Agriculture Reference
In-Depth Information
sites (mg kg
-1
); and
S
irr
represents the amount retained on concurrent irre-
versible sites (mg kg
-1
). The retention reactions associated with the MRTM
are similar to those presented earlier in Chapter 3:
θ
ρ
C
b
S
e
=
K
e
( 7.16 )
∂
∂
S
t
θ
ρ
1
n
=
k
CkS
−
( 7.1 7 )
1
2
1
∂
∂
S
t
θ
ρ
m
2
=
k
−
kS
−
k
s
S
( 7.18)
3
4
2
2
∂
∂
S
s
t
=
k
s
S
2
( 7.19)
θ
ρ
S
irr
=
k
irr
C
( 7. 2 0 )
where
b
is the reaction order;
K
e
is a dimensionless equilibrium constant
(cm
3
g
-1
);
k
1
and
k
2
(h
-1
) are the forward and backward rate coefficients asso-
ciated with
S
1
, respectively, and
n
is the reaction order;
k
3
and
k
4
(h
-1
) are
the forward and backward rate coefficients associated with
S
2
, respectively,
and
m
is the reaction order;
k
s
(h
-1
) is the irreversible rate coefficient; and
k
irr
(h
-1
) is the rate coefficient associated with
S
irr
. In the above equations, we
assumed
n
=
b
since there is no method for estimating
n
a n d/o r
m
indepen-
dently. Zhang and Selim (2007) modified the MRM to account for competi-
tive Freundlich-type retention such that:
n
i
−
1
l
∑
()
SKC
=
α
C
( 7. 2 1)
ei
ei
,
i
i j
,
j
j
=
1
n
−
1
i
l
∂
()
S
t
θ
ρ
∑
1
i
=
kC
α
C
−
k
()
S
( 7. 2 2)
1,
i
i
ij
,
j
2,
i
1
i
∂
j
=
1
Search WWH ::
Custom Search