Metallurgy — Question 12

(a) Roasting — It is the process of heating the concentrated ore to a high temperature in the presence of excess air.

Example — Zinc blende (ZnS) is roasted to yield it's oxide, zinc oxide

$2\text{ZnS} + 3\text{O}<em>2 \xrightarrow{800 \degree\text{C}} \text{2ZnO} + \text{2SO}</em>{2}$

(b) Calcination — If an ore is carbonate or a hydrated oxide, it is heated in the absence of air to a temperature that is high but insufficient to melt the ore. The process is known as Calcination.

Example — carbonate and hydrated ores are calcinated like ZnCO₃

$\text{ZnCO}<em>3 \rightarrow \text{ZnO} + \text{CO}</em>{2} [\text{g}]$