A Model for Aluminium Trihydroxide Crystallisation from Pure and Impure Solutions
Mannitol has been used as a model hydroxy organic compound to simulate the influence or organic compounds on the growth, nucleation and agglomeration mechanisms of aluminium trihydroxide crystallization. As little as 151·6rngmannitol/m3 of seed was sufficient to completely suppress the crystallization. A population balance equation including terms for nucleation, growth and agglomeration, coupled with a mass balance equation forms the basis of a mechanistic model for batch crystallization of aluminium trihydroxide. The presence of mannitol at a level as low as 92·2 mg mannitol/m2 of seed reduced the growth rate coefficient by an order of magnitude and the nucleation rate coefficient by two orders of magnitude. This low mannitol concentration also increased the agglomeration parameter. Four different kernels of shear flow, turbulent flow, size independent, and an empirical kernel were checked for best fit in the present study. Crystallization in the absence of mannitol was best fitted with no agglomeration term in the model.