These qualities concern size, granulometry, purity and facies.
1) Size is the result of a compromise, since regular crystals of large size are expensive to produce. Typically, we accept a size that allows easy dewatering (or filtration), storage and transport. Occasionally, a small size is preferable (pigments and charges for plastic materials, later dissolution).
2) The size distribution required is often as tight as possible, though this is not always the case.
3) Purity is attained by the careful choice of bleeding.
4) Facies (shape) is influenced by both the impurities present and supersaturation (dendrite growth for high supersaturations).
Crystallizers
We will not attempt to apply a classification to crystallizers, which would be a futile exercise. However, we will review the main types of devices currently in use, with a particular focus on their operating mechanisms.
This study will lead us to establish several simple criteria for choosing the crystallizer best adapted to the work in question.