Changes in the Surface Structure of Coal Caused by Igneous Intrusions and Their Effect on the Wettability

Abstract

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.

Experimental Study on the Wettability of Tectonic Soft Coal in Huaibei Mining Area, China

“…In this work, the contact angle was measured with distilled water; the volume of one water drop was about 2 μL, and the test procedure was the same as in the previous study. 19 The infrared spectrum analysis was conducted, and the testing range is 4000−400 cm −1 with a resolution of 4 cm −1 according to the Chinese National Standard GB/T 6040-2019. The test method of low-temperature N 2 physisorption is the same as in the previous study.…”

“…In recent years, various studies have been undertaken to investigate the relationship between wettability and coal surface roughness. Li 20 and Zhou 21 reported that the rougher the solid surface, the poorer the wettability, and some scholars gave a contrary finding, 19,22 while other scholars found that a certain degree of surface roughness is best for coal wetting. 23 In conclusion, the mineral content, chemical structure and element composition, pore structure, surface morphology, and particle size of coal dust are the factors affecting coal wettability, while the coal-forming environment such as tectonic stress and magma intrusion has an important influence on those factors.…”

“…23 In conclusion, the mineral content, chemical structure and element composition, pore structure, surface morphology, and particle size of coal dust are the factors affecting coal wettability, while the coal-forming environment such as tectonic stress and magma intrusion has an important influence on those factors. 19,20 Due to tectonic deformation, factors affecting coal wettability such as coal composition, chemical structure, and pore characteristics of coal were changed. 24−26 Therefore, it is essential to study the influence mechanism of tectonic soft coal wettability so as to implement corresponding dust control measures.…”

“…The higher the mineral content in coal, the better the coal wettability, , and the smaller the particle size of coal dust, the poorer the coal wettability . Some scholars reported that the oxygen content and oxygen-containing functional groups such as hydroxyl and carboxyl groups are the factors that contribute to the hydrophilicity of coal, while the carbon-containing macromolecular structure is the factor causing the hydrophobicity of coal. ,− Shi indicated that magmatic intrusion can change the structure and physicochemical properties of coal, and then improve the wettability of coal. In recent years, various studies have been undertaken to investigate the relationship between wettability and coal surface roughness.…”

Experimental Study on the Wettability of Coal with Different Metamorphism Treated by Surfactants for Coal Dust Control

“…Semenova 37 studied the chemical structure of coal with different metamorphic degrees and concluded that the higher the content of hydroxyl and carboxyl, the better the coal wettability. Shi et al 38 indicated that the pore structure, ash, and minerals are the main factors to improve the wettability of magmatic intrusive coal. In summary, all of the concentrations and structures of surfactants and the physicochemical properties of coal are influencing factors of the coal wettability.…”