Extracting Iron
Chemistry: Cambridge International GCSE Supplement, topic 9.6.2
Extracting Iron (Blast Furnace)
A blast furnace is an industrial reactor that is used to extract iron from its ore (called haematite). The extraction of iron from its ore uses the principle of reduction reactions. Oxygen is removed from iron using the more reactive carbon.
Carbon dioxide formed
- Iron ore, limestone and coke (carbon) are fed into the top of the blast furnace.
- Hot air is blasted in from the bottom.
- The carbon reacts with the oxygen to form carbon dioxide and a lot of heat.
- C(s) + O2(g) → CO2(g)
- This reaction is exothermic and provides the high temperature that the other reactions need.
Carbon monoxide formed
- The carbon dioxide reacts with more coke higher up the blast furnace. Carbon monoxide is formed.
- C02 + C(s) → 2CO(g)
- This reaction is endothermic.
Molten iron formed
- The haematite is reduced by the carbon monoxide to molten iron.
- Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)
Limestone decomposes
- Limestone is added as a cleaning agent to react with acidic oxides (Al2O3 and SiO2) impurities.
- The limestone decomposes because of the high temperatures.
- CaCO3 → CaO(s) + CO2(g)
Molten slag formed
- The calcium oxide reacts with silicon(IV) oxide, which is one of the main impurities in the blast furnace.
- This reaction forms calcium silicate, which forms a layer of slag above the molten iron.
- CaO(s) + SiO2(s) → CaSiO3(l)
Uses
- Slag is used in road and rail construction.
- The iron produced is called pig/cast iron. Most pig iron is turned into steel.
Test yourself on Extracting Iron
Blast Furnace
Which of these isn't formed at some stage in a blast furnace?
Which of these chemical reactions does not take place inside a blast furnace?