Describe the three steps involved in the leaching of bauxite to get pure alumina.

Explanation

(a) Bauxite ore is heated with concentration solution of NaOH at 473 K to 523 K and 35-36 bar pressure. `Al_(2)O_(3)` dissolves out as sodium aluminate leaving behind impurities.
`Al_(2)O_(3) + 2NaOH + 3H_(2)O rarr 2Na[Delta l(OH)_(4)]`
(b) The aluminate in solution is neutralised by passing `CO_(2)` gas and hydrated `Al_(2)O_(3)` is precipitated.
`2Na[Al(OH)_(4)] + 2CO_(2) rarr Al_(2)O_(3) 3H_(2)O + 2NaHCO_(3)`
(c ) Hydrated alumina is filtered, dried and heated to give pure alumina.
`Al_(2)O_(3).3H_(2)O overset(Al_(2)O_(2)1170 K)rarr Delta l_(2)O_(3) + 3H_(2)O`