PNNL-13501 - Pacific Northwest National Laboratory

Use of Shear-Thinning Fluids for Injection of Colloidal Size Reactive Particles
Study Control Number: PN00091/1498
Kirk J. Cantrell, Tyler J. Gilmore
In situ remediation is an important technique for creating an in situ permeable reactive barrier against halogenated
hydrocarbons. This project has identified a shear-thinning polymer that is effective in porous materials for reducing most
halogenated hydrocarbons to harmless and less-mobile forms.
Project Description
Shear-thinning polymers have been used in slurry
formulations for the injection of colloidal size zero-valent
iron particles into porous media for the purpose of
forming a permeable reactive barrier for in situ
remediation of contaminated groundwater (Cantrell et al.
1997a,b). Successful proof-of-principle of the concept
has been conducted at the bench scale using pure quartz
sand as the porous media. When the same formulations
that were successful in quartz sand media were applied to
natural Hanford sediments or aquifer materials plugging
at the inlet occurred almost immediately upon injection.
This plugging was attributed to adsorption of the shearthinning
polymers onto mineral surfaces in the Hanford
sediments and solubility reduction due to interaction with
dissolved calcium. Identification of a suitable shearthinning
polymer that will not strongly adsorb to natural
minerals or become insoluble in the presence of calcium
is critical for the development of an effective slurry
formulation for injecting zero-valent iron particles into
porous media. One particularly promising compound has
been identified. This compound will be referred to as
AMX.
Batch and column adsorption experiments indicated that
this compound does not adsorb to Hanford sediments to
any significant extent. A series of experiments were
conducted to determine the effectiveness of slurry
formulations developed with this polymer for injection of
micron size iron particles. The results of these
experiments indicate that slurry formulations using AMX
will be effective for creation of an in situ permeable
reactive barrier composed of zero-valent iron particles by
slurry injection through wells. This approach has many
advantages over current approaches for constructing a
permeable reactive barrier. The most important
advantages are that the treatment zone can be injected to
any depth or location that can be reached by drilling, and
zero-valent iron is a very strong reductant. Zero-valent
iron is capable of reducing most chlorinated hydrocarbon
254 FY 2000 Laboratory Directed Research and Development Annual Report
contaminants (trichloroethylene, trichloroethane, carbon
tetrachloride), explosive compounds (TNT, HMX, RDX,
and Tetryl), and inorganic contaminants such as Cr, Tc,
and U at rates that are practical.
To assess the impact of the injection process on the
permeability of the porous media, pressure measurements
were taken before, during, and after slurry injection.
These results indicate that the slurry injection process
used does not adversely impact the permeability of the
porous media.
Introduction
Significant effort has been directed to laboratory and field
research studies on the use of zero-valent iron as a
material to remediate certain groundwater contamination
problems (Tratnyek 1996; Fairweather 1996; Wilson
1995). Zero-valent iron is a strong chemical reductant
and has the capability to render most halogenatedhydrocarbon
compounds harmless (Gillham and
O’Hannesin 1994; Matheson and Tratnyek 1994; Orth
and Gillham 1996; Roberts et al. 1996). Recently
published data have shown that zero-valent iron can
effectively destroy RDX (Singh et al. 1999) and can
reduce TNT to its corresponding aromatic polyamine
(Hofstetter et al. 1999). Zero-vlaent iron can also
chemically reduce many highly mobile oxidized metal
contaminants (e.g., CrO42-, UO22+, and TcO4-) to their
less mobile forms (Gould 1982; Cantrell et al. 1995).
Zero-valent iron shows great promise as an permeable
reactive barrier material because of its applicability to a
broad range of contaminants, rapid reaction kinetics, and
the low cost and wide availability of the material (Wilson
1995). Permeable reactive barriers are permeable zones
emplaced within the aquifer that react with contaminants
as contaminated groundwater flows through the zone.
Between 1994 and 1998, 24 pilot-scale and full-scale
zero-vlaent iron permeable reactive barriers have been
installed (EPA 1999).