As you use the sand it brakes up as stated above. If you use it and reuse it will end up being just powder. You end up with less and less as you reuse it. Just a plain dust mask is silly. Use at least a resperator like used when shooting paint.
Coal slag cuts better but lets face it nothing we do is realy good for you, Sand blasting, epoxy primer, 2 K primer,Spraying/Sanding everything ect. is not good.
I used to remove old floors and sand them that had Asbestos in it. Sand and screape cement slabs, Use of glues that had realy bad solvents in them{worse than many paints}