Experimental and emulational study on the role of ion in coal adsorbing kerosene: Water–kerosene interface and catenoid characteristics

Abstract Understanding the effect of ions on the interfacial tension (IFT) between kerosene and water is a prerequisite to predicting kerosene–mineral adsorption. Using a high-speed motion acquisition system, we investigated the height evolution of the catenoid with different IFTs. As the IFT increased, the height of catenoid first increased slowly and then increased sharply. The catenoid height of the oil–water interface was larger than was that of the water–gas, whereas the IFT was the opposite, indicating that height was related not only to the IFT, but also to the viscosity of the phases when the ring diameter was constant. The cation valence had a significant influence on the IFT. Interaction between the cation and water molecules led to the generation of cationic clusters. The literature indicates that the higher the valence of ion the easier it would be to form a cationic cluster, resulting in decreasing of the IFT. Our results matched these findings. At low ionic concentration, the IFT increased as the ion concentration increased. At high ionic concentration, the IFT decreased with increasing concentration because of the ionic pairs. The results of molecular dynamics simulation showed that the water molecules only moved toward kerosene molecules without ions. The hydrophilic groups in kerosene molecules spontaneously arranged toward the water–oil interface, whereas the hydrophobic groups stayed away from this interface. The water molecules burst into the kerosene phase in the presence of ions. The number of water molecule entering the kerosene phase increased with increasing ion concentrations. Our results can provide valuable insight into the development of technology for surfactant adsorption and mineral flotation.