Abstract: The present invention is directed to a method of removing sulfur dioxide from flue gases derived from furnaces burning high sulfur content fuels. The method comprises spraying flue gases with an aqueous medium containing (i) a material either dissolved or slurried therein, which material reacts with the sulfur dioxide in the flue gas to produce calcium sulfate and calcium sulfite, and (ii) a composition comprising a substantially linear water-soluble sulfonated polystyrene, and an organo-phosphonic acid derivative having the structural formula (X).sub.2 N--R--N(X).sub.2 where R is a lower alkyl of from 1 to 7 carbon atoms, X is hydrogen or the group -- CH.sub.2 PO.sub.3 M.sub.2, where M is a water-soluble cation, the compound being further characterized in that at least one but preferably all X's are --CH.sub.2 PO.sub.3 M.sub.2. In certain instances it is desirable to use in conjunction with the invention a water-soluble lignosulfonate.