Long-term desorption behavior of uranium and neptunium in heterogeneous volcanic tuff materials /

Dean, Cynthia A.

doi:10.2172/982224

Cited by 2 publications

(2 citation statements)

References 68 publications

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“…Given that the final pH was lowest in the 0.2 g experiments, it is reasonable that the desorption rate constant would be smallest in the 0.2 g experiments. We note that the trend of less uranium adsorption per unit mass of solids as the solids mass increased in the batch experiments is the opposite of what is expected for a nonlinear adsorption isotherm, which has frequently been observed for uranium on various mineral surfaces (Arnold et al, 2011;Dean, 2010;Davis, 2001;Kohler and Davis, 2001;Kohler et al, 1996;Waite et al, 1994). We attribute this trend to the tendency for uranium to adsorb more strongly at the lower pHs of the experiments with lower solid-to-solution ratios.…”

Section: Batch Sorption Experimentsmentioning

confidence: 48%

Uranium transport in a crushed granodiorite: Experiments and reactive transport modeling

Dittrich

Reimus

2015

Journal of Contaminant Hydrology

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The primary objective of this study was to develop and demonstrate an experimental method to refine and better parameterize process models for reactive contaminant transport in aqueous subsurface environments and to reduce conservatism in such models without attempting to fully describe the geochemical system. Uranium was used as an example of a moderately adsorbing contaminant because of its relevance in geologic disposal of spent nuclear fuel. A fractured granodiorite from the Grimsel Test Site (GTS) in Switzerland was selected because this system has been studied extensively and field experiments have been conducted with radionuclides including uranium. We evaluated the role of pH, porous media size fraction, and flow interruptions on uranium transport. Rock cores drilled from the GTS were shipped to Los Alamos National Laboratory, characterized by x-ray diffraction and optical microscopy, and used in uranium batch sorption and column breakthrough experiments. A synthetic water was prepared that represented the porewater that would be present after groundwater interacts with bentonite backfill material near a nuclear waste package. Uranium was conservatively transported at pH8.8. Significant adsorption and subsequent desorption was observed at pH ~7, with long desorption tails resulting after switching the column injection solution to uranium-free groundwater. Our experiments were designed to better interrogate this slow desorption behavior. A three-site model predicted sorption rate constants for a pH7.2 solution with a 75-150 μm granodiorite fraction to be 3.5, 0.012, and 0.012 mL/g-h for the forward reactions and 0.49, 0.0025, and 0.001 h(-1) for the reverse reactions. Surface site densities were 1.3, 0.042, and 0.042 μmol/g for the first, second, and third sites, respectively. 10-year simulations show that including a slow binding site increases the arrival time of a uranium pulse by ~70%.

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Section: Batch Sorption Experimentsmentioning

confidence: 48%

Uranium transport in a crushed granodiorite: Experiments and reactive transport modeling

Dittrich

Reimus

2015

Journal of Contaminant Hydrology

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“…This approach to modeling sorption assumes that rates of sorption/desorption between radionuclides and the sorptive medium are orders of magnitude more rapid than the advective groundwater velocity. However, recent studies have shown that desorption rates of U and 237 Np may yield a 3-4 order of magnitude range of desorption rate constants despite uniform flow fields approximating equilibirum conditions (Arnold et al, 2011;Dean, 2010). We recommend from a cost savings perspective that candidate rock masses be screened on the basis of sorption coefficients determined from laboratory batch experiments.…”

Section: Radionuclide Adsorptionmentioning

confidence: 99%

Hydrogeologic Characterization of Fractured Rock Masses Intended for Disposal of Radioactive Waste

Reeves¹,

Parashar²,

Zhang³

2012

Radioactive Waste

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Long-term desorption behavior of uranium and neptunium in heterogeneous volcanic tuff materials /

Cited by 2 publications

References 68 publications

Uranium transport in a crushed granodiorite: Experiments and reactive transport modeling

Uranium transport in a crushed granodiorite: Experiments and reactive transport modeling

Hydrogeologic Characterization of Fractured Rock Masses Intended for Disposal of Radioactive Waste

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