Difference Between Calcination and Roasting

Difference Between Calcination and Roasting

Calcination and roasting are two important thermal processes used in metallurgy to extract metals from their ores. Though both involve heating, they are different in purpose, method, and chemical reactions.

1. Definition

• Calcination: Heating a metal ore in the absence of air or limited supply of air to remove volatile substances or decompose carbonates/ hydroxides.
• Roasting: Heating a sulfide ore in the presence of excess air to convert it into an oxide or to remove sulfur.

2. Purpose

• Calcination:
  • Removes water of crystallization from hydrated ores.
  • Decomposes carbonates into oxides.
  • Prepares ore for further extraction.
• Roasting:
  • Converts sulfide ores into oxides.
  • Removes sulfur or other volatile impurities.
  • Makes ore suitable for reduction.

3. Environment

• Calcination: Performed in limited air or an inert atmosphere.
• Roasting: Performed in the presence of excess oxygen or air.

4. Chemical Reaction

• Calcination:
  • Thermal decomposition reaction
  • Example: $$\text{CaCO}_3 \xrightarrow{\text{heat}} \text{CaO} + \text{CO}_2$$CaCO3​heat​CaO+CO2​
• Roasting:
  • Oxidation reaction
  • Example: $$2\text{ZnS} + 3\text{O}_2 \xrightarrow{\text{heat}} 2\text{ZnO} + 2\text{SO}_2$$2ZnS+3O2​heat​2ZnO+2SO2​

5. Type of Ore

• Calcination: Usually done for carbonate and hydroxide ores.
• Roasting: Done for sulfide ores.

6. Products

• Calcination: Produces metal oxides ready for reduction.
• Roasting: Produces metal oxides and sulfur dioxide gas.