PROCESSO PARA A RECUPERACAO DE HIDROXIDO DE SODIO DE UM LICOR RESIDUAL ALCALINO

摘要

Sodium hydroxide is recovered from an alkaline waste liquor ("black liquor") containing substantially no sulfur compounds discharged from a process comprising soda cooking wood fibers, washing and optionally bleaching them, by a direct causticization process. This process comprises: (a) adding a gas comprising carbon dioxide to the black liquor as it is or after concentration to adjust the pH of the black liquor to 9.5 to 12.5 (determined at a black liquor solids concentration of 40% and 80 DEG C), (b) concentrating the above described black liquor to a solids concentration of 50 to 95%, (c) adding the above described carbon dioxide-treated and concentrated black liquor, oxygen and iron oxide to a combustion furnace, subjecting the mixture to combustion and thus burning organic substances and converting inorganic soda components into sodium carbonate and sodium carbonate into sodium ferrite, and (d) hydrolyzing the thus resulting product to recover sodium hydroxide and recycling the recovered iron oxide to step (c). r