Fractional crystallization (chemistry)

Fractional crystallization is a method of separation of the chemical, the use for the separation of crystals of the differences in solubility of the substances. Natural model is, among other things, the fractional crystallization during the solidification of molten rock.

The precipitation of two or more substances present in a solvent from the solution occurs at different rates. Crystallization or precipitation reaction may be caused by changes in concentration, changes in temperature or other triggers such as the use of seed crystals.

This fact is exploited in chemical engineering processes of fractional crystallization. The substance mixture is to be separated is mixed with a solvent and heated. In the slow cooling, the individual substances one after the other to crystallize so that it can be recovered in a suitable device in a pure form from the solution. The method can also be repeatedly applied, in order to increase the purity of the materials obtained.

The method is used in the chemical technique, not only for the production of chemically pure substances or for the treatment of waste, but also used as a chemical analysis method. Examples include the representation of rare earths or no separation of the lanthanides from the naturally- occurring always mixed crystals of these elements.