Question

Purification of aluminium by electrolytic refining is called

• A. Hall’s process
• B. Froth floatation process
• C. Bayer’s process
• D. Hoope’s process
• E. Serpeck’s process

Hint:

Remember sequence for aluminium: Bayer → Hall → Hoope (Purification → Extraction → Refining)

Answer 1

The Correct Option is D

Concept:
Metallurgy involves three major steps:
• Concentration of ore
• Extraction of metal
• Refining (purification) of metal For aluminium:
• Bayer’s process → purification of bauxite (removal of impurities)
• Hall-Héroult process → extraction of aluminium metal from alumina
• Hoope’s process → electrolytic refining (final purification)

Step 1: Understanding electrolytic refining.
Electrolytic refining is used to obtain very high purity metal. The impure metal acts as anode, and pure metal is deposited at cathode.

Step 2: Hoope’s process setup.
In Hoope’s process, a special electrolytic cell is used consisting of three layers:
• Bottom layer: impure molten aluminium (acts as anode)
• Middle layer: fused electrolyte mixture (cryolite + fluorides)
• Top layer: pure molten aluminium (acts as cathode)

Step 3: Working of the process.

• When electric current is passed, aluminium from the impure layer loses electrons: \[ \text{Al} \rightarrow \text{Al}^{3+} + 3e^- \]
• These ions move through the electrolyte.
• At the cathode (top layer), aluminium ions gain electrons: \[ \text{Al}^{3+} + 3e^- \rightarrow \text{Al} \]
• Pure aluminium gets deposited in the top layer.

Step 4: Removal of impurities.
Impurities either:
• remain in the bottom layer, or
• get trapped in electrolyte Thus, highly pure aluminium is obtained.

Step 5: Why other options are incorrect.

• Hall’s process → extraction, not refining
• Froth flotation → ore concentration
• Bayer’s process → purification of bauxite, not metal
• Serpeck’s process → used for nitrogen fixation, not aluminium Final Conclusion:
Electrolytic refining of aluminium is carried out by Hoope’s process.