Sorting
Once commingled recyclates are collected and delivered to a central collection facility, the different types of materials must be sorted. This is done in a series of stages, many of which involve automated processes such that a truck-load of material can be fully sorted in less than an hour.
Initially, the commingled recyclates are removed from the collection vehicle and placed on a conveyor belt spread out in a single layer. Large pieces of cardboard and plastic bags are removed by hand at this stage, as they can cause later machinery to jam.
Next, automated machinery separates the recyclates by weight, splitting lighter paper and plastic from heavier glass and metal. Cardboard is removed from the mixed paper and the most common types of plastic (PET and HDPE) are collected. This separation is usually done by hand, but has become automated in some sorting centres: a spectroscopic scanner is used to differentiate between different types of paper and plastic based on the absorbed wavelengths, and subsequently divert each material into the proper collection channel.
Strong magnets are used to separate out ferrous metals (tin-plated or steel cans), while non-ferrous metals are ejected by "magnetic eddy currents". A rotating magnetic field induces an electric current around the aluminum cans, which in turn creates a magnetic eddy current inside the cans. This magnetic eddy current is repulsed by the large magnetic field, and the cans are ejected from the rest of the recyclate stream.
Finally, glass must be sorted by hand based on its color: brown, amber, green or clear.
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