General Principles and Processes of Isolation of Elements

Bihar Board Class 12 Chemistry – Willer Academy

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1

Introduction to Metallurgy & Ores

• Objectives:
• Define minerals, ores, and gangue
• Classify ores based on metal compounds

• Key Concepts:
• Mineral: Naturally occurring inorganic substance
• Ore: Mineral with high metal content, economical for extraction
• Gangue: Impurities like sand, clay in ore

Metallurgy: Science of extracting metals from ores
Ore Types:

• Oxide ores: Bauxite (Al), Haematite (Fe)
• Sulphide ores: Zinc blende (Zn), Copper pyrites (Cu)
• Carbonate ores: Siderite (Fe), Calamine (Zn)

Main processes: Concentration → Conversion to oxide → Reduction → Refining

• Examples:
• Haematite (Fe₂O₃) is an ore; clay in bauxite is gangue

• Practice Questions:
• Differentiate between mineral and ore
• Name two sulphide ores

2

Concentration of Ores

• Objectives:
• Explain physical/chemical methods to remove gangue

• Key Concepts:
• Gravity Separation: Based on density (e.g. haematite)
• Froth Flotation: For sulphide ores (e.g., ZnS) using pine oil
• Leaching: Chemical dissolution (e.g. bauxite with NaOH)

Gravity Separation: Washed with water, lighter gangue removed
Froth Flotation: Ore + water + frother; air blown to form froth with ore particles
Leaching: Al₂O₃ dissolved in NaOH; impurities filtered (Bayer’s process)

• Examples:
• Bauxite purification by chemical leaching

• Practice Questions:
• Why is froth flotation used for ZnS?
• How is leaching applied to bauxite?

3

Oxidation & Reduction (Calcination/Roasting)

• Objectives:
• Differentiate calcination and roasting
• Explain oxide conversion of ores

• Key Concepts:
• Calcination: Heating without air (e.g., carbonates)
• Roasting: Heating with air (e.g., sulphide ores)

Calcination: ZnCO₃ → ZnO + CO₂ (removal of CO₂, H₂O)
Roasting: 2ZnS + 3O₂ → 2ZnO + 2SO₂ (conversion of sulphides)

• Examples:
• Calcination of limestone (CaCO₃ → CaO)
• Roasting of zinc blende (ZnS)

• Practice Questions:
• Contrast calcination and roasting
• Write roasting reactions for copper pyrites

4

Reduction Processes (Smelting, Auto-reduction, Electrolysis)

• Objectives:
• Explain different reduction methods

• Key Concepts:
• Smelting: Reduction by carbon in furnace (e.g., ZnO + C → Zn)
• Auto-reduction: No external reductant (Cu₂S → Cu)
• Electrolytic Reduction: For reactive metals (e.g., Al)

Smelting (blast furnace): Fe₂O₃ + 3CO → 2Fe + 3CO₂
Auto-reduction: 2Cu₂O + Cu₂S → 6Cu + SO₂
Electrolysis: Hall-Héroult process for aluminium from Al₂O₃

• Examples:
• Why Al is not reduced by carbon, but by electrolysis

• Practice Questions:
• Why is Al reduced by electrolysis, not carbon?
• Explain auto-reduction in copper

5

Refining of Metals

• Objectives:
• Describe purification methods for metals

• Key Concepts:
• Electrolytic Refining: Impure anode, pure cathode (e.g. copper)
• Zone Refining: For semiconductors (Si, Ge)
• Distillation: For volatile metals (Zn, Hg)

Electrolytic refining:
Anode: Impure Cu | Cathode: Pure Cu | Electrolyte: CuSO₄
Zone refining: Moving heater purifies crystals
Distillation: Zn purified via vaporization method

• Examples:
• Anode mud (Ag, Au) during electrolytic copper refining

• Practice Questions:
• Sketch electrolytic refining of copper
• Why is distillation used for zinc?

6

Extraction of Aluminium

• Objectives:
• Detail steps for Al extraction (Bayer & Hall-Héroult)

• Key Concepts:
• Bayer's Process: Leaching of bauxite (Al₂O₃) with NaOH
• Hall-Héroult Process: Electrolysis of Al₂O₃ in cryolite (Na₃AlF₆)

Concentration: Bauxite + NaOH → NaAlO₂ → Al(OH)₃ → Al₂O₃
Reduction: Al₂O₃ dissolved in cryolite; electrolyzed at 950°C
Anode: 2O²⁻ → O₂ + 4e⁻
Cathode: Al³⁺ + 3e⁻ → Al

• Examples:
• Cryolite lowers melting point of Al₂O₃

• Practice Questions:
• Why is cryolite used in Al extraction?
• Write anode/cathode reactions in Hall-Héroult process

7

Extraction of Copper

• Objectives:
• Outline Cu extraction from copper pyrites

• Key Concepts:
• Roasting: Partial oxidation
• Smelting: Matte formation (Cu₂S + FeS)
• Bessemerisation: Auto-reduction to blister Cu

Roasting: 2CuFeS₂ + O₂ → Cu₂S + 2FeS + SO₂
Smelting: FeO + SiO₂ → FeSiO₃ (slag)
Auto-reduction:

• 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
• 2Cu₂O + Cu₂S → 6Cu + SO₂

Refining: Electrolytic (99.9% pure Cu)

• Examples:
• Blister copper (98%) has SO₂ blisters

• Practice Questions:
• What is matte in copper extraction?
• Explain auto-reduction in copper

8

Extraction of Zinc

• Objectives:
• Explain Zn extraction from zinc blende

• Key Concepts:
• Roasting: ZnS → ZnO
• Reduction: ZnO + C → Zn (blast furnace)
• Purification: Distillation/electrolytic methods

Concentration: Froth flotation for zinc blende
Roasting: 2ZnS + 3O₂ → 2ZnO + 2SO₂
Reduction: ZnO + C → Zn (vapours), then condensed
Refining: Distillation (for volatile metals)

• Examples:
• Condensed Zn vapour—avoids reoxidation

• Practice Questions:
• Write chemical equations for Zn extraction
• Why is distillation used in Zn purification?

9

Extraction of Iron

• Objectives:
• Describe iron extraction in blast furnace

• Key Concepts:
• Blast Furnace: Reduction by CO, slag formation
• Reaction zones: Fe₂O₃ → Fe₃O₄ → FeO → Fe

Raw Materials: Haematite, coke, limestone
Zones & Reactions:

• Combustion: C + O₂ → CO₂; CO₂ + C → 2CO
• Reduction: Fe₂O₃ + 3CO → 2Fe + 3CO₂
• Slag: CaCO₃ → CaO; CaO + SiO₂ → CaSiO₃

Products: Pig iron (96% Fe), slag for cement

• Examples:
• Limestone removes silica as slag

• Practice Questions:
• What is the role of limestone in blast furnace?
• Write blast furnace zone reactions

10

Revision & Practice Problems

Recap: Metallurgy steps, extraction flowcharts for Al, Cu, Zn, Fe.
MCQs:

• Ore of Al: (a) Bauxite (b) Cinnabar
• Roasting is for: (a) Sulphide ores (b) Carbonate ores

Short Answer:

• Define slag. Give an example.
• Why is froth flotation used?

Long Answer:

• Explain Hall-Héroult process with diagram
• Describe blast furnace for iron extraction

Previous Year Practice:
Discuss 5-mark Bihar Board questions on the chapter.

Teaching Tips:

• Use diagrams & flowcharts for every process and furnace
• Relate chemical steps to their place in the reactivity series
• Assign group/individual problem-solving for metal cases

Last updated: Monday, July 21, 2025, 11:58 AM IST | Willer Academy