And last I checked metal was way heavier than plastic.....if they were both melted in a pot let's say.......well....the metal isn't exactly gonna float at the top is it........And let's say you had a conveyor picking up the metal from the bottom and bringing it out......I just can't picture melted plastic 'clinging' to the steel.......not a whole lot of it anyway......cause last I checked plastic didn't have arms to hold on with.....
Bottom Line: Separating metal from plastic isn't going to take rocket science. I'm sure an elegant solution has already been developed......z