Why are powerful magnets used when recycling crushed automobile bodies?

In the process of recycling crushed automobile bodies, powerful magnets are used to separate ferrous metals—specifically iron and steel—from the remaining shredder residue.1

After an automobile body is crushed, flattened, and shredded into small pieces by hammer mills, the mixture contains a variety of materials. Because ferrous metals possess magnetic properties, the magnets effectively pull these valuable materials out of the waste stream, allowing them to be recovered for scrap steel processing. Other non-metallic materials, such as plastics, textiles, and rubber, are left behind, while remaining nonferrous materials are sorted through other methods like hand-sorting or air jets.1