Abstract: Improvement in processes for the selective removal of sulfur dioxide with respect to carbon dioxide from a gas mixture containing same wherein the gas mixture is contacted with an aqueous absorbent solution, such as alkanolamine, alkali metal hydroxide, ammonium hydroxide or sulfites thereof, to remove sulfur dioxide from the gas mixture and form a SO.sub.2 -rich aqueous absorbent solution which is moved to a stripping zone where sulfur dioxide is driven off to form a SO.sub.2 -depleted aqueous absorbent solution which is recycled and re-contacted with the gas mixture, the improvement comprising removing sulfur oxyanions of heat stable salts which accumulate in the aqueous absorbent solution by contacting a portion of it with an anion exchange resin having hydroxyl anions displaceable by the heat stable sulfur oxyanions whereby the hydroxyl anions of the resin are replaced by the heat stable divalent sulfur oxyanions which are thus taken out of the solution.