Effects of surfactant on bubble hydrodynamic behavior under flotation-related conditions in wastewater

Abstract

Bubble behavior is fundamental to the performance of froth flotation operations used in wastewater treatment processes. To fully understand and characterize bubble behavior under flotation-related conditions in wastewater, the high-speed photographic method has been employed to examine the motion of single bubbles and size distribution of bubble swarms with intermediate sizes ranging from 1 to 4 mm in the presence of surfactants in a laboratory scale flotation column. Both distilled water and synthetic municipal wastewater have been used to make solutions as well as two types of common surfactants. The instantaneous bubble motion has been recorded by a high speed camera. Subsequently, bubble trajectory, dimensions, velocity and distribution have been determined from the recorded frames using the image analysis software. The experimental results show that the addition of surfactant into wastewater has similar effects on bubble hydrodynamic behavior as in pure water (e.g., improving trajectory stabilization, dampening bubble deformation, slowing down terminal velocity, reducing bubble size and increasing the specific surface area of bubble swarm) due to the Marangoni effect. However, it is interesting to note that surfactant effects on single bubble hydrodynamics in wastewater are slightly stronger than those in pure water while surfactant effects on size parameters of bubble swarms in wastewater are significantly stronger than those in pure water. This finding suggests that besides surfactant, inorganic salts present in synthetic wastewater have an important influence on bubble dispersion.

Biosurfactants as Alternatives to Chemosynthetic Surfactants in Controlling Bubble Behavior in the Flotation Process

“…Because the bubble with 2.5 mm in size generally shows an ellipsoid shape [27], the dimensions parallel and perpendicular to the direction of bubble movement were measured by the best-fitted projected ellipsoid. The equivalent volume diameter (d eq ) and aspect ratio (A r ) of bubble were then calculated as follows [6,28], respectively:…”

“…As essential reagents, surfactants, also called frothers, are frequently added to flotation system to modify properties of the liquid-gas interface and to promote generation of small bubbles. Many recent investigations have been conducted regarding the role of surfactants in the flotation process by analyzing surfactant effects on bubble motion, gas holdup and removal or collecting efficiency [4][5][6][7][8][9]. A common viewpoint is that surfactants distributed unevenly over the bubble surface can induce a surface tension gradient, so-called Marangoni effect, which retards bubble deformation, slows down bubble velocity and prevents bubble coalescence, resulting in small bubble size and high gas holdup.…”

Rebound and attachment involving single bubble and particle in the separation of plastics by froth flotation

“…U im and U re ) is reduced evidently. According to Li et al [33], as the bubble rises in water contaminated by surfactant, the surfactant moves off the bubble front and accumulates in the bubble rear, which induces surface tension gradient and further causes the so-called Marangoni tangential shear stress on the bubble surface. The shear stress can make the bubble surface stiff.…”

Lateral Force Microscopy of Interfacial Nanobubbles: Friction Reduction and Novel Frictional Behavior

“…Interfacial friction in ambient environment has been extensively studied due to its importance in fields such as micro- and nanoelectromechanical systems (MENS and NENS) 1 , 2 , shear in particle or colloidal suspensions 3 , 4 , froth flotation 5 , 6 , and micro-fluidics 7 – 11 . In practice, low-friction surfaces can be achieved chemically by coating the surface with lubricants such as silicone oil, glycerin, jelly-type materials, and other modified molecular thin films 2 , 12 .…”