Microscopic spreading characteristics of non-polar oil droplet on low rank coal surface: Effects of surfactant pretreatment and oxygen-containing groups

Abstract

Numerous oxygen-containing groups present on the low rank coal (LRC) surface makes a poor flotation performance of LRC only using common oily collector. Increasing the spreading strength of oily collector on the LRC surface is of great significance for improving its flotation behavior. In this study, molecular dynamics simulation (MDS) was employed to investigate the microscopic spreading characteristics of non-polar oil droplet on the LRC surface. For this purpose, the configurations of non-polar oil droplet, spreading area, and interaction energy were calculated. It was found that on the raw LRC surface, the non-polar oil droplet remained spherical with a small spreading area and weak interaction strength. Besides, a non-ionic surfactant, dodecyl nonaethoxyl ether (C12EO9) was used to modify the surface wettability of LRC to enhance the non-polar oil droplet spreading. After surfactant pretreatment, a pancake-like oil film was formed on the LRC surface with a larger spreading area and more negative interaction energy compared with the case of the raw LRC surface. Based on these observations, the microscopic insights were provided about the spreading of non-polar oil droplet on the surface of LRC, as well as the role of surfactant enhancing its spreading intensity. In addition, the effect of the oxygen-containing groups on the spreading behaviors of non-polar oil droplet was also explored. The results suggested that carboxyl and hydroxyl are the main groups that hinder the spreading of the non-polar oil droplet on LRC surface. The simulation results are in accordance with the available experimental data.