Wettability and mechanism of AEO₃ for lignite wetting

To explore the wettability and wetting mechanism of a non-ionic surfactant, fatty alcohol polyoxyethylene ether AEO₃, on lignite, some experimental and simulation methods were applied in this study. The surface tension and contact angle were used to evaluate the AEO₃ wetting performance on lignite. The experimental results show that when the concentration of AEO₃ solution gradually increased to 1.37×10⁻⁶ mol/L, the surface tension was reduced from 71.97 mN/m to 26.38 mN/m and the contact angle was decreased from 73.35° to 28.43°. The critical micelle concentration (CMC) of an AEO₃ solution was 2.80 mmol/L. Before reaching the CMC, the ability of AEO₃ to reduce the surface tension and contact angle of an aqueous solution increased with the increase of its concentration. The high-speed camera technology was used to carry out the droplet impact experiment and the dimensionless spreading coefficient was introduced to characterize the droplet shape change when it impacted the coal. The dynamic transformation between kinetic energy, surface energy, viscous dissipation, and friction dissipation occurs in the droplet spreading process. Increasing the droplet impact velocity and adding AEO₃ reasonably can increase the spreading area of the solution on the coal surface, shorten the wetting time, and improve the wetting effect. Using the Materials Studio software, the electrostatic potential of experimental material molecules was calculated through the quantum chemistry method and a correlation analysis was conducted with wettability. The results show that the maximum electrostatic potential of lignite molecules and AEO₃ molecules is greater than the electrostatic potential of water molecules. Water molecules are easier to be adsorbed, thus showing a wetting phenomenon. Through the molecular dynamics simulation and study, the relative concentration distribution, mean square displacement, and interaction energy of molecules in the system are at an equilibrium state. The results show that AEO₃, as a water molecule adsorption carrier, could increase the relative concentration of water molecules on the surface of lignite, limit the diffusion of water molecules, strengthen the interaction between molecules in the water/AEO₃/lignite system, and improve the wettability of solution.