Cryogenic laser induced fluorescence characterization of U(VI) in Hanford vadose zone pore waters

Zheming Wang, John M. Zachara, Wassana Yantasee, Paul L. Gassman, Chongxuan Liu, Alan G. Joly

Research output: Contribution to journalArticle

120 Scopus citations

Abstract

Ambient and liquid helium temperature laser-induced time-resolved uranyl fluorescence spectroscopy was applied to study the speciation of aqueous uranyl solutions containing carbonate and phosphate and two porewater samples obtained by ultracentrifugation of U(VI)-contaminated sediments. The significantly enhanced fluorescence signal intensity and spectral resolution found at liquid helium temperature allowed, for the first time, direct fluorescence spectroscopic observation of the higher aqueous uranyl complexes with carbonate: UO2(CO3)22-, UO2(CO 3)34-, and (UO2)2(OH) 3CO3-. The porewater samples were nonfluorescent at room temperature. However, at liquid helium temperature, both porewater samples displayed strong, well-resolved fluorescence spectra. Comparisons of the spectroscopic characteristics of the porewaters with those of the standard uranyl-carbonate complexes confirmed that U(VI) in the porewaters existed primarily as UO2(CO3)34- along with a small amount of other minor components, such as dicalcium-urano-tricarbonate complex, Ca2UO2(CO 3)3, consistent with thermodynamic calculation. The U(VI)-carbonate complex is apparently the mobile species responsible for the subsurface migration of U(VI), even though the majority of the in-ground U(VI) inventory at the site from which the samples were obtained exists as intragrain U(VI)-silicate precipitates.

Original languageEnglish (US)
Pages (from-to)5591-5597
Number of pages7
JournalEnvironmental Science and Technology
Volume38
Issue number21
DOIs
StatePublished - Nov 1 2004

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

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