Title: Uranium(IV) adsorption by natural organic matter in anoxic sediments

Abstract

Uranium is an important fuel source and a global environmental contaminant. It accumulates in the tetravalent state, U(IV), in anoxic sediments, including ore deposits, marine basins, and contaminated aquifers. However, very little is known about the speciation of U(IV) in low temperature geochemical environments, inhibiting the development of a conceptual model of U behavior. Until recently, U(IV) was assumed to exist predominantly as the sparingly soluble mineral uraninite (UO₂) in anoxic sediments; yet studies now show that UO₂ is not often dominant in these environments. However, a model of U(IV) speciation under environmentally relevant conditions has not yet been developed. Here we show that complexes of U(IV) adsorb on organic carbon and organic carbon-coated clays in an organic-rich natural substrate under field-relevant conditions. Whereas previous research assumed that the U(IV) product depended on the reduction pathway, our results demonstrate that UO₂ formation can be inhibited simply by decreasing the U:solid ratio. Thus, it is the number and type of surface ligands that controls U(IV) speciation subsequent to U(VI) reduction. Projections of U transport and bioavailability, and thus its threat to human and ecosystem health, must consider retention of U(IV) ions within the local sediment environment.

Authors:

Bone, Sharon E. ^[1]; Dynes, James J. ^[2]; Cliff, John ^[3]; Bargar, John R. ^[1]

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+ Show Author Affiliations

1. Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025,
2. Canadian Light Source, Saskatoon, SK S7N 2V3, Canada,
3. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354

Publication Date:

Mon Jan 09 00:00:00 EST 2017

Research Org.:

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

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1338629

Alternate Identifier(s):

OSTI ID: 1340156; OSTI ID: 1344623

Report Number(s):

SLAC-PUB-16909; PNNL-SA-119314
Journal ID: ISSN 0027-8424

Grant/Contract Number:  

AC02-76SF00515; AC05-76RL01830

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 114 Journal Issue: 4; Journal ID: ISSN 0027-8424

Publisher:

Proceedings of the National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; 36 MATERIALS SCIENCE; EARTH, ENV; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Environmental Molecular Sciences Laboratory