On the Dispersion of Solid Particles in a Liquid Agitated by a Bubble Swarm
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INTRODUCTION
THE capture of solid particles by bubbles in liquid solutions is a phenomenon of importance in many industrial practices such as mineral processing, petrochemical refining, paper manufacturing, and waste water treatment. In addition, flotation can be used to promote the suspension and dispersion of solids in the liquid phase. When dispersed in a suspension, the activity of solids increases; they are either acting as a catalyst or undergoing a chemical reaction. This is why three-phase flows are also used in industrial catalytic processes, biological waste water treatment, and bacterial leaching processes.[1,2] In practice, it has been found that flotation is a complex process affected by numerous factors, such as particle-bubble surface chemistry, particle-bubble size, hydrophilic and hydrophobic properties of surfaces, electrostatic interactions, and hydrodynamic conditions. Two approaches are generally used to handle this problem. The first of these is to consider the full system and to study the influence of the global parameters (liquid and gas flow rates, chemical composition, and nature of particles) on the overall flotation efficiency.[3–6] The other approach focuses on the simplified system of one or few particles interacting with a single bubble.[7–14] The modeling of the flotation process is based on three elementary microprocesses, namely, the bubble-particle encounter collision,[15–21] the subsequent attachment,[19,22–25] and the detachment.[17,26,27] The aim of THOMAS BONOMETTI, Postdoctoral Associate, is with the Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611. Contact e-mail: thomas.bonometti@ imft.fr JACQUES MAGNAUDET, Research Director, is with the Institut de Me´canique des Fluides de Toulouse, UMR CNRS/INPT/ UPS, 5502, Alle´e Camille Soula 31400 Toulouse, France. PASCAL GARDIN, Technical Manager, is with the Process Engineering Department, Arcelor Research, Voie Romaine, BP30320, 57283 Maizie`res-le`s-Metz Cedex, France. Manuscript submitted January 11, 2007. Article published online September 18, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
the modeling of the flotation at this microprocess scale is to predict the global efficiency probability that can be used to size full plants. The ultimate purpose of this study is to obtain a better understanding of inclusion interaction with argon bubbles rising in liquid steel, taking into account interactions of bubbles as they occur in many steelmaking processes, such as ladle or continuous casting mould. The efficiency of inclusion entrapment by argon bubbles was already investigated by different authors.[28,29] The main conclusion is that an optimum bubble size could be obtained, but studies are restricted to single spherical bubbles. In the present study, the scale under consideration lies between the macroscopic plant scale and the microprocess scale. Our approach consists of investigating the motion and dispersion of solid particles in a liquid agitated by rising bubbles, which have spherical, spheroi
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