Impact of mixing pattern on oil-mineral aggregation and oil removal in coastal waters: A lab-scale study

Ensuing an oil spill, oil-mineral aggregates (OMAs) are formed due to the aggregation of dispersed oil droplets with suspended sediment particles such as clay minerals. This process mainly occurs in coastal areas where suspended sediments interact with the oil droplets formed by the turbulent action of the waves. To better understand the effect of the mixing patterns on OMA formation, we study the formation and oil removal percentage (ORP) of OMAs under two mixing conditions: (1) orbital shaker and (2) magnetic stirrer, representing inward and outward directional flow patterns, respectively, at similar mixing energies. It impacts OMA formation by altering droplet-particle collision frequency and the balance between aggregation and shear-induced breakup. The experiments are conducted using bentonite and kaolinite clay at various concentrations. The kinetics of ORP are analysed using a logistic saturation curve, and the kinetic parameters are determined. The findings of the study indicate that the ORP is higher for mixing conditions of the orbital shaker, which causes the fluid to move along the container wall creating a swirling motion. The fastest removal occurred at a concentration of 1 g/L for kaolinite OMAs. The maximum ORP was observed to be 70% for kaolinite and 65% for bentonite. This work establishes a clear understanding of the effect of the mixing flow directionality on ORP and OMA formation under various concentrations. These findings provide valuable insights into the natural attenuation of dispersed oil in coastal environments and improve the mitigation of the impacts of oil spills.