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Title: Characterization of U9VI) Sorption-Desorption Processes and Model Upscaling

Abstract

Long-term sequestration of uranium at sites within the DOE complex is a significant problem that requires molecular-level information on the speciation, phase association, and spatial distribution of uranium

Authors:
; ; ;
Publication Date:
Research Org.:
Stanford Univ., CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
911851
Report Number(s):
DOE/E/63495
TRN: US0800002
DOE Contract Number:
FG07-02ER63495
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; SPATIAL DISTRIBUTION; URANIUM; SORPTION; DESORPTION; PHASE STUDIES; CHEMICAL STATE; UNDERGROUND DISPOSAL

Citation Formats

Gordon Borwn Jr., Jeffrey Catalano, David Singer, and John Zachara. Characterization of U9VI) Sorption-Desorption Processes and Model Upscaling. United States: N. p., 2007. Web. doi:10.2172/911851.
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Gordon Borwn Jr., Jeffrey Catalano, David Singer, & John Zachara. Characterization of U9VI) Sorption-Desorption Processes and Model Upscaling. United States. doi:10.2172/911851.
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Gordon Borwn Jr., Jeffrey Catalano, David Singer, and John Zachara. Thu . "Characterization of U9VI) Sorption-Desorption Processes and Model Upscaling". United States. doi:10.2172/911851. https://www.osti.gov/servlets/purl/911851.
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@article{osti_911851,
title = {Characterization of U9VI) Sorption-Desorption Processes and Model Upscaling},
author = {Gordon Borwn Jr. and Jeffrey Catalano and David Singer and John Zachara},
abstractNote = {Long-term sequestration of uranium at sites within the DOE complex is a significant problem that requires molecular-level information on the speciation, phase association, and spatial distribution of uranium},
doi = {10.2172/911851},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu May 24 00:00:00 EDT 2007},
month = {Thu May 24 00:00:00 EDT 2007}
}
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Technical Report:
View Technical Report (2.36 MB)
DOI:  10.2172/911851
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  • The objectives of the overall collaborative EMSP effort (with which this project is associated) are to characterize sorption and desorption processes of U(VI) on pristine and contaminated Hanford sediments over a range of sediment facies and materials properties. The research is intended to provide new insights on the mechanisms of U(VI) retardation at Hanford, and to develop approaches by which laboratory-characterized geochemical models can be upscaled for defensible predictions of uranium transport in field.

  • In order to apply predictive reactive transport models to the Hanford site, detailed knowledge of the speciation of contaminants is required. Important speciation parameters include: (1) oxidation state; (2) the local molecular structure surrounding contaminant elements; (3) the type and binding of a contaminant ion sorption complex (if adsorbed); (4) the type(s) of phase within which a contaminant is structurally incorporated [e.g., present in a three-dimensional precipitate(s)]; (5) the phase associations of a contaminant; (6) the microscopic distribution of a contaminant within sediments and soils. In the present study, we have used synchrotron-based X-ray spectroscopic methods to study the speciationmore » of U and Cu in contaminated soil and sediment samples from the Hanford Site. To complement and complete our initial XAFS investigation of U speciation in contaminated vadose zone sediments below tank BX-102, we have also performed mXRD studies of two sediment sample to identify the specific U(VI)-silicate phase present. Samples from the 300 Area were examined by mSXRF to determine the microscopic distribution and element associations of Cu and U. These samples were also analyzed by U LIII- and Cu K-edge XAFS spectroscopy to determine the chemical speciation of these elements. Conclusions to Date (1) Uranium occurs primarily as sodium-boltwoodite [Na2(UO2)2(SiO3OH)2-3H2O] in the BX-102 sediment samples. (2) The dissolution kinetics of sodium-boltwoodite will be a major control on the future transport of U beneath tank BX-102. (3) In the 300 Area soils and sediments, uranium occurs as U(VI) and copper as Cu(II). (4) U and Cu are often found together or adjacent to one another; however, these elements don?t appear to be spatially associated with Fe. (5) U appears to be bound to carbonate groups, and is likely contained in a CaCO3 mineral (calcite or aragonite). (6) It is unclear what phase(s) Cu is bound to or associate with, although the data are consistent with an association with CaCO3 minerals. (7) Future U release in the 300 Area will be controlled by the dissolution of CaCO3 minerals.« less

  • The objectives of the overall collaborative EMSP effort (with which this project is associated) are to characterize sorption and desorption processes of U(VI) on pristine and contaminated Hanford sediments over a range of sediment facies and materials properties. The research is intended to provide new insights on the mechanisms of U(VI) retardation at Hanford, and to develop approaches by which laboratory-characterized geochemical models can be upscaled for defensible predictions of uranium transport in field.

  • ; ; ; ...
    The objectives of the overall collaborative EMSP effort (with which this project is associated) are to characterize sorption and desorption processes of U(VI) on pristine and contaminated Hanford sediments over a range of sediment facies and materials properties and to relate such characterization both to fundamental molecular-scale understanding and fieldscale models of geochemistry and mass transfer. The research is intended to provide new insights on the mechanisms of U(VI) retardation at Hanford, and to allow the development of approaches by which laboratory-developed geochemical models can be upscaled for defensible field-scale predictions of uranium transport in the environment.

  • ; ;
    The objectives of the overall collaborative EMSP effort (with which this project is associated) were to characterize sorption and desorption processes of U(VI) on pristine and contaminated Hanford sediments over a range of sediment facies and materials properties and to relate such characterization both to fundamental molecular-scale understanding and field-scale models of geochemistry and mass transfer. The research was intended to provide new insights on the mechanisms of U(VI) retardation at Hanford, and to allow the development of approaches by which laboratory-developed geochemical models could be upscaled for defensible field-scale predictions of uranium transport in the environment. Within this broadermore » context, objectives of the JHU-based project were to test hypotheses regarding the coupled roles of adsorption and impermeable-zone diffusion in controlling the fate and transport of U(VI) species under conditions of comparatively short-term exposure. In particular, this work tested the following hypotheses: (1) the primary adsorption processes in the Hanford sediment over the pH range of 7 to 10 are surface complexation reactions of aqueous U(VI) hydroxycarbonate and carbonate complexes with amphoteric edge sites on detrital phyllosilicates in the silt/clay size fraction; (2) macroscopic adsorption intensity (at given aqueous conditions) is a function of mineral composition and aquatic chemistry; and (3) equilibrium sorption and desorption to apply in short-term, laboratory-spiked pristine sediments; and (4) interparticle diffusion can be fully understood in terms of a model that couples molecular diffusion of uranium species in the porewater with equilibrium sorption under the relevant aqueous conditions. The primary focus of the work was on developing and applying both models and experiments to test the applicability of "local equilibrium" assumptions in the modeling interpretation of sorption retarded interparticle diffusion, as relevant to processes of U(VI) diffusion in silt/clay layers. Batch isotherm experiments were first used to confirm sorption isotherms under the intended test conditions and diffusion cell experiments were then conducted to explore the diffusion hypotheses. Important new information was obtained about the role of aqueous calcium and solid calcium carbonate in controlling sorption equilibrium with Hanford sediments. The retarded interparticle diffusion model with local sorption equilibrium was shown to very successfully simulate diffusion at high aqueous concentration of U(VI). By contrast, however, diffusion data obtained at low concentration suggested nonequilibrium of sorption even at diffusion time scales. Such nonequilibrium effects at low concentration are likely to be the result of sorption retarded intraparticle diffusion, and strong U(VI) sorption in the low concentration range.« less