Question

How is aluminium obtained from pure ore?

Answer 1

Aluminium is obtained from pure ore by Hall - Heroult's 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.
iv. Temperature of the electrolytic bath : 950°C
Reactions: On passage of electricity through electrolyte aluminium and oxide ions are formed.
At cathode: Aluminium ions get reduced as:
Al³⁺ + 3e^- → Al
At anode: oxygen gas is liberated as:
O^2- - 2e^- → [ O ]
[ O ] + [ O ] → O₂
The oxygen formed at anode oxidizes the carbon of the anode to carbon dioxide.
C + O₂ → CO₂
As a result the anode gets oxidized and it has to be replaced periodically.

Figure: Extraction of aluminium from pure ore.