Agriculture Reference
In-Depth Information
0.25
Hg - Transport
Reference Sand
0.20
0.15
Experimental
Multireaction model
0.10
0.05
0.00
0
2
4
6
8
10
12
Pore Volume (V/V o )
FIGURE 5.7
Experimental Hg (II) breakthrough curve (BTC) from the reference sand column ( C o = 8 mg
L -1 ). The solid curve is multireaction model simulation where the rates of reactions were 0.340
± 0.019, 0.033 ± 0.001, and 0.001 ± 0.001 h -1 for k 1 , k 2 , and k 3 , respectively.
in 0.01 M Ca(NO 3 ) 2 background solution. In the sand column, a noticeable Hg
peak was observed and did not exceed 2 mg/L (see Figure 5.7). In fact, for
the BTC of the reference sand, which exhibited symmetry, the recovery of Hg
from the soil column was only 17.3% of that applied. Therefore, more than
80% of the applied Hg was strongly retained by the reference sand column.
Recently, Wernert, Frimmel, and Behra (2003) reported strong Hg retention
in a column experiment of quartz sand (99% quartz and amorphous silica)
where continuous Hg pulse application of 100 mg/L was maintained. In fact,
no Hg was observed in the column effluent during the first 100 pore vol-
umes. Some 500 pore volumes of Hg application were needed before a con-
centration maximum of 22 mg/L was reached. Wernert, Frimmel, and Behra
(2003) did not report the percent of Hg retained in their quartz column.
The mercury BTC for the reference sand column was successfully
described using the multireaction model. Liao, Delaune, and Selim (2009)
concluded that a simple model formulation with reversible kinetic and irre-
versible sites ( S 1 and S irr ) is recommended for the case of this sand column.
Here the irreversible reaction associated with S i may be considered as inner-
sphere complexation as suggested by Sarkar, Essington, and Misra (1999).
Interparticle diffusion is another process that is responsible for retention of
Hg. Such a process is often considered as a rate-limiting step (see Yin, Allen,
and Huang, 1997; Miretzky, Bisinoti, and Jardim, 2005). Nevertheless, model
validation and verification are needed, which require further experimental
investigation of the processes associated with Hg sorption and transport in
soils.
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