Extraction of Metals

📚 Key Concepts

🔹 Real-Life Example

Getting aluminum from bauxite ore is like getting a cake from its ingredients – you need the right temperature, right chemicals, and right process. Aluminum extraction needs electricity (electrolysis), iron needs heat and carbon (blast furnace), while mercury just needs heat. The method depends on how strongly the metal holds onto its compounds!

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🧪 General Steps in Extraction

🔸 Step 1: Concentration of Ore

Purpose: Remove gangue (unwanted material)

Methods:

  1. Hand Picking: Based on color/size differences
  2. Washing: Based on density differences
  3. Magnetic Separation: If ore/gangue has magnetic properties
  4. Froth Flotation: For sulfide ores
    • Ore particles stick to froth
    • Gangue settles down
    • Used for copper, zinc, lead ores

🔸 Step 2: Conversion to Oxide

Why: Metals are easier to extract from oxides

Roasting (for sulfides): 2ZnS + 3O₂ → 2ZnO + 2SO₂ Calcination (for carbonates): CaCO₃ → CaO + CO₂

🔸 Step 3: Reduction to Metal

Method depends on metal’s reactivity:

🔍 Extraction Methods by Reactivity

🔸 Most Reactive Metals (K, Na, Ca, Mg, Al)

Method: Electrolysis of molten compounds

Example – Sodium extraction:

  • Electrolyte: Molten NaCl
  • Cathode: 2Na⁺ + 2e⁻ → 2Na
  • Anode: 2Cl⁻ → Cl₂ + 2e⁻

Why electrolysis: Too reactive for chemical reduction

🔸 Medium Reactive Metals (Zn, Fe, Pb, Cu)

Methods: Chemical reduction

  1. Reduction by Carbon/CO:
    • ZnO + C → Zn + CO
    • Fe₂O₃ + 3CO → 2Fe + 3CO₂ (blast furnace)
  2. Auto-reduction (for some sulfides):
    • 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
    • 2Cu₂O + Cu₂S → 6Cu + SO₂
  3. Reduction by active metals:
    • TiCl₄ + 4Na → Ti + 4NaCl

🔸 Thermite Process

Reaction: Fe₂O₃ + 2Al → Al₂O₃ + 2Fe + Heat

Uses:

  • Welding railway tracks
  • Repairing large machine parts
  • Emergency welding

🔸 Least Reactive Metals (Cu, Hg, Ag, Au)

Methods:

  • Heat alone: 2HgO → 2Hg + O₂
  • Occur free in nature: Gold, silver