Unit 10
Inorganic Chemistry
Class 11 Chemistry
Chemistry of Metals
Metals and Metallurgical Principles
Class 11 Chemistry – Chemistry of Metals Notes PDF
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Chapter Overview
Metallurgy is the science and technology of extracting metals from their ores, purifying them and preparing them for use. The current Grade 11 curriculum emphasizes the general principles of metallurgy rather than memorizing long industrial descriptions of every metal.
The core pathway is: ore → concentration → conversion to suitable oxide/compound → reduction → crude metal → refining.
Diagram 1 — General Metallurgical Flow
The exact route varies with the ore, metal reactivity and economics.
10.1 Metallurgy and Its Types
Metallurgical processes can be classified according to the medium or energy used.
| Type | Principle | Typical idea |
|---|---|---|
| Pyrometallurgy | Uses high temperature | Roasting, calcination, smelting and thermal reduction |
| Hydrometallurgy | Uses aqueous chemistry | Leaching a desired metal species into solution followed by recovery |
| Electrometallurgy | Uses electrical energy | Electrolytic extraction or electro-refining |
10.2 Essential Metallurgical Terms
| Term | Meaning |
|---|---|
| Mineral | Naturally occurring substance containing a metal or metal compound |
| Ore | Mineral from which a metal can be extracted economically |
| Gangue / Matrix | Unwanted earthy or rocky impurities associated with ore |
| Flux | Substance added to react with gangue during smelting |
| Slag | Fusible product formed from flux and gangue |
| Alloy | Metallic material containing two or more elements, at least one of which is a metal |
Mineral Resources of Nepal
Nepal contains a variety of metallic and non-metallic mineral occurrences. In school chemistry, the important learning point is to recognize that metallurgy begins with naturally occurring mineral resources and that whether a deposit becomes an economically useful ore depends on grade, accessibility, technology, energy, environmental impact and market conditions.
Concentration of Ore
Concentration, also called ore dressing or beneficiation, removes as much gangue as practical before extraction. The method depends on differences in physical or chemical properties of ore and gangue.
Gravity / Hydraulic Washing
Uses density difference; heavier ore particles can separate from lighter gangue.
Magnetic Separation
Uses difference in magnetic behavior of ore and gangue.
Froth Flotation
Common for sulfide ores; selective wetting allows ore particles to attach to bubbles.
Leaching
Desired metal compound is selectively dissolved into a suitable solution.
Diagram 2 — Froth Flotation Principle
Froth flotation is especially associated with concentration of sulfide ores.
Calcination and Roasting
Calcination
Strong heating of an ore in the absence or limited supply of air. It is often used for carbonate or hydrated ores.
Roasting
Strong heating of an ore in excess air or oxygen. It is commonly used for sulfide ores to convert them toward oxides and release sulfur dioxide.
| Feature | Calcination | Roasting |
|---|---|---|
| Air supply | Absent or limited | Excess air/oxygen |
| Common ore type | Carbonates, hydrated ores | Sulfide ores |
| Typical gases | CO₂, H₂O | SO₂ |
| Main objective | Convert ore to more reducible oxide and remove volatiles | Oxidize sulfide and remove sulfur |
Diagram 3 — Calcination vs Roasting
Both processes prepare the ore for later reduction, but their atmospheric conditions differ.
Smelting, Flux and Slag
Smelting is high-temperature extraction in which the charge is heated with suitable reducing agents and/or fluxes so that metal or a metal-rich phase can separate from impurities.
A flux reacts with gangue to form a more easily fusible slag.
Diagram 4 — Flux and Slag Formation
The lower-density slag can separate from the molten metal phase.
Reduction of Metal Compounds
The reduction method is selected mainly according to metal reactivity and thermodynamic/economic feasibility.
Carbon / Carbon Monoxide Reduction
Oxides of suitably less-reactive metals can often be reduced using carbon or carbon monoxide at high temperature.
Thermite Reduction
Aluminium can reduce oxides of some metals very exothermically.
Electrochemical Reduction
Very reactive metals cannot generally be obtained by ordinary carbon reduction; electrolysis of suitable molten ionic compounds can be used.
Diagram 5 — Choosing a Reduction Method
The more reactive the metal, the more difficult chemical reduction becomes.
Refining of Metals
Poling
Poling is a refining method used for certain metals in which the molten impure metal is stirred with green wood poles or another suitable reducing environment so that oxide impurities are reduced.
Electrolytic Refining
A common electro-refining arrangement uses impure metal as the anode, a thin sheet of pure metal as the cathode and a soluble salt of that metal as electrolyte.
- Anode metal atoms oxidize and enter solution.
- Metal ions are reduced at the cathode and deposit as purer metal.
- Some less-reactive impurities may collect as anode mud.
Diagram 6 — Electrolytic Refining
Electro-refining transfers the desired metal from an impure anode to a purer cathode deposit.
Key Reactions and Concepts
| Process | Representative expression / idea |
|---|---|
| Calcination | MCO₃ → MO + CO₂ |
| Roasting | 2MS + 3O₂ → 2MO + 2SO₂ |
| Slag formation | Flux + gangue → slag |
| Carbon reduction | MO + C → M + CO |
| Thermite | Fe₂O₃ + 2Al → Al₂O₃ + 2Fe + heat |
| Electrolysis | Mⁿ⁺ + ne⁻ → M at cathode |
| Electro-refining anode | M → Mⁿ⁺ + ne⁻ |
Important Exam Questions
Short Questions
- Define metallurgy and name its three broad types.
- Differentiate mineral and ore.
- Define gangue, flux and slag.
- What is concentration of ore?
- Differentiate calcination and roasting.
- Define smelting.
- Why is flux added during smelting?
- What is thermite reduction?
- Why are highly reactive metals commonly extracted electrolytically?
- Define poling and electro-refining.
Long Questions
- Explain the general steps involved in metallurgy with a flow diagram.
- Explain methods of ore concentration.
- Compare calcination and roasting with equations.
- Explain the role of flux and slag in smelting.
- Discuss carbon reduction, thermite reduction and electrochemical reduction.
- Explain electrolytic refining with a labelled diagram.
- Discuss the significance of Nepal’s mineral resources in metallurgy.
Application Questions
- A sulfide ore is given. Which thermal treatment is normally preferred before reduction and why?
- A carbonate ore is given. Which treatment is normally preferred?
- Why is electrolysis selected for very reactive metals?
- Given acidic gangue, choose the general type of flux needed and explain slag formation.
One-Minute Revision
- Metallurgy = extraction and purification of metals.
- Three broad types: pyro-, hydro- and electrometallurgy.
- An ore is an economically workable mineral.
- Gangue is unwanted material associated with ore.
- Concentration removes gangue.
- Froth flotation is important for many sulfide ores.
- Calcination uses little/no air.
- Roasting uses excess air/oxygen.
- Flux reacts with gangue to produce slag.
- Smelting is high-temperature extraction.
- Carbon/CO can reduce suitable metal oxides.
- Thermite uses aluminium as a powerful reducing agent.
- Very reactive metals commonly require electrochemical reduction.
- Electro-refining purifies metal using electrolysis.
Syllabus Coverage Checklist
| Current Chemistry of Metals scope | Covered |
|---|---|
| Metallurgy and its types: hydro-, pyro- and electrometallurgy | Yes |
| Ore, gangue/matrix, flux, slag and alloy | Yes |
| Mineral resources context | Yes |
| Concentration of ores | Yes |
| Calcination and roasting | Yes |
| Smelting and slag formation | Yes |
| Carbon, thermite and electrochemical reduction | Yes |
| Refining: poling and electro-refining | Yes |
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