Extraction of Iron from Hematite (Cambridge O Level Chemistry)

• Iron is extracted in a large container called a blast furnace from its ore, hematite 
• Modern blast furnaces produce approximately 10,000 tonnes of iron per day 
• The process is demonstrated and explained below:

Diagram showing the carbon extraction of iron

• The raw materials: iron ore (hematite), coke (an impure form of carbon), and limestone are added into the top of the blast furnace
• Hot air is blown into the bottom
• Zone 1:
  • Coke burns in the hot air forming carbon dioxide 
  • The reaction is exothermic so it gives off heat, heating the furnace

carbon + oxygen → carbon dioxide

• Zone 2:
  • At the high temperatures in the furnace, more coke reacts with carbon dioxide forming carbon monoxide
  • Carbon dioxide has been reduced to carbon monoxide

carbon + carbon dioxide → carbon monoxide

• Zone 3:
  • Carbon monoxide reduces the iron(III) oxide in the iron ore to form iron 
  • This will melt and collect at the bottom of the furnace, where it is tapped off:

iron(III) oxide + carbon monoxide  →  iron + carbon dioxide

• Limestone (calcium carbonate) is added to the furnace to remove impurities in the ore.
  • The calcium carbonate in the limestone thermally decomposes to form calcium oxide

calcium carbonate → calcium oxide + carbon dioxide

• The calcium oxide formed reacts with the silicon dioxide, which is an impurity in the iron ore, to form calcium silicate
• This melts and collects as a molten slag floating on top of the molten iron, which is tapped off separately

calcium oxide + silicon dioxide →  calcium silicate

• The symbol equations for the different stages of the extraction of iron from hematite are:
  
  
• Zone 1: The burning of carbon (coke) to provide heat and produce carbon dioxide:

C (s)  +  O₂ (g)  →  CO₂ (g)

• Zone 2: The reduction of carbon dioxide to carbon monoxide:

CO₂ (g)  +  C (s)  →  2CO (g)

• Zone 3: The reduction of iron(III) oxide by carbon monoxide:

Fe₂O₃ (s)  +  3CO (g)  →  2Fe (I)  +  3CO₂ (g)

• The thermal decomposition of calcium carbonate (limestone) to produce calcium oxide:

CaCO₃ (s)  →  CaO (s)  +  CO₂ (g)

• The formation of slag:

CaO (s)  +  SiO₂ (s)  →  CaSiO₃ (l)