Calcination Process Description

Have you ever wondered how lime is produced from limestone? This process is carried out in the absence of oxygen, known as the calcination process. In simple words, the process in which the ore of any metal is heated in the absence of oxygen or air to high temperature is called the calcination process. 

This process has a wide range of applications in industries and chemistry. You can carry out this process easily in your chemistry lab under supervision. Heating in the absence of oxygen and air can make such products. It is also used to transform anatase to rutile and devitrification of glass materials. Muffle, reverberatory, and shaft furnaces are three common tools used to carry out the process of calcination. Calcination is also a widely used thermo-chemical process used in the cement industry. The primary condition to carry out this process is that it should be done without oxygen. It instead can have inert gases. 

It is a unique chemical process, a thermal treatment used to separate the chemicals. A calciner is a steel cylinder that is kept inside a heating furnace. It rotates and performs high-temperature processing indirectly in a controlled atmosphere.

Processes induced during the calcination process

Calcination uses heat sometimes in the absence of oxygen too. The calcination process can lead to any of the following processes:

• Phase change

The presence or absence of heat during this process can change the state of the chemical or metal, which can produce a different product.

• Volatile fraction removal

The calcination process occurs under melting point, changing the state from solid to liquid or liquid form to gas. These changing states of material need to be removed so that the process can be carried out smoothly.

• Decomposition

The decomposition during the calcination process mainly means the separation of reactants to form more products in which one product would be our desired product.

• Crystalline water removal

The water of crystallisation can be removed by heating to get pure crystals of a substance from an impure mixture.

Examples of the calcination process

• Removal of ammonium ions during the production of zeolites
• Decomposition of volatile material which is contained in raw petroleum coke
• Decomposition of hydrated minerals (in calcination of bauxite and gypsum) to remove the water of crystallisation in the form of water vapour
• Decomposition of ores of carbonate (in calcination of limestone) to remove carbon dioxide

Calcination process of gypsum

Calcium sulphate dihydrate as known as Gypsum (CaSo4.2H2O), is a calcium mineral that is mined all over the world. This process includes heating gypsum to evaporate crystalline water. If calcination is carried out above the temperature of 130oC, all water is removed. Here is the reaction for the calcination of gypsum.

CaSO4. 2H2O → CaSO4 + 2H2O

Calcination Process of Limestone

Limestone is the most basic material which is used in industry. It is used for making both iron and steel. This process occurs at a temperature where standard Gibbs’s free energy is equal to zero. The chemical reaction for calcination of limestone is:

CaCO3 = CaO + CO2 (g)

This process of decomposition gives calcium oxide (CaO).

 Some chemical reactions of the calcination process

• ZnCO3 -> ZnO + CO2
• CuCO3 -> CuO + CO2
• CaCO3 -> CaO + CO2
• CaCO3 , MgCO3 -> CaO + MgO + 2CO2
• 2Fe2O33H2O -> 2Fe2O3 + 3H2O

 Applications of the calcination process

• Calcination is done to change a material’s physical or chemical state.
• It is done to oxidise a substance in the process of heating solids.
• It is done to convert concentrated ore into its oxide.
• To produce many useful substances such as gypsum, calcium oxide, etc.

Conclusion

The calcination process is widely carried out in industries that show you how chemistry is used to produce a wide range of products that you use in daily life. Calcination is carried out in the absence of oxygen, where the ore of the metal is heated to get the desired product.

A typical example of calcination is the manufacture of lime from limestone. Limestone is brought in contact with a high enough temperature to separate carbon dioxide from it. In rare cases, calcination is carried out in furnaces to exclude air, and inert gases may be added.

It is used to manufacture hard goods, such as machines and raw materials for industries. It is also used to produce soft goods, such as chemicals, foodstuffs, apparel, etc. Some of the commonly calcined materials are refractory, alumina, spodumene ore, kaolin clay, technical ceramics, etc.  

Calcination also can promote climate change, because in every calcination process, carbon dioxide (CO2) is released, and it is a harmful gas for our environment and ecosystem.

Gypsum is a major product that is produced during this process. It is used in building construction, food additives, medical devices, etc.