Abstract

An improved method for recovering spent sodium and sulfur components in sodium sulfite and sodium bisulfite pulping operations. The method involves reduction burning of spent liquor to convert it to smelt and the treatment of this smelt in a sequence of operations that accelerate the reaction steps used to produce sodium hydrosulfide, hydrogen sulfide, sulfur dioxide, sodium carbonate, sodium bicarbonate and to recover sodium sulfite, sodium bisulfite, sodium carbonate and/or sodium hydroxide while preventing formation of sodium thiosulfate. The method utilizes a sufficient quantity of recycled sodium bicarbonate addition to precarbonated liquor to maintain the partial pressure of carbon dioxide created by the solution above that provided by the carbon dioxide in the gas used for stripping out the hydrogen sulfide, recovering the carbon dioxide and water vapor for stripping and precarbonation by decomposition of the sodium bicarbonate and recovering carbon dioxide by pressure decarbonation and pressure neutralization, for the high pressure carbonation to produce the sodium bicarbonate.