Effect Of Surface Active Agent On The Seeded Precipitation Process Of Sodium Aluminate Solution

With the increasingly strict requirement of energy saving and environmental protection, sandy alumina is used widely in the industry of aluminum electrolysis, because of its particular microstructure, suitable size distribution and high strength. Agglomeration and crystal growth must be promoted for producing sandy alumina. The influences of the surface active agent on the seeded agglomeration process of sodium aluminate solution were studied.In this thesis, effect of precipitation conditions, including precipitation temperature, seed coefficient, seed size and precipitation time on seed precipitation process were first studied. The precipitation conditions and parameters of the follow-up experiment were determined. Then, the effect of industrial crystallization additive (NALCO and SNF)on seed agglomeration process and its mechanism was studied. For the particularity of the bauxite in China, effect of different surfactant on seed agglomeration process and its mechanisms were then studied. The presence of impurities in aluminate solution in actual industrial production was studied at last, possible solutions were proposed. Following results were obtained:For agglomeration study the suitable condition was as follows: precipitation temperature was70℃, NK was170g·L-1, AO was187g·L-1, agitation speed was150r/min and seed coefficient(Ks) was0.25.In the seed precipitation process, the particle size distribution of gibbsite will be improved with the addition of CGM(Crystal Growth Modifier), the precipitation yield was also increased. The precipitation yield of alunimate solution will be increased by2.56%with the addition of CGM NALCO was50μ·L-1, D(0.1) will be increased by3.51μm.Effect of fatty alcohols on seed precipitation was studied first time in this paper. It was found that the particle size of gibbsite increases with the increase of straight chain and branch chain carbon atoms of fatty alcohols, and the precipitation yield was also increased.In the research, the surfactant was first emulsificated to disperse in solution system. Compared with CGM NALCO, with the addition of dodecanol and octyl polyethylene glycol phenyl ether emulsification mixture, the seed agglomeration process will be improved, the amount of small particles will be reduced, D(0.1) will be increased from32.65μm to33.76μm, precipitation yield will be increased from23.72%to24.50%.It was found that the fatty acid can not improve the particle size distribution, and it was inconsistent with relevant references.Effect of surfactant on seed precipitation in the presence of sodium oxalate was studied. Fine sodium oxalate crystals will cause excess fine gibbsite formation. With the addition of fatty alcohols surfactant, the adverse effects of sodium oxalate will be reduced.