Uranium Phases in Contaminated Sediments below Hanford’s U Tank Farm
- 12 May 2009
- journal article
- research article
- Published by American Chemical Society (ACS) in Environmental Science & Technology
- Vol. 43 (12), 4280-4286
- https://doi.org/10.1021/es900203r
Abstract
Macroscopic and spectroscopic investigations (XAFS, XRF, and TRLIF) on Hanford contaminated vadose zone sediments from the U-tank farm showed that U(VI) exists as different surface phases as a function of depth below ground surface (bgs). Secondary precipitates of U(VI) silicate precipitates (boltwoodite and uranophane) were present dominantly in shallow-depth sediments (15−16 m bgs), while adsorbed U(VI) phases and polynuclear U(VI) surface precipitates were considered to dominate in intermediate-depth sediments (20−25 m bgs). Only natural uranium was observed in the deeper sediments (>28 m bgs) with no signs of contact with tank wastes containing Hanford-derived U(VI). Across all depths, most of the U(VI) was preferentially associated with the silt and clay size fractions of sediments. Strong correlation between U(VI) and Ca was found in the shallow-depth sediments, especially for the precipitated U(VI) silicates. Because U(VI) silicate precipitates dominate in the shallow-depth sediments, the released U(VI) concentration by macroscopic (bi)carbonate leaching resulted from both desorption and dissolution processes. Having different U(VI) surface phases in the Hanford contaminated sediments indicates that the U(VI) release mechanism could be complicated and that detailed characterization of the sediments using several different methods would be needed to estimate U(VI) fate and transport correctly in the vadose zone.Keywords
This publication has 24 references indexed in Scilit:
- Boltwoodite [K(UO2)(SiO3OH)(H2O)1.5] and compreignacite K2[(UO2)3O2(OH)3]2·7H2O characterized by laser fluorescence spectroscopySpectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2009
- Characterization of Direct Push Vadose Zone Sediments from the 241-U Single-Shell Tank FarmPublished by Office of Scientific and Technical Information (OSTI) ,2007
- Geochemical Controls on Contaminant Uranium in Vadose Hanford Formation Sediments at the 200 Area and 300 Area, Hanford Site, WashingtonVadose Zone Journal, 2007
- A Site Wide Perspective on Uranium Geochemistry at the Hanford SitePublished by Office of Scientific and Technical Information (OSTI) ,2007
- Syntheses and spectroscopic characterization of uranium(VI) silicate mineralsJournal of Radioanalytical and Nuclear Chemistry, 2007
- Spectroscopic Evidence for Uranium Bearing Precipitates in Vadose Zone Sediments at the Hanford 300-Area SiteEnvironmental Science & Technology, 2007
- Adsorbed U(VI) Surface Species on Muscovite Identified by Laser Fluorescence Spectroscopy and Transmission Electron MicroscopyEnvironmental Science & Technology, 2006
- Changes in Uranium Speciation through a Depth Sequence of Contaminated Hanford SedimentsEnvironmental Science & Technology, 2006
- Fluorescence spectroscopy of U(VI)-silicates and U(VI)-contaminated Hanford sedimentGeochimica et Cosmochimica Acta, 2005
- Spectroscopic investigation of U(VI) sorption at the calcite-water interfaceGeochimica et Cosmochimica Acta, 2004