Changes in U(VI) speciation upon sorption onto montmorillonite from aqueous and organic solutions Page: 3 of 21
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Introduction
Past waste management practices at U.S. Department of Energy
complexes have resulted in significant levels of organic solvents,
neutral donor extractants, and actinides in the underlying soil and
groundwater. To evaluate the mobility and fate of such "co-
contaminant" (actinide/organic) wastes in clay-rich soils and
groundwaters, we have conducted spectroscopic experiments on a
model system: U(VI) in aqueous or 20% tributyl-phosphate
(TBP)/docecane solutions, and sorbed on montmorillonite (SAz-1
from the Missouri Clay Repository) from these solutions.
Tributylphosphate (TBP) is a complexing organic reagent
common to the contaminant inventories at a number of U.S.
Department of Energy sites. TBP is key high-volume reagent in the
nuclear complex, being used widely with hydrocarbon diluents as the
extractant in reprocessing of spent fuel (the PUREX process)[2] and
in combination with a chelating phosphonate for lanthanide/actinide
group separations (the TRUEX process) [2,3]. Subsurface
contamination by TBP and related neutral-donor extractants has
been identified at U.S. Department of Energy transuranic processing
sites such as the Hanford and Savannah River facilities, and at low-
level waste disposal sites including Maxey Flats, Kentucky and West
Valley, New York [4-6]. More specifically, large TBP/solvent
releases to the environment have occurred at the Hanford site, yet
TBP has not been detected in near-surface groundwaters [7]. This
interesting observation could be related to TBP uptake by soil and/or
rock column constituents.
The influence of neutral-donor extractants on the sorption
properties and the subsurface migration behavior of radionuclides is
largely unknown, even with dominant soil constituents such as clays.
We are characterizing the speciation properties of actinides and
transition metals in the presence of neutral donor extractants at the
interface between solutions and common subsurface mineral
matrices. We have chosen the smectite clay SAz-1 as our initial
reference substrate because it is representative of the ubiquitous
2:1 layered clay materials found at many contaminant sites in the
U.S. Recently we found that TBP is taken up extensively by SAz-1
with large concomitant swelling of the clay interlayer region [8]. It
appears that a major fraction of the intercalated TBP undergoes a
bonding interaction with interlayer cations.2
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Chisholm-Brause, Catherine; Morris, David E.; Eller, P. Gary; Buscher, Tom & Conradson, Steven D. Changes in U(VI) speciation upon sorption onto montmorillonite from aqueous and organic solutions, article, January 1, 1991; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1056633/m1/3/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.