If I were you, I'd try a magnet. Get the strongest magnet you can
This is exactly the method I would use BUT I would put the magnet in
a small polythene bag. This keeps the magnet and the iron away from
each other so that you don’t have to spend hours trying to remove the
irn dust from the magnet. When you have done, you simply take the
magnet out of the bag and the iron dust falls away.
Ian W. Wright