Complexation by Organic Matter Controls Uranium Mobility in Anoxic Sediments

Journal Article · Thu Dec 26 00:00:00 EST 2019 · Environmental Science and Technology

DOI:https://doi.org/10.1021/acs.est.9b04741· OSTI ID:1600519

Bone, Sharon E. ^[1]; Cliff, John ^[2]; Weaver, Karrie ^[3]; Takacs, Christopher J. ^[1]; Roycroft, Scott ^[3]; Fendorf, Scott ^[3]; Bargar, John R. ^[1]

---

1. Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
2. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
3. Earth System Science Department, Stanford University, Stanford, California 94305, United States

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.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States). Environmental Molecular Sciences Laboratory (EMSL); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: Canadian Institutes of Health Research (CIHR); National Research Council Canada (NRC); Natural Sciences and Engineering Research Council of Canada (NSERC); Province of Saskatchewan; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); Western Economic Diversification Canada
• Grant/Contract Number: AC02-76SF00515; AC05-76RL01830
• OSTI ID: 1600519
• Alternate ID(s): OSTI ID: 1605282
• Report Number(s): PNNL-SA--142857
• Journal Information: Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 3 Vol. 54; ISSN 0013-936X
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
Clay
Geological materials
Minerals
Nanoparticles
Uranium