METHOD FOR TREATING SODIUM NITRATE AND/OR SODIUM CARBONATE-CONTAINING SUBSTANCE

PURPOSE: To produce sulfate pulp cooking solutions high and different in sulfidity while restraining sulfur emission amounts and corrosion of a soda recovery boiler. CONSTITUTION: Ash containing sodium sulfate and/or sodium carbonate such as fly ash from a stack gas of the soda recovery boiler and by-products from a chlorine dioxide production plant in a cellulose pulp mill and a sulfur- containing gas consisting of an ethene series hydrocarbon and hydrogen sulfide or an ethene series hydrocarbon/hydrogen sulfide mixture are brought into contact with the melt from the soda recovery boiler or black liquor is combusted under oxidizing conditions to produce sodium sulfide. The sodium sulfide thus produced is directly added to a cooking vessel of cellulose pulp or to the cooking liquid of the former cooking stage to increase the sulfidity and is not added to the cooking liquid of the latter stage to cook the pulp by preparing different sulfidity cooking liquids.