Dynamic simulation of periodic attenuation in seeded precipitation of sodium aluminate solution

Abstract

Periodic attenuation in seeded precipitation of sodium aluminate solution has been known to adversely influence the production of alumina in the Bayer process. In this paper, a mathematical model is established to simulate the dynamics of the periodic attenuation. A Population Balance Method is used in the model to define the particle size distribution (PSD) of aluminum hydroxide precipitates. Factors considered in the model include the particle characteristics, growth, and agglomeration of seed crystals, and the nucleation in sodium aluminate solution. This model is calculated by using the discretized population balance method and the simulation results are validated with experimental data. The dynamic evolution of the PSD during seeded precipitation is believed to involve the following key process. The ratio of the liquor supersaturation to the specific surface area of finer seeds (L<45μm) first reaches its maximum. It is then followed by a rapid grain refinement. Understanding this process is very useful in determining the optimal moment when the operational parameters should be adjusted in order to eliminate the periodic attenuation in industrial production.