Study on the mechanism of the influence of surfactant alkyl chain length on the wettability of anthracite dust based on EDLVO theory and inverse gas chromatography

The dispersion of coal dust on roadways adversely affects the productivity of coal mines and threatens the lives of mine workers. Accordingly, it is crucial to enhance the wettability of coal dust to improve its suppression efficiency. Herein, the mechanism of the influence of the surfactant alkyl chain length on the wettability of anthracite was investigated by systematically analyzing the degree of modification of anthracite with sodium dodecyl, tetradecyl, hexadecyl, and octadecyl sulfates using the “macroscopic + mesoscopic + microscopic + theoretical calculation” method. First, the differences in the macroscopic effects of different surfactants on modified anthracite were investigated via contact angle, settling time, and water retention rate experiments. It was concluded that surfactants with shorter alkyl chains exhibit a stronger ability to enhance the wettability of anthracite. Second, the mesoscopic characterization of different coal samples via laser particle size distribution, zeta potential, X-ray photoelectron spectroscopy, and inverse gas chromatography surface energy analyses revealed that the adsorption amount and intensity of surfactants on the anthracite surface increased with shortening surfactant alkyl chains owing to the spatial site resistance effect. Furthermore, molecular dynamic simulations of the microscopic molecular mechanism of adding different surfactants to enhance the wettability of anthracite showed that the interaction energy between coal dust and water molecules as well as the number of hydrogen bonds formed in the system rapidly increased with the shortening of the alkyl chains of anionic surfactants, which had a stronger binding ability to water molecules. Finally, the extended Derjaguin, Landau, Verwey, and Overbeek theory was employed to explain the relationship between the variation in electrostatic interaction, van der Waals, hydrophobic interaction, and total interaction energies and confirm that the wettability of anthracite particles increases with their dispersion in water. The ability of the surfactants to improve the wettability of anthracite increased at different degrees with the shortening surfactant alkyl chains. This study can provide breakthrough inspiration for the fields of coal flotation and haze control.