Extracting iron

The blast furnace

Iron is extracted from iron ore in a huge container called a blast furnace. Iron ores such as haematite contain iron(III) oxide, Fe2O3. The oxygen must be removed from the iron(III) oxide in order to leave the iron behind. Reactions in which oxygen is removed are called reduction reactions.

Blast furnace. Iron ore, carbon, limestone enter at top. Air enters at side near bottom. Three zones. Air into zone 1, waste gases out above zone 3. Slag out below zone 1, iron out at very bottom.

Carbon is more reactive than iron, so it can displace iron from iron(III) oxide. Here are the equations for the reaction:

Iron(III) oxide + carbon → iron + carbon dioxide

2Fe2O3(s) + 3C(s) → 4Fe(l) + 3CO2(g)

In this reaction, the iron(III) oxide is reduced to iron, and the carbon is oxidised to carbon dioxide.

In the blast furnace, it is so hot that carbon monoxide can be used, in place of carbon, to reduce the iron(III) oxide:

iron(III) oxide + carbon monoxide → iron + carbon dioxide

Fe2O3(s) + 3CO(s) → 2Fe(l) + 3CO2(g)

Raw materials for the reaction

Raw materialContainsFunction
Iron ore (haematite)Iron(III) oxideA compound that contains iron
CokeCarbonBurns in air to produce heat, and reacts to form carbon monoxide (needed to reduce the iron oxide)
LimestoneCalcium carbonateHelps to remove acidic impurities from the iron by reacting with them to form molten slag
AirOxygenAllows the coke to burn, and so produces heat

Removing impurities

The calcium carbonate in the limestone thermally decomposes to form calcium oxide.

calcium carbonate → calcium oxide + carbon dioxide

CaCO3(s) → CaO(s) + CO2(g)

The calcium oxide then reacts with silica (sand) impurities in the haematite, to produce slag - which is calcium silicate.

calcium oxide + silica → calcium silicate

CaO(s) + SiO2(s) → CaSiO3(l)

This reaction is a neutralisation reaction. Calcium oxide is basic (as it is a metal oxide) and silica is acidic (as it is a non-metal oxide).