Particle-to-bubble adhesion in gas/liquid/solid slurries (original) (raw)
Related papers
Adhesion of solid particles to gas bubbles. Part 1: Modelling
Chemical Engineering Science, 2006
Particle-to-bubble adhesion is important in the areas of anti-foaming, in flotation processes and in multiphase slurry reactors. In the present work we particularly address the latter. The behaviour of fine catalyst particles adhering to gas bubbles in aqueous media is governed by the surface hydrophobicity. This adhesion on its turn influences the G-L mass transfer, bubble coalescence and the particle agglomeration. Existing models for the quantitative description of adhesion of particle to a G-L interface usually assume nonporous, spherical particles with a smooth surface and a well-defined contact angle. As catalyst particles are normally highly porous, have a rough surface, and an irregular shape, we developed a generalised model describing the adhesion of particles to a gas bubble based on maximum adhesive and cohesive forces as the main parameters. This model describes adhesion of: (i) a single spherical particle, (ii) a monolayer of particles, and (iii) a particle agglomerate. The cohesive forces between particles play a key role. For small cohesive forces, the particles can either adhere as a single particle or as a monolayer, while stronger cohesive forces allow multilayer adhesion or adhesion of particle clusters via one or few particles.
Chemical Engineering Science, 1991
The adhesion of small particles to a gas bubble in water is studied with the aid of a modified bubble pickup (BPU) method. The particle-to-bubble adhesion is revealed in the angle cc,, by which the gas-bubble surface is covered by adhering particles under static conditions. The value of u,,, depends on the particle and bubble sizes and on the physical properties of the three phases involved, especially on the eflective contacz angle 8,. A "particles-to-bubble adhesion" (PBA) model, baaed on a balance of forces under static conditions, is developed to calculate the value of eE from the measured values of amrx. The value of eE measured according to the BPU method reflects the particle-to-bubble adhesion encountered during flotation processes and in slurry reactors. Experiments carried out under static conditions with air bubbles in water and commercially available catalyst particles showed that 8, is smaller than the contact angle 0 which occurs at "flat" solid and liquid surfaces. In accordance with the extended Young-Duprt equation, the value of i3 can be obtained by extrapolation of measured B, values to a value where the curvatures of the surfaces are zero. The particle-to-bubble adhesion for the hydrogen-water-Pd/C system is much larger than that for the air-water-Pd/C system. For the hydrogen-water-Pd/Al,0, and the hydrogenwater-Pd/BaSO, systems, the particle-to-particle cohesion dominates the particle-to-bubble adhesion resulting in hardly any attachment of the catalyst particles to the hydrogen bubbles.
Particle–Bubble Attachment in Mineral Flotation
Journal of Colloid and Interface Science, 1999
Attachment efficiencies of rough, angular, methylated quartz particles with nitrogen bubbles are derived from experimental capture efficiency data in conjunction with a collision model termed the Generalized Sutherland Equation (GSE). The methylated quartz particles ranged in size from 7.5 to 70 m equivalent diameter and had advancing contact angles between 33°and 74°. They heterocoagulated with nitrogen bubbles between 0.77 and 1.52 mm in diameter in 0, 0.01, or 0.1 mol dm ؊3 KCl. The attachment efficiencies decreased with increasing particle size and bubble size, but increased with particle contact angle and KCl electrolyte concentration. These attachment efficiency data were then used to test the Dobby-Finch attachment model for potential flow conditions. The latter model was modified so that the conditions of approach of the particle toward the bubble surface are the same as those defined previously in the GSE collision model . Satisfactory agreement was obtained between the experimental attachment efficiencies obtained in this study and those calculated with the Dobby-Finch model. In the attachment efficiency calculations, the induction time (t ind ) varied with particle size (d p ) according to the well-known equation, t ind ؍ Ad p B . The parameter B, with a value of 0.6, was found to be independent of particle size, particle contact angle, bubble size, and KCl electrolyte concentration. Conversely, the value of the parameter A was dependent on the particle contact angle, especially for contact angles smaller than 50°, and on the bubble size but to a lesser extent on the electrolyte concentration. The value of A decreased with an increase in particle contact angle and an increase in bubble size. The values of the induction time obtained in this study are in a reasonable agreement with experimental and calculated induction times reported in the literature.
Journal of Colloid and Interface Science, 1999
Fine bubble attachment onto a solid surface in an impinging jet flow was analyzed within the framework of DLVO theory. The effects of hydrodynamic convection, van der Waals (VDW) interaction, electrostatic double-layer (EDL) interaction, and gravitational force on bubble attachment rate (in terms of the Sherwood number) were examined in detail. The analyses showed that due to large Peclet number and gravity number for gas bubbles the behavior of the bubble attachment is significantly different from that of colloidal particle deposition in some aspects. Specifically, it was demonstrated that within a certain range of physicochemical conditions, gas bubbles can attach onto a solid surface despite the existence of repulsive VDW interaction force and the fact that the surfaces of both the bubble and the solid collector carry the same sign of electrostatic potentials. This is attributed to the role played by the short-range attractive asymmetric EDL interaction and the strong hydrodynamic and gravity forces, without any need for the so-called hydrophobic interaction force. In addition, it was also shown that the models derived for the impinging jet system can be used to evaluate transport of fine gas bubbles onto a large particle surface, suggesting that the information extracted from the impinging jet geometry can be applied to the analysis of flotation processes.
Bubble–particle attachment and detachment in flotation
International Journal of Mineral Processing, 1999
The mechanism by which particles and bubbles interact captures many of the central concepts of colloid science and hydrodynamics and is an example of heterocoagulation. Hydrodynamics, Ž . interfacial including capillary forces, particle and bubble behaviour and solution chemistry are all interwoven. The processes of attachment and detachment are focused upon here. We deal with the identification of a flotation 'domain', the deformation of a bubble surface upon interaction with a solid surface, the kinetics of three phase contact line expansion and the determination of attachment efficiencies through to the direct measurement of bubble-particle interaction forces. The results, concepts and implications of this work are discussed. q 1999 Elsevier Science B.V. All rights reserved. 0301-7516r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
Chemical Engineering Science, 1992
The effect of small gas-adsorbing particles on the quasi steady-state absorption rate of a gas into a degassed slurry is investigated in an agitated slurry reactor in which no chemical reaction occurs. This investigation shows that, in a slurry reactor, gas-adsorbing particles can adhere to gas bubbles so that during steady-state operation a fraction r of the gas-liquid interface ls covered by adhering particles, resulting in an enhancement of the gas-absorption rate with respect to the particle-free situation. A model is derived to calculate the enhancement of the physical gas-absorption rate as a function of the fraction of bubble-surface coverage r at different particle concentrations in the slurry. This Enhanced Gas-Absorption mode1 is experimentally verified by flotation experiments and by hydrogen absorption into aqueous solutions containing different concentrations of small catalyst particles.
Industrial & Engineering Chemistry Research, 2000
The impinging jet technique, a direct microscopic observation method, is presented to fundamentally study micron bubble attachment onto a solid surface (collector) under wellcontrolled stagnation flow conditions. The bubble-collector attachment near the stagnation point of an impinging jet is analogous to bubble-fine solid interaction, which is of interest to flotation processes. In this work, bubble attachment experiments were conducted for sodium chloride solutions with various concentrations (10-1-10-4 M) and pH values (2.5-9.0) under a fixed flow intensity (in terms of Reynolds number Re) 200). In addition, the effect of metal ion valence on the bubble attachment was examined as well. Results have showed that the bubble attachment flux was dependent on both solution concentration (ionic strength) and pH, suggesting a strong impact of the electrostatic double layer interaction. In the presence of multivalent metal ions, the bubble attachment rate was noticeably enhanced.
Influence of particle shape and roughness on the induction period for particle-bubble attachment
2012
Within the flotation community a belief has developed that some particle shapes are more 'floatable' than others. This is usually attributed to an influence of particle shape or roughness on the induction period required to achieve attachment between the particles and the air bubbles in the pulp. Up to now, such measurements have not been able to readily isolate the effect on individual flotation subprocesses. In contrast, our experimental apparatus, the CSIRO Milli-Timer, enables us to directly observe the process of particle-bubble interaction and attachment by means of a high-speed video recording, thus providing a direct measure of the induction period for attachment.
Particle–bubble interaction and attachment in flotation
Chemical Engineering Science, 2011
Flotation is an important unit operation in the minerals industry, among others. Current state-of-theart flotation modelling combines computational fluid dynamics (CFD) with user-defined algorithms based on the ''induction time'' concept to describe selective bubble-particle attachment and separation of hydrophobic and hydrophilic particles.
Attachment of solid particles to air bubbles in surfactant-free aqueous solutions
Chemical Engineering Science, 2004
This paper presents a mechanism to explain the attachment of solid particles to air bubbles in surfactant-free aqueous solutions where both solids and air bubbles have the same sign of zeta potential via investigating the mechanical properties of micro air bubbles and the adsorption of hydroxide on air bubble surfaces.