10.1 Metals and Metallurgical Principles

Unit 10.1: Metals and Metallurgical Principles (5 Teaching Hours)

1. Definition of Metallurgy and Its Types

   • Definition
     • Metallurgy: The science and technology of extracting metals from their ores, purifying, and processing them for use.
   • Types of Metallurgy
     • Hydrometallurgy: Extraction using aqueous solutions (e.g., leaching of gold with cyanide).
     • Pyrometallurgy: Extraction using high temperatures (e.g., smelting of iron).
     • Electrometallurgy: Extraction using electricity (e.g., electrolysis of aluminium).

2. Introduction of Ores

   • Ores
     • Naturally occurring minerals from which metals can be extracted economically (e.g., haematite for iron, bauxite for aluminium).
   • Gangue or Matrix, Flux and Slag, Alloy and Amalgam
     • Gangue or Matrix: Impurities in ores (e.g., silica, clay).
     • Flux: Substance added to remove gangue by forming slag (e.g., limestone for silica).
     • Slag: Fusible product of flux and gangue (e.g., CaSiO₃).
     • Alloy: Homogeneous mixture of metals or metal with non-metal (e.g., steel).
     • Amalgam: Alloy of metal with mercury (e.g., silver amalgam).
     • Figure 1: Components of Ore and Metallurgy (Diagram showing ore, gangue, flux, and slag formation).

3. General Principles of Extraction of Metals

   • Concentration
     • Removal of gangue from ore to enrich metal content.
     • Methods: Gravity separation (e.g., for heavy ores), Froth flotation (e.g., sulphide ores), Magnetic separation (e.g., iron ores), Leaching (e.g., bauxite with NaOH).
     • Figure 2: Froth Flotation Process (Diagram showing froth flotation setup).
   • Calcination and Roasting
     • Calcination: Heating ore in absence of air to remove volatile impurities, moisture, or convert carbonates to oxides (e.g., CaCO₃ → CaO + CO₂).
     • Roasting: Heating ore in presence of air to remove sulphur, convert sulphides to oxides (e.g., 2ZnS + 3O₂ → 2ZnO + 2SO₂).
     • Figure 3: Calcination and Roasting (Diagram showing furnace setups for calcination and roasting).
   • Smelting
     • Heating ore with reducing agent (e.g., carbon) and flux to extract molten metal (e.g., Fe₂O₃ + 3C → 2Fe + 3CO).
   • Carbon Reduction
     • Reduction of metal oxides using carbon or CO (e.g., Fe₂O₃ + 3CO → 2Fe + 3CO₂).
   • Thermite Reduction
     • Reduction using aluminium powder (highly exothermic): Cr₂O₃ + 2Al → 2Cr + Al₂O₃.
     • Figure 4: Thermite Process (Diagram showing thermite reaction setup).
   • Electrochemical Reduction
     • Electrolysis of molten ores to extract metals (e.g., Al from Al₂O₃ in Hall-Héroult process).
     • Figure 5: Electrochemical Reduction of Aluminium (Diagram showing electrolysis cell for Al extraction).

4. Refining of Metals

   • Poling
     • Purification of metals (e.g., Cu, Sn) by stirring molten metal with green wooden poles to reduce oxides and remove impurities.
   • Electro-Refinement
     • Purification using electrolysis; impure metal as anode, pure metal as cathode (e.g., copper refining: Cu²⁺ from anode deposits as pure Cu on cathode).
     • Figure 6: Electro-Refinement of Copper (Diagram showing electrolysis setup for Cu refining).