Describe the extraction of aluminum from its ores, including key processes and materials involved.

*a) Apart from Bauxite, two other ores of aluminium are:

• Corundum ($\text{Al}_2\text{O}_3$)
• Cryolite ($\text{Na}_3\text{AlF}_6$)

*b) The method used to extract aluminium from Bauxite is electrolysis (specifically, the Hall-Héroult process).

*c) (i) Two major impurities in Bauxite are:

• Iron(III) oxide ($\text{Fe}_2\text{O}_3$)
• Silicon dioxide ($\text{SiO}_2$)

*c) (ii) The impurities are removed using the Bayer process. Bauxite is crushed and heated with concentrated sodium hydroxide solution. Aluminium oxide dissolves to form soluble sodium aluminate, while impurities like iron(III) oxide remain undissolved and are filtered off. Silicon dioxide reacts to form insoluble sodium silicate, which is also removed. The sodium aluminate solution is then cooled and seeded with aluminium hydroxide crystals to precipitate pure aluminium hydroxide, which is then heated to obtain pure aluminium oxide.

*d) Cryolite is used as a solvent for aluminium oxide in the electrolytic cell. It lowers the melting point of aluminium oxide from over $2000^\circ C$ to about $950^\circ C$, reducing energy costs, and also increases the electrical conductivity of the electrolyte.

*e) Aluminium is a reactive metal, but it does not corrode easily because it rapidly forms a thin, tough, and impervious layer of aluminium oxide ($\text{Al}_2\text{O}_3$) on its surface when exposed to air. This oxide layer protects the underlying metal from further reaction with oxygen and moisture.

*f) Economic and environmental benefits of recycling aluminium over extraction from Bauxite:

• Economic: Recycling aluminium requires significantly less energy (about 5% of the energy needed for primary extraction), leading to lower production costs. It also reduces the need for mining new bauxite ore, saving resources and transportation costs.
• Environmental: Recycling reduces greenhouse gas emissions, air pollution, and water pollution associated with mining and refining bauxite. It also conserves natural resources and reduces the amount of waste sent to landfills.