The researchers studied how the surface chemistry of coal pyrite affects its ability to float during coal cleaning. They found that the floatability of coal pyrite is low compared to mineral pyrite, even after oxidation. Mineral pyrite becomes less hydrophobic with longer oxidation times and higher pH levels, while coal pyrite remains difficult to float. X-ray photoelectron spectroscopy showed that an oxidized iron layer on the surface of pyrite reduces its floatability, while a sulfur-containing species may help it float. Adding frother improved the floatability of both coal and mineral pyrite at all pH levels.