Investigating agglomeration of kaolinite particles in the presence of dodecylamine by force testing and molecular dynamics simulation

Abstract

Kaolinite, one of the main components of clay minerals, is detrimental to slime water sedimentation. Sedimentation, adsorption, surface tension, contact angle, and interaction force measurements were conducted to study the hydrophobic agglomeration mechanism in kaolinite particles in the presence of dodecylamine (DDA). The results showed that DDA could be adsorbed on the kaolinite surface, improving the surface hydrophobicity and promoting hydrophobic particle agglomeration. Kaolinite hydrophobic sedimentation was enhanced with increased DDA concentration. The settling velocity and the adsorption of DDA on slurry particles were optimal when the DDA concentration was 14 × 10-4 mol/L. The shape and size distribution significantly affected the particle-surface interaction. Reliable force data could not be obtained from colloidal probes made of actual clay particles. Therefore, silica-silica and silica-alumina systems were used to replace clay mineral particles for force testing. AFM results showed that electrostatic repulsion existed in silica-silica and silica-alumina particles in ultrapure water. With DDA addition, the electrostatic repulsive force in silica-silica and silica-alumina particles decreased, the hydration film was destroyed, and an adhesion force was generated. In addition, the silicon-oxygen (001) surface of kaolinite adsorbed DDA more easily than the aluminum-oxygen (001̅) surface. The adsorption behavior of DDA+ on the kaolinite (001) and (001̅) surfaces was calculated by molecular dynamics simulation to explore the adsorption mechanism of DDA on kaolinite surfaces. The results suggested that the DDA+ polar head groups were adsorbed on the kaolinite surface, whereas the non-polar groups faced the solution. DDA+ adsorbed more easily on the (001) surface than on the (001̅) surface.