Effects of chemical dispersant on the surface properties of kaolin and aggregation with spilled oil

After oil spills occur, dispersed oil droplets can collide with suspended particles in the water column to form the oil-mineral aggregate (OMA) and settle to the seafloor. However, only a few studies have concerned the effect of chemical dispersant on this process. In this paper, the mechanism by which dispersant affects the surface properties of kaolin as well as the viscosity and oil-seawater interfacial tension (IFTow) of Roncador crude oil were separately investigated by small scale tests. The results indicated that the presence of dispersant impairs the zeta potential and enhances the hydrophobicity of kaolin. The viscosity of Roncador crude oil rose slightly as the dosage of dispersant increased while IFTow decreased significantly. Furthermore, the oil dispersion and OMA formation at different dispersant-to-oil ratio (DOR) were evaluated in a wave tank. When DOR was less than 1:40, the oil enhancement of dispersant was not significant. In comparison, it began to contribute when DOR was over 1:40 and the effect became more pronounced with the increasing DOR. The adhesion between oil droplets and kaolin was inhibited with the increasing DOR. The size ratio between oil droplets and particles is the significant factor for OMA formation. The closer the oil-mineral size ratio is to 1, the more difficultly the OMA forms.