Extraction of metals/Iron

Subject classification: this is a chemistry resource.

Reduction with carbon

• Iron is extracted from its ore, haematite, by reduction with carbon.
• This takes place in a blast furnace (named after blasts of air [20% oxygen], heated to 1000 °C, which are blasted into the bottom of the furnace):
• A mixture of crushed iron ore, coke (an almost pure form of carbon) and limestone is fed into the top of the blast furnace.
• The coke is oxidised to carbon dioxide:

C + O₂ → CO₂

The reaction is exothermic.

• The carbon dioxide reacts with coke to form carbon monoxide.

CO₂ + C → 2CO

The reaction is endothermic.

• Iron(III) oxide in the ore is reduced to iron by the carbon monoxide.

Fe₂O₃ + 3CO → 2Fe + 3CO₂

The reaction is exothermic.

• The iron falls to the bottom of the blast furnace where it melts

Removing impurities

SiO₂ and Al₂O₃ impurities

• Limestone, or calcium carbonate (CaCO₃), is used to removed impurities
• CaCO₃ decomposes in the blast furnace to calcium oxide:

CaCO₃(s) → CaO(s) + CO₂(g)

• The CaO then reacts with SiO₂ and Al₂O₃ impurities:

CaO(s) + SiO₂ → CaSiO₃(s)

CaO(s) + Al₂O₃ → CaAl₂O₄(s)

• The CaSiO₃ and CaAl₂O₄ is less dense than the iron so it forms a slag which floats on top of the iron
• The slag can then be removed.

Sulphur impurities

• Magnesium powder is added to the molten pig iron to remove sulphur impurities
• Magnesium reacts with sulphur to form magnesium sulphides which are removed as slag

See also

• media files (at commons)

References

• List of the world's largest producers of iron ore