Comparison of pyrolysis and oxidation actions on chemical and physical property of anthracite coal surface

Hydrophobicity of coal surface is determined by its physical property and chemical composition. Once coal was oxidized or spontaneously ignited under natural conditions, the surface properties would change greatly, which inevitably affect the hydrophobicity of coal surface. To reveal the changing regulations of coal surface’s hydrophobicity after oxidation and pyrolysis treatment, in this paper, two conditions (pyrolysis and oxidation) of heating treatment were used to produce a series of coal surfaces, and then characterizing their physical and chemical properties through SEM and XPS. Meanwhile, induction time and flotation tests were performed to measure the hydrophobicity of coal. Results showed that the pores and cracks were well developed on the coal surface after both oxidation and pyrolysis processes. But they contributed to opposite aspects later in the flotation test. Additionally, the content of oxygen-containing functional groups on the surface decreased after pyrolysis, whereas having a sharp increase after the oxidation process, which predicted that the hydrophobicity of coal surface under two heating conditions would be completely different. Coal after pyrolysis owned a very short induction time, and its flotation recovery was high. For oxidation process, the coal surface became more hydrophilic and their induction time could reach at about 4000 ms, very hard to float.