Determining the effect of the non-ionic surfactant AEO9 on lignite adsorption and wetting via molecular dynamics (MD) simulation and experiment comparisons

Abstract

By combining a molecular dynamics (MD) simulation approach with experimental measurements, this study elucidated the molecular interactions between the fatty alcohol polyoxyethylene ether-9 (AEO9; i.e., a surfactant) and lignite. Moreover, the micro-dynamic process of wetting and adsorption of surfactant molecules onto coal dust molecules were also studied. In the wettability test, the evaporation rate of coal decreased significantly after AEO9 addition. The measured contact angle first decreased and then increased with increased AEO9 concentration. A lower contact angle was indicative of better wetting performance. Using the Materials Studio software, the motion process of the water/AEO9/lignite system was simulated. The resulting structural chart indicated that AEO9 can be adequately adsorbed onto the coal surface. By analyzing the changes in the relative concentration curves along the Z-axis and water mobility before and after AEO9 addition, it was found that AEO9 can enhance the hydrophilicity of lignite. The simulated adsorption isotherms and the calculated interaction energy between molecules suggested simultaneous adsorption onto the lignite surface. X-ray photoelectron spectroscopy (XPS) analysis also revealed that the elemental C content of the surface decreased while the O content increased after coating the lignite surface with AEO9. Given that a great number of oxyethylene groups are present in AEO9, we concluded that AEO9 efficiently adsorbed onto the lignite surface. The present study is of great significance to the enhancement of dust suppressant performance and reducing coal dust hazards.