2.5 From soil to soda cans
An aluminium drinks can is made of about 15 g of aluminium. Aluminium is the third most abundant element in the Earth’s crust (the bit we can ‘get at’) after oxygen and silicon, but is only about 8.4% of the material. If you wanted to extract the necessary aluminium from the Earth's crust, you would need to grind up 178 g of material to get enough aluminium to make one can:
How about a fairly typical rock, like a granite?
Well, granite is ~ 14% alumina (Al2O3). First you need to convert this to % aluminium, which we do by multiplying the percentage of Al2O3 by the percentage of Al in Al2O3:
The atomic mass of Al is 27. The atomic mass of O is 16.
So you’d actually need more granite to get the necessary aluminium than if you just ground up the crust.
Don't worry if this seems a bit too complicated – this video clip reiterates the above material and explores the maths a bit more closely.
What about bauxite? Bauxite is formed from rocks like granite – how effective is the geological process in concentrating the aluminium? Test your understanding with the next activity.