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Environmental Processes
Organic Functional Group Chemistry in Mineralized Deposits containing U(IV) and U(VI) from the Jackpile Mine in New Mexico Carmen A. Velasco, Kateryna Artyushkova, Abdul-Mehdi S. Ali, Christopher L. Osburn, Jorge Gonzalez-Estrella, Juan S. Lezama-Pacheco, Stephen E. Cabaniss, and Jose M Cerrato Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 18 Apr 2019 Downloaded from http://pubs.acs.org on April 18, 2019
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Environmental Science & Technology
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Organic Functional Group Chemistry in Mineralized
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Deposits containing U(IV) and U(VI)
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from the Jackpile Mine in New Mexico
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Carmen A. Velasco1, Kateryna Artyushkova2, Abdul-Mehdi S. Ali3, Christopher L. Osburn4,
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Jorge Gonzalez-Estrella1, Juan S. Lezama Pacheco5, Stephen E. Cabaniss6, and
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José M. Cerrato1*
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*Corresponding email address:
[email protected] 8
Telephone: (001) (505) 277-0870
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Fax: (001) (505) 277-1918
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Department of Civil, Construction & Environmental Engineering, MSC01 1070, University of New Mexico, Albuquerque, New Mexico 87131, USA Department of Chemical and Biological Engineering, MSC01 1120, University of New Mexico, Albuquerque, New Mexico 87131, USA Department of Earth and Planetary Sciences, MSC03 2040, University of New Mexico, Albuquerque, New Mexico 87131, USA Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, United States Department of Environmental Earth System Science, Stanford University, California 94305
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA
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ABSTRACT: We investigated the functional group chemistry of natural organic matter (NOM)
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associated with both U(IV) and U(VI) in solids from mineralized deposits exposed to oxidizing
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conditions from the Jackpile Mine, Laguna Pueblo, NM. The Uranium (U) content in unreacted
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samples was 0.44% to 2.6% by weight determined by X-ray fluorescence (XRF). In spite of
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prolonged exposure to ambient oxidizing conditions, ≈49% of U(IV) and ≈51% of U(VI) were
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identified on U-LIII edge extended X-ray absorption fine structure (EXAFS) spectra. Loss on
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ignition and thermogravimetric analyses (TGA) identified from 13% to 44% of NOM in the
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samples. Carbonyl, phenolic and carboxylic functional groups in the unreacted samples were
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identified by fitting of high-resolution X-ray photoelectron spectroscopy (XPS) C 1s and O 1s
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spectra. Peaks corresponding to phenolic and carbonyl functional groups had higher intensity
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than those corresponding to carboxylic groups in samples from the supernatant from batch
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extractions conducted at pH 13, 7 and 2. U(IV) and U(VI) species were detected in the
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supernatant after batch extractions conducted under oxidizing conditions by fitting of high-
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resolution XPS U 4f spectra. The outcomes from this study highlight the importance of the pH
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influence on the organic functional group chemistry and U speciation in mineralized deposits.
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Environmental Science & Technology
TOC Art
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Jackpile Mine pH2 pH7 pH13
Spectroscopy
solid samples
A, C: terrestrial humic substances
Batch Reactions
13% - 44% organic matter
A
C
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Introduction
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The legacy of operations for uranium (U) mining in the USA has impacted several sites,
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many of which are located in Native American communities. Studies have reported U
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concentrations of 35.3-772 μg L−1 in surface waters near the Pueblo of Laguna, New Mexico
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(NM) neighboring the Jackpile Mine.1 These concentrations exceed the US Environmental
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Protection Agency maximum contaminant limit of 30 μg L−1.2 Additionally, the U concentration
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detected in solid samples from the Jackpile Mine, adjacent to the Rio Paguate, was 9300 mg
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kg−1.1 A recent study in the Grants Mining District in NM reports that the mineralogy of U-
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bearing dust affects the extent of U dissolution in simulated lung fluids, which could have
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potential health implications. 3 The Jackpile Mine has been listed in the EPA National Priorities
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List for CERCLA cleanup.4
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Natural organic matter (NOM) and U co-occur in the Jackpile Sandstone Member of the
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Morrison Formation. Sandstone formations are characterized by varied sizes of sorted pebbles
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and sands, and lenses of concentrated NOM.5 Uranium is trapped within the NOM-layers of
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detritus and humus, leading to the formation of NOM-U rich deposits.6 Reduced U was found in
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solid samples from mineralized deposits in the Jackpile Mine despite being exposed to oxidizing
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conditions for several decades.1 Studies have found coffinite (USiO4(s)) either as crystals
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precipitated or embedded in layers of amorphous NOM-bearing grain coatings in the Grants
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region, NM.7-11 Natural organic matter may enhance the preservation of U(IV) phases for more
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than 30 million years exposed to oxidizing fluids.5, 12
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Organic functional groups play a key role in the chemical speciation and reactivity of U
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and other metals in the environment. Dissolved humic substances facilitate the transport of U and
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other metals as a function of pH by affecting the sorption on mineral surfaces.13-16 Soluble U
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complexes with humic substances in peats.17 The formation of U(VI)-humate complexes between
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pH 4 and 6 can influence sorption of U on NOM.17, 18 Previous studies found U is predominantly
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bound in bidentate-mononuclear complexes to carboxyl ligands in natural NOM, inhibiting the
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precipitation of U minerals.19-22 Furthermore, U(IV) can complex with NOM functional groups,
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resulting in the formation of monomeric U(IV) species that have been observed in anoxic
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sediments and ore deposits together with other crystalline U(IV) phases such as uraninite.23-26
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Other studies reported NOM complexation influences the abiotic oxidation rate of Fe(II) by O2.27,
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anaerobic microbial respiration, while phenols serve as electron donors for the reduction of
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electron acceptors, such as Fe(III), Mn(IV), arsenate, Cr(VI), and U(IV).30-32 Despite these
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findings, the influence of pH on the organic functional group chemistry and U(IV) and U(VI) co-
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occurring in U mine sites remained unknown.
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For example, functional groups such as quinones act as terminal electron acceptors in
While the presence of NOM in sandstone formations is well established, the functional
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groups have not been identified.1,
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functional group chemistry found in sandstone formations and mineralized U deposits will help
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to identify the binding mechanisms influencing the interactions of U and NOM. These
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interactions may ultimately affect the reactive transport of U in soils, surface water and
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groundwater, and uptake in plants.36 Although several methods have been used to understand the
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mineralogy of sandstone formations and U mineralized deposits, the analysis of particulate NOM
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is challenging.6 The application of X-ray photoelectron spectroscopy (XPS) to observe changes
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of organic functional groups in U mineralized deposits as a result of pH changes is not well
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documented.37,
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Improving the current understanding on the organic
Integrating XPS analyses with other physical and chemical methods could
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provide new information about NOM functional chemistry in U samples from mineralized
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deposits.
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The objective of this study is to identify the organic functional group chemistry in U
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mineralized deposits from the Jackpile Mine. We integrated excitation emission matrix
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spectroscopy (EEMS), XPS, XAS, thermal analyses and batch extraction experiments. A novel
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aspect of this investigation is identifying the influence of pH on the organic functional group
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chemistry, U(IV) and U(VI) co-occurring in samples of complex mineralogy from a sandstone
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geological formation through the integration of a variety of analytical techniques with laboratory
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experiments. The results of this study provide insights about the reactions between NOM and U
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in mineralized deposits which are relevant for risk assessment and remediation strategies.
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Materials and Methods
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Sample Collection. Two solid samples (JP1 and JP2) from mineralized deposits from the
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Jackpile Mine (35° 8'28.09"N, 107°20'19.67"W) were collected from a location described in a
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previous study.1 Samples were collected in the summer of 2017, crushed, and sieved with a US
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Standard #230 mesh (63 m). We referred as “unreacted samples” to the crushed and sieved
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solids before any treatment was applied to them.
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Solid analyses. Solid phase analyses were conducted on unreacted samples by X-Ray
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Fluorescence (XRF); and C, H, N, and O elemental analysis. X-ray absorption spectroscopy
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(XAS) and XPS were performed on unreacted samples, on reacted solids after loss-on-ignition
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(LOI), and on solids remaining from batch extraction experiments. X-ray absorption
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spectroscopy measurements were conducted at Beamline 7-3 at the Stanford Synchrotron
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Radiation Laboratory (SSRL) at the U LIII Edge in fluorescence mode. Data was collected at
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room temperature in a He purged environmental chamber. Linear combination fitting was
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performed using the following reference materials as end-members as measured from other
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studies: monomeric U(IV),39 uraninite,40 U(VI) adsorbed with ferrihydrite,41 and the coffinite
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reference was obtained from the Mineral Library from the University of New Mexico.
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References and standards were pulverized and pressed into the slots of aluminum holders and
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sealed with Kapton tape on both sides Data processing and analyses for XAS was conducted
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using Athena and Artemis.42 A Kratos Ultra DLD X-ray Photoelectron Spectrometer was used to
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acquire the near surface (
