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Title: Microscopic mass transfer and its influence on microbial reduction of U(VI)

Abstract

In contaminated subsurface sediments, U(VI) resides in both intergrain (where active water flow occurs) and intragrain domains (where static water resides). Dissimilatory metal reducing bacteria (DMRB) can reduce aqueous (intergrain) U(VI) to U(IV) under anoxic conditions yielding an insoluble precipitate [U(IV)O{sub 2}]. Intragrain U(VI) becomes bioavailable if it dissolves and diffuses to the intergrain domain, or if the DMRB release soluble reductants that can diffuse to, and react with intraparticle U(VI) precipitates. Microscopic and spectroscopic analyses of uranium-contaminated sediments from Hanford have revealed that U(VI) often exists as a precipitate within intragrain domains of sediment clasts. Intragrain U(VI) dissolves slowly into undersaturated pore water with kinetics limited by the mass transfer from intragrain domains to bulk solution. This research investigated the microscopic mass transfer process and its effects on the microbial reduction of intragrain U(VI). The research has used Hanford sediments, but the resulting understanding and models are relevant to the Oak Ridge FRC, where a critical issue is the long term diffusion of U(VI) from a fine-grained saprolite matrix that is physically inaccessible to DMRB. The objectives are: (1) characterize and develop numerical models to describe the microscopic mass transfer process in intragrain domains of Hanford sediment; (2) identifymore » and characterize biogeochemical strategies used by DMRB to access intragrain U(VI) by representative dissimilatory reducing bacteria; and (3) evaluate the coupling of dissolution kinetics, uranyl speciation, mass transfer, and microbial activities in the microbial reduction of intragrain U(VI) precipitates.« less

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA; Yonsei University, Kongwon-Do, Korea; Argonne National Laboratory (ANL), Argonne, IL
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
894569
Report Number(s):
CONF-ERSP2006-32
TRN: US0700185
Resource Type:
Conference
Resource Relation:
Conference: Annual Environmental Remediation Sciecnes Program, April 3-5, 2006, Warrenton, VA
Country of Publication:
United States
Language:
English
Subject:
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; 59 BASIC BIOLOGICAL SCIENCES; BACTERIA; DIFFUSION; DISSOLUTION; KINETICS; MASS TRANSFER; SEDIMENTS; WATER

Citation Formats

Chongxuan Liu, Zheming Wang, Zachara, John M., Fredrickson, James K., Byong-Hun Jeon, Majors, Paul D., McKinley, James P., and Heald, Steve M.. Microscopic mass transfer and its influence on microbial reduction of U(VI). United States: N. p., 2006. Web.
Chongxuan Liu, Zheming Wang, Zachara, John M., Fredrickson, James K., Byong-Hun Jeon, Majors, Paul D., McKinley, James P., & Heald, Steve M.. Microscopic mass transfer and its influence on microbial reduction of U(VI). United States.
Chongxuan Liu, Zheming Wang, Zachara, John M., Fredrickson, James K., Byong-Hun Jeon, Majors, Paul D., McKinley, James P., and Heald, Steve M.. Wed . "Microscopic mass transfer and its influence on microbial reduction of U(VI)". United States. doi:. https://www.osti.gov/servlets/purl/894569.
@article{osti_894569,
title = {Microscopic mass transfer and its influence on microbial reduction of U(VI)},
author = {Chongxuan Liu and Zheming Wang and Zachara, John M. and Fredrickson, James K. and Byong-Hun Jeon and Majors, Paul D. and McKinley, James P. and Heald, Steve M.},
abstractNote = {In contaminated subsurface sediments, U(VI) resides in both intergrain (where active water flow occurs) and intragrain domains (where static water resides). Dissimilatory metal reducing bacteria (DMRB) can reduce aqueous (intergrain) U(VI) to U(IV) under anoxic conditions yielding an insoluble precipitate [U(IV)O{sub 2}]. Intragrain U(VI) becomes bioavailable if it dissolves and diffuses to the intergrain domain, or if the DMRB release soluble reductants that can diffuse to, and react with intraparticle U(VI) precipitates. Microscopic and spectroscopic analyses of uranium-contaminated sediments from Hanford have revealed that U(VI) often exists as a precipitate within intragrain domains of sediment clasts. Intragrain U(VI) dissolves slowly into undersaturated pore water with kinetics limited by the mass transfer from intragrain domains to bulk solution. This research investigated the microscopic mass transfer process and its effects on the microbial reduction of intragrain U(VI). The research has used Hanford sediments, but the resulting understanding and models are relevant to the Oak Ridge FRC, where a critical issue is the long term diffusion of U(VI) from a fine-grained saprolite matrix that is physically inaccessible to DMRB. The objectives are: (1) characterize and develop numerical models to describe the microscopic mass transfer process in intragrain domains of Hanford sediment; (2) identify and characterize biogeochemical strategies used by DMRB to access intragrain U(VI) by representative dissimilatory reducing bacteria; and (3) evaluate the coupling of dissolution kinetics, uranyl speciation, mass transfer, and microbial activities in the microbial reduction of intragrain U(VI) precipitates.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Apr 05 00:00:00 EDT 2006},
month = {Wed Apr 05 00:00:00 EDT 2006}
}

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  • No abstract prepared.
  • The purposes of this report are to: (1) to determine how flow and transport influence the distribution of U(VI) under field-relevant conditions and the transfer of reductive equivalents to the aqueous and solid phases by DMRB; and (2) to examine the solid-phase stability of bioreduced uranium phases--effects of mass transfer on reoxidation of U(IV) by O{sub 2} and other oxidants (e.g., NO{sub 3}{sup -}, denitrification products).
  • Short communication.
  • In contaminated subsurface sediments, U(VI) resides in both interparticle (where active water flow occurs) and intraparticle domains (where static water resides). Dissimilatory metal reducing bacteria (DMRB) can reduce aqueous (interparticle) U(VI) to U(IV) under anoxic conditions yielding an insoluble precipitate [U(IV)O{sub 2}]. Intraparticle U(VI) can only be reduced by DMRB if it dissolves and diffuses to the interparticle domain populated by microbiota, or if the DMRB release, or dispose of electron to soluble compounds that can diffuse to, and react with intraparticle U(VI) precipitates. At DOE Hanford site, recent characterization of U(VI) speciation and physical location in 30-year contaminated sedimentsmore » demonstrated that U(VI) resides as a U(VI)-silicate microprecipitates in small fractures and cleavages within sediment particle grains exhibiting pore sizes of a few microns or less. The U(VI) microprecipitates dissolved slowly into undersaturated pore water, but the dissolution kinetics and diffusive rate of U(VI) transport from intraparticle regions was slow when compared to the reduction rate of aqueous U(VI) by DMRB. These results indicated that: (1) a majority of the sorbed U(VI) pool was not physically accessible to DMRB due to size restrictions of the grain porosity, and (2) the bioavailability and overall rates of microbial U(VI) reduction in the sediments could be limited by the mass transfer rates of U(VI) from intraparticle regions. This research is focused on the bioavailability and kinetic rates of microbial reduction of U(VI) associated with intraparticle regions. The understanding of the influence of mass transfer on microbial reduction of U(VI) is needed not only at the Hanford site, but also at Oak Ridge FRC, where a critical issue is the long term diffusion of U(VI) from fine-grained saprolite matrix that is physically inaccessible to DMRB. The objectives are: (1) Develop approaches to characterize microscopic properties of mass transfer processes. (2) Identify and characterize biogeochemical strategies for accessing intraparticle U(VI) by representative dissimilatory metal reducing bacteria. (3) Evaluate the influence of mass transfer on U(VI) bioavailability, microbiologic reduction rate and location. (4) Develop coupled kinetic models of the U(VI) dissolution, mass transfer processes, and microbially mediated U(VI) reduction.« less