>>> bb/116693@108935
Burn the sulfur with an oxidant, not with air, and it'll be fine.
But I said it too simply. I don't know what sulfur will react gently with, and what gunpowder will turn out with. So you'll have to experiment. Permanganate with chlorates and nitrates disappear immediately, the cathode mass of batteries can be sampled, and iron scale. Maybe there are other metallic oxides you can try, I don't know what you can get.