blast furnace

• Iron ore is the source of iron
• Coke is used as a fuel and to produce carbon monoxide for the reduction
• The BF process involves heating iron ore, coke, and limestone at high temperatures (1500-2000°C) in a large cylindrical container called a blast furnace.
• Limestone is added to remove impurities from the iron oxides
• Slag formation when limestone breaks down and reacts with sand from the rocks
• Hot air provides oxygen so that coke can burn and release carbon dioxide
• Blast furnace

  A) slag outlet

  B) hot air blast

  C) iron outlet

  D) brick lining

  E) reaction mixture

  F) iron ore, coke and limestone

  G) waste gases (CO2) used to heat air for blast

  H) the furnace

  
• Reduction reactions are exothermic because they involve breaking bonds between atoms which releases energy
• There are 4 main stages to the extraction of iron using the blast furnace: combustion, reduction, decomposition and neutralisation
• Combustion – carbon to carbon monoxide
• Reduction – iron (III) oxide to iron
• Decomposition – calcium carbonate to calcium oxide
• Neutralisation – calcium oxide and silicon oxide neutralisation
• Combustion:

  The coke (carbon) is burned to form carbon monoxide:

  carbon + oxygen -> carbon monoxide

  2C (s) + O2 (g) -> 2CO (g)
• Stage 2 – Reduction

  The carbon monoxide reduces the iron (III) oxide to iron:

  Iron (III) oxide + carbon monoxide -> Iron + carbon dioxide

  Fe2O3 (s) + 3CO (g) -> 2Fe (l) + 3CO2 (g)
• decomposition and neutralisations are used to remove impurities
• slag is molten rock that floats on top of the liquid iron and can be easily skimmed off.
• Stage 3 – Decomposition

  The limestone (calcium carbonate) decomposes in the heat to form calcium oxide:

  calcium carbonate + heat -> calcium oxide + carbon dioxide CaCO3 (s) + heat -> CaO (s) + CO2 (g)
• Stage 4 – Neutralisation

  The calcium oxide (stage 3) then reacts with silica (sand) impurities in the haematite, to produce slag - which is calcium silicate. The calcium oxide (which is basic – metal oxide) from neutralises the silica (which is acidic – non-metal oxide): calcium oxide + silicon dioxide (silica) -> calcium silicate (slag)

  CaO (s) + SiO2 (s) -> CaSiO3 (l)