Interaction of macro- and micromixing on particle size distribution in reactive precipitation

The effects of mixing factors (stirrer speed, feed time, feed location and viscosity) on particle size distribution (PSD) in the precipitation of BaSO4 conducted in a semi-batch stirred tank reactor were investigated It was found that there exist critical points on the curves of mean size and dimensionless variance versus the mixing factors, at which the mean size or the dimensionless variance is minimal These results originate from the interaction of macromixing and micromixing. A new mixing-precipitation model including micromixing, turbulent dispersion (mesomixing) and backmixing (macromixing) was proposed to predict PSD Critical effects of mixing factors, stirrer speed and feed time on PSD were quantitatively predicted by the present model. The results coincided satisfactorily with those of the experiments.