Agriculture Reference
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columns packed with different calcareous (Bustan) soils and a Windsor soil.
Although accurate prediction for Cu transport was not attained for both
soils, the assumption that Cu retention occurs via kinetic ion exchange can-
not be ignored. The results presented in Figure 7.10 also illustrate the capa-
bility of the multireaction and transport model (MRTM) in predicting Cu
transport in different soils.
7.5 Competitive Freundlich Model
This model was originally developed by Sheindorf, Rebhun, and Sheintuch
(1981) and is commonly referred to as the Sheindorf-Rebhun-Sheintuch
(SRS) model. Here competitive or multicomponent sorption is assumed
to follow that for single-component sorption based on the Freundlich
equation:
b
SKC
F
=
(7.14)
The derivation of the SRS equation was based on the assumption of an expo-
nential distribution of adsorption energies for each component. Specifically,
the SRS model was developed to describe competitive equilibrium sorption
for multicomponent systems where the sorption isotherms of single compo-
nents follow the Freundlich equation. A general form of the SRS equation
can be written as:
n
i
−
1
l
∑
S
i
=
K
i
C
i
α
C
( 7.1 5 )
ij
,
j
j
=
1
where the subscripts
i
and
j
denote metal components
i
and
j
,
l
is the total
number of components, and α
i,j
is a dimensionless competition coefficient
for the adsorption of component
i
in the presence of component
j
. The
parameters
K
i
and
n
i
are the Freundlich parameters representing a single
component system
i
as described in Equation 7.14. By definition, α
i,j
equals
1 when
i
=
j
. If there is no competition, that is, α
i,j
= 0 for all
j
≠
i
, Equation
7.15 yields a single-species Freundlich equation for component
i
identical to
Equation 7.14.
The suitability of the multicomponent SRS equation for describing the com-
petitive adsorption isotherms of trace elements on soil and soil minerals has
been investigated by several researchers. A general procedure for applying
the SRS equation is first to obtain the Freundlich distribution coefficient
K
F
and reaction exponent
b
or
n
by fitting the single-component isotherms to the
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