ADSORPTION:
MT3D allows 3 options for adsorption isotherms and uses
them to reduce the velocity term in the solution through the retardation factor
as follows:
Linear Isotherm
![](moceq27.gif)
is the sorbed concentration
![](Kd.gif)
= dry bulk density
= effective porosity
![](moceq28.gif)
Freundlich
isotherm:
![](moceq29.gif)
![](moceq30.gif)
![](moceq30a.gif)
Langmuir isotherm:
![](moceq31.gif)
![](moceq32.gif)
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To define adsorption in MT3D the user specifies:
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= dry bulk density
= effective porosity
S1 and S2
For the Linear
Isotherm, S1 = Kd
and S2is not used:
For the Freundlich Isotherm, S1
= Kf and S2is a, the Freundlich
exponent:
For the Langmuir Isotherm, S1
= Kl and S2is the total concentration of sorption sites:
![](moceq35.gif)
Non-equilibrium Sorption is represented as a first-order reversible kinetic reaction:
![](non_eq_sorp.gif)
= first-order mass transfer rate between
dissolved and sorbed phases
Kd = distribution coefficient for the sorbed phase
As
increases,
the mass transfer rate increases and approaches the equilibrium-controlled linear
sorption