C1aL9 Blast Furnace and Uses of Iron

Key Words

Blast furnace - Giant furnace in which hot air is blown in at high rate;

Brittle - breaks which hit hard.

Carbon dioxide - CO2, a gas.

Carbon monoxide - CO, a poisonous and reactive gas.

Cast iron - iron from a blast furnace, cast in a mould.

Coke - coal which has been heated (but not burned) to remove gases and other impurities.

Exothermic - reaction that gives out heat.

Haematite - iron ore, from which iron is extracted.

Hard - difficult to deform.

Impurities - other substances within the crystal structure of a metal.

Iron - element with a proton (atomic) number of 26 and a mass number of 56.

Layers - atoms within a crystal arranged one on top of another in a regular way.

Limestone - a rock containing calcium carbonate as its main mineral.

Molten - melted

Oxidation - adding oxygen to a substance

Reduction - taking oxygen away from a substance.

Regular - in a repeated and predictable pattern.

Rust - iron oxide.

Slag - calcium silicate, a waste product of producing iron.

Steel - an alloy between carbon and iron.

Strong - does not change shape easily.

 

Test Yourself

Homework
Chemistry GCSE
Home

Grade E

Iron is extracted from its ore, haematite, in a blast furnace.  Haematite is a mineral of which most is iron (III) oxide, Fe2O3.  Haematite is mixed with the following before it is heated in the blast furnace:

  • coke - the main element is carbon.

  • limestone - calcium carbonate to remove impurities.

  • hot air.

Cast iron is the product of the blast furnace.  It is hard and does not rust easily.  It is brittle due to the impurities contained in it.

Wrought iron is iron in its purest form.  It is easily shaped, but it's rather soft.

Steel is an alloy between iron and carbon.  Other elements can be added to alter the properties of the steel.  The alloy is easily shaped, but is strong, especially when in tension (pulling).

 

Grade C

The blast furnace is shown in the diagram:

It gets pretty hot in there, as shown in this diagram:

At the bottom, carbon reacts with the oxygen in the hot air:

carbon + oxygen  ® carbon dioxide

C + O2 ® CO2

The reaction is very exothermic, and it raises the temperature to 1900 oC.

The carbon dioxide reacts with carbon to give carbon monoxide:

carbon dioxide + carbon  ® carbon monoxide

CO2 + C  ® 2CO

The carbon monoxide reacts with the iron oxide, since carbon is more reactive than iron.  It snatches the oxygen from the iron:

carbon monoxide + iron oxide  ® carbon dioxide + iron

3CO + Fe2O3  ® 3CO2 + 2Fe

The limestone is there to remove impurities like silicon dioxide.  At  the high temperature in the furnace, limestone decomposes to calcium oxide and carbon dioxide:

calcium carbonate ®  calcium oxide + carbon dioxide

CaCO3 ® CaO + CO2

The calcium oxide reacts with the silicon dioxide to form calcium silicate:

calcium oxide + silicon dioxide ® calcium silicate

CaO + SiO2 ®  CaSiO3

The slag is less dense than the iron, so it floats.  It is removed and allowed to cool.  Although a waste product, the slag has a number of uses.

Iron from the blast furnace is not pure.  In the early days the iron from the blast furnace was cast into blocks called ingots.  The moulds were arranged in rows, and looked like little pigs feeding from a sow, hence the term "pig iron".  Nowadays it is poured straight into a giant railway vehicle called a torpedo wagon and taken for processing immediately.  Oxygen is blown through the molten iron, and reacts with the carbon.

 

Pure iron is rather weak and not very useful.  The atoms are arranged in layers like this:

This regular arrangement is called a crystal lattice.  The layers of atoms can move easily across each other, so that the material is easily shaped, but not very strong.

 

 

Grade A

In the blast furnace, oxidation and reduction reactions happen:

  • When a substance gains oxygen, it gets oxidised.
  • When a substance has the oxygen removed, the substance is reduced.

The oxidation and reduction are the reverse of each other, and occur at the same time.  Consider the reaction:

carbon monoxide + iron oxide  ® carbon dioxide + iron

3CO + Fe2O3  ® 3CO2 + 2Fe

The carbon monoxide is oxidised to carbon dioxide.  The iron oxide  is reduced to iron by the carbon monoxide.  Carbon monoxide is a reducing agent.

 

Steel is made when carbon and other impurities are added to the iron to make an alloy.  The crystal lattice is distorted:

The atoms of other elements stop the layers of iron moving across each other so easily, making steel a very strong material.

Specialist steels are made in an electric arc furnace.