What is the significance of leaching in the extraction of aluminium?

Answer

Leaching is significant as it helps in removing the impurities like` SiO_(2), Fe_(2)O_(3)`, etc. from the bauxite ore.

Explanation

Aluminum contains sililca `(SiO_(2))` iron oxide `(Fe_(2)O_(3))` and titanium oxide `(TiO_(4))` as impurite these impurites can be removed by the process of lesaching During , the powderd bauxite ore is heated with a concentrated (45%)` solution of NaOH 473 - 523 K where alumina dissoles as sodium meta aluminate and silica as sodium silcate leaving `Fe_(2)O_(3) TiO_(2)` and other impurites behind
`Al_(2)O_(3) (s) +2NaOH (aq)+ 3H_(2)O(l) overset( 473-523 ) to 2 Na[Al(OH)_(4)](aq) `
Sodium meta -aluminate
`SiO_(2)(l) +2NaOH (aq) overset(473-523K) to Na_(2)SiO_(3) (aq) +H_(2)O(l)`
the impurities are filtered off and solution o fsodium meta - aluminate is neutralised by passing `CO_(2)` when hydraed alumina separates out while sodium silicate remains in solution , the hydrated aluminathus obtained is filled drireid and heated to give back pure alumina .
` AL_(2)O_(3) .XH_(2)O(s) overset(1473 K) to Al_(2)O_(3) (s) + xH_(2)O(g)`
thus by leching pure alumina can be obtained from buuxite ore .