Skip to content
Skip to main content

About this free course

Download this course

Share this free course

An introduction to geology
An introduction to geology

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

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:

equation left hand side 15 times g times cap a times l times prefix solidus of 8.4 percent divided by 100 postfix times equals right hand side 178 times g

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.

multiline equation line 1 two postfix times multiplication prefix times of cap a times l postfix times plus three times prefix multiplication of cap o postfix times equals 102 line 2 two times prefix multiplication of cap a times l postfix times equals 54 line 3 14 postfix times percent cap a times l sub two times cap o sub three postfix times prefix multiplication of left parenthesis 54 divided by 102 right parenthesis equals Granite postfix times i times s postfix times seven and seven divided by 17 postfix times percent cap a times l line 4 15 times g postfix times cap a times l divided by left parenthesis seven times seven postfix times divided by 17 division 100 right parenthesis postfix times equals 202 postfix times eight divided by 21 times g postfix times Granite

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.

Download this video clip.Video player: Video 2.2 Extracting enough aluminium
Copy this transcript to the clipboard
Print this transcript
Show transcript|Hide transcript
Video 2.2 Extracting enough aluminium
Interactive feature not available in single page view (see it in standard view).

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.