Agriculture Reference
In-Depth Information
Webster Soil
Sequential Pulses
200
Cd
P
150
P
100
50
Cd
0
0
5
10
15
20
25
30
Pore Volume (V/V
o
)
FIGURE 7.43
Cadmium and P breakthrough curve results for a Webster soil column that received pulses of
Cd and P. The solid and dashed curves are multireaction model predictions.
concentrations were added (0 to 100 mg/L). All Cd isotherms appear non-
linear regardless of the initial P concentration in solution in Webster soil.
The influence of P on increased Cd sorption was clearly manifested by the
increased Freundlich distribution coefficient
K
F
from 532 to 601 ml/g for ini-
tial P concentrations of 0 and 100 ml/g. In contrast, the nonlinear parameter
N
did not exhibit much variation (0.50 to 0.54) for all P concentrations.
In Figure 7.43, the BTCs for Cd and P are presented for a Webster soil col-
umn that received a Cd pulse followed by a P pulse, that is, sequential pulses.
Figure 7.44 shows BTCs for Cd and P for a Webster soil column that received
two consecutive pulses of a mixed P and Cd solution. Cadmium BTCs indi-
cate strong retention with low Cd concentration in the effluent solution,
especially for the mixed column. Peak concentration of the BTC results was
70 mg/L (
C
/
C
o
of 0.37); compared to 30 and 60 mg/L associated with the first
and second pulses of the mixed column. Based on the area under curve, the
amount of Cd recovery was 28% for the sequential column and only 18% for
the mixed column, which indicates higher sorption of Cd in the presence of
P. The observed strong Cd retention exhibited by the results of Figures 7.43
and 7.44 is supported by the sorption isotherm shown in Figure 7.42, which
indicates high Cd sorption, which is likely due to high clay content, organic
matter, amorphous Fe and Al, and the presence of carbonates. In addition,
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