### 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 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.