Depression mechanisms of sodium humate and 3-mercaptopropionic acid on pyrite in fine coal flotation

Pyrite in coal causes serious environmental pollution in the utilization of coal. Flotation is an appropriate method to remove pyrite present in fine coal. Sodium humate (HA-Na) and 3-mercaptopropionic acid (3-MPA) were used as depressants for pyrite removal in the flotation of fine coal, and their depression mechanisms were investigated by molecular dynamics simulation. The results showed that a relatively lower concentration of HA-Na solution can effectively reduce the sulfur content of flotation cleaned coal, whereas 3-MPA had little effect on its desulfurization. This difference in the desulfurization effect can be attributed to the modification effect of depressants on the surface wettability of pyrite. HA-Na molecules were adsorbed on the FeS2 (1 0 0) surface mainly by van der Waals forces, while 3-MPA molecules were adsorbed by hydrogen bonds, with a strong directionality. The –COO– groups in the HA-Na molecules formed strong hydrogen bonds with the water molecules. The –SH groups in the 3-MPA molecules pointed to the water layer and had weak interactions with the water molecules. Therefore, 3-MPA had a stronger selectivity than HA-Na, while HA-Na had a better effect on enhancing the surface wettability. These results are beneficial to the development of depressants for pyrite removal from fine coal.