CONTINUOUS CRYSTALLIZATION OF POTASH ALUM - MSMPR KINETICS

The crystallization kinetics of potash alum (aluminium potassium sulphate) from aqueous and aqueous acetone solutions respectively in a continuous mixed‐suspension, mixed‐product‐removal (MSMPR) crystallizer (capacity 4 L) are reported. Growth and nucleation rates are determined by direct model estimation via the population balance analysis of crystal size distribution measured using laser light scattering and sieve analysis. The overall growth rate during drowning‐out precipitation strongly decreases with increasing acetone concentration in the crystallizing solution. Nucleation rates evaluated at zero‐size, however, are virtually unaffected while the “effective” nucleation rates are strongly increased by the presence of acetone with a reduction in the supersaturation order. Magma density dependence is approximately first order during cooling crystallization while a somewhat lower dependence is detected during drowning‐out precipitation. Copyright © 1990 Canadian Society for Chemical Engineering