Persistence of the isotopic signature of pentavalent uranium in magnetite

DOI: 10.1021/acs.est.1c06865

Authors: Zezhen Pan (Fudan University; École Polytechnique Fédérale de Lausanne) , Yvonne Roebbert (Universität Hannove) , Aaron Beck (Karlsruhe Institute of Technology) , Barbora Bartova (École Polytechnique Fédérale de Lausanne) , Tonya Vitova (Karlsruhe Institute of Technology) , Stefan Weyer (Universität Hannover) , Rizlan Bernier-Latmani (École Polytechnique Fédérale de Lausanne)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Environmental Science & Technology

State: Published (Approved)
Published: January 2022
Diamond Proposal Number(s): 17472

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.

Journal Keywords: pentavalent uranium; isotope fractionation; uranium remediation; redox tracer

Subject Areas: Materials, Earth Science, Environment


Instruments: I20-Scanning-X-ray spectroscopy (XAS/XES)

Other Facilities: CAT-ACT at KIT

Added On: 24/01/2022 08:32

Documents:
acs.est.1c06865.pdf

Discipline Tags:

Desertification & Pollution Earth Sciences & Environment Radioactive Materials Mineralogy Materials Science Nuclear Waste Geology

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS)