Introduction to Extraction of Metals

The extraction of metals involves obtaining metals from their naturally occurring ores.

• NEET focuses on concepts of metallurgical processes rather than calculations.

• Extraction methods depend on metal reactivity, ore type, and economic factors.

Key Concept: Metals are generally found as oxides, sulfides, or carbonates in nature and need purification and reduction to obtain elemental metals.

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Occurrence of Metals

• Metals occur in three forms:

  1. Native Metals: Found in free state (e.g., gold, platinum)

  2. Combined State (Ores): Bound with oxygen, sulfur, or carbonates (e.g., hematite Fe₂O₃, galena PbS)

  3. Alloys: Naturally occurring metal mixtures (e.g., electrum – gold + silver)

NEET Tip: Conceptually, highly reactive metals (like Na, K) do not occur free, while noble metals (like Au, Pt) do.

Steps in the Extraction of Metals

1. Concentration of Ores

• Purpose: Remove impurities (gangue) from ores.

• Methods:

  • Gravity separation: Uses density differences (e.g., tin, gold)

  • Froth flotation: Used for sulfide ores; collectors and frothing agents separate metal from gangue

  • Magnetic separation: For magnetic ores like magnetite (Fe₃O₄)

  • Leaching: Uses chemical solvents (e.g., extraction of Al from bauxite using NaOH)

Conceptual Focus: Understand why concentration is necessary before reduction.

2. Conversion of Ore into Oxide (Roasting and Calcination)

• Roasting: Heating sulfide ores in presence of oxygen → converts to oxides + SO₂ gas (e.g., ZnS → ZnO)

• Calcination: Heating carbonate ores → decomposes into oxides + CO₂ gas (e.g., CaCO₃ → CaO)

NEET Tip: Focus on difference between roasting and calcination and why oxides are easier to reduce.

3. Reduction of Oxides to Metal

• Definition: Removal of oxygen from metal oxide to obtain metal.

• Methods:

  1. Chemical Reduction (using carbon or CO):

     • Metals below carbon in reactivity series (e.g., Fe from Fe₂O₃)

  2. Thermal Reduction (self-reduction or heating):

     • Highly reactive metals like Zn, Pb can be reduced at high temperature

  3. Electrolytic Reduction:

     • For very reactive metals like Na, K, Mg, and Al

     • Uses electrolysis of molten salts

Conceptual Tip: Link metal reactivity to the choice of reduction method.

Electrolytic Reduction (Electrolysis)

• For highly reactive metals that cannot be reduced by carbon.

• Example: Extraction of Aluminum from bauxite using cryolite (Na₃AlF₆) as a solvent.

• Conceptual understanding:

  • Molten metal ions migrate to cathode to gain electrons

  • Anions migrate to anode to lose electrons

• NEET Focus: Emphasize why electrolysis is used for highly reactive metals.

Metallurgy of Common Metals (Conceptual Overview)

1. Iron (Fe):

   • Ore: Hematite (Fe₂O₃)

   • Method: Blast furnace → reduction with coke → pig iron → steel

2. Aluminium (Al):

   • Ore: Bauxite (Al₂O₃·2H₂O)

   • Method: Bayer process (purification) + Electrolysis

3. Copper (Cu):

   • Ore: Cu₂S

   • Method: Roasting → smelting → electrorefining

4. Zinc (Zn):

   • Ore: ZnO

   • Method: Reduction with carbon → distillation

NEET Tip: Understand conceptual differences in extraction based on metal reactivity.

Refining of Metals

• Purpose: Remove impurities from crude metals.

• Methods:

  1. Distillation: For metals with low boiling points (e.g., Zn)

  2. Electrolytic Refining: Most common; used for Cu, Ag, Au

     • Impure metal → anode, pure metal → cathode, impurities → anode mud

  3. Liquation and Zone Refining: For specific metals

Conceptual Tip: Focus on why refining is needed and conceptual mechanism of electrorefining.

Reactivity Series of Metals (Conceptual Link)

• Determines method of extraction:

  • Highly reactive (Na, K, Ca, Al) → Electrolysis

  • Moderately reactive (Zn, Fe, Ni) → Reduction by carbon/CO

  • Least reactive (Cu, Ag, Au) → Found native, may need roasting/smelting

NEET Tip: Conceptually link metal reactivity → extraction method → energy efficiency.

Environmental and Industrial Importance

• Extraction of metals consumes energy and resources.

• Electrolysis and smelting produce greenhouse gases (CO₂, SO₂).

• Understanding the principles of extraction is crucial for sustainable metallurgy.

Quick Concept Summary Table

Conclusion

The General Principles of Extraction of Metals is a critical NEET Chemistry chapter that links metal reactivity, ores, concentration, reduction, and refining. Conceptual understanding is key:

• Know why metals occur in ores,

• Why concentration and roasting/calcination are needed,

• Which metals are reduced chemically or electrolytically,

• And how refining purifies metals.

Understanding conceptual links between reactivity and extraction method enables NEET aspirants to answer reasoning-based questions confidently. StudentBro.in provides structured, fully conceptual notes to help NEET aspirants master this chapter efficiently.