Abstract: A method for purifying industrial exhaust gases containing nitrogen oxides and sulfur oxides, by treating the gases with a circulating absorbing solution containing Fe-EDTA complex salt and ammonium sulfite is provided.The treatment comprises a combination of the main absorbing step with the following steps:(a) a circulation step of the absorbing solution in part or total, (b) an oxidation step of sulfite, (c) a separation step of EDTA, (d) a decomposition step of dithionate, etc., (e) a separation step of iron compound, and (f) a separation step of ammonium sulfate.According to this invention, a long time continuous operation for said purification is possible.

Abstract: Industrial exhaust gas containing nitrogen oxides is treated with an aqueous solution of an iron chelate complex salt which contains essentially a sulfite salt at the time of treatment whereby nitrogen oxides which have been difficult to catch can be absorbed with a high absorbing rate even when the concentration of nitrogen oxides is low in the exhaust gas or sulfur dioxide is included in the gas, and simultaneous desulfurizing can be attained in this case. Said aqueous solution has a large absorbing capacity and may contain an ion or ions of alkali metal, alkali earth metal or ammonium.

Abstract: In the process wherein industrial exhaust gases containing nitrogen oxides and SO.sub.2 are treated with an absorbing solution containing an iron chelate complex and a sulfite to remove nitrogen oxides and SO.sub.2, the absorptivity of the solution is reduced sometimes on account of dithionate formed during the treatment. The absorptivity-reduced absorbing solution is regenerated by heat-treating the solution at a pH of 3.0 or lower and a temperature of 80.degree. C or higher whereby the dithionate is decomposed.