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

摘要

Flotation is an efficient pretreatment technology for oily water. In this paper, the effect of NaCl concentration on the process of an oil droplet covering a gas bubble was investigated experimentally. The results show that capillary waves are formed on the surface of the oil droplet during the coverage process. After capillary wave propagation, the surface of the droplet will form a constricted neck area, and the interfacial force of this area generates negative pressure, which induces the bubble to enter the inside of the oil droplet. The increase in NaCl concentration in water makes the neck area have greater suction. This results in the oil droplet stretching the bubbles more vigorously, promotes the spreading of the oil droplet on the surface of the bubble, and shortens the covering time. Moreover, in water with higher NaCl concentration, there is a greater flow velocity in the confluence region of the oil droplet.