Short Answer:

Calcination is a metallurgical process in which ores are heated strongly in the absence or limited supply of air. This process is used to remove moisture, carbon dioxide, and other volatile impurities from ores, producing an oxide form of the metal.

For example, limestone (CaCO₃) is calcined to form calcium oxide (CaO) and carbon dioxide (CO₂). Calcination is an important step in metallurgy because it prepares ores for further extraction of metals and improves the efficiency of reduction processes.

Detailed Explanation:

Calcination

Calcination is a process in metallurgy in which metallic ores are heated to high temperatures in a limited supply of air or in the absence of oxygen. It is primarily used for carbonates and hydrated ores. The main objective of calcination is to remove volatile substances and convert the ore into a metal oxide, which is easier to reduce during metal extraction.

Purpose of Calcination

1. Removal of Moisture:
   • Many ores, such as bauxite or limestone, contain water in their crystal structure.
   • Heating these ores drives off water as steam, producing a dry, powdery oxide.
   • Example: CaCO₃·H₂O → CaCO₃ + H₂O
2. Removal of Carbon Dioxide and Other Volatile Impurities:
   • Carbonates decompose upon heating to produce metal oxides and CO₂.
   • Example: CaCO₃ → CaO + CO₂
   • This makes the ore ready for reduction to pure metal.
3. Conversion to Oxide Form:
   • Oxide ores are easier to reduce using carbon, carbon monoxide, or electrolysis.
   • Calcination ensures that the metal is in a form suitable for further processing.

Examples of Calcination

1. Limestone (Calcium Carbonate):
   • CaCO₃ → CaO + CO₂
   • Calcium oxide (quicklime) is used in cement, steel, and chemical industries.
2. Bauxite (Aluminum Ore):
   • Al₂O₃·xH₂O → Al₂O₃ + xH₂O
   • Calcination removes water and prepares aluminum oxide for electrolysis.
3. Magnesite (Magnesium Carbonate):
   • MgCO₃ → MgO + CO₂
   • Magnesium oxide is used in refractory materials and chemical industries.

Methods of Calcination

• Ores are heated in rotary kilns, reverberatory furnaces, or vertical shaft kilns.
• Temperature is controlled to ensure decomposition without melting.
• The process is carried out in the absence of excess air to prevent oxidation of metals like lead or copper in ores.

Difference from Roasting

Feature	Calcination	Roasting
Air supply	Limited or no air	Excess air
Ores treated	Carbonates and hydrated ores	Sulfide ores
Purpose	Remove moisture and CO₂	Convert sulfides to oxides
Products	Metal oxide + volatile impurities	Metal oxide + SO₂

Industrial Importance

1. Preparation for Reduction:
   • Calcined ores are more reactive and easier to reduce to metals.
2. Production of Industrial Materials:
   • Calcium oxide, magnesium oxide, and aluminum oxide obtained by calcination are important in cement, refractories, and chemical industries.
3. Purification:
   • Removes volatile impurities, making the ore more concentrated and ready for smelting or electrolysis.

Environmental Considerations

• CO₂ released during calcination contributes to greenhouse gas emissions.
• Proper measures, such as capturing CO₂ for industrial use, are important to reduce environmental impact.

Summary

Calcination is a process of heating ores in limited air to remove moisture, carbon dioxide, and other volatile impurities. It converts carbonate or hydrated ores into oxides, making them ready for reduction or further processing in metallurgy.

Conclusion:

Calcination is an essential metallurgical process used to prepare ores for metal extraction. By removing moisture and volatile impurities and converting ores into oxides, calcination increases the efficiency of reduction processes and produces industrially useful oxides. It is widely applied in metallurgy, cement, and chemical industries.