Blast furnaces are used for extracting fairly reactive metals (e.g. iron, zinc) by reducing the metal oxide with carbon.

Iron extraction from its oxides[edit | edit source]

Iron is extracted from haematite and magnetite (different oxides of iron). This happens in a blast furnace. A blast furnace is roughly 50m high, and lined with heat–resistant bricks. The haematite (the ‘charge’) is loaded into the blast furnace, along with coke (heated coal) and limestone. A blast of hot air is sent through two tuyeres near the bottom of the furnace. This makes the haematite glow – as the coke burns in the heated air – C+O2 --> CO2 After this, a number of other reactions take place

  • Limestone decomposes–

CaCO3-->CaO+CO2

  • The carbon dioxide reacts with more coke producing carbon monoxide

CO2+C --> 2CO

  • Carbon monoxide is a reducing agent. It reduces the iron ore (temp. – 700o)

Fe2O3 + 3CO --> 2Fe + 3CO2

  • This molten iron falls to the bottom of the furnace
  • The calcium oxide reacts with impurities (acidic as it is alkaline) to form slag. The main impurity is silicon oxide, meaning that the slag is mainly calcium silicate.

CaO + SiO2--> CaSiO3

  • This slag also trickles to the bottom where it floats on top of the iron as it is less dense.
  • The iron is tapped off out of the furnace (as well as the slag)
  • Waste gases escape from the top of the furnace.
  • Slag is used by builders and road makers for foundations.
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