Interaction between low rank coal and kaolinite particles: A DFT simulation

In the article, the interaction between low rank coal (LRC) and kaolinite particles was studied using density functional theory (DFT) calculations to interpret the mechanisms of kaolinite coating on LRC flotation. Four representative model molecules with different polarities in LRC, namely, benzoic acid, phenol, benzene and toluene, were taken into account in analyzing the interactions with kaolinite surfaces. The calculated results of adsorption configuration and bonding demonstrate that the interaction of LRC model molecules and kaolinite is the result of the joint actions of benzene rings and oxygen-containing groups. By analyzing adsorption energy, density of state (DOS) and charge transfer, it could be deduced that whether the (001) or the (00 (1) over bar) surface of kaolinite, van der Waals attraction governs their interaction with LRC model molecules. It also could be concluded that LRC model molecules are more inclined to adsorb on the (001) surface in comparison with the (00 (1) over bar) surface. However, due to the strong adsorption between the water molecule and the kaolinite (001) surface, it should be difficult to replace the adsorbed water molecules on the (001) surface for LRC model molecules. Therefore, the van der Waals attraction between the LRC model molecules and the kaolinite (0 0 (1) over bar) surface is responsible for the kaolinite coating on LRC flotation. The available literature is in accord with our results.