Extraction Of Aluminium (T5)

Question 1

Break down the steps of aluminium extraction..

Answer 1

• the bauxite is treated to produce pure aluminium oxide
• as aluminium oxide has a very high melting point it is not practical to electrolyse molten aluminium oxide and instead the aluminium oxide is dissolved in molten cryolite
• the electrolyte is a solution of aluminium oxide in molten cryolite at a temperature of about 1000 deg. C
• molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell
• the cell operated at about 5-6 volts but with currents of up to about 10,000 A
• the heat generated by the huge current keeps the electrolyte molten

Question 2

Describe what is happening to the chemistry of the atoms and ions in aluminium extraction..

Answer 2

1) aluminium ions are attracted to the cathode and are reduced to aluminium by gaining electrons

Al 3+ (l) + 3e- > Al(l)

2) the molten aluminium produced sinks to the bottom of the cell
3) the oxide ions are attracted to the anode and lose electrons to form oxygen gas

2O 2-(l) > O2(g) + 4e-

^^ this creates a problem as due to the high temps, the carbon anodes burn in the oxygen to form carbon dioxide. The anodes have to be replaced regularly and this adds to the expense.

Question 3

Describe how aluminium can be used..

Answer 3

Pure aluminium isn’t very string so aluminium alloys are normally used instead.

The aluminium can be strengthened by adding elements like silicon, copper or magnesium.

Aluminium’s uses depend on its:

• low density and strength
• its ability to conduct electricity and heat
• its appearance
• its ability to resist corrosion

Some uses involve aerospace, kitchen equipment and electricity cables.

Question 4

Aluminium is the most common metal in the Earth’s crust, making up 7.5% by mass.

What is its main ore?

Answer 4

It’s main ore is bauxite - a clay mineral which you can think of as impure aluminium oxide.