Though Aluminium occur in most of the minerals, why only Bauxite is
used to extract it?
Answers
The extraction of the metal from bauxite involves the three main steps.
Concentration of Bauxite (Al
2
O
3
.2H
2
O)
Concentration of ore is done by leaching which helps in removing impurities like Fe
2
O
3
,SiO
2
, etc. Bauxite is treated with NaOH to form sodium aluminate which on further reaction with CO
2
gives pure Alumina.
Al
2
O
3
+2NaOH+3H
2
O⟶2Na[Al(OH)
4
]
2CO
2
−2NaHCO
3
Al
2
O
3
.xH
2
O
Δ
1470K
Pure alumina
Al
2
O
3
+xH
2
O
Electrolytic reduction of Alumina (Al
2
O
3
)
Electrolytic reduction of pure alumina takes place in iron box (cathode) with cryolite (Na
3
AlF
6
) and fluorspar (CaF
2
) which lowers the melting point and increases the conductivity of electrolyte. Graphide rods act as anode.
At cathode:-
Al
3+
+3e
−
⟶Al
At anode:- The oxygen liberated at anode reacts with the carbon of anode to produce CO and CO
2
.
C+O
2−
⟶CO+2e
−
C+2O
2−
⟶CO
2
+4e
−