Abstract: Sodium sulfate is purged from a sulfur dioxide removal system involving contact of a sulfur dioxide-containing gas with a solution containing sodium sulfite to absorb sulfur dioxide from the gas. The spent absorbing solution is regenerated by desorbing sulfur dioxide and recycled for further use. To avoid an unduly large build-up of sulfate in the system, at least a portion of the absorbing-desorbing medium containing sodium sulfate and a relatively large amount of sodium bisulfite, e.g. spent absorbing solution, is contacted with a treating gas containing at least a small amount of sulfur dioxide while reducing the amount of water in the medium so that a slurry is obtained having up to about 10, or even up to about 20, weight percent precipitated solids containing sodium sulfate in greater concentration than would otherwise be obtained in the absorption-desorption cycle. Preferably, the sulfur dioxide-containing treating gas is unsaturated with respect to water.