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Mobile‐Immobile Multi‐Reaction Model (MIM‐MRM)
S
e
m
K
e
k
1
k
i
k
3
S
s
m
S
k
m
S
i
m
C
m
k
2
α
k
1
k
i
k
3
S
s
im
C
im
S
k
im
S
i
im
k
2
K
e
S
e
im
FIGURE 8.3
A combined physical and chemical nonequilibrium model based on the mobile-immobile
model and multireaction retention approaches, respectively.
small values of Ω (e.g. Ω = 0.1), the simulated BTC is very similar to that
for a nonretarded solute due to the limited number of sites (
S
max
) in com-
parison to
C
o
. In contrast, large values of Ω resulted in BTCs that indicate
increased retention as manifested by the right shift of peak concentration
of the BTCs. In addition, for high values of Ω, extensive tailing as well as an
overall decrease of effluent concentration was observed. The influence of the
parameter
f,
which represents the fraction of active or dynamic sites within
the mobile region to the total number of sites, on the behavior of solute reten-
tion and transport is shown in Figure 8.13 for several values of
f
. There are
1.0
Tritium
Webster Soil
0.8
0.6
0.4
0.2
0.0
0
1
2
3
4
5
Pore Volume (V/V
o
)
FIGURE 8.4
Breakthrough of tritium in a Webster soil column. Simulations are based on the convection-
dispersion equation where equilibrium is assumed.
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