Question 6Compare roasting and calcination.

Question

Accepted Answer

RoastingCalcinationThe ore is heated in the excess air.The ore is heated in the absence of airGenerally sulphide ores are roasted and hence sulphur dioxide is given out.Generally carbonate and hydrated ores are calcinated and hence carbon dioxide and water vapour is given off.2ZnS+3O2→800−900°C2ZnO+2SO2[g]2	ext{ZnS} + 3	ext{O}_2 \xrightarrow{800 - 900 \degree	ext{C}} 	ext{2ZnO} + 	ext{2SO}_	ext{2}[	ext{g}]2ZnS+3O2​800−900°C​2ZnO+2SO2​[g]ZnCO3→ZnO+CO2[g]	ext{ZnCO}_3 ightarrow 	ext{ZnO} + 	ext{CO}_	ext{2} [	ext{g}]ZnCO3​→ZnO+CO2​[g]Volatile impurities are removed as oxides (SO2, P2O5, As2O3) and the ore becomes porous and more reactive.Moisture and organic impurities are removed and the ore becomes porous and more reactive.

Roasting	Calcination
The ore is heated in the excess air.	The ore is heated in the absence of air
Generally sulphide ores are roasted and hence sulphur dioxide is given out.	Generally carbonate and hydrated ores are calcinated and hence carbon dioxide and water vapour is given off.
$2\text{ZnS} + 3\text{O}_2 \xrightarrow{800 - 900 \degree\text{C}} \text{2ZnO} + \text{2SO}_\text{2}[\text{g}]$	$\text{ZnCO}_3 \rightarrow \text{ZnO} + \text{CO}_\text{2} [\text{g}]$
Volatile impurities are removed as oxides (SO₂, P₂O₅, As₂O₃) and the ore becomes porous and more reactive.	Moisture and organic impurities are removed and the ore becomes porous and more reactive.

Metallurgy — Question 6

Question 6