Causticization process in alumina producing Bayer process

The present invention discloses alumina producing process, and is especially the causticization process in alumina producing Bayer process. The continuous technological process includes the steps of: feeding causticizing liquid and lime milk in controlled amount into a heating tank while introducing fresh vapor to control the causticizing temperature; feeding the heated causticizing reactant liquid into a temperature maintaining tank and causticizing for sufficient time; and depositing separation of the causticized liquid in a depositing tank. The process is an automatic one with high causticization rate with sodium carbonate, resulting in lowered the amount and harm of sodium carbonate in Bayer process, simple operation and lowered labor strength.