Calcination and Roasting - Definition, Example, Principle, FAQs

The calcination and roasting processes in the conversion of ore into its oxide are two important topics that will be discussed in this paper. Calcination involves the process of heating ore without air to remove the volatile substances, whereas roasting is termed a process by which ore is heated in excess oxygen to enhance the removal of sulfur and other impurities. These processes are followed to create pure metal of high grade for use in diverse industries.

Examples

1. Calcium Carbonate (Limestone) CaCO₃→CaO+CO₂↑ Here, limestone is converted into calcium oxide, and carbon dioxide is released.
2. Bauxite (Hydrated Aluminium Oxide) Al₂O₃⋅H₂O→Al₂O₃+2H₂O↑ Bauxite is converted into alumina, releasing water vapor.

Roasting

Roasting It is the heat treatment of ores in excess air to convert metals into their respective oxides and water-insoluble sulphides into water-soluble sulphates. It may, otherwise, be defined as a process for the deelectronation of ores, in which the process is centered on the removal of volatile impurities and the conversion of sulphide ores into the corresponding oxides. It essentially takes place in reverberatory furnaces.

Examples
Iron Sulfide In excess air, pyrite, FeS₂, oxidizes to give iron oxide, Fe₂O₃, and sulfur dioxide,

SO₂: FeS₂ → Fe₂O₃ + SO₂

The above process chain may merely be used as a way of changing the sulfide ore to a more reactive oxide form—the method also removes sulfur impurities.
Cinnabar Mercury ore- Roasting of cinnabar HgS, produces mercury oxide {HgO} and sulfur dioxide, SO₂. The ore becomes an oxide; this making the extraction of mercury to be more comfortable.
Zinc Sulfide Zinc sulfide ZnS is roasted to get zinc oxide {ZnO} and sulfur dioxide {SO₂}. This method turns the sulfide ore into an oxide and makes it fit for further reduction.
Lead Sulphide {PbS} is roasted to yield lead oxide {PbO} and sulphur dioxide {SO₂}. The processing of the ore into the oxide form makes it more reactive and thus easier for reduction to metallic lead.

Related Topics

• Distillation
• Filtration
• Difference between Metallic and Non Metallic Minerals
• Processes of Metallurgy

Significance and Uses

Some of the predominantly used processes in the production of metals, which are used in various industries, include calcination and roasting. For example, the steel industry requires calcined limestone to act as a flux in the elimination of impurities in producing steel. Roasted zinc and copper ores are important in the making of parts donned by electronics, construction, and transport.

Significance in Learning

Processes that are hugely fundamental to the courses for learners in Chemistry and Metallurgy as in Material Science, Environmental Engineering, or Industrial Chemistry, since they assist in having an idea of the applications and the environmental impact caused by the extraction of the metals from their respective ores.

Also read :

Some Solved Examples

Example 1:
Which of the following factors is of no significance for roasting sulphide ores to the oxides and not subjecting the sulphide ores to carbon reduction directly?

1)CO₂ is more volatile than CS₂

2)Metal sulphides are thermodynamically more stable than CS₂

3)CO₂ is thermodynamically more stable than CS₂

4) Metal sulphides are less stable than the corresponding oxides

Solution
The reduction of metal sulphides by carbon reduction is positive whereas, ΔG is negative for the same process with metal oxides. So, metal sulphides are more stable than oxides.

Hence, the statement given in Option 4 is incorrect:

"Metal sulphides are less stable than the corresponding oxides"

Hence, the answer is the option (4).

Example 2:

The purest form of commercial iron is:

1) wrought iron

2)pig iron

3)scrap iron and pig iron

4)cast iron

Solution
The purest form of iron is wrought iron.
Hence, the answer is the option (1).

Example 3:

The process that involves the removal of sulphur from the ores is :

1) Roasting

2)Leaching

3)Smelting

4)Refining

Solution
In the roasting process, metal sulphide (MS) ore is converted into metal oxide, and sulphur is removed in the form of SO₂ gas

2MS+3O₂→Δ2MO+2SO₂↑

Hence, the answer is the option (1).

NCERT Chemistry Notes :

• NCERT notes Class 11 Chemistry
• NCERT notes Class 12 Chemistry
• NCERT Notes For All Subjects