Extraction of iron

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Reduction with carbon[edit]

  • 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[edit]

SiO2 and Al2O3 impurities[edit]

  • 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[edit]

  • 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[edit]

References[edit]