Chemistry Reference
In-Depth Information
6000
5000
4000
3000
2000
1000
0
200 210 220 230 240 250 260 270 280 290 300 310 320
λ
(nm)
Figure 6.16.
Absorption spectra of Mn(III) in 0.1 M HClO
4
with [Mn
2+
] = 2.5 × 10
−4
M
and [O
3
] = 6.5 × 10
−5
M at 25°C. (Δ—HClO
4
and O—H
2
SO
4
) (adapted from Jacobsen
et al. [178] with the permission of Wiley, Inc.).
highly acidic conditions, the
MnO
−
ion was the dominant species [179]. Fe
2+
in
Mn
2+
-containing waters induced the formation of
MnO
−
ion. This reaction may
be playing a significant role in generating
MnO
−
ion because Fe
2+
reacts 650
times faster with O
3
than Mn
2+
does. In neutral solutions, the reactions of O
3
with oxalate, bicarbonate, phosphate, and pyrophosphate complexes of Mn
2+
formed the
MnO
−
ion [179]. Moreover, natural organic matter present in water
may also influence the formation of
MnO
−
ion from Mn
2+
. Overall, the results
showed that the formation of
MnO
−
ion was more influenced by the Fe
2+
ion
rather than inorganic ligands or organics in water [179].
The hydrolysis constant of Mn(III) has been estimated (reaction 6.48) [178]:
Mn
3
+
+
H O Mn OH
→
(
)
2
+
+
H p
+
K
=
0 2
.
.
(6.48)
2
48
Mn(OH)
2+
is the dominant species of Mn(III) in the pH range of 0-2. The
disproportionation of Mn(III) corresponds to reaction (6.49). The final product
of Mn(IV) was determined as MnO
2
(reaction 6.50), which was observed as
an increase in absorption >300 nm:
2Mn III
(
)
Mn II Mn IV
(
)
+
(
)
(6.49)
Mn IV
(
)
→
MnO
2
.
(6.50)
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