Blast furnaces are used for extracting fairly reactive metals (e.g. iron, zinc) by reducing the metal oxide with carbon.
Iron extraction from its oxidesEdit
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–
- 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.