I dont really see what it is they are sorting the different piles into, it all looks like metal to me. I have see them put thick I beams into the crusher, and slice them off in short lengths. So I dont get this pick something up off 1 pile to drop on another pile. Maybe this is where some commentary from maybe the drone operator would help
It's all about "preparation ". Steel mills have guidelines for lengths of material as well as contamination limits. The crane loads the crappy stuff to go to a huge shredder where most contamination like plastic, fiberglass, etc is removed. Ther are also different grades of steel where mixing heavy iron with sheet metal is needed. All about PREPARATION!
