Calcination

A process in chemistry and metallurgy involving heating of substances

A lime shaft kiln used in the calcination process

Calcination is a thermal treatment process applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The process is carried out in furnaces or reactors known as kilns.

Process

Calcination involves heating a substance to a high temperature, but below its melting point, in the presence of air or oxygen. The primary objective is to cause thermal decomposition or phase transition. This process is commonly used in the production of lime from limestone, where calcium carbonate (CaCO_) is decomposed into calcium oxide (CaO) and carbon dioxide (CO_).

Applications

Calcination is used in various industrial processes, including:

• Cement production: The calcination of limestone is a key step in the production of Portland cement.
• Metal extraction: In metallurgy, calcination is used to remove impurities from ores, such as the removal of water from hydrated ores or the decomposition of carbonates and sulfates.
• Refractory materials: Calcination is used to produce materials that can withstand high temperatures, such as refractory bricks.

Equipment

The equipment used for calcination includes:

• Rotary kilns: These are cylindrical vessels that rotate about their axis and are used for continuous calcination processes.
• Shaft kilns: These are vertical kilns where the material moves downwards by gravity and is heated by gases moving upwards.

Chemical Reactions

During calcination, several chemical reactions can occur, including:

• Decomposition: For example, the decomposition of calcium carbonate to calcium oxide and carbon dioxide.
• Oxidation: Some materials may undergo oxidation during calcination, such as the conversion of sulfide ores to oxides.

Related pages

• Lime (material)
• Kiln
• Thermal decomposition
• Metallurgy