A sodium sulfite liquor is formed by reacting sodium carbonate with sulfur dioxide. A CO2 byproduct may be removed from the formed liquor by injecting a stripping gas (e.g., steam and/or air) into the liquor, either into a transfer pipe or into a tank that is vented; by increasing the liquor temperature; and/or by reducing the liquor pressure. The decarbonated sodium sulfite liquor with a reduced carbon dioxide content is introduced into a crystallizer connected to a circulation loop comprising a heater and/or a filter. Additional decarbonation by heating, stripping and/or depressurization of the liquor may be carried out in a circulation loop connected to the crystallizer. The condensing side of the heater may be vented. The flow rate of the circulation loop and/or heater temperature differences may be monitored. Additional CO2 may be vented from a holding tank to maintain circulation loop flows and heater temperature differences.