Geoscience Reference
In-Depth Information
Often, the hydrolysis reaction rate expression in Equation 4.74 is simplified to
a pseudo-first-order reaction rate expression at a given pH and temperature:
dC
/
dt
=
-
k
h
C
(4.75)
where
k
b
[OH
−
]
k
h
=
+
k
a
[H
+
]
+
k
n
(4.76)
4.2.4.5
Oxidation
The oxidation rate of an organic pollutant
R
Ox
can be written as follows:
R
Ox
=
dC
/
dt
=
k
Ox
⋅
[
C
]
⋅
[
Ox
]
(4.77)
where
k
OX
=
specific second-order rate constant for oxidation at a specific temperature
[
C
]
=
molar concentrations of the chemical compound
[
Ox
]
=
molar concentrations of the oxidant
The total rate of oxidation, if more than one oxidant is working simultaneously, is
the sum of the rates of reaction for each oxidant:
R
Ox
=
(
k
Ox
1
[
Ox
1
]
+
k
Ox
2
[
Ox
2
]
+
...
k
Oxn
[
Ox
n
])
⋅
[
C
]
=
(
k
Oxn
[
Ox
n
])
⋅
[C]
(4.78)
Integration of Equation 4.77 between the time limits 0 and
t
gives
=
∑
nn
ln[
CC
] / [
]
=
k
[
Xt
]
⋅
(4.79)
0
t
Oxn
n
n
=
1
assuming [
Ox
n
] for all values of
n
remain constant during the reaction time. If the
time to oxidize half of the chemical, or the reactions half-life,
t
1/2
, is desired:
=
∑
nn
t
=
ln
2
k
[
Ox
]
(4.80)
12
/
Oxn
n
n
=
1
If the oxidant(s) concentration remains constant,
k
Ox
in Equation 4.77 becomes
a first-order rate.
According to Ambrose et al.
78
oxidation can be modeled as a general second-
order process for the various species and phases of each chemical:
K
O
=
[
RO
2
]
Σ
i
Σ
j
k
Oij
f
ij
(4.81)
Search WWH ::
Custom Search