Extraction of Aluminium from Bauxite (Hall-Héroult Process)

Introduction to Aluminium Extraction

Aluminium is extracted from its ore, bauxite, using the Hall-Héroult process. This method involves electrolyzing alumina (Al₂O₃) dissolved in molten cryolite (Na₃AlF₆).

Bauxite is primarily composed of alumina, along with impurities like iron oxides and silica. The extraction process involves two main steps: refining bauxite to obtain alumina and then electrolyzing alumina to produce aluminium.

Steps in the Hall-Héroult Process

1. Purification of Bauxite: Bauxite is purified to produce alumina using the Bayer process. This involves crushing the bauxite and treating it with sodium hydroxide to dissolve the alumina.
2. Electrolysis of Alumina: The purified alumina is dissolved in molten cryolite and subjected to electrolysis in a large carbon-lined cell.
3. Collection of Aluminium: Aluminium is deposited at the cathode, while oxygen is released at the anode.

Chemical Reactions

• At the Cathode:
  $$\text{Al}^{3+} + 3\text{e}^{-} \rightarrow \text{Al}$$
• At the Anode:
  $$2\text{O}^{2-} \rightarrow \text{O}_2 + 4\text{e}^{-}$$

Advantages of the Hall-Héroult Process

• Efficient and cost-effective for large-scale production.
• Produces high-purity aluminium.

Challenges

• High energy consumption due to the need for high temperatures and electrical energy.
• Environmental concerns related to carbon emissions from anode consumption.