Enhancing Flotation Performance of Low-Rank Coal Using Environment-Friendly Vegetable Oil

Flotation is widely used for low-rank coal upgrading, although it is always inefficient due to its rough surface morphology and rich oxygen-containing functional groups. In this study, the environment-friendly vegetable oil 1030# was used to enhance the flotation performance of low-rank coal. The mechanism of 1030# enhancing the flotation of low-rank coal was revealed through surface property analysis of coal particles and bubble-particle adhesion tests. The flotation results showed that the flotation yield of low-rank coal increased with the increase in the collector dosage, and the flotation yield of 1030# as a collector is obviously higher than that of diesel. Scanning electron microscopy (SEM) and chromatography-mass spectrometry (GC-MS) were used to analyze the surface morphology of coal particles and components of the reagent. The SEM results showed that the surface of low-rank coal is loose and contains a large number of pores and cracks, which is not conducive to the spreading of chemicals on the coal surface and the mineralization of bubbles and particles. GC-MS results showed that 1030# mainly contained methyl oleate with more unsaturated double bonds than diesel. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the surface functional groups of the low-rank coal before and after reagent treatment. The results of FTIR and XPS showed that the coal surface of low-rank coal before reagent treatment contained a large number of oxygen-containing functional groups with poor surface hydrophobicity, while the surface of low-rank coal after reagent treatment had reduced oxygen-containing functional groups and increased hydrophobicity. The contact angle of the low-rank coal surface also showed the same variation trend as the FTIR and XPS results. The adhesion force between the bubble and coal surface in different collector solutions was measured. The maximum adhesion between the bubble and coal surface increased with the increase in the collector, and the maximum adhesion force with 1030# treatment was higher than that of diesel. This indicated that 1030# with a large number of polar components is more easily spread on the surface of low-rank coal, thus improving the hydrophobicity of low-rank coal.