Bayer’s process for concentration of bauxite.

Ans.                    

1. Bayer’s process is used to obtain pure aluminium oxide from bauxite ore.
2. The bauxite ore is concentrated by chemical separation. Bauxite contains impurities like iron oxide and silica.
3. The bauxite ore is powdered and heated with sodium hydroxide under high pressure in the furnace.
4. The aluminium oxide present in bauxite reacts with sodium Meta aluminate. Silica reacts with sodium hydroxide to form soluble sodium silicate.
5. The basic iron oxide in the gangue remains unaffected, separated by filtration. 

6. The filtrate containing sodium meta aluminate and sodium silicate is stirred with a little aluminium hydroxide to induce precipitation of aluminium hydroxide

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7. Aluminium hydroxide is then filtered, washed with water, dried and heated to get pure aluminium oxide (alumina)