Mechanism of slime coating on coal surface with different metamorphic degrees

Abstract

Slime coating is an important phenomenon that deteriorates the recovery and quality of clean coal in fine coal flotation process. The quantitative determination and underlying mechanism of slime coating on coal surface with different metamorphic degrees that has discrepancy in both chemical composition and physical structure remains undiscovered. In order to explore the differences of slime coating on the surface of coal with different metamorphic degrees, the degree of slime coating was observed using an in-situ particle vision and measurement (PVM) probe and quantified by image processing. The chemical and physical properties of coal were analyzed using Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Low-Field Nuclear Magnetic Resonance (LF NMR) to underly its mechanism. It was found that slime coating on anthracite was the severest, followed by long flame coal and coking coal. The FTIR and XPS measurements indicated that the chemical composition was contradictory with the slime coating results. The results of SEM and LF NMR showed that there were more cracks and large-scale pores on anthracite compared to long flame coal and coking coal. Therefore, there were more covering sites on anthracite that were favorable for slime coating. The difference in physical property is the controlling factor for the difference of slime coating on coal surface with different metamorphic degrees.