Strengthen The Basic Research Of The Sub-process Of Sodium Aluminate Solution

Seeded precipitation from supersaturated sodium aluminate solution is a crucial step in the Bayer process for alumina production. Whether the control of production conditions is suitable or not will expose direct impact not only on the yield and quality of alumina, but also on recycle efficiency of the Bayer process and other procedures. Seeded precipitation is a complicated crystallization reaction involving a variety of physicochemical sub-processes. At present, the precipitation yield is only 50～55%, which is greatly lower than the theoretic value. The process of seeded precipitation becomes the "bottleneck" of technical development for alumina production. Therefore, intensification of the seeded precipitation process aiming to decrease the precipitation time and increase precipitation yield holds outstanding significance and applying prospect.From the point of view of increasing precipitation yield, the influence of some active seeds on the seeded precipitation is investigated in detail. Meanwhile, the frost active seeds are studied principally. Preliminary discussion on the effect mechanism of the active seeds in the process of seeded precipitation is proposed. Pre-treatment for seeds change the active point of seeds' surface, which result in the difference of seeds' activation. Furthermore, some effective surfactants are selected based on the effect mechanism which surfactants can greatly reduce the surface tension of liquor in aqueous systems and the influence of these surfactants on the seeded precipitation is researched at length. Meanwhile, preliminary explanation about the effect mechanism of surfactants in the sodium aluminate solution is presented. The stability of sodium aluminate solution is on the decline resulting from surfactants is able to reduce the surface intension and viscosity of sodium aluminate solution, which result in the increase of precipitation yield in the seeded precipitation process.The results indicate that the change of sharp peak, rib and flaw, etc of crystal of seeds which are treated with some solutions results in the difference of seeds activation. The seeds treated with hydrochloric acid can markedly increase the precipitation yield. The frost effect contributes to the formation of the frost seeds with special activation. The frost active seeds can increase precipitation yield by 6.52%. Granularity of seeds and caustic soda concentration of sodium aluminate solution have consumedly impact on the activation of frost seeds. The cause that frost seeds can intensify the seeded precipitation process is possibly that frost seeds born in the sodium aluminate solution have more fine grain than the industrial seeds. The optimal addition content of surfactants used in experimentation is determined after measuring the surface tension and viscosity of sodium aluminate solution with adding the surfactants. According to the optimal addition content of surfactants, the precipitation yield of seeded precipitation process can increase by about 4%.