Abstract: Sulfur dioxide is removed from waste gases generated in a thermoelectric plant by contacting the gases countercurrently with an aqueous alkaline solution having a pH of about 9-12 and containing both sodium hydroxide and manganic hydroxide, whereby the sulfur dioxide reacts with the sodium hydroxide to form sodium sulfite until the pH of the solution is about 6-7 and the sodium hydroxide is substantially exhausted and wherein the sulfur dioxide then reacts with the manganic hydroxide to form manganese sulfite. The resultant sodium sulfite and manganese sulfite are oxidized and transformed into sodium sulfate and manganese sulfate respectively, by the action of oxygen in the mixture, in the presence of the manganic ion and also by the direct oxidizing action of the manganic ion.