Crystallization is a process of separating solid compounds from a solution in the form of crystals. It is a technique used for the purification of substances and is primarily employed as a separation technique to obtain pure crystals of a substance. The process of crystallization can be described as follows:

1. Dissolve the solid in a suitable solvent to form a solution.
2. Heat the solution to dissolve the solid completely.
3. Filter the solution to remove any impurities.
4. Allow the solution to cool slowly.
5. As the solution cools, crystals of the solid start to form.
6. Filter the crystals and wash them with a suitable solvent to remove any impurities.

Crystallization is used to separate and purify substances, and in this process, large crystals are formed. The arrangement of particles in the crystals formed is well defined, as in the case of solids. Crystallization is a physical process. The process of crystallization has various applications, including the purification of seawater, separation of alum crystals from impure samples, and in the pharmaceutical industry, crystallization is used as a separation and purification process for the synthesis and isolation of co-crystals, pure active pharmaceutical ingredients (API), controlled release pulmonary drug delivery, and separation of chiral isomers.