Role of Bubble–Drop Interactions and Salt Addition in Flotation Performance

Abstract

Gas flotation is an efficient technique used in the petroleum industry to remove oil contamination from produced water. This method is based on attaching air bubbles to oil droplets to make oil droplets rise faster. We investigated the role of water salinity in the efficiency of the process, using a model flotation column. We show that flotation efficiency increases with water salinity, highlighting the importance of the electrostatic repulsion between oil drops and air bubbles. We also studied the attachment between drops and bubbles, monitoring the temporal evolution of the thin films between them. Stable attachment requires that the water films formed between oil drops and air bubbles break and the oil spreads at the bubble surface. Increasing the salinity of the solution decreases the repulsion between the oil drops and the air bubbles, which in turn decreases the water film stability. The films rupture more readily, improving the drop–bubble attachment and thus the flotation efficiency. The differences in water salinity can therefore lead to important changes in the flotation efficiency.

Interfacial Behavior and Internal Microflow of an Oil Droplet during the Process of the Oil Droplet Covering a Gas Bubble: Without and with NaCl

“…As salinity increases, the zeta potential of the oil droplet decreases. 6 Therefore, electrostatic repulsions are weakened, resulting in a decreasing pressure barrier. It is favorable to decrease the liquid film stability to reduce the induction time by increasing salinity in water.…”

“…Compared with stock tanks and hydrocyclones, flotation has the characteristics of rapid treatment of large amounts of oily wastewater. 6 Either induced gas flotation or dissolved gas flotation can effectively remove suspended micro-oil droplets in wastewater, 7−9 These methods are formed by the attachment of an oil droplet to a gas bubble to form an aggregate. The large density difference between the oil−bubble aggregate and water accelerates the rise in velocity of the aggregate to the surface of the water.…”

“…When the film thickness is less than 100 nm, the disjoining pressure between film surfaces becomes the main driving force. 6 Capillary pressure increases as the size of the gas bubble decreases. This induces high capillary pressure to overcome the pressure barrier.…”

“…For disjoining pressure, with an increase in salinity, the zeta potential of the oil droplet decreases. 6 barrier. It is helpful to reduce the induction time by increasing salinity in water and decreasing bubble size.…”

Atomic Force Microscopy Study of Non-DLVO Interactions between Drops and Bubbles

“…Liquid drops/air bubbles dispersed in another immiscible liquid are ubiquitous in industrial productions including food, pharmacy, cosmetics, and petroleum energy. − Such multiphase systems are, for the most part, noted as emulsions or foams typically consisting of two phases. , A wealth of research works regarding both the static and dynamic interactions between homodispersed monomers have been carried out to provide insight into the stabilization mechanism of emulsions and foams. − The more complicated heterointeraction between drops and bubbles dispersed in liquid has also attracted attention due to its practical significance in applications such as air flotation and surface wetting. − One of the complexities of drop–bubble systems is that the interaction appears to be material specific . For instance, oil drops and bubbles dispersed in aqueous solutions tend to readily flocculate, while water drops and bubbles dispersed in nonpolar liquids intensely repel each other (see Results and Discussion section).…”