reductive remediation of subsurface contamination or to reconstruct paleo-redox environments. However, the mechanistic underpinnings of the isotope fractionation associated with U reduction remain poorly understood. Here, we present a coprecipitation study, in which hexavalent U (U(VI)) was reduced during the synthesis of magnetite and pentavalent U (U(V)) was the dominant species. The measured δ238U values for unreduced U(VI) (∼−1.0‰), incorporated U (96 ± 2% U(V), ∼−0.1‰), and extracted surface U (mostly U(IV), ∼0.3‰) suggested the preferential accumulation of the heavy isotope in reduced species. Upon exposure of the U-magnetite coprecipitate to air, U(V) was partially reoxidized to U(VI) with no significant change in the δ238U value. In contrast, anoxic amendment of a heavy isotope-doped U(VI) solution resulted in an increase in the δ238U of the incorporated U species over time, suggesting an exchange between incorporated and surface/aqueous U. Overall, the results support the presence of persistent U(V) with a light isotope signature and suggest that the mineral dynamics of iron oxides may allow overprinting of the isotopic signature of incorporated U species. This work furthers the understanding of the isotope fractionation of U associated with iron oxides in both modern and paleo-environments.
AB - Uranium isotopic signatures can be harnessed to monitor the reductive remediation of subsurface contamination or to reconstruct paleo-redox environments. However, the mechanistic underpinnings of the isotope fractionation associated with U reduction remain poorly understood. Here, we present a coprecipitation study, in which hexavalent U (U(VI)) was reduced during the synthesis of magnetite and pentavalent U (U(V)) was the dominant species. The measured δ238U values for unreduced U(VI) (∼−1.0‰), incorporated U (96 ± 2% U(V), ∼−0.1‰), and extracted surface U (mostly U(IV), ∼0.3‰) suggested the preferential accumulation of the heavy isotope in reduced species. Upon exposure of the U-magnetite coprecipitate to air, U(V) was partially reoxidized to U(VI) with no significant change in the δ238U value. In contrast, anoxic amendment of a heavy isotope-doped U(VI) solution resulted in an increase in the δ238U of the incorporated U species over time, suggesting an exchange between incorporated and surface/aqueous U. Overall, the results support the presence of persistent U(V) with a light isotope signature and suggest that the mineral dynamics of iron oxides may allow overprinting of the isotopic signature of incorporated U species. This work furthers the understanding of the isotope fractionation of U associated with iron oxides in both modern and paleo-environments.
KW - isotope fractionation
KW - pentavalent uranium
KW - redox tracer
KW - uranium remediation
UR - http://www.scopus.com/inward/record.url?scp=85123523626&partnerID=8YFLogxK
U2 - 10.1021/acs.est.1c06865
DO - 10.1021/acs.est.1c06865
M3 - Article
C2 - 35061941
AN - SCOPUS:85123523626
VL - 56
SP - 1753
EP - 1762
JO - Environmental Science and Technology
JF - Environmental Science and Technology
SN - 0013-936X
IS - 3
ER -