Abstract: There is disclosed a process for obtaining purer sodium sulfate from a mixture of solids containing sodium sulfate and sodium sulfite. The process involves contacting an aqueous slurry of the sulfate-sulfite mixture with a sulfur dioxide-containing gas under conditions which solubilize a significant amount of the sulfite as sodium bisulfite dissolved in the liquid aqueous phase. The remaining solid phase contains sodium sulfate of greater purity than in the mixture treated with sulfur dioxide. The mixture of sodium sulfate and sodium sulfite which is purified by the process may be obtained advantageously as a purge material from a process for removing sulfur dioxide from a gas stream.