Redox, extraction of iron and transition metalsExtracting iron

Redox reactions are involved in the extraction of metals from their ores, eg extracting iron by reduction within the blast furnace. Transition metals have high melting points and densities, form coloured compounds and act as catalysts.

Part of Chemistry (Single Science)Metals and their extraction

Extracting iron

The blast furnace

Iron is extracted from iron 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
Blast furnace. Iron ore, carbon, limestone enter at top. Air enters at side near bottom. Three zones. Air into zone 1, waste gases out above zone 3. Slag out below zone 1, iron out at very bottom.

Carbon is more than iron, so it can iron from iron(III) oxide. Here are the equations for the reaction.

Step 1 – Hot air (oxygen) reacts with the coke (carbon) to produce carbon dioxide and heat energy to heat up the furnace.

C(s) + O2(g) → CO2(g)

Step 2 – More coke is added to the furnace and reduces the carbon dioxide into carbon monoxide, a good reducing agent.

CO2(g) + C(s) → 2CO(g)

Step 3 – iron(III) oxide is reduced.

iron(III) oxide + carbon → iron + carbon dioxide

2Fe2O3(s) + 3C(s) → 4Fe(l) + 3CO2(g)

In this reaction, the iron(III) oxide is to iron, and the carbon is 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 → iron + carbon dioxide

Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)

Removing impurities

The calcium carbonate in the limestone to form calcium oxide.

calcium carbonate → calcium oxide + carbon dioxide

CaCO3(s) → CaO(s) + CO2(g)

The calcium oxide then reacts with silica (sand) impurities in the haematite, to produce slag – which is calcium silicate. This is separated from the iron and used to make road surfaces.

calcium oxide + silica → calcium silicate

CaO(s) + SiO2(s) → CaSiO3(l)

This reaction is a reaction. Calcium oxide is (as it is a metal oxide) and silica is (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.