Extracting iron
The blast furnace
Iron is extracted from iron A rock containing enough quantities of a mineral for extraction to be possible. in a huge container called a blast furnace. Iron ores such as haematite contain iron(III) oxide, Fe2O3. The oxygen must be removed from the iron(III) oxide in order to leave the iron behind. Reactions in which oxygen is removed are called reduction reactions.
Raw materials for the reaction
| Raw material | Contains | Function |
| Iron ore (haematite) | Iron(III) oxide (Fe2O3) | A compound that the iron is extracted from |
| Coke | Carbon (C) | Used as a fuel and reacts to form carbon monoxide (needed to reduce the iron(III) oxide) |
| Limestone | Calcium carbonate (CaCO3) | Helps to remove acidic impurities from the iron by reacting with them to form molten slag |
| Air | Oxygen (O2) | Provides oxygen to allow the coke to burn, and so produces heat |
| Raw material | Iron ore (haematite) |
|---|---|
| Contains | Iron(III) oxide (Fe2O3) |
| Function | A compound that the iron is extracted from |
| Raw material | Coke |
|---|---|
| Contains | Carbon (C) |
| Function | Used as a fuel and reacts to form carbon monoxide (needed to reduce the iron(III) oxide) |
| Raw material | Limestone |
|---|---|
| Contains | Calcium carbonate (CaCO3) |
| Function | Helps to remove acidic impurities from the iron by reacting with them to form molten slag |
| Raw material | Air |
|---|---|
| Contains | Oxygen (O2) |
| Function | Provides oxygen to allow the coke to burn, and so produces heat |
Carbon is more The tendency of a substance to undergo a chemical reaction. than iron, so it can Take the place of another substance in a chemical reaction. For example, a metal can displace a less reactive metal from its oxide, removing oxide ions from the less reactive metal and becoming an oxide itself. iron from iron(III) oxide. Here are the equations for the reaction.
Step 1 鈥 Hot air (oxygen) reacts with the coke (carbon) to produce carbon dioxide and heat energy to heat up the furnace.
C(s) + O2(g) 鈫 CO2(g)
Step 2 鈥 More coke is added to the furnace and reduces the carbon dioxide into carbon monoxide, a good reducing agent.
CO2(g) + C(s) 鈫 2CO(g)
Step 3 鈥 iron(III) oxide is reduced.
iron(III) oxide + carbon 鈫 iron + carbon dioxide
2Fe2O3(s) + 3C(s) 鈫 4Fe(l) + 3CO2(g)
In this reaction, the iron(III) oxide is The loss of oxygen, gain of electrons, or gain of hydrogen by a substance during a chemical reaction. to iron, and the carbon is The gain of oxygen, or loss of electrons, by a substance during a chemical reaction. to carbon dioxide.
In the blast furnace, it is so hot that carbon monoxide can be used, in place of carbon, to reduce the iron(III) oxide:
iron(III) oxide + carbon monoxide 鈫 iron + carbon dioxide
Fe2O3(s) + 3CO(g) 鈫 2Fe(l) + 3CO2(g)
Removing impurities
The calcium carbonate in the Using heat. If a substance decomposes, it breaks down into simpler compounds or elements. to form calcium oxide.
calcium carbonate 鈫 calcium oxide + carbon dioxide
CaCO3(s) 鈫 CaO(s) + CO2(g)
The calcium oxide then reacts with silica (sand) impurities in the haematite, to produce slag 鈥 which is calcium silicate. This is separated from the iron and used to make road surfaces.
calcium oxide + silica 鈫 calcium silicate
CaO(s) + SiO2(s) 鈫 CaSiO3(l)
This reaction is a The reaction between an acid and a base to form a salt plus water. reaction. Calcium oxide is Bases react with acids to make salts, and form alkaline solutions if they dissolve in water. Substances or solutions that act as bases are said to be basic. (as it is a metal oxide) and silica is Having a pH lower than 7. (as it is a non-metal oxide).
Choice of blast furnace site
There are a number of important factors to consider when choosing the site of a blast furnace. A blast furnace should be:
- near the coast to allow for the import of raw materials
- near roads and railway lines to allow for products to be taken to where they are needed
- near a town or city, so that workers have somewhere to live close-by
- away from built-up areas, so that the noise and pollution of the site do not affect the local population
Port Talbot, in south Wales, is a good example of a suitable site for a blast furnace.