Interaction between STAC and coal/kaolinite in tailing dewatering: An experimental and molecular-simulation study

The presence of clay minerals in coal tailings leads to a significant deterioration during the dewatering process. In this study, a cationic surfactant, stearyl trimethyl ammonium chloride (STAC), was considered to enhance the dewatering efficiency of coal tailings. The effect of STAC on coal tailing dewatering was evaluated by the filtration test. Results indicate that STAC can reduce filter cake moisture by increasing the hydrophobicity of particles, decreasing the surface tension of the filtrate, as well as neutralizing the associated charge. Furthermore, to investigate the interactions between STAC and coal tailings, the morphology of adsorbed STAC, interfacial adsorption structure, and dynamic behavior of water molecules were determined by atomic force microscopy (AFM) and molecular dynamics (MD) simulations on an atomic scale. AFM results revealed that the morphologies of STAC adsorbed on coal and kaolinite surfaces differed, owing to distinct interaction mechanisms. The adsorption of STAC on the kaolinite 001 surface is more uniform than on the 00 1 - face and is predominantly based on monolayer adsorption through electrostatic interactions and hydrogen bonding. The MD simulation results suggest that the adsorption of STAC significantly inhibits the attachment of water molecules on coal and kaolinite surfaces. The nitrogen atoms of STAC were adsorbed to the particle surface, such that its alkyl chains were oriented towards water, thereby weakening the interaction between the particles and water. The above findings indicate that the addition of STAC can improve the hydrophobicity of coal and kaolinite effectively and thus, enhance the dewatering performance of coal tailings.