Impact of Natural Organic Matter on Uranium Transport through Saturated Geologic Materials: From Molecular to Column Scale

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• 作者：Yu Yang ; James E. Saiers ; Na Xu ; Stefan G. Minasian ; Tolek Tyliszczak ; Stosh A. Kozimor ; David K. Shuh ; Mark O. Barnett
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2012
• 出版时间：June 5, 2012
• 年：2012
• 卷：46
• 期：11
• 页码：5931-5938
• 全文大小：334K
• 年卷期：v.46,no.11(June 5, 2012)
• ISSN：1520-5851

文摘

The risk stemming from human exposure to actinides via the groundwater track has motivated numerous studies on the transport of radionuclides within geologic environments; however, the effects of waterborne organic matter on radionuclide mobility are still poorly understood. In this study, we compared the abilities of three humic acids (HAs) (obtained through sequential extraction of a peat soil) to cotransport hexavalent uranium (U) within water-saturated sand columns. Relative breakthrough concentrations of U measured upon elution of 18 pore volumes increased from undetectable levels (<0.001) in an experiment without HAs to 0.17 to 0.55 in experiments with HAs. The strength of the HA effect on U mobility was positively correlated with the hydrophobicity of organic matter and NMR-detected content of alkyl carbon, which indicates the possible importance of hydrophobic organic matter in facilitating U transport. Carbon and uranium elemental maps collected with a scanning transmission X-ray microscope (STXM) revealed uneven microscale distribution of U. Such molecular- and column-scale data provide evidence for a critical role of hydrophobic organic matter in the association and cotransport of U by HAs. Therefore, evaluations of radionuclide transport within subsurface environments should consider the chemical characteristics of waterborne organic substances, especially hydrophobic organic matter.