Extraction of Aluminium from Alumina (Al2O3)

Aluminium is an important metal that is widely used in various industries due to its low density, high strength, and excellent corrosion resistance. It is extracted from its ore, alumina (Al2O3), through a process called electrolysis. The correct combination of molten mixture for the extraction of aluminium by electrolysis is given in option 'C', which consists of Al2O3, Na3AlF6, and CaF2.

Electrolysis of Alumina (Al2O3)

The extraction of aluminium from alumina involves the process of electrolysis. In this process, a molten mixture of alumina, Na3AlF6, and CaF2 is used as an electrolyte. The following steps explain the extraction process in detail:

1. Formation of Cryolite (Na3AlF6):
- Cryolite is a mineral that is added to the mixture to lower the melting point of alumina and improve its conductivity.
- Na3AlF6 is formed by the reaction between alumina and sodium fluoride (NaF).
- 2 Al2O3 + 6 NaF → 2 Na3AlF6 + 3 O2

2. Electrolysis of Alumina (Al2O3):
- The mixture of alumina, Na3AlF6, and CaF2 is heated to a high temperature to form a molten electrolyte.
- The mixture is then placed in an electrolytic cell, which consists of a carbon anode and a carbon cathode.
- The carbon anode is connected to the positive terminal of a power supply, while the carbon cathode is connected to the negative terminal.
- The molten mixture acts as the electrolyte, and alumina is dissolved in it.
- When an electric current is passed through the electrolyte, the following reactions occur:
- At the anode (oxidation): 2 O2- → O2 + 4 e-
- At the cathode (reduction): 4 Al3+ + 12 e- → 4 Al
- The oxygen ions (O2-) are attracted to the anode and combine to form oxygen gas (O2), which is released.
- The aluminium ions (Al3+) are attracted to the cathode and gain electrons to form aluminium metal (Al), which is deposited on the cathode.

Advantages of the Molten Mixture

The molten mixture of alumina, Na3AlF6, and CaF2 has several advantages for the extraction of aluminium:
- Lower Melting Point: The addition of cryolite (Na3AlF6) lowers the melting point of alumina, reducing the amount of energy required for the process.
- Improved Conductivity: The presence of the molten mixture enhances the conductivity of the electrolyte, allowing for efficient electrolysis.
- Electrolyte Stability: The molten mixture remains stable at high temperatures, ensuring the continuous flow of current and the extraction of aluminium.

Conclusion
The correct combination of the molten mixture for the extraction of aluminium from alumina (Al2O3) is option 'C', which consists of Al2O3, Na3AlF6, and CaF