Describe Bayer's Process

Explanation

(i) During extractino of aluminium from bauxite. The bauxite ore is concentrated by Bayer's Process.
(ii) During concentration, baxuite is converted into alumina.
(iii) Crude bauxite contains impurities like iron oxide and silica which are removed during Bayers' process.
(iv) The ore is first group in a ball mil. Then it is leached by heating it with concentrated caustic soda solution under high pressure for 2 to 8 hours at `140^(@)C` to `150^(@)C` in a tanke called digester.
(v) Aluminium oxide `(Al_(2)O_(3))` being amphoteric dissolves in aqueous `NaOH` to form water soluble Sodium aliminate `(NaAlO_(2))`.
`Al_(2)O_(3).2H_(2)O_((s))+2NaOH_((aq))+ to 2NaAlO_(2(aq))+3H_(2)O_((l))`
(vi) the impurities like `Fe_(2)O_(3)` do not dissolve in aqueous NaOH and are removed by filteration.
(vii) Silica from the gangue dissolves in aqueous NaOH forming water solubel silicate
(viii) Sodium aliminat is diluted and cooled to `50^(@)C` and hydrolyzed to give aluminium hydroxie as precipitate.
`NaAlP_(3)+2H_(2)O to NaOH+Al (OH)_(3)`
The precipitate of `Al (OH)_(3)` obtained is filtered, washeddried and then calcinated by heating at `1000^(@)c` to obtain alimina.
`2Al(OH)_(3) to Al_(2) O_(3) +3H_(3)O`