Question

Differentiate between calcination and roasting.

Answer 1

Hint: Calcination is derived from a Latin word which means “to burn lime”. It is mostly used in the decomposition of limestone.
Roasting is basically a process of metallurgy where ore is converted into its oxide in the presence of heat.

Complete step-by-step answer:
Roasting: It is defined as the process of heating of sulphide ore, below its melting point, in the excess supply of air.
For example:-.${ 4As+} { 3O }_{ 2 }\rightarrow { 2As }_{ 2 }{ O }_{ 3 }$
This method is commonly used for sulphide ores.
The following changes will take place;

1. Moisture is removed.
2. Volatile impurities of sulphur, phosphorus and carbon are removed as their volatile oxides.

Calcination: It is defined as the process of heating of ore, below its melting point, in the limited supply of air.
For example:- ${ Fe }_{ 2 }{ O }_{ 3 }.{ 3H }_{ 2 }{ O }\rightarrow { Fe }_{ 2 }{ O }_{ 3 }+{ 3H }_{ 2 }{ O }$

This method is commonly used for converting carbonated and hydroxides to their oxides.
The following changes will take place;
1)Moisture is removed.
2)Non-metallic impurities of arsenic are removed as their volatile oxides.

Differences between Roasting and Calcination

Roasting	Calcination

1. Sulphur dioxide is released.| 1)Carbon dioxide is released.
   2)Reaction showing roasting process;${ 2ZnS+ }{ 3O }_{ 2 }\rightarrow { 2ZnO+ }{ 3SO }_{ 2 }$| 2) Reaction showing calcination process;${ CaCO }_{ 3 }\rightarrow { CaO }{ +CO }_{ 2 }$
2. It is not used for dehydrating an ore.| 3)It can be used to drive out moisture from an ore.

Additional Information: During roasting, non-metallic impurities and moisture are removed as their volatile oxides. The process of roasting consists of solid-gas thermal reaction which includes reduction, oxidation, sulfation and chlorination.

Note: The possibility to make a mistake is that you may confuse between these which occur in the presence or absence of heat.