I came across this video yesterday which showcases how recycling is sorted and organized. It's method of sorting through a large variety of materials is a fascinating process. This video clearly explains the step by step process of how it's done.
At one point of the video, it mentions how optics are used to identify each type of material to perform the sort. I needed a refresher of the science behind the process and found a nice article to explain it.
How optics can be used to identify materials
Most Canadian students have already learned this in grade 12 chemistry, whether we remembered it or not.
First, we need to recall that every type of material is made up of atoms which, at the core, is a composition of elements. Each atom carries a specific number of electrons along with it, which rest on certain levels of energy orbits around the atom.
The energy levels that the electrons rest on can be identified as level 1, 2, 3... X, etc. These atoms absorb or release energy whenever the electrons jumps to different energy levels. Since the electrons rest on specific energy levels, the wavelengths of energy that is absorbed or released are specific to the levels of energy.
So, to identify a type of material, energy can be introduced in the form of a laser and shot at the material. This material will absorb a specific wavelength of light from the laser. Then we can analyze the missing wavelength of light when we receive the laser reflected back to us. According to which wavelength is missing, this information will allow us to identify which material the piece of recycling is.
http://classroom.synonym.com/spectroscopy-identify-elements-11256.html
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