Question

Differentiate roasting and calcination with examples?

Answer 1

Hint – We will first define the whole process of Roasting and the whole process of calcination and then in last we will discuss the difference between these two processes with examples.

Complete answer:

We know that Roasting and Calcination both are used in the conversion of ore into metal oxide.
Now, we will define both the processes.

Roasting may be defined as a process of heating the ore, below its melting point, in the excess supply of air. Following changes occur –
(i) Moisture is removed.
(ii) Volatile impurities of Sulphur, Arsenic and Phosphorus are removed as their volatile oxides.
${S_8} + 8{O_2} \to 8S{O_2} \uparrow $
${P_4} + 5{O_2} \to {P_4}{O_{10}}$
(iii) Sulphide ores are decomposed to metallic oxides.
$2PbS + 3{O_2} \to 2PbO + 2S{O_2} \uparrow $

Calcination may be defined as a process of heating the ore, below its melting point,
 in the limited supply of air. Following changes occur –
(i) Moisture is removed.
(ii) Volatile impurities of Sulphur, Arsenic and Phosphorus are removed as their volatile oxides.
${S_8} + 8{O_2} \to 8S{O_2} \uparrow $
${P_4} + 5{O_2} \to {P_4}{O_{10}}$
(iii) Carbonates and hydroxides are decomposed to metallic oxides.
$
  CaC{O_3} \to CaO + C{O_2} \uparrow \\
  2Al{\left( {OH} \right)_3} \to A{l_2}{O_3} + 3{H_2}O \\
 $

So, the difference between Roasting and Calcination is,
1. The process of Roasting is done by heating the ore in excess supply of air whereas the process of Calcination is done by heating the ore in limited supply of air.

2. In the process of roasting, sulphide ores are decomposed to form metallic oxides whereas in the process of calcination, carbonates and hydroxides are decomposed to metallic oxides.

3. Example of Roasting - $4As + 3{O_2} \to 2A{s_2}{O_3}$
Example of Calcination - $F{e_2}{O_3}.3{H_2}O \to F{e_2}{O_3} + 3{H_2}O$

Note – In these types of questions where we have to differentiate two processes, first we should know the definition and the whole process, only then we can differentiate the two processes. So, definitions and examples must be remembered.