THE INFLUENCE OF INTERNAL CRYSTAL PERFECTION ON GROWTH-RATE DISPERSION IN A CONTINUOUS SUSPENSION CRYSTALLIZER

The objective of the work presented here is to demonstrate the influen ce of induced lattice strain on growth behaviour of potassium alum cry stals in a continuously operated mixed suspension mixed product remova l (MSMPR) crystallizer. Therefore crystal size distributions in the cr ystallizer and individual growth velocities, especially of small parti cles (initial size 20-60 mu m) in a flow-through cell, were simultaneo usly determined. Moreover Laue diffraction patterns of crystals withdr awn from the MSMPR crystallizer were carried out indicating lattice de formation and strain. Most crystals exhibit constant crystal growth (C CG) behaviour with significant growth rate dispersion. The mean growth rate of small particles in the sub-sieve size range is considerably s maller than the mean rate of product sized crystals at constant supers aturation. Small potash alum crystals show a clear tendency of increas ed lattice strain with increasing supersaturation which can be explain ed by the refaceting process of attrition nuclei in the crystallizer. The average amount of induced strain in crystals having the same growt h history is obviously related to crystal size. Only slightly strained particles with sufficiently high growth rates will reach the product size range in the MSMPR crystallizer.