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

To access more topics go to the Combined Science Notes page.

Quick NetOne, Telecel, Africom, And Econet Airtime Recharge

If anything goes wrong, chat with us using the chat feature at the bottom right of this screen