Jun Ma, Case Prime Fellow (jxm140@po.cwru.edu)
and
Aaron A. Jennings, Professor
(aaj2@po.cwru.edu)
Department of Civil Engineering
Case Western Reserve University
Cleveland, OH 44106-7201
Aggregate remediation is a process that addresses a class of soil contamination characterized by pollutants that have migrated deep into the particle matrix over long time periods. For large particles, the rate of aggregate remediation can be very slow if it is driven by diffusion, even when an aggressive permeant is applied to cleanup the aggregate surface. Electrokinetically-accelerated (EK-accelerated) aggregate remediation offers the possibility of accelerating the performance of aggregate remediation processes. In general, electrokinetic phenomena can induce flow in soils (electroosmosis), induce particle movement (electrophoresis) or induce ion mobility (electromobility). Previous modeling has shown that an electric field can significantly accelerate the rate of remediation (e.g. removing 90% of the contaminant burden from a 0.3 cm particle after 6 instead 300 days). Based on this, a new model is proposed to explore the impact that anisotropy and sorptive resistance have on EK-enhanced remediation process.
Anisotropic aggregate properties have significant impacts on
the mass transfer rate and contaminant distribution within the aggregate. A
special case where the spatial reference and applied DC field are aligned with
the principal coordinates of anisotropy is considered here to study the
response of mass transfer rate to the anisotropy. Sorption also plays an
important role in mass transfer. Since aggregate remediation is applied to old
contamination it must induce mass transfer out of the domain. Therefore, the phase change is actually desorption.
There are several phase exchange models for describing the relationship between
mobile and immobile contamination. Often, the reactions may not be fast enough
and the kinetic of sorption must be considered. As expected, for a constant
degree of sorption, it takes more time to achieve contaminant removal as the
desorption rate constant decreases. There are also alternative visions of the
solid phase. One may treat this as a single amorphous solid, or consider it to
be a structure pieced by liquid-filled nano. These two visions can result in
dramatically different physical models with different mass transfer pathways.
For the latter vision, it is quite possible that most of the contaminant burden
migrated into the aggregate through these micro-cracks and is present only
within the micro-cracks or on the surfaces surrounding the cracks. Hopefully,
the model presented here together with carefully constructed experimentation will
be able to improve our ability to determine which of these competing visions is
more correct