1 Introduction
Metallurgy is the branch of science that deals with the extraction of metals from their ores and their refinement to obtain pure metals.
Metals are crucial materials used in construction, manufacturing, electronics, transportation, and daily life due to their properties like strength, conductivity, and malleability.
2 Occurrence of Metals
Metals occur in nature in different forms:
Native Metals
Found in pure, uncombined state.
- Gold (Au)
- Silver (Ag)
- Platinum (Pt)
- Copper (Cu) - rarely
Ores
Compounds from which metals can be extracted.
- Hematite (Fe₂O₃) - Iron
- Bauxite (Al₂O₃·2H₂O) - Aluminium
- Copper pyrite (CuFeS₂) - Copper
- Zinc blende (ZnS) - Zinc
Gangue: Unwanted earthy impurities present in ores that must be removed during extraction.
3 Steps in Metallurgy
The extraction of metals generally involves the following steps:
Concentration of Ore
Removal of impurities (gangue) from ore.
Gravity Separation
Based on density differences between ore and gangue.
Froth Flotation
Used for sulphide ores. Ore particles attach to froth and are separated.
Magnetic Separation
Used for magnetic ores like magnetite (Fe₃O₄).
Extraction of Metal from Concentrated Ore
Roasting
Heating in presence of air for sulphide ores to convert to oxide.
Calcination
Heating in absence of air for carbonate ores to remove CO₂.
Reduction of Metal Oxides
Reduction with Carbon
For less reactive metals like Zn, Fe, Pb.
Electrolytic Reduction
For highly reactive metals like Na, K, Al, Ca.
Electric current is passed through molten ore.
Refining of Metals
Process of removing impurities from extracted metal.
Distillation
For metals with low boiling points (e.g., Zn, Hg).
Electrolytic Refining
For high purity (e.g., Cu, Ag, Au).
Liquation
For metals with low melting points (e.g., Sn, Pb, Bi).
4 Reactivity Series of Metals
Metals are arranged in decreasing order of reactivity:
Importance of Reactivity Series:
- Predicts extraction method (reactive metals require electrolysis)
- Predicts displacement reactions (more reactive metals displace less reactive ones)
- Determines corrosion tendency
- Guides selection of reducing agents
5 Extraction of Some Common Metals
6 Alloy Formation
Alloy: A homogeneous mixture of a metal with other metals or non-metals to improve properties.
Steel
Fe + C (0.1-1.5%)
Strong, hard
Brass
Cu + Zn
Corrosion resistant
Bronze
Cu + Sn
Hard, durable
Solder
Pb + Sn
Low melting point
Stainless Steel
Fe + Cr + Ni
Rust resistant
Duralumin
Al + Cu + Mg + Mn
Light, strong
Purpose of Alloys:
- Increased strength and hardness
- Improved corrosion resistance
- Enhanced appearance
- Lower melting point (for some alloys)
- Reduced cost compared to pure metals
7 Corrosion
Corrosion: Gradual destruction of metals due to chemical reaction with environment (oxygen, water, acids).
Example: Rusting of iron - a redox reaction where iron oxidizes to form hydrated iron(III) oxide.
Prevention of Corrosion
Painting
Forms protective coating
Oiling/Greasing
Prevents contact with air and moisture
Galvanization
Coating with zinc (Zn)
Alloying
e.g., Stainless steel
Electroplating
Coating with another metal
Cathodic Protection
Sacrificial anode method
Important Points for Examination
- Know all steps in metallurgy and the reason for each step
- Distinguish clearly between calcination and roasting
- Identify extraction method based on position in reactivity series
- List common alloys, their compositions, and uses
- Explain corrosion process and various prevention methods
- Write balanced chemical equations for extraction processes
- Understand the role of flux and slag formation
- Memorize the reactivity series order