This chapter covers metallurgy, the science of extracting pure metals from their ores through a common four-step pipeline of concentration, conversion to oxide, reduction and refining. It builds the core vocabulary (mineral, ore, gangue, flux, slag), the methods for each step, and the thermodynamic reasoning behind reduction using the Ellingham diagram. It matters for NEET because it blends pure-recall ore formulae with concept-based questions on calcination versus roasting, reducing agents and refining techniques that appear almost every year.
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The Metallurgy Pipeline
Every metal extraction, whatever the ore, follows the same four-step route.
The more reactive the metal, the more energy-intensive (usually electrical) its extraction.
- Unreactive metals (Au, Pt) occur native; reactive ones stay trapped as compounds
- Oxides are the easiest form to reduce, so ores are turned into oxides first
- Memorising this sequence organises the whole chapter
Minerals, Ores, Gangue, Flux, Slag
Five words unlock the chapter; an ore is a mineral that pays.
Every ore is a mineral (TRUE); every mineral is an ore (FALSE).
- Mineral = any natural form of a metal; Ore = mineral extractable profitably & conveniently
- Gangue = earthy impurity; Flux added on purpose to form fusible slag
- Acidic gangue (SiO2) needs basic flux (CaO); CaO + SiO2 → CaSiO3 (slag)
Important Ores
Pure-recall ore formulae that NEET asks directly.
Cryolite Na3AlF6 is a flux/solvent, NOT the ore of Al.
- Iron: Haematite Fe2O3, Magnetite Fe3O4
- Zinc: Zinc blende ZnS, Calamine ZnCO3; Silver: Argentite Ag2S
- Watch lookalikes: Cu2S (copper glance) vs CuFeS2 (chalcopyrite)
Concentration of Ores
Remove gangue by exploiting one physical property where ore and gangue differ.
Froth flotation is for sulphide ores ONLY; leaching is the chemical method.
- Hydraulic washing = density; Magnetic separation = magnetism (Fe3O4, FeWO4)
- Froth flotation: pine oil + air; sulphides go hydrophobic and rise as froth
- Depressant NaCN holds ZnS down to separate it from PbS
Calcination vs Roasting
Convert the concentrated ore to its oxide before reduction.
Calcination = limited/no air; Roasting = excess air, below melting point.
- Carbonate/hydrated ore → calcination (drives off CO2 / H2O, no O2 added)
- Sulphide ore → roasting (excess O2 burns S off as SO2)
- Both steps end at an oxide, the easiest form to reduce
Reduction of the Oxide
Pull oxygen off the oxide using C, CO, or a more reactive metal.
Reduction is feasible only when net ΔG° is negative.
- Common reducing agents: carbon, carbon monoxide, aluminium (thermite)
- ZnO + C → Zn + CO is a standard carbon reduction
- Very reactive metals (Na, Mg, Ca, Al) need electrolysis instead
Ellingham Diagram
A plot of ΔG° of oxide formation vs temperature that tells you which reductant works.
Gives only thermodynamic feasibility, NOT the rate (kinetics).
- Metal-oxide lines slope UP (O2 consumed, ΔS negative)
- C → CO line slopes DOWN, so hot carbon can reduce almost any oxide
- Lower line (more negative ΔG°) reduces the oxide of the higher line
Electrolytic Reduction & Self-Reduction
Reactive metals need electricity; some sulphides reduce themselves.
Reactive metals are reduced from MOLTEN salts, never aqueous (water reduces first).
- Hall–Héroult: Al2O3 in molten cryolite (Na3AlF6) lowers m.p. & raises conductivity
- Carbon anode burns away as CO/CO2; Al collects at the cathode
- Self-reduction is special to Cu, Pb, Hg sulphides (no external reductant)
Refining the Crude Metal
Match the metal’s standout property to the right purification method.
Electrolytic refining: impure metal = ANODE, pure metal = CATHODE.
- Distillation: low-boiling Zn, Hg; Liquation: low-melting Sn, Pb
- Zone refining gives ultra-pure Si, Ge, Ga (impurities prefer the molten zone)
- Anode mud collects valuable Ag, Au, Pt during electrolytic refining
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Frequently Asked Questions
A mineral is any naturally occurring form in which a metal is found, while an ore is a mineral from which the metal can be extracted profitably and conveniently. So every ore is a mineral, but not every mineral is an ore.
Metallurgy follows four steps: concentration of the ore to remove gangue, conversion of the concentrated ore to its oxide by calcination or roasting, reduction of the oxide to the metal, and finally refining or purification of the crude metal. The more reactive the metal, the more energy-intensive its extraction, often needing electrolysis.
Calcination is heating an ore in limited or no air to drive off volatile matter like carbon dioxide or water, used mainly for carbonate and hydrated ores. Roasting is heating a sulphide ore in excess air below its melting point so that sulphur is removed as sulphur dioxide; both steps end at the oxide.
It is a plot of the standard free energy change of oxide formation against temperature, and it tells us which reducing agent can reduce a given oxide. A metal whose line lies lower (more negative free energy) can reduce the oxide of a metal whose line lies above it, but the diagram gives only thermodynamic feasibility and not the rate of reaction.
Yes, it is part of the NEET inorganic chemistry syllabus and usually contributes one or two questions. Expect direct recall of ore names and formulae, comparisons such as calcination versus roasting, choice of reducing agent, and the Hall and Heroult process for aluminium.