Extraction of Aluminium
Objective:
•To Know how aluminium is
extracted from the Bauxite
Ore.
•To know the process of
extraction.
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.
O OOO O O O OO
Al Al Al Al Al Al
Al Al Al Al Al Al
Coating of
oxygen atoms
prevents further
attack
Raw Materials
• Ore bauxite aluminium oxide
• The ore is dissolved in cryolite to lower the
melting point.
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 molten 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.
Electrolytic extraction
A bauxite
/ cryolite
mixture
is the
melted
in aelectrolyte
steel
Graphite
anodes
are inserted
into
molten
container
containing
a carbon lining.
ready
for electrolysis.
Graphite (carbon) anodes
Tank
lined
with
carbon
cathode
Steel
case
Molten electrolyte
bauxite + cryolite
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
Vented cover
siphon
Molten
aluminium
out
Graphite / carbon anodes
Tank
lined
with
carbon
cathode
Steel
case
Molten aluminium
Molten electrolyte
bauxite + cryolite
Unscramble the words to end the sentences.
• Common aluminium ore
bauxite
I axe
tub
• Added to reduce melting point
cryolite
City role
• The electrodes are made out of
Right
graphiteape
• Extracting aluminium is a
reduction
Cretin
duo
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 gases
It reacts with the carbon electrodes to form
carbon dioxide.
It is collected at the bottom of the chamber.