Question

With the help of chemical equations, differentiate between roasting and calcination. How is metal reduced from the product obtained after roasting/calcination of the ore? Write the chemical equation for the reaction involved.

Answer 1

Roasting vs. Calcination:

Roasting involves heating sulphide ores in air, transforming them into metal oxides and releasing sulphur dioxide gas. Example:

\[ 2ZnS(s) + 3O_2(g) \rightarrow 2ZnO(s) + 2SO_2(g) \]

Calcination heats carbonate or hydroxide ores without air, decomposing them into metal oxides and releasing carbon dioxide or water. Examples:

\[ CaCO_3(s) \rightarrow CaO(s) + CO_2(g) \] \[ 2Fe(OH)_3(s) \rightarrow Fe_2O_3(s) + 3H_2O(g) \]

Metal Reduction:

Following roasting or calcination, the metal oxide is reduced to obtain the pure metal. Carbon (coke) is frequently employed as a reducing agent in smelting furnaces. General example:

\[ MO(s) + C(s) \rightarrow M(l) + CO(g) \]