Compare gases released in calcination vs roasting

see full answer

Your Exam Success, Personally Taken Care Of

1:1 expert mentors customize learning to your strength and weaknesses – so you score higher in school , IIT JEE and NEET entrance exams.

An Intiative by Sri Chaitanya

(Unlock A.I Detailed Solution for FREE)

Best Courses for You

JEE

NEET

Foundation JEE

Foundation NEET

CBSE

Detailed Solution

Calcination of carbonates mainly releases CO₂ (and H₂O from hydroxides), while roasting of sulfide ores mainly releases SO₂ (and sometimes SO₃ or volatile metal oxides).

Core difference

Calcination: Done with little or no air; drives off CO₂ or H₂O without full oxidation.
Roasting: Done with excess air; oxidizes sulfides to oxides, generating SO₂-rich off-gas.

Representative reactions

Calcination (carbonate): MCO₃(s) → MO(s) + CO₂(g) Example: CaCO₃(s) → CaO(s) + CO₂(g) Calcination (hydroxide): M(OH)ₙ(s) → MₓOᵧ(s) + (n/2) H₂O(g) Example: Al(OH)₃(s) → Al₂O₃(s) + H₂O(g) Roasting (sulfide): MS(s) + O₂(g) → MO(s) + SO₂(g) Example: 2 ZnS + 3 O₂ → 2 ZnO + 2 SO₂

Gas comparison table

Process	Main gas	Source of gas	Environmental note
Calcination of carbonates	CO₂	Decomposition of CO₃²⁻	Greenhouse gas; requires kiln heat management and CO₂ capture to reduce emissions
Calcination of hydroxides	H₂O (steam)	Dehydroxylation	Low direct pollution; steam can carry dust particulates
Roasting of sulfides	SO₂ (and some SO₃)	Oxidation of sulfide sulfur	Acid rain precursor; usually converted to H₂SO₄ in acid plants
Over-roast or impure feeds	As₂O₃, SeO₂ (trace)	Volatilization of metalloids	Toxic; requires scrubbing and dust collection