Study On Red Mud Settling During Sweetening Process

Sweetening digestion technology is an efficient way to strengthen digestion in Bayer process. But the imported gibbsite bauxite used as sweetening ore usually contains goethite and alumogoethite, which can cause the settling properties of red mud to go bad, the content of overflow suspensions to go too high. This can affect productivity and economic benefits. So it is meaningful to study how to eliminate the adverse effect of goethite on the settling performance.There are two methods to overcome the unfavorable action of goethite in red mud settling. One is to turn goethite into the stable and hydrophobic hematite by phase transition before settling. The other is to choose suitable flocculant for the red mud of high goethite content.In this paper pre-roasting for processing bauxite was studied, which was intended to urge the transition of goethite to occur before digestion. The result showed that all available alumina was digested and all goethite was transformed after the bauxite1#roasted at600℃for30min, followed by digesting at230℃for30min.The results of study on phase transition of goethite with hydrothermal method showed that raising temperature and increasing the amount of lime were beneficial to the phase transition. All goethite, in the three kinds of imported gibbsite, transformed to hematite when the gibbsite was digested alone at260℃for20min, and the addition amount of lime was10%of bauxite.Several common kinds of flocculants used in separation of red mud were studied. The results showed that for the red mud of high goethite content good settling effect could be achieved by using hydroxamic acid flocculant. The supernatant solids were decreased significantly. In addition, the complex formulation of SNF KM-800and NALCO9779was proved to be effective, not only for the clarity of solution, but also for the settling velocity.