A blast furnace is used to extract iron from iron ore. Iron ore, coke and limestone are put into the blast furnace. Coke is a form of carbon that is burned to provide heat and is also involved in some chemical reactions that place in the blast furnace.
When coke is burned it forms carbon dioxide and gives off heat, due to a limited quantity of oxygen, it reacts with carbon and is converted to carbon monoxide.
C + O2 --> CO2
C + CO2 --> 2CO
The carbon monoxide reacts with the iron oxide in the ore and the following reactions take place:
3Fe2O3 + CO --> 2Fe3O4 + CO2
Fe3O4 + CO --> 3FeO + CO2
FeO + CO --> Fe + CO2
The limestone is introduced into the blast furnace to eliminate impurities in the ore. It contains calcium carbonate that undergoes the following chemical reactions:
CaCO3 --> CaO + CO2
SiO2 + CaO --> CaSiO3
The calcium silicate floats on top of the molten ore and is called slag. It is removed regularly. Relatively pure iron is extracted at the base of the blast furnace.