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Title: Iron Vacancies Accommodate Uranyl Incorporation into Hematite

Abstract

Radiotoxic uranium contamination in natural systems and nuclear waste containment can be sequestered by incorporation into naturally abundant iron (oxyhydr)oxides such as hematite (α-Fe 2O 3) during mineral growth. The stability and properties of the resulting uranium-doped material are impacted by the local coordination environment of incorporated uranium. While measurements of uranium coordination in hematite have been attempted using extended X-ray absorption fine structure (EXAFS) analysis, traditional shell-by-shell EXAFS fitting yields ambiguous results. We used hybrid functional ab initio molecular dynamics (AIMD) simulations for various defect configurations to generate synthetic EXAFS spectra which were combined with adsorbed uranyl spectra to fit experimental U L 3-edge EXAFS for U 6+-doped hematite. We discovered that the hematite crystal structure accommodates a trans-dioxo uranyl-like configuration for U 6+ that substitutes for structural Fe 3+, which requires two partially protonated Fe vacancies situated at opposing corner-sharing sites. Surprisingly, the best match to experiment included significant proportions of vacancy configurations other than the minimum-energy configuration, pointing to the importance of incorporation mechanisms and kinetics in determining the state of an impurity incorporated into a host phase under low temperature hydrothermal conditions.

Authors:
ORCiD logo; ORCiD logo; ORCiD logo; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo
  1. Research Centre for Radwaste Disposal and Williamson Research Centre for Molecular Environmental Science, School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester M13 9PL, United Kingdom
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Argonne National Lab. (ANL), Argonne, IL (United States); Stanford Univ., CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1459051
Alternate Identifier(s):
OSTI ID: 1508821
Grant/Contract Number:  
[AC05-76RL01830; AC02-06CH11357; AC02-76SF00515]
Resource Type:
Published Article
Journal Name:
Environmental Science and Technology
Additional Journal Information:
[Journal Name: Environmental Science and Technology Journal Volume: 52 Journal Issue: 11]; Journal ID: ISSN 0013-936X
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

McBriarty, Martin E., Kerisit, Sebastien, Bylaska, Eric J., Shaw, Samuel, Morris, Katherine, and Ilton, Eugene S. Iron Vacancies Accommodate Uranyl Incorporation into Hematite. United States: N. p., 2018. Web. doi:10.1021/acs.est.8b00297.
McBriarty, Martin E., Kerisit, Sebastien, Bylaska, Eric J., Shaw, Samuel, Morris, Katherine, & Ilton, Eugene S. Iron Vacancies Accommodate Uranyl Incorporation into Hematite. United States. doi:10.1021/acs.est.8b00297.
McBriarty, Martin E., Kerisit, Sebastien, Bylaska, Eric J., Shaw, Samuel, Morris, Katherine, and Ilton, Eugene S. Mon . "Iron Vacancies Accommodate Uranyl Incorporation into Hematite". United States. doi:10.1021/acs.est.8b00297.
@article{osti_1459051,
title = {Iron Vacancies Accommodate Uranyl Incorporation into Hematite},
author = {McBriarty, Martin E. and Kerisit, Sebastien and Bylaska, Eric J. and Shaw, Samuel and Morris, Katherine and Ilton, Eugene S.},
abstractNote = {Radiotoxic uranium contamination in natural systems and nuclear waste containment can be sequestered by incorporation into naturally abundant iron (oxyhydr)oxides such as hematite (α-Fe2O3) during mineral growth. The stability and properties of the resulting uranium-doped material are impacted by the local coordination environment of incorporated uranium. While measurements of uranium coordination in hematite have been attempted using extended X-ray absorption fine structure (EXAFS) analysis, traditional shell-by-shell EXAFS fitting yields ambiguous results. We used hybrid functional ab initio molecular dynamics (AIMD) simulations for various defect configurations to generate synthetic EXAFS spectra which were combined with adsorbed uranyl spectra to fit experimental U L3-edge EXAFS for U6+-doped hematite. We discovered that the hematite crystal structure accommodates a trans-dioxo uranyl-like configuration for U6+ that substitutes for structural Fe3+, which requires two partially protonated Fe vacancies situated at opposing corner-sharing sites. Surprisingly, the best match to experiment included significant proportions of vacancy configurations other than the minimum-energy configuration, pointing to the importance of incorporation mechanisms and kinetics in determining the state of an impurity incorporated into a host phase under low temperature hydrothermal conditions.},
doi = {10.1021/acs.est.8b00297},
journal = {Environmental Science and Technology},
number = [11],
volume = [52],
place = {United States},
year = {2018},
month = {5}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1021/acs.est.8b00297

Figures / Tables:

Table 1 Table 1: Local Structure and Energetic Details for U6+ Incorporated in Hematite from AIMD Calculations at 300 K

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.