Extraction of metals/Iron

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 &rarr; CO2
 * The reaction is exothermic.


 * The carbon dioxide reacts with coke to form carbon monoxide.
 * CO2 + C &rarr; 2CO
 * The reaction is endothermic.


 * Iron(III) oxide in the ore is reduced to iron by the carbon monoxide.
 * Fe2O3 + 3CO &rarr; 2Fe + 3CO2
 * The reaction is exothermic.


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

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