Title: Complexation by Organic Matter Controls Uranium Mobility in Anoxic Sediments

Abstract

Uranium contamination threatens the availability of safe and clean drinking water globally. This toxic element occurs both naturally and as a result of mining and ore-processing in alluvial sediments, where it accumulates as tetravalent U [U(IV)], a form once considered largely immobile. Changing hydrologic and geochemical conditions cause U to be released into groundwater. Knowledge of the chemical form(s) of U(IV) is essential to understand the release mechanism, however, the relevant U(IV) species are poorly characterized. There is growing belief that natural organic matter (OM) binds U(IV) and mediates its fate in the subsurface. In this work, we combined nanoscale imaging (nano secondary ion mass spectrometry and scanning transmission X-ray microscopy) with a density-based fractionation approach to physically and microscopically isolate organic and mineral matter from alluvial sediments contaminated with uranium. We identified two populations of U (dominantly +IV) in anoxic sediments. Uranium was retained on OM and adsorbed to particulate organic carbon, comprising both microbial and plant material. Surprisingly, U was also adsorbed to clay minerals and OM-coated clay minerals. The dominance of OM-associated U provides a framework to understand U mobility in the shallow subsurface, and, in particular, emphasizes roles for desorption and colloid formation in its mobilization.

Authors:

Bone, Sharon E.  ^[1];

• Search DOE PAGES for author "Bone, Sharon E."
• Search DOE PAGES for ORCID "0000-0002-7521-9627"

Cliff, John ^[2]; Weaver, Karrie  ^[3];

• Search DOE PAGES for author "Weaver, Karrie"
• Search DOE PAGES for ORCID "0000-0002-7094-3501"

Takacs, Christopher J. ^[1]; Roycroft, Scott ^[3]; Fendorf, Scott  ^[3];

• Search DOE PAGES for author "Fendorf, Scott"
• Search DOE PAGES for ORCID "0000-0002-9177-1809"

Bargar, John R.  ^[1]

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• Search DOE PAGES for ORCID "0000-0001-9303-4901"

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+ Show Author Affiliations

1. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
3. Stanford Univ., CA (United States). Earth System Science Dept.

Publication Date:

Thu Dec 26 00:00:00 EST 2019

Research Org.:

SLAC National Accelerator Lab., Menlo Park, CA (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); Natural Sciences and Engineering Research Council of Canada (NSERC); Canadian Institutes of Health Research (CIHR); National Research Council Canada (NRC); Western Economic Diversification Canada; Province of Saskatchewan

OSTI Identifier:

1605282

Alternate Identifier(s):

OSTI ID: 1600519

Report Number(s):

PNNL-SA-142857
Journal ID: ISSN 0013-936X; TRN: US2104413

Grant/Contract Number:  

AC02-76SF00515; AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Environmental Science and Technology

Additional Journal Information:

Journal Volume: 54; Journal Issue: 3; Journal ID: ISSN 0013-936X

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; Geological materials; Uranium; Nanoparticles; Minerals; Clay; 54 ENVIRONMENTAL SCIENCES