title: (99)Tc(VII) Retardation, Reduction, and Redox Rate Scaling in Naturally Reduced Sediments.
abstract: An experimental and modeling study was conducted to investigate pertechnetate (Tc(VII)O4(-)) retardation, reduction, and rate scaling in three sediments from Ringold formation at U.S. Department of Energy's Hanford site, where (99)Tc is a major contaminant in groundwater. Tc(VII) was reduced in all the sediments in both batch reactors and diffusion columns, with a faster rate in a sediment containing a higher concentration of HCl-extractable Fe(II). Tc(VII) migration in the diffusion columns was reductively retarded with retardation degrees correlated with Tc(VII) reduction rates. The reduction rates were faster in the diffusion columns than those in the batch reactors, apparently influenced by the spatial distribution of redox-reactive minerals along transport paths that supplied Tc(VII). X-ray computed tomography and autoradiography were performed to identify the spatial locations of Tc(VII) reduction and transport paths in the sediments, and results generally confirmed the newly found behavior of reaction rate changes from batch to column. The results from this study implied that Tc(VII) migration can be reductively retarded at Hanford site with a retardation degree dependent on reactive Fe(II) content and its distribution in sediments. This study also demonstrated that an effective reaction rate may be faster in transport systems than that in well-mixed reactors.
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Chongxuan
authors.initials: C
authors.lastname: Liu
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Ravi K
authors.initials: RK
authors.lastname: Kukkadapu
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: James P
authors.initials: JP
authors.lastname: McKinley
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: John
authors.initials: J
authors.lastname: Zachara
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Plymale
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Micah D
authors.initials: MD
authors.lastname: Miller
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Tamas
authors.initials: T
authors.lastname: Varga
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Charles T
authors.initials: CT
authors.lastname: Resch
mesh_terms: D001345:Autoradiography; D019015:Geologic Sediments / Q000032:analysis / Q000737:chemistry*; D060587:Groundwater; D062070:Hydrology / Q000379:methods; D008855:Microscopy, Electron, Scanning; D008962:Models, Theoretical; D010084:Oxidation-Reduction; D013670:Sodium Pertechnetate Tc 99m / Q000737:chemistry*; D015204:Spectroscopy, Mossbauer; D014057:Tomography, X-Ray Computed / Q000379:methods; D014861:Washington; D014875:Water Pollutants, Radioactive / Q000737:chemistry*
chemical_list: D014875:Water Pollutants, Radioactive; D013670:Sodium Pertechnetate Tc 99m