Extraction of metals/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
editSiO2 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- media files (at commons)