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 (mcsomixing) and baekmixing (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.
INTRO DUCTIO N
Precipitation processes have found wide applications in the manufacture of sparingly soluble particles, used as fillers, pigments and ceramics. In these cases, fast or very fast chemical reactions and very fast nucleation kinetics are often involved ( Garside and Tavare, 1985 ). Therefore, mixing effects would be significant in determining the distribution of supersaturation and subsequently the particle size distribution (PSD) of the product.