The alkali in the red mud of the Bayer process is mainly divided into two parts: one is soluble alkali, which is the attached alkaline liquid brought in during the dissolution of bauxite. During the production of alumina by the Bayer process, NaOH reacts with bauxite to produce aluminum Sodium, sodium silicate and other soluble substances, unreacted NaOH and sodium aluminate are discharged with the red mud, the longer the red mud stacking time