Metallurgical operations- Step 3- Reduction of oxide(Pyrometallurgy of iron)

Question 1

What is pyrometallurgy?

Answer 1

The process of extracting a metal by heating a metal oxide with a suitable reducing agent to an appropriate temperature. It is thermal reduction in the presence of a reducing agent.

Question 2

What is smelting?

Answer 2

The process of extracting a metal by reduction of its oxide by heating with carbon

Question 3

What are the steps in the extarction of iron

Answer 3

1. Concentration by magnetic separation
2. Calcination
3. Smelting in a Blast furnace
4. Refining by heating pig iron in a reverberatory
   furnace lined with haematite

Question 4

What is the furnace charge consist of in the extration of iron in the blast furnace?

Answer 4

Iron ore(oxides of iron) + coke + limestone

Question 5

What is the reducing agent in the upper part of the blast furnace at lower temperature?

Answer 5

CO

Question 6

What is the role of coke in the blast furnace?

Answer 6

Acts as a fuel and areducing agent in the lower part of the blast furnace at high temperature

Question 7

What is the role of limestone?

Answer 7

It decomposes to give the flux- CaO

CaCO3 → CaO + CO2

Question 8

What is the gangue present in the iron ore? How is it removed?

Answer 8

Silica or sand is the gangue(acidic). It is removed by heating with the basic flux CaO to form slag CaSiO3
CaO + SiO2 → CaSiO3
The slag is in molten state and separates out from iron.

Question 9

What is pig iron?

Answer 9

The molten iron as it comes out of the blast furnace is called as pig iron

Question 10

Write down the reactions taking place in different zones in the blast furnace during the extraction of iron.

Answer 10

At 500 – 800 K (lower temperature range in the blast furnace) –
3 Fe2O3 + CO → 2 Fe3O4 + CO2 
Fe3O4 + 4 CO → 3Fe + 4 CO2 
Fe2O3 + CO → 2FeO + CO2
At 900 – 1500 K (higher temperature range in the blast
furnace):
C + CO2 → 2 CO 
FeO + CO → Fe + CO2

Question 11

What is wrought iron? How is pig iron converted to wrought iron?

Answer 11

Wrought iron or malleable iron is the
purest form of commercial iron and is
prepared from cast iron by oxidising impurities in a
reverberatory furnace lined with haematite. This
haematite oxidises carbon to carbon monoxide:
Fe2O3 + 3 C → 2 Fe + 3 CO

Question 12

Distinguish between cast iron and wrought iron

Answer 12

Cast iron is brittle while wrought is malleable and ductile..

Question 13

Name the oxide ores of iron

Answer 13

haematite- Fe2O3

magnetite- Fe3O4

Question 14

Name the sulphide ore of iron

Answer 14

iron pyrites-FeS2

Question 15

Name the carbonate ore of iron

Answer 15

Siderite-FeCO3