Question

What is the difference between calcination and roasting?

Answer 1

Hint: Calcination is a thermal process and roasting is a metallurgical process. Roasting, as we know, is done in the presence of air. Start by using this difference and then proceed.

Complete answer:
Calcination refers to the process of heating an ore at a temperature below its melting point, either in absence of air or limited supply of oxygen. The purpose of calcification is to remove volatile impurities like arsenic or to remove moisture.
Example –Calcination of Limestone
\[CaC{{O}_{3}}\to CaO+C{{O}_{2}}\] (g)

Roasting is the process used to heat the ore at a high temperature (below its melting point) in presence of air. The purpose of roasting is purification of the ore by oxidising the impurities.
Example – Heating of chalcocite -
\[2C{{u}_{2}}S+3{{O}_{2}}\to 2C{{u}_{2}}O+2S{{O}_{2}}\](g)
In this reaction, we can see that the impurity (\[S\]) in chalcocite is removed as \[S{{O}_{2}}\] gas.
Roasting can be further categorised as Oxidising roasting, Volatizing roasting, Chloridizing roasting, Sulfating roasting, Magnetic roasting, Reduction roasting and Sinter roasting.
Summarising the difference between calcination and roasting –

Calcination	Roasting
Thermal treatment process	Metallurgical process
Heating in absence or limited supply of \[{{O}_{2}}\]	Heating in presence of excess \[{{O}_{2}}\]or air
Purpose of Calcination is to bring thermal decomposition of the compound	Purpose of roasting is to remove impurities from ores as its oxidised form
Used for Carbonate ores	Used for Sulphide ores
\[C{{O}_{2}}\]gas is released	Toxic, metallic and acidic (mostly \[S{{O}_{2}}\]) is released
Dehydration of ore takes place	No dehydration of ore

NOTE: The term Calcination is derived from a Latin word ‘calcinare’ which means “to burn lime”. Therefore, we can remember calcination as a process which is used in the decomposition of limestone (calcium carbonate) to lime (calcium oxide) and carbon dioxide.