Nucleation and morphology of barium carbonate crystals in a semi-batch crystallizer

A double-jet feed, semi-batch crystallization system was used to explore the nucleation kinetics, growth kinetics and morphology of barium carbonate crystals under a constant pH value. The nucleation rate and the growth rate can be determined successfully by the initial rate method. The results showed that heterogeneous nucleation is dominant in the primary nucleation mechanism, and the effect of specific power input on the nucleation rate is obvious. The results also showed that the pH and initial concentration of the solution play an important role on the morphology of barium carbonate crystals. The crystal forms are floc, candy-like, olivary with end dendrite, olivary-like and needle-like, depending on the operating conditions. At high to moderate concentrations the flee precipitates are the major products in the pH range of 9.0-10.0. At moderate to low concentrations the candy-like and olivary with end dendrite crystals become the major products. At low concentrations and low pH values the crystal forms are olivary-like and needle-like precipitates. However, the results showed that the crystal forms of barium carbonate are concerned with the nucleation rates. On the other hand, the investigations showed that the well-sharp crystal forms follow the surface-integration growth mechanism and the dendrite crystals obey the diffusion growth mechanism. (C) 2001 Elsevier Science B.V. All rights reserved.