Difference Between Calcination and Roasting (With Table)

Calcination is the process of converting ore into oxide by heating it. It is heated below its melting point. It can be done either in a limited supply of air or in the absence of air. It is commonly used for converting hydroxides and carbonates to their respective oxides. For example, metal carbonates will be decomposed to produce metal oxides. It is considered to be a purification process of metals. 

Roasting is one of the steps in the processing of certain ores. It is a metallurgical process that involves gas-solid reactions at elevated temperatures. It is done to purify metal components. This process can convert a metal sulfide to a metal oxide. It can also convert them to free metal. The furnace used for roasting is a blast furnace. 

Comparison Table Between Calcination and Roasting

What is Calcination?

It is a thermal treatment of a solid chemical compound. It is heated at a high temperature while it stays below the melting point. This process helps to remove volatile substances. It also oxidizes any mass of the substance. It removes the moisture or water from the wet or hydrated ores. During calcination, the ore becomes porous and dry. The process of calcination is done typically, in a retort. It has a chamber in which the object or material to be treated will be placed and heated.

It will not melt or oxidize to the point of melting. The retort is usually gas-tight. It has one wat valve that allows volatiles to be driven out of the retort chamber. During this process, it won’t let any air come in. In some instances, these retorts are purged with noble gas or nitrogen before heating. This is to prevent oxidation or other chemical reaction with ordinary atmospheric gases. Some sterilizers can also use a vacuum pump to exhaust the gas generated during the heating process. 

Some of the examples of calcination are decomposing carbonate ores and removing carbon dioxide. This process is done to remove the calcination of limestone. Calcination of gypsum and bauxite is done for removing the crystallization of water in the form of water vapor. It is also used for decomposing volatile components from raw petroleum coke. 

What is Roasting?

It is the process of heating a sulfide ore. It will be heated at a high temperature in the presence of air. During the process of roasting, non-metallic impurities and moisture in the form of volatile gases will be released. The process consists of solid-gas thermal reaction which includes reduction, chlorination, oxidation, sulfation, and pyro hydrolysis. For the process, it involved sulfides which act as a major source of air pollution.

But the main drawback is it releases a large amount of metallic, toxic, and acidic components. It can cause harm to the environment. When you roast zinc sulfide, it will convert it into zinc oxide. This process is generally applied to sulfide minerals. This process is done because reducing sulfide directly is not the best method. Here, the ore will be subjected to very high temperatures when they are exposed to air. 

So, the ore reacts and forms an oxide in some cases. It also forms metal as well. It is done with excess air whereas in calcination the air supply will be limited. So, it cannot be carried out on carbonate ores. This process is mainly used in sulfide ores because while removing the sulfur might get escaped in the form of gas. Roasting will stop the escaping of air. 

Main Differences Between Calcination and Roasting

1. Calcination is used for thermal decomposition or treatment of carbonate ores. On the other hand, roasting is used for thermal decomposition or treatment of sulfide ores.
2. Toxic compounds are not released during the calcination process. On the other hand, toxic and acidic compounds will be released in the roasting process.
3. In the calcination process, moisture organic impurities are removed. On the other hand, in the roasting process, volatile impurities are removed.
4. During the calcination process, carbon dioxide will be produced along with metal oxide. On the other hand, during the roasting process, sulfur dioxide will be produced along with metal oxide.
5. In calcination, the ore will be heated with a limited supply of air. On the other hand, in roasting the ore will be heated along with the presence of air. 

Conclusion

Both Calcination and Roasting are used in the process of heating ore so that carbonate and sulfide ores can be heated. This process should be carefully carried out and the steps should be properly performed so that the ore can be separated properly. It uses a blast furnace for carrying out the process. This process also helps to remove the impurities from the ore. 

But in calcination toxic compounds will be released which is considered a good advantage. Whereas, in the roasting process, toxic compounds along with acidic ones will be released so that it works as an advantage for sulfide ores. In both these metals, the chemical compounds will be produced along with the metal oxide. 

References

1. https://journals.co.za/doi/abs/10.10520/AJA0038223X_1842
2. https://www.sciencedirect.com/science/article/pii/S0892687519304406