The only demagnetizer I know of is the ones I have seen for screwdrivers. Do you think pouring the coal through one will work?
@Avanti good to know about anthracite. The local steam/stationary club might be able to spot me some. I don't know if it's expensive.
When I was a lad, anthracite was $5.00 a ton. Of course, we lived over a coal mine in the semi beautiful Scranton area. Could it have gone up that much?