Abstract: This process for purifying a sulfur dioxide containing gas, for example stack gas, comprises the steps of washing the gas with aqueous ammonia or ammonium sulfite, vaporizing sulfur dioxide and ammonia therefrom, reacting vaporized sulfur dioxide with hydrogen sulfide and recycling an ammonia containing stream. To avoid the drawbacks resulting from the presence of hydrogen sulfide in the recycle stream, a further oxidation step is provided to convert hydrogen sulfide to sulfur dioxide.

Abstract: Process for purifying a gas containing hydrogen sulfide and sulfur dioxide, comprising substantially removing sulfur dioxide, absorbing hydrogen sulfide on a solid contact mass, intermittently regenerating said mass by means of an oxygen-containing gas, so as to produce a gas containing sulfur dioxide, and reacting the latter gas with hydrogen sulfide to produce sulfur.

Abstract: Molten ammonium sulfates containing iron sulfate as an impurity may be reduced with sulfur or a sulfur compound over long periods provided a fraction of these impure ammonium sulfates is withdrawn, treated for iron removal and fed back to the reduction zone.

Abstract: A sulfur dioxide containing gas is purified by successive contact with an ammonia solution and then a dilute ammonium sulfite solution; the latter solution is regenerated by electrodialysis while the ammonia solution, after SO.sub.2 absorption, is vaporized in order to recover ammonia and sulfur dioxide.

Abstract: A SO.sub.2 containing gas, for example a stack gas, is purified according to a multi-step process, which comprises washing said gas with an aqueous ammonia solution, treating the resulting solution with hydrochloric acid, whereby SO.sub.2 and an aqueous ammonium chloride solution are obtained and separated. The ammonium chloride solution is then reacted with magnesium oxide to recovery ammonia and the resulting magnesium chloride is cracked to produce hydrochloric acid and magnesium oxide, the ammonia, hydrochloric acid and magnesium oxide being recycled to the process.

Abstract: A solution of sodium sulfite or sulfide is reacted with ammonium sulfate, so as to produce a gas containing SO.sub.2 or H.sub.2 S, NH.sub.3 and H.sub.2 O, which is thereafter treated for sulfur production and NH.sub.3 recovery, and a liquid outflow containing sodium sulfate which is reacted with CO.sub.2 and NH.sub.3, in order to produce NaHCO.sub.3 and regenerate the ammonium sulfate. NaHCO.sub.3 may be converted to sodium carbonate and CO.sub.2, the latter being re-used in the process.

Abstract: Process for purifying industrial gases containing hydrogen sulfide and for simultaneously producing elemental sulfur, comprising contacting said gases with an aqueous solution of sodium hydroxide and/or sodium carbonate, thereby forming a sodium sulfide solution, contacting said solution with an aqueous solution of ammonium hydrogen carbonate or with a gaseous mixture of CO.sub.2 and NH.sub.3 so as to precipitate sodium hydrogen carbonate, decomposing the latter to CO.sub.2 and neutral sodium carbonate which is recycled, heating the resulting liquid phase to produce NH.sub.3 and H.sub.2 S and producing sulfur by reacting the H.sub.2 S with sulfurous anhydride.

Abstract: Sulfur dioxide and ammonia remaining in waste-gas after partial purification thereof, for example by means of ammonia or ammonium sulfite solutions, are withdrawn from said gas by washing with a diluted aqueous solution of ammonium sulfate; the resulting ammonium sulfite containing solution is oxidized thereafter either by means of air or in an electrochemical cell.