In a blast furnace the iron (iii) oxide Fe2O3 is converted to iron. There are different temperature zones created a blast furnace. At each of the temperature zones a different chemical reaction takes place.
At temperatures ranging between 200 and 700 degree Celsius, the iron(iii) oxide Fe2O3 is converted to iron(ii, iii) oxide Fe3O4. The reaction for this is: 3Fe2O3 + CO --> 2Fe3O4 + CO2
At a higher temperature around 850 degree Celsius, iron(ii, iii) oxide is converted to iron(ii) oxide
Fe3O4 + CO --> 3FeO + CO2
Finally at temperatures around 1200 degree Celsius, iron(ii) oxide is converted to iron
FeO + CO --> Fe + CO2
All the equations taken together describe how iron(iii) oxide is converted to iron and carbon dioxide.