What is Calcination?

Calcination refers to a thermal treatment process applied to ores and other solid materials in the absence of oxygen or air. The process involves heating a substance to high temperatures, typically between 700 ℃ to 1200 ℃, although the specific temperature can vary based on the melting point of the material and the desired outcome.

During calcination, volatile compounds such as water and carbon dioxide are driven off, resulting in chemical and physical changes within the material. This process can lead to various transformations, such as decomposition, oxidation, and reduction of the original substance, ultimately altering its physical and chemical properties.

Examples of Calcination

Few of the examples of extraction of minerals from their ores through the process of calcination is given below:

Limestone (calcium carbonate – CaCO₃)

When heated, limestone undergoes calcination to produce quicklime (calcium oxide – CaO) and carbon dioxide (CO₂).

Gypsum (calcium sulfate dihydrate – CaSO₄·2H₂O)

Calcination of gypsum removes the water molecules, resulting in the formation of calcium sulfate hemihydrate, commonly known as plaster of Paris.

Bauxite (aluminum ore – Al₂O₃·nH₂O)

Calcination of bauxite removes water and impurities, converting it into alumina (aluminum oxide – Al₂O₃), a precursor for aluminum production.

Read More,

• Calcium Oxide
• Aluminum Oxide

Mechanism and Process of Calcination

The detailed process of calcination involves several crucial steps:

• Preparation of Material: The raw material is selected and prepared for calcination, ensuring it is free from impurities and suitable for the intended transformation.
• Heating: The material is subjected to controlled high temperatures in a furnace. The temperature and duration of heating are critical and vary depending on the specific material and desired outcome.
• Chemical Reactions: During heating, chemical reactions occur within the material. These reactions lead to the expulsion of volatile compounds like water, carbon dioxide, sulfur dioxide, etc., resulting in the alteration of the material’s composition.
• Cooling and Handling: After the calcination process, the material is cooled down gradually to avoid sudden changes that could affect its properties. Proper handling post-calcination is essential to maintain the integrity of the transformed material.
• Utilization: The calcined material, with its altered properties, is used in various industries, such as construction, metallurgy, ceramics, and pharmaceuticals, based on its specific characteristics post-calcination.

Calcination and Roasting are processes used to convert ore into oxide. The difference between the two is the presence or absence of air. Roasting involves heating ores with oxygen below their melting point in the presence of air. Calcination involves heating ore to a high temperature in the absence of air.

In this article, we will understand what is Calcination and Roasting, their examples, and processes, along with a comparison between calcination and roasting.