· The effect of dust on the efficiency of electrostatic separation of pyrite from a closely sized coal is shown in table 3 and table 4 and the accompanying graphs (figs. 56). Figure 5 shows the results with a lowsulfur dust. Separation efficiency is not significantly decreased until more than 10 pct dust is added.
· Since the dawn of humanity, the world's most dangerous minerals endangered the lives of iron age peoples. In the industrial revolution, miners quickly learned about the risks of rocks, acting as the proverbial 'canary in the coal mine' for later safety advances. Many minerals create an invisible hazard in dust form, as detailed in Reviews in Mineralogy.