Environmental Engineering Reference
In-Depth Information
4.4.1 Effect of the Sole SO
3
2
A series of Na
2
SO
3
solutions with concentrations of 0 - 0.02 mol/L were used in
the NO
2
removal experiments. Fig. 4.6 shows the acquired results. It can be seen
that the NO
2
removal efficiency initially increases rapidly with the concentration
within the concentration of 0 - 0.01 mol/L and then varies slightly. This result
indicates that the redox reaction between SO
3
2
and NO
2
plays a more important
role in the increase of
(i.e., the increasing factor of absorption reactions, see Eq.
(4.1)) than that of the NO
2
hydrolysis.
Fig. 4.6
NO
2
removal efficiency in different SO
3
2
solution concentrations
Fig. 4.7 outlines the product analysis of the solution absorption with different
SO
3
2
concentrations. When the concentration is nil, the NO
2
hydrolysis (as shown
in Eq. (4.4)) is the only reaction occurring in the system. The concentrations of
NO
2
and NO
3
are matched (Fig. 4.4). After the appearance of SO
3
2
in the liquid
phase, the initial NO
2
concentration of 5.45×10
5
mol/L increases rapidly to
5.64×10
4
mol/L at the added SO
3
2
concentration of 0.005 mol/L. Meanwhile, the
NO
3
concentration decreases to an ultra-low level which is almost impossible to
be detected. An explanation of these observations is provided. With the SO
3
2
existence in the solution, the redox reaction between SO
3
2
and NO
2
(generating a
high NO
2
concentration) is much stronger that the NO
2
hydrolysis reaction
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