Metallurgical operations-Step 2- Conversion of ore to oxide

Question 1

Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?

Answer 1

The Gibbs energy of formation of most sulphides are greater than that for CS2(endothermic compond) but lesser for CO or CO2(exothermic compound). So sulphides are converted to oxides and then reduced to metal

Question 2

What is roasting?

Answer 2

Roasting: In roasting, the ore is heated in a
regular supply of air in a furnace at a
temperature below the melting point of the
metal. Some of the reactions involving
sulphide ores are:
2ZnS + 3O2 → 2ZnO + 2SO2 
2PbS + 3O2 → 2PbO + 2SO2 
2Cu2S + 3O2 → 2Cu2O + 2SO2

Question 3

What is calcination?

Answer 3

Calcination: Calcination involves heating in a limited supply of air when the volatile matter
escapes leaving behind the metal oxide:
Fe2O3.xH2O(s) → Fe2O3 (s) + xH2O(g) (6.6)
ZnCO3 (s) → ZnO(s) + CO2(g) (6.7)
CaCO3.MgCO3(s) → CaO(s) + MgO(s ) + 2CO2(g)

Question 4

Which ores are roasted?

Answer 4

sulphide ores

Question 5

Which ores are calcined?

Answer 5

carbonate ores or hydrated ores

Question 6

What is flux?

Answer 6

Flux is a substance added to remove gangue in the form of slag. Slag separates more easily from
the ore than the gangue. This way, removal of gangue becomes easier
Flux + gangue → Slag

Question 7

What are the types of flux? give examples for each type

Answer 7

Flux is of two kinds- Acidic(SiO2) and basic(CaO)

Question 8

What is the physical state of slag?

Answer 8

Molten