Industrial Extraction Processes for Zinc and Aluminum

Extraction of Zinc (Zn)

Major Ores of Zinc

• Zinc blende (ZnS)
• Calamine (ZnCO₃)
• Zincite (ZnO)

Zinc is primarily extracted from calamine and zinc blende ores.

Extraction from Calamine Ore

Zinc oxide is obtained by calcining calamine:

ZnCO₃ → ZnO + CO₂↑

Zinc metal is then obtained by heating zinc oxide (ZnO) with coal powder:

ZnO + C → Zn + CO↑

Extraction from Zinc Blende

Zinc oxide (ZnO) is obtained by roasting concentrated zinc blende at high temperatures in the presence of air:

2ZnS + 3O₂ → 2ZnO + 2SO₂↑

The resulting ZnO is reduced using the carbon method described above.

Purification of Zinc

The zinc obtained is impure and is purified via electrolysis. A pure aluminum sheet serves as the cathode, while impure zinc acts as the anode in a zinc sulfate (ZnSO₄) electrolyte solution. Upon passing an electric current, pure zinc collects at the cathode.

Extraction of Aluminum (Al)

Important Ores

• Bauxite (Al₂O₃·xH₂O)
• Corundum (Al₂O₃)

Bauxite is the most commercially important ore for aluminum. Extraction involves two main stages:

1. Purification of Bauxite

Bauxite is treated with NaOH to remove impurities like Fe₂O₃, TiO₂, and SiO₂:

Al₂O₃ + 2NaOH + 3H₂O → 2Na[Al(OH)₄]

The resulting solution reacts with CO₂ to precipitate pure alumina:

2Na[Al(OH)₄] + 2CO₂ → Al₂O₃·xH₂O + 2NaHCO₃

2. Electrolytic Reduction

Pure alumina undergoes electrolytic reduction in an iron box cathode using cryolite (Na₃AlF₆) and fluorspar (CaF₂) to lower the melting point. Graphite rods act as the anode.

• At Cathode: Al³⁺ + 3e⁻ → Al
• At Anode: 2O²⁻ → O₂ + 4e⁻

This process yields 98.8% pure aluminum.