It is certainly possible that a fluidized bed density separator can make a separation of stainless steel from plastic flakes. If the shape and size of the two different materials is similar, I would expect a very good separation. Sizing may be required before density separation, or some amount of small stainless can mix with larger pieces of plastic. More information can be reviewed at http://www.sssdynamics.com/downloads/pdfs/TD1006%20%20dry%20separations.pdf