Question

Heating pyrites to remove sulphur is called:
A ) smelting
B ) calcination
C ) liquation
D ) roasting

Answer 1

Hint: In all the processes, the ore is heated. But each process has its own purpose. Find out the process in which ore is heated to convert sulphide into oxide.

Complete answer:
Roasting involves heating the ore. The process of heating is carried out in a furnace in presence of air. Air is continuously supplied to the air. The temperature of the furnace is below the temperature at which the metal melts.
When sulphide ores are roasted, the following reactions occur.
\[{\text{2 ZnS}}{\text{ + 3}}{{\text{O}}_2}{\text{ }} \to {\text{ 2 ZnO + 2S}}{{\text{O}}_2} \\
{\text{2 PbS}}{\text{ + 3}}{{\text{O}}_2}{\text{ }} \to {\text{ 2 PbO + 2S}}{{\text{O}}_2} \\
{\text{2 C}}{{\text{u}}_2}{\text{S}}{\text{ + 3}}{{\text{O}}_2}{\text{ }} \to {\text{ 2 C}}{{\text{u}}_2}{\text{O + 2S}}{{\text{O}}_2} \\
{\text{ }} \\\]
Oxidation of zinc sulphide gives zinc oxide. Sulphur dioxide gas is the byproduct.
Oxidation of lead sulphide gives lead(II) oxide. Sulphur dioxide gas is the byproduct.
Oxidation of cuprous sulphide gives cuprous oxide. Sulphur dioxide gas is the byproduct.
In the above reactions, sulphide ore reacts with oxygen and is converted to oxide ore. Gain of oxygen is known as oxidation. Hence, metal sulphide ore is oxidized to metal oxide.
Heating pyrites to remove sulphur is called roasting. Pyrites are metal sulphide ores. Upon heating in presence of air, metal pyrites are converted to metal oxides and sulphur is removed as sulphur dioxide gas.

Hence, the option D ) is the correct option.

Additional Information: During smelting, metal ore is heated beyond its melting point to obtain either metal in elemental form or in simple compounds. Air and coke are the frequently used oxidising agents.
> Calcination is used to remove volatile substances such as water from metal ores. Calcination is also used to oxidise metal ores.
> In liquidation, one of the metals is separated from the ore or alloy by heating to its melting temperature.

Note: During roasting various reactions that occur are reduction, oxidation, chlorination, sulfation and pyro hydrolysis. Toxic by products such as acidic compounds and metallic compounds are obtained.