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8
Ni Isotherms
Webster
6
Olivier
4
Windsor
2
0
0.0
0.2
0.4
0.6
8
Cd Isotherms
Webster
Olivier
6
4
Windsor
2
0
0.0
0.2
0.4
0.6
Ion Concentration (mM)
FIGURE 7.13
Adsorption isotherms for Ni (top) and Cd (bottom) for Windsor, Olivier, and Webster soils.
Solid curves are Freundlich model calculations.
0.982 to 0.999 (Liao and Selim, 2010). The dimensionless parameter
n
may
be regarded as a representation of energy distribution of heterogeneous
adsorption sites for solute retention by matrix surfaces (Sheindorf, Rebhun,
and Sheintuch, 1981). Nonlinearity and competition are often regarded as
characteristics of site-specific adsorption processes. Here adsorption occurs
preferentially at the sites with highest adsorption affinities and sites with
lower adsorption potential are occupied with increasing concentration. The
n v
alues for Windsor, Olivier, and Webster soils are 0.64, 0.57, and 0.55 for
Cd and 0.50, 0.56, and 0.52 for Ni, respectively. These
n
values were within a
narrow range (0.50-0.64) for all three soils and reflect the observed similari-
ties of the overall shape of both Ni and Cd sorption isotherms as shown in
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