Recrystallization is a method employed to purify solid compounds. It involves dissolving the impure solid in a heated solvent until the solution reaches saturation, followed by gradual cooling. As the solution cools, pure crystals form while impurities are left behind. These crystals are then collected, washed, and dried, resulting in a purified solid product. Recrystallization is a crucial technique for obtaining high levels of purity in solid compounds.
The underlying mechanisms, dissolution, and recrystallization can also minimize the crystal's internal energy in order to reach a more global energy equilibrium resulting a stable polymorph. While recrystallization is usually applied deliberately to optimize crystals and processes, uncontrolled recrystallization can lead to the unwanted formation of hydrates and solvates or polymorph transformation.