What is the difference between sodium sulfite removal of free chlorine under acidic and alkaline conditions?
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This post was last edited by sunjl1981 at 2013-1-6 23:00 Hello everyone! After the light brine from the tank passes through the dechlorination tower, sodium sulfite must be added to remove free chlorine. In the chlor-alkali industry, the pH of the light brine is usually adjusted to 9-11 and then sodium sulfite is added to remove the part of free chlorine that cannot be removed by physical methods. Based on the knowledge I have learned, I used to think that sodium sulfite is unstable under acidic conditions and easily generates sulfurous acid and releases sulfur dioxide, causing the loss of sodium sulfite. Therefore, it must be adjusted to alkaline, because sodium sulfite is relatively stable under alkaline conditions. Now I think about it again, even if the sulfur dioxide released under acidic conditions is reducing, it can also undergo an oxidation-reduction reaction with free chlorine, so adding alkali is unnecessary. I hope you guys can help me clear up my doubts. I’m very grateful! Thanks! ! ! # , , &
Under acidic conditions, sodium sulfite will dissolve and produce SO2, but the speed at which the gaseous SO2 reacts with free chlorine must be very slow (or ideal). Moreover, the temperature of the light brine is also higher, and the SO2 volatilizes. Moreover, you need a lot of sodium sulfite at this time and it will not have the desired effect. It will be different if you adjust the pH value (9-10) first. First of all, sodium sulfite will not react with acid, but will directly react with free chlorine. Moreover, it is very thorough and the amount used is very small. Usually 70M3/H, light salt water only requires 5% sodium sulfite 70L/H.
In addition to the reason for the second floor, I think there are also: Under acidic conditions, free chlorine is very unstable and chlorine gas will precipitate, while under alkaline conditions, free chlorine is relatively stable, so adding sodium subsides can play its due role.