Reduction of slime coating: effects of sodium silicate and sodium carbonate on lean coal flotation in sodium oleate system

High-ash fine slime has an adverse effect on coal flotation. In this study, the roles of sodium silicate (SS) and sodium carbonate (SC) in the facilitating effect on lean coal flotation (a type of coking coal) were studied when sodium oleate (NaOL) was used as a collector through flotation tests, Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) observations, turbidity measurements, and particle interaction energy calculations. The flotation tests found that SS has a stronger capacity than SC for the improvement of flotation performance of lean coal. Moreover, SEM-EDS observations and turbidity measurements showed that SS presents a stronger weakening effect for the coating of high-ash fine slime on the surface of low-ash coal particles than SC. Furthermore, the particle interaction energy calculations verified that the increase in the energy barrier for the attachment between low-ash coal particle and high-ash fine slime caused by SS is larger than SC, providing theoretical supports for the experiments. Compared to kerosene as a collector, based on the similar ash content, the yield of clean coal increases greatly with the synergistic effect of SS and NaOL. In summary, SS is an appropriate dispersant for lean coal flotation in sodium oleate system.