Calcination and Roasting: Definition, Process and Examples

Calcination and Roasting - Definition, Example, Principle, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:26 PM IST

The calcination and roasting processes in the conversion of ore into its oxide are two important topics that will be discussed in this paper. Calcination involves the process of heating ore without air to remove the volatile substances, whereas roasting is termed a process by which ore is heated in excess oxygen to enhance the removal of sulfur and other impurities. These processes are followed to create pure metal of high grade for use in diverse industries.

This Story also Contains

Roasting
Significance and Uses
Significance in Learning
Some Solved Examples

Calcination and Roasting - Definition, Example, Principle, FAQs

Examples

Calcium Carbonate (Limestone) CaCO₃→CaO+CO₂↑ Here, limestone is converted into calcium oxide, and carbon dioxide is released.
Bauxite (Hydrated Aluminium Oxide) Al₂O₃⋅H₂O→Al₂O₃+2H₂O↑ Bauxite is converted into alumina, releasing water vapor.

Roasting

Roasting It is the heat treatment of ores in excess air to convert metals into their respective oxides and water-insoluble sulphides into water-soluble sulphates. It may, otherwise, be defined as a process for the deelectronation of ores, in which the process is centered on the removal of volatile impurities and the conversion of sulphide ores into the corresponding oxides. It essentially takes place in reverberatory furnaces.

Examples
Iron Sulfide In excess air, pyrite, FeS₂, oxidizes to give iron oxide, Fe₂O₃, and sulfur dioxide,

SO₂: FeS₂ → Fe₂O₃ + SO₂

The above process chain may merely be used as a way of changing the sulfide ore to a more reactive oxide form—the method also removes sulfur impurities.
Cinnabar Mercury ore- Roasting of cinnabar HgS, produces mercury oxide {HgO} and sulfur dioxide, SO₂. The ore becomes an oxide; this making the extraction of mercury to be more comfortable.
Zinc Sulfide Zinc sulfide ZnS is roasted to get zinc oxide {ZnO} and sulfur dioxide {SO₂}. This method turns the sulfide ore into an oxide and makes it fit for further reduction.
Lead Sulphide {PbS} is roasted to yield lead oxide {PbO} and sulphur dioxide {SO₂}. The processing of the ore into the oxide form makes it more reactive and thus easier for reduction to metallic lead.

Significance and Uses

Some of the predominantly used processes in the production of metals, which are used in various industries, include calcination and roasting. For example, the steel industry requires calcined limestone to act as a flux in the elimination of impurities in producing steel. Roasted zinc and copper ores are important in the making of parts donned by electronics, construction, and transport.

Significance in Learning

Processes that are hugely fundamental to the courses for learners in Chemistry and Metallurgy as in Material Science, Environmental Engineering, or Industrial Chemistry, since they assist in having an idea of the applications and the environmental impact caused by the extraction of the metals from their respective ores.

Also read :

NCERT Exemplar Class 11th Chemistry Solutions	NCERT notes Class 12 Chemistry Chapter 6 GeneralPrinciples and Processes of Isolation of elements
NCERT Exemplar Class 12th Chemistry Solutions	NCERT Solutions for Class 12 Chemistry Chapter 6 General Principles and Processes of Isolation of elements
NCERT Exemplar Solutions for All Subjects	NCERT Exemplar Class 12 Chemistry Solutions Chapter 6 General Principles and Processes of isolation of elements

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Some Solved Examples

Example 1:
Which of the following factors is of no significance for roasting sulphide ores to the oxides and not subjecting the sulphide ores to carbon reduction directly?

1)CO₂ is more volatile than CS₂

2)Metal sulphides are thermodynamically more stable than CS₂

3)CO₂ is thermodynamically more stable than CS₂

4) Metal sulphides are less stable than the corresponding oxides

Solution
The reduction of metal sulphides by carbon reduction is positive whereas, ΔG is negative for the same process with metal oxides. So, metal sulphides are more stable than oxides.

Hence, the statement given in Option 4 is incorrect:

"Metal sulphides are less stable than the corresponding oxides"

Hence, the answer is the option (4).

Example 2:

The purest form of commercial iron is:

1) wrought iron

2)pig iron

3)scrap iron and pig iron

4)cast iron

Solution
The purest form of iron is wrought iron.
Hence, the answer is the option (1).

Example 3:

The process that involves the removal of sulphur from the ores is :

1) Roasting

2)Leaching

3)Smelting

4)Refining

Solution
In the roasting process, metal sulphide (MS) ore is converted into metal oxide, and sulphur is removed in the form of SO₂gas

2MS+3O₂→Δ2MO+2SO₂↑

Hence, the answer is the option (1).

NCERT Chemistry Notes :

Frequently Asked Questions (FAQs)

1. What Does Burning Without Oxygen Mean?

Burning Without Oxygen is called pyrolysis. There, pyrolysis is a reaction to chemical decomposition that involves ranging from low to very low oxygen, or at least the insufficient oxygen required for heating.

2. What is the role of calcination in iron carbonates?

In iron carbonates, a calcination process is performed to convert iron carbonates into carbon dioxides and iron oxides.

3. Explain the purpose of the calcination?

Calcination is sometimes called solid cleaning because the high temperature of the material used is used to remove the flexible material and other oxidizing part of the weight etc.

4. List some types of frying?

Volatilizing Frying,

Oxygen frying,

Frying sulfur.

5. How does roasting differ from calcination?

Roasting differs from calcination primarily in the presence of air. Roasting is carried out in the presence of excess air or oxygen, while calcination typically occurs in the absence or limited supply of air. Roasting often involves chemical reactions with oxygen, while calcination focuses more on thermal decomposition.

6. Can you explain the principle behind roasting in metallurgy?

The principle behind roasting in metallurgy is to use heat and oxygen to convert metal sulfides into metal oxides. This process removes sulfur from the ore as sulfur dioxide gas and produces a metal oxide that is easier to reduce to the pure metal in subsequent steps.

7. What is the difference between oxidative and reductive roasting?

Oxidative roasting involves heating the ore in the presence of excess oxygen to convert metal sulfides to oxides. Reductive roasting, on the other hand, involves heating the ore in a reducing atmosphere (e.g., with carbon monoxide or hydrogen) to remove oxygen from metal oxides, producing a more reduced form of the metal.

8. What is self-roasting in metallurgy?

Self-roasting, also known as autogenous roasting, is a process where the heat required for roasting is generated by the oxidation of the sulfide ore itself. This occurs when the reaction between the sulfide and oxygen is highly exothermic, providing enough heat to sustain the roasting process without additional external heating.

9. What is flash roasting?

Flash roasting is a rapid roasting technique used for fine sulfide concentrates. In this process, the finely ground ore is blown into a hot furnace where it reacts quickly with oxygen in the air. The high temperature and fine particle size allow for very rapid oxidation, often completing the roasting process in just a few seconds.

10. Why is roasting often preferred over direct smelting for sulfide ores?

Roasting is often preferred over direct smelting for sulfide ores because it removes sulfur as sulfur dioxide gas, which can be captured and used to produce sulfuric acid. This process also makes the subsequent smelting step more efficient and reduces environmental pollution by preventing the release of sulfur compounds during smelting.

11. What is the main purpose of calcination in metal extraction?

The main purpose of calcination in metal extraction is to remove volatile impurities, decompose carbonate ores, and convert hydroxides or other compounds into oxides. This process helps to prepare the ore for further processing steps like reduction or smelting.

12. What are some common examples of calcination reactions?

Common examples of calcination reactions include:

13. How does temperature affect the calcination process?

Temperature plays a crucial role in calcination. Higher temperatures generally increase the rate of decomposition and the removal of volatile components. However, the specific temperature required depends on the material being calcined and the desired outcome. Too high temperatures may cause unwanted reactions or changes in the material's structure.

14. How does the presence of moisture affect the calcination process?

The presence of moisture can significantly affect the calcination process. In some cases, it can hinder the process by absorbing heat and slowing down the decomposition reactions. However, in other cases, the presence of steam can actually enhance certain calcination reactions, such as in the production of quicklime from limestone.

15. How does the Ellingham diagram relate to roasting processes?

The Ellingham diagram is a graphical tool that shows the stability of metal oxides at different temperatures. In roasting processes, it helps predict whether a particular metal sulfide will oxidize under given conditions. The diagram can be used to determine the minimum temperature and oxygen partial pressure required for successful roasting of a specific ore.

16. What is calcination in metallurgy?

Calcination is a thermal treatment process in metallurgy where a material is heated to a high temperature below its melting point in the absence of air or in a limited supply of air. This process causes chemical or physical changes to the material, often resulting in the removal of volatile components or the decomposition of compounds.

17. How does calcination differ from pyrolysis?

While both calcination and pyrolysis involve heating materials in the absence of oxygen, they differ in their primary purposes and typical applications. Calcination usually aims to decompose or phase-transition inorganic compounds, often metal carbonates or hydroxides. Pyrolysis, on the other hand, typically refers to the thermal decomposition of organic materials, often resulting in the production of char, bio-oil, and gases.

18. How does the concept of Gibbs free energy apply to calcination reactions?

Gibbs free energy is a thermodynamic potential that measures the maximum reversible work that may be performed by a closed system under constant temperature and pressure. In calcination reactions, the change in Gibbs free energy (ΔG) determines whether the reaction will occur spontaneously. If ΔG is negative, the calcination reaction is thermodynamically favorable. The temperature at which ΔG becomes negative is the minimum temperature required for the calcination to proceed.

19. How does the presence of impurities affect the calcination process?

Impurities can significantly impact the calcination process. They may:

20. How does the particle size of the ore affect roasting efficiency?

Particle size significantly affects roasting efficiency. Smaller particles have a larger surface area-to-volume ratio, which increases their reactivity and allows for more complete and faster roasting. However, extremely fine particles can cause issues with dust formation and may require special handling techniques.

21. What are the environmental concerns associated with roasting processes?

The main environmental concerns associated with roasting processes include:

22. How does the fluidized bed roasting technique work?

In fluidized bed roasting, a stream of hot air or oxygen is blown upward through a bed of finely divided ore particles. This causes the particles to become suspended and behave like a fluid. The technique provides excellent heat transfer and gas-solid contact, resulting in rapid and uniform roasting of the ore particles.

23. What is the role of calcination in the cement manufacturing process?

In cement manufacturing, calcination is a crucial step where limestone (calcium carbonate) is heated to produce lime (calcium oxide) and carbon dioxide. This process occurs in the cement kiln and is essential for creating the reactive components of cement. The calcination reaction is: CaCO3 → CaO + CO2.

24. What is selective roasting?

Selective roasting is a technique used when an ore contains multiple metal sulfides. By carefully controlling the roasting conditions (temperature, air flow, time), it's possible to oxidize one metal sulfide while leaving others largely unchanged. This can be useful for separating different metals in complex ores.

25. How does calcination affect the porosity of materials?

Calcination often increases the porosity of materials. As volatile components are driven off during heating, they leave behind small voids or pores. This increased porosity can be beneficial in many applications, such as creating more reactive lime for steel making or producing catalysts with high surface areas.

26. What is the difference between dead roasting and partial roasting?

Dead roasting refers to the complete conversion of metal sulfides to oxides, with virtually all sulfur removed. Partial roasting, on the other hand, involves only partially oxidizing the sulfides, leaving some sulfur in the product. Partial roasting is sometimes used when a mixture of oxide and sulfide is desired for subsequent processing steps.

27. What is the significance of the dissociation temperature in calcination?

The dissociation temperature is the temperature at which a compound begins to break down into simpler substances. In calcination, it's crucial to reach and maintain temperatures above the dissociation temperature of the target compound to ensure complete decomposition. However, exceeding this temperature excessively may lead to unwanted side reactions or energy waste.

28. What is the role of roasting in the extraction of copper from chalcopyrite?

Roasting plays a crucial role in copper extraction from chalcopyrite (CuFeS2). The process converts the sulfide ore into an oxide, which is easier to reduce to metallic copper. The roasting reaction can be represented as:

29. What are some industrial applications of calcined materials?

Calcined materials have numerous industrial applications, including:

30. How does the presence of a reducing agent affect the roasting process?

The presence of a reducing agent during roasting can significantly alter the process and outcomes. Instead of oxidizing the ore, it may lead to reduction, changing the chemical composition of the product. This can be intentional, as in the case of reductive roasting, where the aim is to remove oxygen from metal oxides. However, unintended presence of reducing agents (like carbon from incomplete fuel combustion) can interfere with oxidative roasting processes.

31. What is the importance of air flow control in roasting operations?

Air flow control is crucial in roasting operations for several reasons:

32. How does the heat of reaction affect the calcination process?

The heat of reaction plays a significant role in calcination:

33. What is the difference between batch and continuous calcination processes?

Batch calcination involves processing a fixed amount of material at a time, with distinct loading, heating, cooling, and unloading steps. Continuous calcination, on the other hand, involves a constant flow of material through the calcination system, with continuous feeding and discharge. Continuous processes are often more efficient for large-scale operations, while batch processes may offer more flexibility for smaller operations or when frequent changes in material or conditions are needed.

34. How does the concept of activation energy relate to calcination and roasting processes?

Activation energy is the minimum energy required for a chemical reaction to occur. In calcination and roasting:

35. What is the role of residence time in calcination and roasting processes?

Residence time, the duration for which the material remains in the calcination or roasting environment, is crucial because:

36. How does the thermal conductivity of the material affect the calcination process?

Thermal conductivity of the material being calcined affects:

37. What are some methods used to monitor and control calcination processes in industry?

Industrial calcination processes are monitored and controlled using various methods:

38. How does the concept of thermogravimetric analysis (TGA) relate to calcination studies?

Thermogravimetric analysis (TGA) is a technique where the mass of a sample is measured over time as the temperature changes. It's highly relevant to calcination studies because:

39. What is the significance of the calcination atmosphere?

The atmosphere in which calcination occurs is significant because:

40. How does the concept of sintering relate to calcination processes?

Sintering, the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction, can occur during high-temperature calcination. It's important because:

41. What are some energy-efficient technologies used in modern calcination processes?

Modern calcination processes employ various energy-efficient technologies:

42. How does the presence of a catalyst affect roasting reactions?

Catalysts in roasting reactions can:

43. What is the role of roasting in the beneficiation of refractory gold ores?

Roasting plays a crucial role in the beneficiation of refractory gold ores:

44. How does the concept of heat capacity influence calcination processes?

Heat capacity, the amount of heat required to raise the temperature of a substance by one degree, is important