title: Spectroscopic evidence of uranium immobilization in acidic wetlands by natural organic matter and plant roots.
abstract: 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 2 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 reoxidized 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 stewardship of U-contaminated wetlands.
authors: Savannah River National Laboratory, Aiken, South Carolina 29808, United States.
authors: Dien
authors: D
authors: Li
authors: Daniel I
authors: DI
authors: Kaplan
authors: Hyun-Shik
authors: HS
authors: Chang
authors: John C
authors: JC
authors: Seaman
authors: Peter R
authors: PR
authors: Jaffé
authors: Paul
authors: P
authors: Koster van Groos
authors: Kirk G
authors: KG
authors: Scheckel
authors: Carlo U
authors: CU
authors: Segre
authors: Ning
authors: N
authors: Chen
authors: De-Tong
authors: DT
authors: Jiang
authors: Matthew
authors: M
authors: Newville
authors: Antonio
authors: A
authors: Lanzirotti
mesh_terms: D019015:Geologic Sediments / Q000737:chemistry; D008903:Minerals / Q000737:chemistry; D010084:Oxidation-Reduction; D018517:Plant Roots / Q000737:chemistry*; D045483:Rivers / Q000737:chemistry; D014501:Uranium / Q000737:chemistry*; D014875:Water Pollutants, Radioactive / Q000737:chemistry; D053833:Wetlands; D056928:X-Ray Absorption Spectroscopy
chemical_list: D008903:Minerals; D014875:Water Pollutants, Radioactive; D014501:Uranium