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 pierced by liquid-filled
nano-scale pores. 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