Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction Page: 1 of 5
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2006 ERSD Annual Report
DOE-BER Environmental Remediation Sciences Project # 1024842
Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI)
PI: Scott C. Brooks*'
Co-PIs: Wenming Dong', Sue CarrollI, Jim Fredrickson2, Ken Kemner3, and Shelly Kelly3
'Oak Ridge National Laboratory, Oak Ridge, TN
2Pacific Northwest National Laboratory, Richland, WA
3Argonne National Laboratory, Argonne, IL
The proposed research will elucidate the principal biogeochemical reactions that govern the
concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium.
The results will provide an improved understanding and predictive capability of the mechanisms
that govern the biogeochemical reduction of uranium in subsurface environments. In addition,
the work plan is designed to:
" Generate fundamental scientific understanding on the relationship between U(VI)
chemical speciation and its susceptibility to biogeochemical reduction reactions.
" Elucidate the controls on the rate and extent of contaminant reactivity.
" Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under
representative groundwater conditions.
These goals and objectives will be met through a series of hypothesis-driven tasks that focus
on (i) the use of well-characterized mineral isolates and natural subsurface mineral assemblages,
(ii) advanced spectroscopic techniques to monitor changes in the aqueous and solid-phase
speciation of uranium, and (iii) close collaboration between microbiologists, geochemists, and
physicists to provide for rigorous design and interpretation of experiments.
Research Progress and Implications
This report summarizes work after two years of a three year project.
Mission Relevance. The experimental and numerical results of this research will quantify the
conditions that govern the rate and extent of U(VI) reduction under representative subsurface
conditions. By providing an improved understanding of the competitive processes that affect
contaminant reactivity in multicomponent systems, we will enhance the successful application of
microbially mediated contaminant stabilization in the field. The enhanced understanding derived
from this research will allow for the development of innovative approaches for in situ
bioimmobilization of radionuclides at DOE contaminated sites and a better understanding of the
requirements for maintaining contaminants as reduced and poorly soluble phases.
Uranium(VI) Analysis and Quantification. Kinetic phosphorimetry analysis (KPA) is used to
quantify U(VI) and, following sample oxidation, total U. The difference between total U and
U(VI) provides concentration of U(IV) in samples. Using procedures outlined in Oppenheimer
et al. (1983) and adopting Type I and Type II error rates of 5%, the following practical analytical
limits for our laboratory are (definitions from (OPPENHEIMER et al., 1983) and (GIBBONS and
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Brooks, Scott C.; Dong, Wenming; Carroll, Sue; Fredrickson, Jim; Kemner, Ken & Kelly, Shelly. Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction, report, June 1, 2006; Oak Ridge, Tennessee. (digital.library.unt.edu/ark:/67531/metadc888473/m1/1/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.