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Title: Trace Uranium Partitioning in a Multiphase Nano-FeOOH System

Abstract

The characterization of trace elements in nanomaterials using extended X-ray absorption fine structure (EXAFS) spectroscopy constitutes a first step toward understanding how impurities or dopants affect the properties of the host phase. However, limitations to EXAFS interpretation complicate the analysis of trace concentrations of impurities that are distributed across multiple phases in a heterogeneous system. Ab initio molecular dynamics (AIMD)-informed EXAFS analysis was employed to investigate the immobilization of trace uranium associated with nanophase iron (oxyhydr)oxides, a model system for the geochemical sequestration of radiotoxic contaminants. The reductive transformation of ferrihydrite (Fe(OH)3) to nano-particulate iron oxyhydroxide minerals in the presence of uranyl (UO2)2+(aq) resulted in the preferential incorporation of U into goethite (a-FeOOH) over lepidocrocite (g-FeOOH), even though reaction conditions favored the formation of excess lepidocrocite. This unexpected result is supported by atomically resolved transmission electron microscopy. Using this model system, we demonstrate how AIMD-informed EXAFS analysis lifts the strict statistical limitations of traditional shell-by-shell EXAFS modeling, enabling the detailed analysis of the local bonding environment, charge compensation mechanisms, and oxidation states of polyvalent impurities in complex multi-phase nano-systems.

Authors:
ORCiD logo; ; ORCiD logo; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1356488
Report Number(s):
PNNL-SA-123284
Journal ID: ISSN 0013-936X; 49691; 48389; 49383; KC0302060
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Science and Technology; Journal Volume: 51; Journal Issue: 9
Country of Publication:
United States
Language:
English
Subject:
ab initio molecular dynamics; iron oxides; reductive transformation; actinide chemistry; uranium sequestration; geochemistry; Environmental Molecular Sciences Laboratory

Citation Formats

McBriarty, Martin E., Soltis, Jennifer A., Kerisit, Sebastien, Qafoku, Odeta, Bowden, Mark E., Bylaska, Eric J., De Yoreo, James J., and Ilton, Eugene S. Trace Uranium Partitioning in a Multiphase Nano-FeOOH System. United States: N. p., 2017. Web. doi:10.1021/acs.est.7b00432.
McBriarty, Martin E., Soltis, Jennifer A., Kerisit, Sebastien, Qafoku, Odeta, Bowden, Mark E., Bylaska, Eric J., De Yoreo, James J., & Ilton, Eugene S. Trace Uranium Partitioning in a Multiphase Nano-FeOOH System. United States. doi:10.1021/acs.est.7b00432.
McBriarty, Martin E., Soltis, Jennifer A., Kerisit, Sebastien, Qafoku, Odeta, Bowden, Mark E., Bylaska, Eric J., De Yoreo, James J., and Ilton, Eugene S. Tue . "Trace Uranium Partitioning in a Multiphase Nano-FeOOH System". United States. doi:10.1021/acs.est.7b00432.
@article{osti_1356488,
title = {Trace Uranium Partitioning in a Multiphase Nano-FeOOH System},
author = {McBriarty, Martin E. and Soltis, Jennifer A. and Kerisit, Sebastien and Qafoku, Odeta and Bowden, Mark E. and Bylaska, Eric J. and De Yoreo, James J. and Ilton, Eugene S.},
abstractNote = {The characterization of trace elements in nanomaterials using extended X-ray absorption fine structure (EXAFS) spectroscopy constitutes a first step toward understanding how impurities or dopants affect the properties of the host phase. However, limitations to EXAFS interpretation complicate the analysis of trace concentrations of impurities that are distributed across multiple phases in a heterogeneous system. Ab initio molecular dynamics (AIMD)-informed EXAFS analysis was employed to investigate the immobilization of trace uranium associated with nanophase iron (oxyhydr)oxides, a model system for the geochemical sequestration of radiotoxic contaminants. The reductive transformation of ferrihydrite (Fe(OH)3) to nano-particulate iron oxyhydroxide minerals in the presence of uranyl (UO2)2+(aq) resulted in the preferential incorporation of U into goethite (a-FeOOH) over lepidocrocite (g-FeOOH), even though reaction conditions favored the formation of excess lepidocrocite. This unexpected result is supported by atomically resolved transmission electron microscopy. Using this model system, we demonstrate how AIMD-informed EXAFS analysis lifts the strict statistical limitations of traditional shell-by-shell EXAFS modeling, enabling the detailed analysis of the local bonding environment, charge compensation mechanisms, and oxidation states of polyvalent impurities in complex multi-phase nano-systems.},
doi = {10.1021/acs.est.7b00432},
journal = {Environmental Science and Technology},
number = 9,
volume = 51,
place = {United States},
year = {Tue Apr 11 00:00:00 EDT 2017},
month = {Tue Apr 11 00:00:00 EDT 2017}
}
  • The characterization of trace elements in minerals using extended X-ray absorption fine structure (EXAFS) spectroscopy constitutes a first step toward understanding how impurities and contaminants interact with the host phase and the environment. However, limitations to EXAFS interpretation complicate the analysis of trace concentrations of impurities that are distributed across multiple phases in a heterogeneous system. Ab initio molecular dynamics (AIMD)-informed EXAFS analysis was employed to investigate the immobilization of trace uranium associated with nanophase iron (oxyhydr)oxides, a model system for the geochemical sequestration of radiotoxic actinides. The reductive transformation of ferrihydrite [Fe(OH)3] to nanoparticulate iron oxyhydroxide minerals in themore » presence of uranyl (UO 2) 2+(aq) resulted in the preferential incorporation of U into goethite (α-FeOOH) over lepidocrocite (γ-FeOOH), even though reaction conditions favored the formation of excess lepidocrocite. This unexpected result is supported by atomically resolved transmission electron microscopy. We demonstrate how AIMD-informed EXAFS analysis lifts the strict statistical limitations and uncertainty of traditional shell-by-shell EXAFS fitting, enabling the detailed characterization of the local bonding environment, charge compensation mechanisms, and oxidation states of polyvalent impurities in complex multiphase mineral systems.« less
  • Incorporation of economically or environmentally consequential polyvalent metals into iron (oxyhydr)oxides has applications in environmental chemistry, remediation, and materials science. A primary tool for characterizing the local coordination environment of such metals, and therefore building models to predict their behavior, is extended X-ray absorption fine structure spectroscopy (EXAFS). Accurate structural information can be lacking, yet is required to constrain and inform data interpretation. In this regard, ab initio molecular dynamics (AIMD) was used to calculate the local coordination environment of minor amounts of U incorporated in the structure of goethite (α-FeOOH). U oxidation state (VI, V, and IV) and chargemore » compensation scheme (CCS) were varied. Simulated trajectories were used to calculate the U LIII-edge EXAFS function and fit experimental EXAFS data for U incorporated into goethite under reducing conditions. Calculations that closely matched the U EXAFS of the well-characterized mineral uraninite (UO2), and constrained the S02 parameter to be 0.909, validated the approach. The results for the U-goethite system indicated that U(V) substituted for structural Fe(III) in octahedral uranate coordination. Charge balance was achieved by the loss of one structural proton coupled to injection of one electron into the solid (–1 H+, + 1 e-). The ability of AIMD to model higher-energy states thermally accessible at room temperature is particularly relevant for protonated systems such as goethite, where proton transfers between adjacent octahedra had a dramatic effect on the calculated EXAFS. Vibrational effects as a function of temperature were also estimated using AIMD, allowing separate quantification of thermal and configurational disorder. In summary, coupling AIMD structural modeling and EXAFS experiments enables modeling of the redox behavior of polyvalent metals that are incorporated in conductive materials such as iron (oxyhydr)oxides, with applications over a broad swath of chemistry and materials science.« less
  • An aqueous suspension of amorphous iron(III) hydroxide was kept at room temperature (298 K) for 23 years. During this period of time the pH of the liquid phase changed from 4.3 to 2.85, and nano size crystals of goethite, {alpha}-FeOOH crystallized from the amorphous iron(III) hydroxide. Transmission electron microscopy (TEM) investigations, Moessbauer spectra, and powder X-ray diffraction using Co K{alpha} radiation showed that the only iron containing crystalline phase present in the recovered product was {alpha}-FeOOH. The size of these nano particles range from 10 to 100 nm measured by TEM. The thermal decomposition of {alpha}-FeOOH was investigated by time-resolvedmore » in situ synchrotron radiation powder X-ray diffraction and the data showed that the sample of {alpha}-FeOOH transformed to {alpha}-Fe{sub 2}O{sub 3} in the temperature range 444--584 K. A quantitative phase analysis shows the increase in scattered X-ray intensity from {alpha}-Fe{sub 2}O{sub 3} to follow the decrease of intensity from {alpha}-FeOOH in agreement with the topotactic phase transition.« less
  • An aqueous suspension of amorphous iron(III) hydroxide was kept at room temperature (298 K) for 23 years. During this period of time the pH of the liquid phase changed from 4.3 to 2.85, and nano size crystals of goethite, {alpha}-FeOOH crystallised from the amorphous iron(III) hydroxide. Transmission electron microscopy (TEM) investigations, Moessbauer spectra, and powder X-ray diffraction using Co K{alpha} radiation showed that the only iron containing crystalline phase present in the recovered product was {alpha}-FeOOH. The size of these nano particles range from 10 to 100 nm measured by TEM. The thermal decomposition of {alpha}-FeOOH was investigated by time-resolvedmore » in situ synchrotron radiation powder X-ray diffraction and the data showed that the sample of {alpha}-FeOOH transformed to {alpha}-Fe{sub 2}O{sub 3} in the temperature range 444-584 K. A quantitative phase analysis shows the increase in scattered X-ray intensity from {alpha}-Fe{sub 2}O{sub 3} to follow the decrease of intensity from {alpha}-FeOOH in agreement with the topotactic phase transition. - Graphical abstract: Nano size crystals of goethite, {alpha}-FeOOH formed from amorphous iron(III) hydroxide after 23 years, and transforms faster to {alpha}-Fe{sub 2}O{sub 3} upon heating.« less
  • The U.S. Department of Energy is currently working on coupling coal gasification and high temperature fuel cell to produce electrical power in a highly efficient manner while being emissions free. Many investigations have already investigated the effects of major coal syngas species such as CO and H2S. However coal contains many trace species and the effect of these species on solid oxide fuel cell anode is not presently known.Warm gas cleanup systems are planned to be used with these advanced power generation systems for the removal of major constituents such as H2S and HCl but the operational parameters of suchmore » systems is not well defined at this point in time. This paper focuses on the effect of anticipated warm gas cleanup conditions has on trace specie partitioning between the vapor and condensed phase and the effects the trace vapor species have on the SOFC anode. Results show that Be, Cr, K, Na, V, and Z trace species will form condensed phases and should not effect SOFC anode performance since it is anticipated that the warm gas cleanup systems will have a high removal efficiency of particulate matter. Also the results show that Sb, As, Cd, Hg, Pb, P, and Se trace species form vapor phases and the Sb, As, and P vapor phase species show the ability to form secondary Ni phases in the SOFC anode.« less