Energy & Fuels, Vol.32, No.9, 9371-9379, 2018
Changes in the Surface Structure of Coal Caused by Igneous Intrusions and Their Effect on the Wettability
In this paper, normal and thermally altered coals were sampled to investigate the surface characteristic changes of coals after igneous intrusions and their effects on the wettability. The chemical compositions, pore structures, surface morphology, and functional groups of coals after igneous intrusions were comparatively analyzed. A contact angle experiment and wetting time test were employed to analyze the wettability of coals. The results showed that the coals after igneous intrusions exhibited much more epigenetic carbonates and higher ash contents as compared to the normal coals, which would improve the wettability of these coals. Pore structure analysis revealed that the macropore volume and surface roughness of the altered coals were further increased due to igneous intrusions. In addition, the altered coals formed much larger pores and more cracks on their surface, which made these coals more easily wetted by water. XPS analysis revealed decreased contents of oxygen-containing groups after igneous intrusions. The contact angle and wetting time test results indicated that the altered coals demonstrated an improved wettability as compared to the normal coals. This conclusion could be evidenced by a smaller contact angle and shorter wetting time for the altered coals. This paper concluded that the surface structure of bituminous coal was obviously influenced by igneous intrusions, finally enhancing the wettability of the altered coals, which was mainly due to changes in ash contents, minerals, pore structures, and surface morphology.