Agriculture Reference
In-Depth Information
500
Zn-Hysteresis
400
300
200
Initial Zn = 60 ppm
Initial Zn = 80 ppm
Initial Zn = 100 ppm
Sorption
Sorption
Desorption
100
Windsor Soil
0
0
10
20
30
40
50
60
1600
Zn-Hysteresis
1400
1200
1000
800
600
Initial Zn = 80 ppm
Initial Zn = 100 ppm
Initial Zn = 150 ppm
Sorption
Sorption
Desorption
400
200
Webster soil
0
0
2
4
6
8
10
12
Zn Concentration (mg/L)
FIGURE 2.13
Adsorption and desorption isotherms for Zinc (Zn) in Windsor and Webster soils.
and 50 hours and desorption (dashed) curves initiated after 10 and 50 hours
of adsorption. The simulated desorption isotherms shown were obtained
by reducing the solute solution concentration one-half successively, every
10 hours (or 50 hours) until the solution concentration was less than 5 mg L
-1
.
This procedure is similar to that used in desorption studies in the labora-
tory. As seen from the family of (dashed) curves, desorption did not follow
the same path (i.e., nonsingularity) as the respective adsorption isotherm
(solid curves). Obviously, this nonsingularity or hysteresis results from fail-
ure to achieve equilibrium adsorption prior to desorption. If adsorption as
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