What is fractional crystallization?
Fractional crystallization is a method of separating mixtures based on differential solubility.
If a solute containing 2 or more components is taken up into solution and allowed to crystallize from that solution, the resultant crystals will be enriched in that component which is LESS soluble.
And of course the supernatant solution will be enriched in that component that is more soluble. This technique is often used to effect separation of solutes of differential solubility.