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7. Adsorption under Partially-Saturated Conditions
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the pores is important in determining the transport properties.
In this study, we have used a MDPN model to simulate fluid flow and transport
of adsorptive solute within the pore space of a porous medium. We have
considered adsorption at the solid-water (SW) interfaces as well as air-water
(AW) interfaces to obtain BTCs of average concentration obtained from the
pore network. Our results showed that, even if there is equilibrium adsorption
at the solid-water and air-water interfaces at the pore scale, one may need to
use a non-equilibrium description of adsorptive process at the macro scale. The
equilibrium description of adsorption at the macro scale produced by an ADE
model could not appropriately fit the computed BTCs. Applying the equilibrium
macro scale model required higher values of dispersivity which, in addition
to saturation, will depend on the value of pore scale adsorption coefficient.
On the other hand, we found that the kinetic description of adsorptive process
at the macro scale could accurately model the resulting BTCs obtained from
the pore network simulations. Using the kinetic description, we could use the
same dispersivity values which were obtained from tracer simulations. We
have applied pore-scale distribution coefficient to each pore element of the
network and, utilizing the BTCs of average concentrations, calculated macro
scale distribution coefficient, under different saturations. Decrease in saturation
causes increase in average specific surface area which in turn results in an
increase of macro-scale distribution coefficient.
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