Recrystallization is the process of recrystallizing crystals from a solution or melt after they have been dissolved in a solvent or melted. Recrystallization can purify impure substances or separate mixed salts from each other.

Crude salt contains insoluble impurities such as silt and sand, and soluble impurities such as Ca2+, Mg2+, SO42- and so on. Insoluble impurities can be removed by filtration, while soluble impurities such as Ca2+, Mg2+, SO42- can be removed by adding BaCl2, NaOH and Na2CO3 solution to produce precipitation, or by adding BaCO3 solid and NaOH solution. The water is then evaporated to obtain a purer refined salt.