Recrystallization, also known as fractional crystallization, is a procedure for purifying an impure compound in a solvent.
An impure compound is dissolved to prepare a highly concentrated solution at a high temperature
The solution is cooled
Decreasing the temperature causes the solubility of the impurities in the solution and the substance being purified to decrease
The pure substance then crystallizes before the impurities- assuming that there was more impure substance than there were impurities