PROCESS FOR RECOVERING SODIUM HYDROXIDE FROM AN ALKALINE PULP WASTE LIQUOR

摘要

TITLE OF THE INVENTION A process for recovering sodium hydroxide from an alkaline pulp waste liquor Sodium hydroxide is recovered from an alkaline waste liquor containing substantially no sulfur compounds discharged from a process comprising soda cooking wood fibers, washing and optionally bleaching, by the direct causticization process capable of functioning as a system. This process comprises: a step (a) of adding a carbon dioxide-containing gas to the black liquor as it is or after concentrated to adjust the pH of the black liquor to 9.5 to 12.5 (at a solid concentration of black liquor 40 %, 80 .degree.C), a step (b) of concentrating the above described black liquor to a solid concentration of 50 to 95 %, a step (c) of 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 a step (d) of hydrolyzing the thus resulting product to recover sodium hydroxide and recycling the recovered iron oxide to the above described step (c).