ZIMSEC O Level Combined Science Notes: Extraction of iron: The blast furnace

  • After iron ore is mined it is send to the blast furnace
  • Iron is extracted from its ore in a blast furnace


The structure of a blast furnace. Image credit s-cool.co.uk

The structure of a blast furnace. Image credit s-cool.co.uk

  • The oxide ores are reduced to iron by removing the oxygen from them
  • Coke, limestone and iron ore are fed into the top of the furnace
  • Hot air is forced through tuyeres (openings)
  • This burns the coke and in the process provide the heat required for the smelting process to take place
  • Near the base of the furnace the carbon in the coke combines with oxygen to give carbon monoxide
  • The equation for this process is:
  • \text{carbon+oxygen}\rightarrow\text{carbon dioxide}
  • Carbon monoxide is formed because there is not enough oxygen to make carbon dioxide
  • Higher up in the furnace the carbon monoxide reduces the iron oxide
  • Iron and carbon dioxide are given off as end products
  • \text{carbon monoxide+iron oxide}\rightarrow\text{iron+carbon dioxide}
  • In the middle of the furnace the iron oxide is reduced by the carbon in the coke
  • \text{iron oxide+carbon}\rightarrow\text{iron+carbon monoxide}
  • Molten iron formed by the reduction of the ore flows down the furnance and collections in the hearth
  • It is then run off through tap holes into large ladles and
  • Taken to the steel plants
  • Limestone added with the ore at the top of the furnace decomposes in the furnace
  • To give calcium oxide
  • The equation for the process is:
  • \text{calcium carbonate}\xrightarrow{heat}\text{calcium oxide+carbon oxide}
  • The calcium oxide reacts with silicon dioxide (sand impurities) in the iron ore to form calcium silicate
  • Calcium silicate is also known as slug
  • \text{calcium oxide+silicon dioxide}\rightarrow\text{calcium silicate}
  • The molten slug collects at the base of the furnace
  • The slug is less dense than the molten iron so it floats on top and
  • Can be tapped off at a different part of the furnace

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