During the extraction of iron, the reduction of iron oxides takes place in the blast furnace. In this process, hot air is blown from the bottom of the furnace and coke is burnt to raise the temperature up to 2200 K in the lower portion itself. The temperature is lower in the upper part. Thus, it is the lower part where the reduction of iron oxides (Fe₂O₃ and Fe₃O₄) takes place.

The reactions taking place in the lower temperature range (500 - 800 K) in the blast furnace are:

3Fe₂O₃ + CO   →  2Fe₃O_{4 +} CO₂

Fe₃O₄ + 4CO   →  3Fe  + 4CO₂

Fe₂O₃ + CO    →  2Fe₃ + CO₂  

The reactions taking place in the higher temperature range (900 - 1500 K) in the blast furnace are:

C +CO₂   →  2CO

FeO + CO  → Fe  + CO₂

The silicate impurity of the ore is removed as slag by calcium oxide (CaO), which is formed by the decomposition of limestone (CaCO₃).

CaCO₃  →  CaO  + Co₂

CaO + SiO₂   →  CaSiO₃

                   Calcium silicate (Slag)