Aluminium and its alloys are among the most important metals
Aluminium and its alloys are among the most important metals

in everyday life.
in everyday life.

They resist the effects of other chemicals, are strong yet flexible,
They resist the effects of other chemicals, are strong yet flexible,

and are light in weight.
and are light in weight.

Aluminium is the third most common element in the earth's crust.
Aluminium is the third most common element in the earth's crust.

It is extracted from its oxide by electrolysis.
It is extracted from its oxide by electrolysis.

This plant is situated close to a deep water port
This plant is situated close to a deep water port

for importing the raw material. The site is really three plants in one.
for importing the raw material. The site is really three plants in one.

Electrolysis takes place in four covered areas
Electrolysis takes place in four covered areas

each half a kilometre in length and each containing 78 electrolysis cells.
each half a kilometre in length and each containing 78 electrolysis cells.

The aluminium is alloyed and cast in the metal finishing shops.
The aluminium is alloyed and cast in the metal finishing shops.

Anodes for the process are produced here.
Anodes for the process are produced here.

Aluminium oxide, often called alumina,
Aluminium oxide, often called alumina,

is stored here fed by an underground conveyor belt from the docks.
is stored here fed by an underground conveyor belt from the docks.

This white powder is alumina. The aluminium
This white powder is alumina. The aluminium

is extracted from it. Alumina is imported from Jamaica,
is extracted from it. Alumina is imported from Jamaica,

Ireland and Spain, where it's been purified from bauxite ore.
Ireland and Spain, where it's been purified from bauxite ore.

This is one of the four rows of electrolysis cells
This is one of the four rows of electrolysis cells

where the electrolysis takes place. The current
where the electrolysis takes place. The current

is about 157,000 amps at 4.5 volts.
is about 157,000 amps at 4.5 volts.

This is one of the 312 cells. The electrolysis cell consists of a
This is one of the 312 cells. The electrolysis cell consists of a

rectangular steel shell
rectangular steel shell

lined with heat-resistant brick and then carbon.
lined with heat-resistant brick and then carbon.

Each cell is filled with molten cryolite. The aluminium oxide
Each cell is filled with molten cryolite. The aluminium oxide

is dissolved in molten cryolite so that it conducts electricity.
is dissolved in molten cryolite so that it conducts electricity.

18 carbon anodes dip into the electrolyte.
18 carbon anodes dip into the electrolyte.

During the electrolysis aluminium ions move to the cathode,
During the electrolysis aluminium ions move to the cathode,

gain electrons, and become aluminium metal. Oxide ions
gain electrons, and become aluminium metal. Oxide ions

move to the anode where each iron loses two electrons
move to the anode where each iron loses two electrons

and the atoms pair up to become oxygen molecules.
and the atoms pair up to become oxygen molecules.

These are the chemical equations.
These are the chemical equations.

As the electrolysis proceeds
As the electrolysis proceeds

the aluminium oxide is decomposed into aluminium
the aluminium oxide is decomposed into aluminium

and oxygen. A crust forms on the electrolyte
and oxygen. A crust forms on the electrolyte

and this has to be broken to feed in new aluminium oxide.
and this has to be broken to feed in new aluminium oxide.

This happens every three to four minutes. The hoppers on the cells
This happens every three to four minutes. The hoppers on the cells

are filled from an overhead ore bucket every 16 hours.
are filled from an overhead ore bucket every 16 hours.

The electrolyte
The electrolyte

is at about 955 degrees Celsius. At this temperature
is at about 955 degrees Celsius. At this temperature

the carbon anodes gradually burn away in the oxygen from the electrolysis.
the carbon anodes gradually burn away in the oxygen from the electrolysis.

Eventually the anodes have to be replaced.
Eventually the anodes have to be replaced.

This happens every 28 days or so.
This happens every 28 days or so.

The remaining carbon is broken off the old anodes, crushed, mixed with new coke and pitch,
The remaining carbon is broken off the old anodes, crushed, mixed with new coke and pitch,

and pressed into shape. The newly pressed
and pressed into shape. The newly pressed

anodes are baked for about 24 hours in gas heated pits.
anodes are baked for about 24 hours in gas heated pits.

Steel stubs
Steel stubs

are fitted onto the baked anodes. The anodes are sprayed with molten aluminium
are fitted onto the baked anodes. The anodes are sprayed with molten aluminium

to protect the top and sides.
to protect the top and sides.

Electrolysis takes place twenty four hours a day,
Electrolysis takes place twenty four hours a day,

365 days a year. A loss of power of
365 days a year. A loss of power of

more than a couple of hours would be disastrous, as the electrolyte
more than a couple of hours would be disastrous, as the electrolyte

and the aluminium would solidify.
and the aluminium would solidify.

Liquid aluminium is sucked from the cell into a brick lined steel crucible.
Liquid aluminium is sucked from the cell into a brick lined steel crucible.

Each cell produces about 50 kilograms of aluminium per hour.
Each cell produces about 50 kilograms of aluminium per hour.

Some of the aluminium is cast as almost pure metal.
Some of the aluminium is cast as almost pure metal.

Some is made into alloys by adding other metals.
Some is made into alloys by adding other metals.

This metal being added is magnesium.
This metal being added is magnesium.

Aluminium alloys or pure metal can be cast into different shapes.
Aluminium alloys or pure metal can be cast into different shapes.

The liquid metals are poured into molds where they solidify
The liquid metals are poured into molds where they solidify

and can be lifted out.
and can be lifted out.