Blast furnaces are structures used mainly in extracting metals, mainly iron and copper, from their ores. The ores are reduced by the action of CO and the removal of oxygen from the metal oxide in order to obtain the metal.
Iron usually occurs in the Earth’s crust as ore. The most common ore is Haematite, which is iron oxide. This is a compound of iron combined with oxygen. In blast furnaces, the oxygen is removed from the iron. The iron is reduced.
Hematite is fed into the top of the furnace along with limestone and carbon. Hot air is ‘blasted’ through the base of the furnace.
Â Blast furnace reactions:
1. The carbon burns in the oxygen of the air to form carbon dioxide.
carbon + oxygen ->carbon dioxide
2. The carbon dioxide reacts with more carbon to form carbon monoxide (CO).
Fe2O3 + 3CO -> 2Fe + 3CO2
The iron still contains lots of impurities. The heat of the furnace changes the limestone into calcium oxide and carbon dioxide. The calcium oxide reacts with the silicon oxide impurities in the iron to produce calcium silicate. The calcium silicate (slag) is skimmed off the top of the molten iron. The slag is use for making roads.