Fractional Freezing

Fractional freezing is a process used in process engineering and chemistry to separate two liquids with different melting points. It can be done by partial melting of a solid, for example in zone refining of silicon or metals, or by partial crystallization of a liquid, for example "freeze distillation", also called "normal freezing" or "progressive freezing".

Partial crystallization can also be achieved by adding a dilute solvent to the mixture, and cooling and concentrating the mixture by evaporating the solvent, a process called "solution crystallization". Fractional freezing is generally used to produce ultra-pure solids, or to concentrate heat-sensitive liquids.