Question
How is aluminium obtained from pure ore?
✓
Answer
Aluminium is obtained from pure ore by Hall - Heroults process as follows:
i. Electrolyte used :
a. Pure alumina
b. Cryolite
c. Aluminium fluoride
d. Calcium fluoride or Fluorspar
ii . Electrolytic cell : It is a rectangular steel tank with a thick inner lining of carbon .
iii . Electrodes used :
a. Cathode: inner lining of carbon
b. Anode: Thick carbon rods dipping into the fused electrolytes.
Reactions: On passage of electricity through electrolyte aluminium and oxide ions are formed.
At cathode: Aluminium ions get reduced as:
$Al^{3+} + 3e^- → Al$
At anode: oxygen gas is liberated as:
$O^{2-} - 2e^- → [ O ]$
$[ O ] + [ O ] → O_2$
The oxygen formed at anode oxidizes the carbon of the anode to carbon dioxide.
$C + O_2 → CO_2$
As a result the anode gets oxidized and it has to be replaced periodically.
Figure: Extraction of aluminium from pure ore.
i. Electrolyte used :
a. Pure alumina
b. Cryolite
c. Aluminium fluoride
d. Calcium fluoride or Fluorspar
ii . Electrolytic cell : It is a rectangular steel tank with a thick inner lining of carbon .
iii . Electrodes used :
a. Cathode: inner lining of carbon
b. Anode: Thick carbon rods dipping into the fused electrolytes.
Reactions: On passage of electricity through electrolyte aluminium and oxide ions are formed.
At cathode: Aluminium ions get reduced as:
$Al^{3+} + 3e^- → Al$
At anode: oxygen gas is liberated as:
$O^{2-} - 2e^- → [ O ]$
$[ O ] + [ O ] → O_2$
The oxygen formed at anode oxidizes the carbon of the anode to carbon dioxide.
$C + O_2 → CO_2$
As a result the anode gets oxidized and it has to be replaced periodically.
Figure: Extraction of aluminium from pure ore.
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