Cambridge (CIE) IGCSE Your notes
Chemistry
Extraction of Metals
Contents
Extraction of Metals
Extraction of Iron from Hematite
Extraction of Aluminium from Bauxite
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Extraction of Metals
Your notes
Extraction of Metals
The Earth’s crust contains metals and metal compounds such as gold, copper, iron oxide
and aluminium oxide
Useful metals are often chemically combined with other substances forming ores:
A metal ore is a rock that contains enough of the metal to make it worthwhile
extracting
They have to be extracted from their ores through processes such as electrolysis, using
a blast furnace or by reacting with more reactive material
In many cases the ore is an oxide of the metal, therefore the extraction of these metals is
a reduction process since oxygen is being removed
Common examples of oxide ores are iron and aluminium ores which are
called hematite and bauxite respectively
Unreactive metals do not have to be extracted chemically as they are often found as
the uncombined element
This occurs as they do not easily react with other substances due to
their chemical stability
They are known as native metals and examples include gold and platinum which can
both be mined directly from the Earth’s crust
The position of the metal on the reactivity series influences the method of extraction
Those metals placed higher up on the series (above carbon) have to be extracted using
electrolysis
Metals lower down on the series can be extracted by heating with carbon
The Extraction Method Depends on the Position of a Metal in the Reactivity Serie
Metal Method of Extraction
Most reactive
Potassium Extracted by electrolysis of molten chloride or molten oxide
Large amount of electricity required so expensive process
Sodium
Lithium
Calcium
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Magnesium
Your notes
Aluminium
Carbon
Zinc Extracted by heating with reducing agent such as carbon or carbon
monoxide
Iron
Hydrogen
Copper Found as pure elements (copper may have to be extracted from it's ore by
heating with carbon or hydrogen)
Silver
Gold
Least reactive
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Extraction of Iron from Hematite
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Extraction of iron from hematite
Iron is extracted in a large container called a blast furnace from its ore, hematite
Modern blast furnaces produce approximately 10,000 tonnes of iron per day
The blast furnace
Diagram showing the carbon extraction of iron
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The raw materials: iron ore (hematite), coke (an impure form of carbon), and limestone
are added into the top of the blast furnace
Your notes
Hot air is blown into the bottom
Zone 1
Coke burns in the hot air forming carbon dioxide
The reaction is exothermic so it gives off heat, heating the furnace
carbon + oxygen → carbon dioxide
Zone 2
At the high temperatures in the furnace, more coke reacts with carbon dioxide forming
carbon monoxide
Carbon dioxide has been reduced to carbon monoxide
carbon + carbon dioxide → carbon monoxide
Zone 3
Carbon monoxide reduces the iron(III) oxide in the iron ore to form iron
This will melt and collect at the bottom of the furnace, where it is tapped off
iron(III) oxide + carbon monoxide → iron + carbon dioxide
Limestone (calcium carbonate) is added to the furnace to remove impurities in the ore
The calcium carbonate in the limestone thermally decomposes to form calcium
oxide
calcium carbonate → calcium oxide + carbon dioxide
The calcium oxide formed reacts with the silicon dioxide, which is an impurity in the iron
ore, to form calcium silicate
This melts and collects as a molten slag floating on top of the molten iron, which is
tapped off separately
calcium oxide + silicon dioxide → calcium silicate
Examiner Tips and Tricks
For Core students, the symbol equations are not needed for the different reactions
involved in the extraction of iron from hematite.
Equations for extraction of iron from hematite
Extended tier only
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Zone 1
The burning of carbon (coke) to provide heat and produce carbon dioxide: Your notes
C (s) + O2 (g) → CO2 (g)
Zone 2
The reduction of carbon dioxide to carbon monoxide:
CO2 (g) + C (s) → 2CO (g)
Zone 3
The reduction of iron(III) oxide by carbon monoxide:
Fe2O3 (s) + 3CO (g) → 2Fe (I) + 3CO2 (g)
The thermal decomposition of calcium carbonate (limestone) to produce calcium oxide:
CaCO3 (s) → CaO (s) + CO2 (g)
The formation of slag:
CaO (s) + SiO2 (s) → CaSiO3 (l)
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Extraction of Aluminium from Bauxite
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Extraction of aluminium from bauxite
Aluminium is a reactive metal, above carbon in the reactivity series
Its main ore, is bauxite, which contains aluminium oxide
Aluminium is higher in the reactivity series than carbon, so it cannot be extracted by
reduction using carbon
Instead, aluminium is extracted by electrolysis
The electrolysis of aluminium
Diagram showing the extraction of aluminium by electrolysis
Examiner Tips and Tricks
If you are a Core student, you do not need to explain the process of extraction of
aluminium by electrolysis.
The process of aluminium extraction by
electrolysis
Extended tier only
Bauxite is first purified to produce aluminium oxide, Al2O3
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Aluminium oxide is then dissolved in molten cryolite
This is because aluminium oxide has a melting point of over 2000 °C which would Your notes
use a lot of energy and be very expensive
The resulting mixture has a lower melting point without interfering with the reaction
The mixture is placed in an electrolysis cell, made from steel, lined with graphite
The graphite lining acts as the negative electrode, with several large graphite blocks as
the positive electrodes
At the cathode (negative electrode):
Aluminium ions gain electrons (reduction)
Molten aluminium forms at the bottom of the cell
The molten aluminium is siphoned off from time to time and fresh aluminium oxide is
added to the cell
Al3+ + 3e- → Al
At the anode (positive electrode):
Oxide ions lose electrons (oxidation)
Oxygen is produced at the anode:
2O2- → O2 + 4e-
The overall equation for the reaction is:
2Al2O3 → 4Al + 3O2
The carbon in the graphite anodes reacts with the oxygen produced to produce CO2
C (s) + O2 (g) → CO2 (g)
As a result the anode wears away and has to be replaced regularly
A lot of electricity is required for this process of extraction, this is a major expense
Examiner Tips and Tricks
Use OIL RIG to remember whether oxidation or reduction has occurred at the
electrodes:
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