Question

The difference between roasting and calcination is:
This question has multiple correct options.
a) Roasting is highly endothermic while calcination is not.
b) Partial fusion occurs in roasting but not in calcination.
c) Calcination is performed in a limited amount of air but roasting employs excess air.
d) Combustion reaction occurs in roasting but not in calcination.

Answer 1

Hint: You know that the conversion of metal from metal ores is mostly done through the processes of calcination or roasting. So, here you have to choose the correct options regarding their properties.

Complete step by step answer:

Usually metals are obtained from oxide ores after going through a reduction or electrolysis process. While oxide ores are easy to reduce it is not the same with sulphides and carbonates. These ores can be turned to metals only after converting carbonates and sulphides to an oxide ore.

Calcination - As per the popular definition, calcination is defined as the process of converting an ore into an oxide by heating it strongly.
The ore is heated below its melting point either in absence of air or in a limited supply. This method is commonly used for converting carbonates and hydroxides to their respective oxides.
During calcination, moisture and volatile impurities are also removed. In calcination, reaction most of the time occurs at or above the thermal decomposition temperature.
Calcination is derived from a Latin word calcinare which translates as “to burn lime”. So, calcination is mostly used in the decomposition of limestone (calcium carbonate) to lime (calcium oxide) and carbon dioxide.
$CaCO_{ 3 }\quad \rightarrow \quad CaO\quad +\quad CO_{ 2 }$

Roasting - When we talk about roasting, it is basically a process of metallurgy where an ore is converted into its oxide by heating it above its melting point in the presence of excess air.
While calcination is mostly used in the oxidation of carbonates, roasting is a method that is used for converting sulphide ores. During roasting, moisture and non metallic impurities in the form of volatile gases are released.
However, roasting which involves sulphides is a major source of air pollution and the main drawback of this process is that it releases large amounts of metallic as well as toxic and acidic compounds which causes harm to the environment.
An example of roasting is when Zinc sulphide is converted into zinc oxide.
$2ZnS\quad +\quad 3O_{ 2 }\quad \rightarrow \quad 2ZnO\quad +\quad CO_{ 2 }$

Hence, from all these statements we can conclude that the correct options are C and D.

Note: You can get an idea why other two options are incorrect.
Roasting is an exothermic process. Thus, option A is incorrect.
During roasting and calcination, the ore is heated to a temperature which is below its melting point. Thus, option B is incorrect.