# Metallurgy

> Metallurgy for JEE Chemistry: concentration methods, roasting and calcination, Ellingham diagrams, extraction of iron, copper, zinc and aluminium.

- Canonical URL: https://prepelephant.com/topics/jee/chemistry/metallurgy
- Exam / course: JEE · Subject: Chemistry
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Metallurgy", PrepElephant, https://prepelephant.com/topics/jee/chemistry/metallurgy

## Direct answer

Metallurgy is the craft of winning a metal from its ore: concentrate, convert to an oxide, reduce, then refine. Sulphide ores are concentrated by froth flotation and roasted; carbonates and hydroxides are calcined; the oxide is then reduced by carbon, a reactive metal or electrolysis — a choice governed by the Ellingham diagram, which plots oxide-formation free energy against temperature.

## What you must remember

- Froth flotation suits sulphides: powdered ore with pine oil agitated so sulphide rides the froth; depressants like NaCN selectively hold back ZnS when it is mixed with galena.
- Bayer leaching: bauxite in hot NaOH dissolves as sodium aluminate, reprecipitated as Al(OH)3 and calcined to alumina.
- Roasting heats sulphides in excess air (2ZnS + 3O2 → 2ZnO + 2SO2); calcination heats carbonates and hydroxides in limited air (CaCO3 → CaO + CO2).
- Ellingham rules: the lower the line, the more stable the oxide; a metal reduces any oxide whose line sits above it; the downward C → CO line crosses most metal lines at high temperature, making carbon the universal reductant — Al2O3 and MgO lie too low, forcing electrolysis.
- Aluminothermite: Cr2O3 + 2Al → 2Cr + Al2O3; Fe2O3 + 2Al welds rails.
- Blast furnace: Fe2O3 + 3CO → 2Fe + 3CO2, with limestone flux; the product is carbon-rich pig iron.
- Copper: chalcopyrite smelted to matte (Cu2S-FeS), then bessemerisation — 2Cu2O + Cu2S → 6Cu + SO2 — giving blister copper.
- Zinc: ZnO reduced by coke; zinc boils near the reaction temperature, so the metal leaves as vapour and is condensed.
- Aluminium: alumina electrolysed in molten cryolite Na3AlF6 (lowering the melting point); carbon anodes burn away and need replacement.
- Refining: electrolytic (impure anode dissolves, pure metal deposits; silver and gold collect in the anode mud), Mond for nickel via volatile Ni(CO)4, van Arkel for titanium and zirconium, zone refining for semiconductor-grade silicon and germanium.

## Common confusion

The classic muddle is roasting versus calcination: roasting suits sulphides with SO2 evolving, calcination suits carbonates and hydroxides with CO2 or water. Students misread Ellingham diagrams by comparing lines at room temperature — reduction is decided by delta G at the working temperature. They also forget why cryolite is added: molten alumina alone would demand too high a temperature.

## Exam-focused takeaway

JEE Main frames metallurgy as direct NCERT facts: match ore with process, name the depressant, write roasting equations, pick the refining method. JEE Advanced builds multi-step extraction sequences, reads Ellingham diagrams for threshold temperatures, and probes electrode reactions and the anode mud. Draw the ore-to-refined-metal flowchart before answering; sequence questions reward students who have traced the path.

## Frequently asked questions

### What does a depressant do in froth flotation?

It selectively stops one sulphide from floating — NaCN added to a PbS-ZnS mixture depresses ZnS so only galena rises.

### How is an Ellingham diagram used?

Compare free-energy lines at the reaction temperature: the lower-line metal reduces the one above it; carbon's falling C → CO line is why high temperature enables carbon reduction.

### Why is aluminium won by electrolysis rather than carbon reduction?

Alumina's line lies below the carbon lines at practical temperatures, so carbon cannot reduce it; electrolysis in molten cryolite is required.

### What is the thermite reaction?

Fe2O3 + 2Al → 2Fe + Al2O3, so exothermic that molten iron forms — used to weld rails; chromium is won likewise.

### Why is zinc collected as a vapour?

Zinc boils near the reduction temperature, so it leaves the retort as vapour and condenses in cooled receivers, protected from reoxidation.

### What is zone refining for?

Ultra-pure silicon and germanium: a molten zone sweeps the rod, carrying impurities that dissolve better in the liquid.