title: Impact of natural organic matter on uranium transport through saturated geologic materials: from molecular to column scale.
abstract: 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.
authors.affiliation: School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511, USA. yutou.one@gmail.com
authors.forename: Yu
authors.initials: Y
authors.lastname: Yang
authors.forename: James E
authors.initials: JE
authors.lastname: Saiers
authors.forename: Na
authors.initials: N
authors.lastname: Xu
authors.forename: Stefan G
authors.initials: SG
authors.lastname: Minasian
authors.forename: Tolek
authors.initials: T
authors.lastname: Tyliszczak
authors.forename: Stosh A
authors.initials: SA
authors.lastname: Kozimor
authors.forename: David K
authors.initials: DK
authors.lastname: Shuh
authors.forename: Mark O
authors.initials: MO
authors.lastname: Barnett
mesh_terms: D000327:Adsorption; D002244:Carbon / Q000032:analysis; D003102:Colloids; D003198:Computer Simulation; D004777:Environment; D019015:Geologic Sediments / Q000737:chemistry*; D006801:Humans; D006812:Humic Substances / Q000032:analysis; D007700:Kinetics; D008970:Molecular Weight; D009038:Motion; D009930:Organic Chemicals / Q000032:analysis*; D010316:Particle Size; D013997:Time Factors; D014501:Uranium / Q000032:analysis*
chemical_list: D003102:Colloids; D006812:Humic Substances; D009930:Organic Chemicals; D014501:Uranium; D002244:Carbon