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Aluminum is the most abundant metal of earth's crust (8.3%) and exist as oxide and fluoride ores. The metal is extracted from bauxite ore (Al 2 O 3 .2H 2 O). The extraction process involve three stages or steps step 1 Purification of bauxite step 2 Electrolytic reduction of Al 2 O 3 step 3 Electrolytic purification of aluminium 1. Purification of bauxite The bauxite ore contain iron oxide and silicon dioxide as impurities. It is purified by leaching method using concentrated sodium hydroxide solution in which bauxite dissolve forming sodium meta aluminate. On agitating this solution with freshly precipitated Al(OH) 3 for several hours Al(OH) 3 is precipitated. NaAlO 2   +  2H 2 O  ------------>  NaOH  +  Al(OH) 3  The precipitate is filtered and dried and NaOH is concentrated and used again for leaching . The aluminium hydroxide precipitate is calcined at 1500 o C to obtain pure alumina. 2. Electrolytic reduction of pure alumina ...

The extraction of aluminium involves two steps that is, purification of bauxite by Baeyer's process and electrolysis of alumina . 1. Purification of bauxite by Baeyer's process In the Baeyer's process, the bauxite ore is heated with concentrated NaOH solution under pressure ( Aluminum is purified by leaching method ). The alumina dissolves as sodium meta aluminate. The other materials present in the ore are left as insoluble part. This solution is filtered in ore are left as insoluble part. This solution is filtered off. From the solution Al(OH)3 is precipitated by adding freshly prepared Al(OH)3 to the cold dilute solution and agitating. Al2O3 + 2NaOH -------> 2NaAlO2 + H2O NaAlO2 + 2h2o -------> NaOH + Al(OH)3 The precipitated Al(OH)3 is dried and ignited to get pure alumina. 2Al(OH)3 --------> Al2O3 + 3H2O 2. Electrolysis of alumina The alumina is dissolved in a mixture of molten cryolite and fluorspar which lowers the melting point. It is then elect...