Question

Choose the correct code regarding the roasting process:
(I) It is the process of heating ore in air to obtain the oxide.
(II) It is an exothermic process.
(III) It is used for hydrated oxide and oxysalt ore.
(IV) It is used after the concentration of ore
A. I, II and III
B. I,II,IV
C. I,III,IV
D. I,II,III and IV

Answer 1

Hint: Roasting leads to the formation of a volatile oxide by heating the ore in the presence of oxygen. It occurs at very high temperatures just above the fusion point of the metal. Sulphides undergo this process as it can from a volatile oxide even in the presence of normal air containing oxygen.

Complete step by step answer:
Roasting always occurs after the ore undergoes concentration by the process called Froth Floatation. It is an important step that has to be carried out so as to form an oxide that can be acted upon by a reducing agent. This process occurs in the complete presence of air. It is generally exothermic in nature and can release large amounts of heat. It is carried out for the ores that contain sulphide in them.
For example: $PbS$ (lead sulphide), $ZnS$ (Zinc sulphide) etc.
These ores undergo combustion and can be represented by the following reactions:
$2$$PbS$$ + 2O_2 \to $ $2$$PbO + 2SO_2$
$2ZnS + 2O_2 \to 2ZnO + 2SO_2$
Thus, the oxides formed on combustion are volatile meaning that they can be easily reduced by different reducing agents like $CO$ , Coke and others to form an unrefined metal. This unrefined metal must further be processed in order to form a refined metal ready to be used.

So, the correct answer is Option B.

Note: Concentration in sulphide ores is carried out by the process of froth floatation. It is a characteristic feature of sulphide ore. Froth floatation uses the principle of Preferential wetting of gangue particles where in the gangue particles are wetted by water whereas the ore particles covered by pine oil floats to the top and is part of the froth.
Carbonate ores and oxy ores cannot undergo roasting. They are converted into volatile oxides by the process of Calcination. Calcination occurs in the complete or partial absence of air. It also employs the use of combustion.