extraction of aluminium what is the answer of table 4.7 ?
Answers
Answer:
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
−
By this process 98.8% pure aluminium is obtained.