Extraction of Aluminium from Bauxite | Chemistry for Grade 11 (IGCSE) PDF Download

Extraction of Aluminium from Bauxite

• Aluminium is a reactive metal, positioned above carbon in the reactivity series.
• Bauxite is the primary ore, containing aluminum oxide.
• Due to aluminum's higher reactivity compared to carbon, it cannot be extracted by carbon reduction.
• Instead, the extraction of aluminum is achieved through electrolysis.

Diagram showing the extraction of aluminium by electrolysis:

The Process of Aluminium Extraction by Electrolysis

• Bauxite undergoes a purification process to yield aluminium oxide (Al₂O₃)

Dissolving Aluminium Oxide in Molten Cryolite

• Aluminium oxide is dissolved in molten cryolite due to its high melting point above 2000°C, which is energy-intensive and costly
• The resulting mixture with cryolite lowers the overall melting point without affecting the reaction

Electrolysis Process

• The mixture is placed in an electrolysis cell constructed from steel and lined with graphite
• Graphite acts as the negative electrode while large graphite blocks serve as the positive electrodes
• At the cathode, aluminium ions undergo reduction, forming molten aluminium at the cell's base
• Periodically, the molten aluminium is extracted, and fresh aluminium oxide is introduced into the cell

Aluminium Extraction Process

• Aluminium ions undergo reduction by gaining electrons.
• Molten aluminium is formed at the bottom of the cell.
• The molten aluminium is periodically siphoned off, and fresh aluminium oxide is introduced into the cell.

Reduction Process at the Anode

• At the anode (positive electrode), oxide ions lose electrons through oxidation.
• Oxygen is generated at the anode:
  Al³⁺ + 3e^- → Al

Overall Reaction Equation

• The overall reaction is represented as: 2Al₂O₃ → 4Al + 3O₂

Role of Graphite Anodes

• The carbon in the graphite anodes reacts with the oxygen produced, forming CO₂.
  C(s) + O₂(g) → CO₂(g)
• As a consequence, the anode gradually wears out and necessitates regular replacement.
• This extraction process demands a substantial amount of electricity, leading to significant expenses.