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O
OH
HO
N
O
O
N
H
O
HO
OH
OH
O
Iminodiacetate
Nitrilotriacetate
(IDA)
(NTA)
O
O
O
OH
OH
OH
N
HO
N
OH
N
N
N
HO
O
O
O
O
O
OH
O
OH
OH
Ethylenediaminetetraacetate
Diethylenetriaminepentaacetate
(EDTA)
(DTPA)
O
O
O
OH
OH
HO
O
N
N
N
N
OH
HO
OH
O
O
Triethylenetriaminehexaacetate
(TTHA)
Figure 6.36.
Structures of aminopolycarboxylates.
where
[
2
; α
ij
and β
ij
rep-
resent the respective species distribution coefficients for Fe(VI) and the sub-
strate;
i
and
j
represent each of the four species of Fe(VI) and each species of
the substrate, and
k
ij
is the species-specific second-order rate constant for the
reaction between the Fe(VI) species,
i
, with the substrate species,
j
. In the pH
range studied for Gly, the four forms of Fe(VI) (
H FeO
3
Fe VI
(
)]
tot
=
[
H FeO
+
]
+
[
H FeO
]
+
[
HFeO
−
]
+
[
FeO
−
]
3
4
2
4
4
4
+
, H
2
FeO
4
,
HFeO
−
,
and
FeO
2−
) could potentially react with the three forms of Gly (H
2
Gly
+
, HGly,
and Gly
−
). Of the possible 12 reactions, it has been determined that only 3
reactions (Eqs. 6.133-6.135 [model I] or Eqs. 6.133, 6.134, 6.136 [model II])
were necessary to fit the experimental
k
values (see Fig. 6.35):
4
+
−
H FeO
+
H N-CH -COO
→
Fe OH
(
)
+
product s
( )
2
4
3
2
3
(6.133)
1
k
=
3 0 0 6
. (
±
. )
×
10
/
M/s
143
−
+
−
HFeO
+
H N-CH -COO
→
Fe OH
(
)
+
product s
( )
4
3
2
3
(6.134)
1
k
=
2 5 0 3
. (
±
. )
×
10
/
M/s
144
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