Agriculture Reference
In-Depth Information
100
Cu Adsorption - McLaren Soil
Multireaction Model version II
80
C
o
= 100 mg/L
60
40
50
20
10
20
10
0
5
0
25 0 5 00
125 50
175 00
Time, Hours
FIGURE 5.6
Experimental adsorption results of Cu from soil solution in McLaren soil versus time for sev-
eral initial concentrations (
C
o
). The solid curves were obtained using the multireaction model
with
S
1
and
S
s
.
(for all values of
C
o
) using parameter optimization (see Table 5.1). Reduced
standard errors for the model parameters
k
1
,
k
2
, and
k
irr
were realized when
the entire data set is used. Of significance is the fact that one set of model
parameters can thus be used for the entire concentration range, which lends
credence to the model in describing the Cu.
To further test the applicability of the multireaction model, the solid curves
shown in Figure 5.6 were obtained based on a different version of the model.
Specifically, this model version accounted for two sorbed phases, one revers-
ible (
S
2
) and the other irreversible (
S
s
). It is obvious from the simulations
shown in Figures 5.5 and 5.6 that a number of model versions are capable
of producing indistinguishable simulations of the data. Similar conclusions
were arrived at by Amacher, Selim, and Iskandar (1988, 1990) for Cd, Cr(VI),
and Hg for several soils. They also stated that it was not possible to deter-
mine whether the irreversible reaction is concurrent or consecutive, since
both model versions provided similar fit of their batch data. This finding
implies that the adsorption data for Cu alone is insufficient and that addi-
tional data are needed to arrive at a recommendation for the adoption of a
specific model version.
In Figure 5.7, results of mercury (Hg) transport in a sand column are pre-
sented along with multireaction model simulations (see Liao, Delaune, and
Selim, 2009). This is one of the few studies that indicate significant Hg mobil-
ity in soil columns. (See also the results of Miretzky, Bisinoti, and Jardim,
2005, on alluvial, podozol and humic gley soils from the Amazon region.)
The Hg input pulse concentration used here was 8 mg/L Hg(NO
3
)
2
prepared
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