The purification method used for mineral Al2O3.2H2O is

Leaching : It involves the treatment of the impure ore with a suitable reagent [NaOH] and make the reagent to react with ore and not with impurity or vice versa.BAEYERS PROCESS → The red bauxite ore contains Fe2O3 as impurity ,this impurity will not react with NaOH.→Therefore when red bauxite ore is treated with NaOH it only reacts with Al2O3 and converted to highly soluble NaAlO2.→ while Fe2O3 donot react and seperated out  as precipitate.This precipitate can be removed by filteration.→ The above formed NaAlO2 is diluted with water and converted to Al(OH)3 precipitate,on strong heating of Al(OH)3gives Al2O3 (Bauxite) .