I work for a mill that cleans and sorts grains and beans (taking the rocks out, stems out, etc.), and it's fascinating to see the parallel invention of something really similar! We have a bunch of different steps:
1) Air is blown through the product and any dust is taken out.
2) The product is run through a bunch of screens that take out anything too big or too small.
3) The product is put through a gravity separator to separate based on mass.
4) Finally, the product is put through an optical sorter (https://www.youtube.com/watch?v=O0gWUeqzk_o) which uses blasts of air to push out unwanted materials from a stream of falling product.
I'm sure you could use the same process for Legos. Not sure about how to distinguish between branded and unbranded Legos though.
1) Air is blown through the product and any dust is taken out. 2) The product is run through a bunch of screens that take out anything too big or too small. 3) The product is put through a gravity separator to separate based on mass. 4) Finally, the product is put through an optical sorter (https://www.youtube.com/watch?v=O0gWUeqzk_o) which uses blasts of air to push out unwanted materials from a stream of falling product.
I'm sure you could use the same process for Legos. Not sure about how to distinguish between branded and unbranded Legos though.