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


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 Fe2O4) takes place.

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

                    3Fe2O3 + CO  2Fe3O4  + CO2Fe3O4 + 4CO  3Fe + 4CO2Fe2O3 + CO  2Fe3 + CO2

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

                           C + CO2     2COFeO + 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 + CO2CaO + SiO2   CaSiO3                              Calcium silicate                               (Slag)