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Title: Spectroscopic evidence of uranium immobilization in acidic wetlands by natural organic matter and plant roots

Biogeochemistry of uranium in wetlands plays important roles in U immobilization in storage ponds of U mining and processing facilities but has not been well understood. The objective of this work was to study molecular mechanisms responsible for high U retention by Savannah River Site (SRS) wetland sediments under varying redox and acidic (pH = 2.6–5.8) conditions using U L₃-edge X-ray absorption spectroscopy. Uranium in the SRS wetland sediments existed primarily as U(VI) bonded as a bidentate to carboxylic sites (U–C bond distance at ~2.88 Å), rather than phenolic or other sites of natural organic matter (NOM). In microcosms simulating the SRS wetland processes, U immobilization on roots was two orders of magnitude higher than on the adjacent brown or more distant white sands in which U was U(VI). Uranium on the roots were both U(IV) and U(VI), which were bonded as a bidentate to carbon, but the U(VI) may also form a U phosphate mineral. After 140 days of air exposure, all U(IV) was re-oxidized to U(VI) but remained as a bidentate bonding to carbon. This study demonstrated NOM and plant roots can highly immobilize U(VI) in the SRS acidic sediments, which has significant implication for the long-term stewardshipmore » of U-contaminated wetlands.« less
Authors:
 [1] ;  [1] ;  [2] ;  [2] ;  [3] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [8]
  1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
  2. Savannah River Site (SRS), Aiken, SC (United States). Savannah River Ecology Lab. (SREL)
  3. Princeton Univ., NJ (United States). Dept. of Civil and Environmental Engineering
  4. US Environmental Protection Agency (EPA), Cincinnati, OH (United States). National Risk Management Research Lab.
  5. Illinois Inst. of Technology, Chicago, IL (United States). Physics Dept. and CSRRI
  6. Canadian Light Sources, Inc., Saskatoon, SK (Canada)
  7. Univ. of Guelph, ON (Canada). Dept. of Physics
  8. Univ. of Chicago, IL (United States). Center for Advanced Radiation Sources (CARS)
Publication Date:
OSTI Identifier:
1174137
Report Number(s):
SRNS-STI--2015-00177
Journal ID: ISSN 0013-936X
Grant/Contract Number:
AC09-96SR18500; FC09-07SR22506; AC09-08SR22470; SC0006847; AC02-06CH11357; FG02-94ER14466
Type:
Accepted Manuscript
Journal Name:
Environmental Science and Technology
Additional Journal Information:
Journal Volume: 49; Journal Issue: 5; Journal ID: ISSN 0013-936X
Publisher:
American Chemical Society (ACS)
Research Org:
Savannah River Site (SRS), Aiken, SC (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); Office of Environmental Management (EM)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 54 ENVIRONMENTAL SCIENCES ray-absorption-spectroscopy; savanna river site; in-situ; contaminated sediments; hydroxyapatite addition; chemical speciation; reducing conditions; u(vi) bioreduction; humic acids; reduction