The correct option is Calcination.
Explanation
In metallurgy, the extraction of metals from their ores often involves converting the concentrated ore into a metal oxide prior to reduction. The method chosen depends on the chemical nature of the ore, specifically whether it is a carbonate or a sulfide.
Detailed Analysis:
- Calcination (Correct): This is the process of heating an ore below its melting point in the absence or limited supply of air. It is primarily used for carbonate ores and hydrated ores. During this process, volatile impurities are removed, and carbon dioxide is released, leaving behind a metal oxide.
Example: Zinc carbonate is heated to form zinc oxide and carbon dioxide ($ZnCO_3 \xrightarrow{\text{heat}} ZnO + CO_2$). - Roasting: This process involves heating the ore below its melting point in the presence of excess air. It is generally applied to sulfide ores to convert them into oxides while releasing sulfur dioxide.
Example: Zinc sulfide is heated with oxygen ($2ZnS + 3O_2 \xrightarrow{\text{heat}} 2ZnO + 2SO_2$). - Smelting: This is a pyrometallurgical process where the roasted or calcined ore is mixed with a reducing agent (such as coke) and heated to a high temperature to extract the metal in a molten state.
- Electrorefining: This is a purification technique where impure metal is refined using electrolysis to obtain high-purity metal.
Key Takeaway:
Calcination is used for Carbonate ores in limited air (C for C), whereas Roasting is used for Sulfide ores in excess air.