Abstract: A method of treating an exhaust gas at a high temperature containing nitrogen oxides and sulfur oxides by bringing the exhaust gas into contact with an absorbing solution containing at least an iron chelate salt and potassium sulfite to thereby convert said nitrogen oxides and sulfur oxides into a mixture of potassium imidodisulfonate, potassium dithionate and potassium sulfate, characterized in that (1) the exhaust gas at a high temperature is cooled to a temperature below 80.degree. C. before bringing it into contact with the absorbing solution, (2) the concentration of potassium sulfite as the sulfite component in the absorbing solution is kept at least at 0.8 mol/kg, and (3) the mixture of salts produced in the absorbing solution is crystallized by cooling and separated by filtering the absorbing solution.

Abstract: A process is described for treating an exhaust gas containing NO.sub.x and SO.sub.x in which NO.sub.x and SO.sub.x are effectively converted into industrially useful products of NH.sub.3, or sulfur by use of an aqueous absorbing solution containing at least iron chelate salt and potassium sulfite.