Cryogenic Laser Induced U(VI) Fluorescence Studies of a U(VI) Substituted Natural Calcite: Implications to U(VI) Speciation in Contaminated Hanford Sediments
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- 作者：Zheming Wang ; John M. Zachara ; James P. McKinley ; and Steven C. Smith
- 刊名：Environmental Science & Technology
- 出版年：2005
- 出版时间：April 15, 2005
- 年：2005
- 卷：39
- 期：8
- 页码：2651 - 2659
- 全文大小：462K
- 年卷期：v.39,no.8(April 15, 2005)
- ISSN：1520-5851
文摘
Time-resolved laser-induced fluorescence spectroscopy(TRLFS) and imaging spectromicroscopy (TRLFISM) wereused to examine the chemical speciation of uranyl incontaminated subsurface sediments from the U.S. Departmentof Energy (U.S. DOE) Hanford Site, Washington. Spectroscopic measurements for contaminant U(VI) were comparedto those from a natural, uranyl-bearing calcite (NUC)that had been found via X-ray absorption spectroscopy(XAS) to include uranyl in the same coordination environmentas calcium. Spectral deconvolution of TRLFS measurementson the NUC revealed the unexpected presence of twodistinct chemical environments consistent with publishedspectra of U(VI)-substituted synthetic calcite and aragonite.Apparently, some U(VI) substitution sites in calcitedistorted to exhibit a local, more energetically favorablearagonite structure. TRLFS measurements of the Hanfordsediments NP4-1 and NP1-6 were similar to the NUC interms of peak positions and intensity, despite a smallCaCO3 content (1.0 to 3.2 mass %). Spectral deconvolutionof the sediments revealed the presence of U(VI) incalcite and aragonite structural environments. A third,unidentified U(VI) species was also present in the NP1-6sediment. TRLFISM measurements at multiple locationsin the different sediments displayed only minor variation,indicating a uniform speciation pattern. Collectively,the measurements implied that waste U(VI), long-residentbeneath the sampled disposal pond (32 y), hadcoprecipitated within carbonates. These findings havemajor implications for the solubility and fate of contaminantU(VI).