Extraction of Aluminium

• I know how aluminium is extracted from its ore.

L.O.

Aluminium: properties

• Aluminium is a reactive metal.• We might expect it to corrode easily but a

strong coating of oxide on it’s surface prevents this in most everyday situations.

• It has a low density which leads to its extensive use in the aerospace industry.

Al Al Al AlAl Al

Al Al Al AlAl AlO O O O O OO OO

Coating of oxygen atoms

prevents further attack

Aluminium: ores

• It occurs as bauxite ore which is a form of aluminium oxide.

• Because aluminium is so reactive carbon is unable to pull away the oxygen from it.

• It is extracted by electrolysis of moltenmolten bauxite. Early attempts at this failed because bauxite is so hard to melt.

• If cryolite is added, the bauxite melts more easily. This is an essential step in the extraction process.

A bauxite / cryolite mixture is melted in a steel container containing a carbon lining.

Graphite (carbon) anodes

Tanklinedwith

carboncathode

Molten electrolytebauxite + cryolite

Steelcase

Graphite anodes are inserted into the molten electrolyte ready for electrolysis.

Electrolytic extraction

Aluminium formation

• Opposite charges attract.

• And so positive aluminium ions move towards the negative cathode.

• At the cathode these ions gain electrons and turn into aluminium atoms.

Oxygen formation

• Negatively charged oxide ions move to the anode.

• Here they lose 2 electrons and so turn into neutral oxygen atoms.

• These atoms rapidly join into pairs to form normal oxygen gas.

Carbon dioxide formation

• Remember the electrolysis is carried out at high temperature.

• Under these conditions quite a lot of the oxygen reacts with the carbon anode.

• Carbon dioxide is formed and the anode is rapidly eaten away and frequently has to be replaced.

Extraction of aluminium: overall

siphon

Graphite / carbon anodes

Molten aluminiumMolten electrolytebauxite + cryolite

Tanklinedwith

carboncathode

Moltenaluminiumout

Steelcase

Vented cover

• Compounds can be split up into the elements which make them using electricity. This is called electrolysis.

• The aluminium ore is aluminium oxide.

• Common aluminium ore

I axe tub

• Added to reduce melting point

City role

• The electrodes are made out of

Right ape

• Extracting aluminium is a

Cretin duo

bauxite

cryolite

graphite

reduction

Unscramble the words to end the sentences.

Aluminium – the overall process

1. What do we call the substance added to the aluminium ore prior to electrolysis?

Bauxite

Electrolyte

Cryolite

2. What substance are the cathodes made from?

Carbon

Iron

Aluminium

3. What happens to the oxygen given off during electrolysis?

It is given off as waste gasesIt reacts with the carbon electrodes to form carbon dioxide.It is collected at the bottom of the chamber.