An economical way of scrubbing SO2 from flue gases is by treating the effluent with Ca(OH)2 hydrated lime or CaCO3 limestone.

[3] Scrubbing with limestone follows the following idealized reaction: Scrubbing with hydrated lime follows the following idealized reaction:[4][5] The resulting calcium sulfite oxidizes in air to give gypsum: The gypsum, if sufficiently pure, is marketable as a building material.

Sulfites are strong reducers in solution, they act as oxygen scavenger antioxidants to preserve food, but labeling is required as some individuals might be hypersensitive.

[citation needed] There is a possibility to use calcium sulfite to produce gypsum by oxidizing (adding O2) it in water mixture with the manganese (Mn2+) cation or sulfuric acid catalyzers.

The mixed sulfite-sulfate represents an intermediate in the oxidation of the sulfite to the sulfate, as is practiced in the production of gypsum.