Calcination Reactions

Calcination is a thermal treatment of something like a solid chemical compound, for instance. The mixture is heated to high temperatures without heating up in the presence of a limited supply of ambient oxygen, i.e. the gaseous O2 fraction of air. This is generally done to remove impurities or volatile substances and induce thermal decomposition. 

The term calcination derives from its most common application: extracting carbon from limestone using burning to produce calcium oxide (quicklime). 

CaCO3(s) → CaO(s) + CO2 is the calcination reaction (g). Calcium oxide is an essential component of contemporary cement and a chemical flux for smelting. 

Read on to learn more about calcination reactions.

Definition of calcination

Calcination may be described as the procedure of heating a solid material or chemical in a controlled atmosphere. Typically, the temperature is also controlled during the process. Calcination is used to alter the physical or chemical composition of a material. Solids are heated to high temperatures during calcination. This is generally done to remove contaminants, water, or to oxidise the material. This procedure is also termed a purifying procedure. Calcination is based on the Latin phrase Calcinare, which means ‘to burn lime’.

Calcination reactions

Calcination processes often occur at or around the thermal decomposition temperature, which is used for decomposition and volatilisation reactions, or the transition temperature used for phase transitions. This temperature is commonly described as a temperature at which the standard Gibbs free energy for a specific calcination reaction equals zero.

Limestone calcination

Limestone is among the most basic raw materials used in steel production, and it is utilised in iron and steelmaking processes and auxiliary activities. The vast majority of lime used in the iron and steel industry is fluxing impurities in the steelmaking furnace and several other steelmaking processes.

A chemical process of decomposition that occurs during the calcination of limestone is an example of calcination.

CaCO3(s) → CaO(s) + CO2

Meanwhile, when the temperature is adjusted to 1,121 K or 848°C, the standard free energy of the reaction equals zero.

Hence, limestone deposits are widely distributed. The physical and chemical qualities of limestone vary according to the source. The chemical composition can also vary substantially between regions and deposits within the same region. Limestone may be divided into three types based on its chemical composition, texture, and geological formation.

Calcination process

Calcination is the process of heating solids to high temperatures to extract volatile compounds, oxidise a portion of the mass, or make them friable. As a result, calcination is sometimes thought of as a purification method. 

A common example is the production of lime from limestone. The limestone is heated to a high enough temperature to release the carbon dioxide, resulting in a highly friable or readily pulverised lime. 

Calcination may be carried out in specific situations in furnaces built to exclude air, in which an inert gas may be replaced. Heating a material below its melding or melting temperatures at a high temperature produces an oxidation-reduction reaction, moisture loss, carbonate, and other substance disintegration. As a result, this is what occurs throughout the calcination process. 

Most of the time, the reaction occurs at or above the thermal decomposition temperature. Calcination results are referred to as calcining, independent of the actual compounds undergoing heat treatment.

Examples of calcination reactions 

The conversion of calcium carbonate to calcium oxide is a common calcination process.

Other typical calcination instances include:

• Limestone calcination – entails the breakdown of carbonate ores and the removal of carbon dioxide.
• Calcination of bauxite and gypsum – requires the elimination of water vapour from crystallisation.
• The breakdown of volatile components in raw petroleum coke
• Making rutile by anatase or devitrification of glass materials.
• Zeolit synthesis with ammonium ions eliminated.
• Anhydrous alumina is left behind when bauxite is calcined and the water is removed.

Al2O3.2H2O → Al2O3 + 2H2O

Conclusion

Calcination is an essential step in the production of cadmium pigments to produce certain pigmentary properties. The temperature of calcination, residence duration, and calcining environment all have an impact on the colour and texture of cadmium pigments. 

A lower calcination temperature produces a lighter and brighter pigment shade with less strength, whereas a higher temperature produces a darker shade. This method is also important for titanium dioxide pigments. 

Calcination reactions are an important part of chemistry. Organic pigments may also be calcined to increase their performance, so it’s not just inorganic pigments that can be calcined.