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 is the process of heating sulphide ores in the presence of air. It converts the sulphide ores into metal oxides, liberating sulphur dioxide gas. A general example for a sulphide ore:

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

Calcination is the process of heating carbonate or hydroxide ores in the absence of air. This decomposes the ores into metal oxides, liberating carbon dioxide or water. General examples for a carbonate and hydroxide ore:

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

Metal Reduction:

After roasting or calcination, the metal oxide is reduced to obtain the pure metal. This is commonly done using carbon (coke) as a reducing agent in a smelting furnace. A general example:

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