Bubble-particle Interaction Research Articles

On the mechanism of hematite deposition on a metal surface under nucleate boiling conditions

The deposition of colloidal hematite particles on a stainless steel surface under nucleate boiling conditions at 100°C was studied using video and scanning electron microscopy techniques. Deposition was found to occur primarily at the interface boundary of the gas-bubble-liquid-solid (heated surface). The amount of deposit depended mainly on the size of the bubble and its residence time on the surface. Particle-bubble collisions apparently result in attachment of the particles to the bubble because of their hydrophobic nature and subsequent accumulation at the triple interface. These results suggest a mechanism of deposition which is different from the generally employed microlayer evaporation model. A “Partiubble Theory” which emphasizes the central role of particle-bubble interaction in the deposition of hydrophobic hematite suspensions appears more appropriate and is suggested.

Predicting flotation rates using a rate equation derived from first principles

Abstract A flotation rate equation was derived from first principles by Yoon and Mao (1996) by considering both hydrodynamic and surface forces involved in bubble-particle interactions. In the present communication, the equation is used to predict flotation results as functions of several important parameters such as contact angle, double-layer potentials of air bubbles and particles, and bubble size. The predictions are consistent with experience, and can be explained in view of the various subprocesses considered in the model development. Furthermore, the model suggests optimum conditions for achieving maximum separation efficiency.

The effect of external gas/slurry contact on the flotation of fine particles

An external contractor was investigated in order to evaluate its efficiency in collecting fine particles. For this purpose, a flotation column was equipped with an external flow-through sparger/contactor. The device was fitted on a slurry recycle stream and consisted of a porous stainless steel tube around which an air-tight rigid jacket was sealed. The device acted as a bubble generator and a bubble-particle interaction chamber. Variables including contractor length, pore size, collection tubing length, device placement, column length, and superficial slurry rate (inside the porous tube) were investigated. Size-by-size recovery plots were generated using a Brinkmann particle size analyzer. The results show that the slurry rate plays a significant role in the recovery of fine particles. Other parameters, such as collection tubing length, porous tube length and pore size, all play a role in fine particle recovery to varying extents. It is concluded that a combination of conventional internal bubble-coursing and external contact is ideal for the recovery of a wide range of particle sizes.

Cloning of a cDNA encoding the small subunit of cytochrome b 558 (cybS) of mitochondrial fumarate reductase (complex II) from adult Ascaris suum: Biochimica et Biophysica Acta — Bioenergetics Volume 1276 (1) (1996), Page 1-5

In the flotation process, bubble is a key factor in studying bubble-particle interaction and fine particle flotation. Knowledge on size distribution of bubbles in a flotation system is highly important. In this study, bubble distributions in different reagent concentrations, electrolyte concentrations, cathode apertures, and current densities in electroflotation are determined using a high-speed camera. Average bubble sizes under different conditions are calculated using Image-Pro® Plus (Media Cybernetics®, MD, USA) and SigmaScan® Pro (Systat Software, CA, USA) software. Results indicate that the average sizes of bubbles, which were generated through 38, 50, 74, 150, 250, 420, and 1000 μm cathode apertures, are 20.2, 29.5, 44.6, 59.2, 68.7, 78.5, and 88.8 μm, respectively. The optimal current density in electroflotation is 20 A/m2. Reagent and electrolyte concentrations, current density, and cathode aperture are important factors in controlling bubble size and nucleation. These factors also contribute to the control of fine-particle flotation.

Bubble-particle interactions in three-phase fluidised beds: effect of bed voidage

Bubble-particle interactions in three-phase fluidised beds: effect of bed voidage

Application of Extended DLVO Theory, IV: Derivation of Flotation Rate Equation from First Principles

A flotation model was developed by considering both hydrodynamic and surface forces involved in the process. The hydrodynamic forces were determined using a stream function and then used for estimating the kinetic energies that can be used for thinning the water films between bubbles and particles. The kinetic energies were compared with the energy barriers created by surface forces to determine the probability of adhesion. The surface forces considered included ion-electrostatic, London–van der Waals, and hydrophobic forces. Due to the insufficient information available on the hydrophobic forces for bubble–particle interactions, contributions from the hydrophobic force were back-calculated from the values of the flotation rate constants determined experimentally with methylated silica spheres. The results show that the hydrophobic force constants ( K 132) for bubble–particle interaction are larger than those ( K 131) for particle–particle interactions but smaller than that ( K 232) for air bubbles interacting with each other in the absence of surfactants. The K 132values determined in the present work are close to the geometric means of K 131and K 232, suggesting that the combining rules developed for dispersion forces may be useful for hydrophobic forces. The flotation rate equation derived in the present work suggests various methods of improving flotation processes.

Rheological investigations of sulphide mineral slurries

The flotation separation of ultrafine (−5 μm) sulphide mineral particles is inherently problematic, since even strongly hydrophobic fines have relatively low flotation rate constants. Selective aggregation of fines provides a route for enhanced flotation selectivity, but requires detailed knowledge and ultimately control of the electrostatic and hydrophobic inter-particle forces acting in concentrated sulphide mineral slurries. Rheological investigations offer insight into these inter-particle interactions. Rheological studies of ultrafine sphalerite particle slurries at pulp densities akin to those experienced in flotation practice were undertaken; the influence of pH, electrolyte concentration, activating copper (II) ions and ethyl xanthate ions on the level of pulp aggregation, as defined by the yield values and viscosities, are reported. The rheological behaviour of oxidised, and effectively hydrophillic, sphalerite particles (in the pH range 4 to 10) are controlled by electrostatic repulsive forces and yield values scale inversely with electrophoretic mobilities. Copper (II) activation, ethyl xanthate treatment and addition of slime particles dramatically affect pulp rheology and, depending on the particular concentrations and conditions employed, cause either aggregation or dispersion of the pulp. We show that an understanding of the theological behaviour of sulphide mineral pulps enhance our knowledge of particle-particle (and bubble-particle interactions) and may enable fine particle flotation performance to be optimised.

Colloidal Interaction between a Rigid Solid and a Fluid Drop

We present results of a theoretical study of the effect of surface deformation on a macroscopic system composed of a solid surface interacting with a fluid drop through electrostatic double-layer forces. The analysis involves numerically solving a Laplace equation suitably modified to describe the shape of a liquid drop subjected to a repulsive double-layer force. The latter is evaluated in nonlinear mean-field theory. Some analytical results are also given. The results indicate that although deformation need not be significant on the macroscopic scale, its effect on the interaction is significant and modifies the picture usually presented in DLVO theory. The decay length of the exponential repulsion deviates marginally from the Debye length, dependent on the interfacial tension of the drop. More significantly, at separations where the double-layer force becomes comparable to the internal pressure of the drop, the net force between the two bodies, the local radius of curvature of the drop, and the amount of deformation grow abruptly. The results of this work are relevant to emulsion stability, micelle, vesicle, and cell interactions, and recent experiments on bubble-particle interaction.

Principles and applications of dissolved air flotation

Principles of dissolved air flotation (DAF) discussed include: bubble formation and size, bubble-particle interactions, measures of supplied air, and modeling of the reaction and clarification zones of the flotation tank. Favorable flotation conditions for bubble attachment or adhesion to particles requires a reduction in the charge of particles and production of hydrophobic particles or hydrophobic spots on particle surfaces. A conceptual model for the bubble-particle reaction zone based on the single collector collision efficiency is summarized and discussed. An alternative modeling approach is considered. Clarification or separation zone modeling is based on particle-bubble agglomerate rise velocities. The application of DAF in drinking water treatment is addressed beginning with summaries of design and operating parameters for several countries. DAF should not be considered as a separate process, but integrated into the design and operation of the overall treatment plant. This concept shows that flocculation ahead of DAF has different requirements regarding floc size and strength compared to sedimentation. The efficiency of DAF in removing particles and reducing particle loads to filters needs to be integrated into DAF plant design. The impact on filtration performance is illustrated. Finally, fundamental and applied research needs are addressed.

Principles and applications of dissolved air flotation

Principles of dissolved air flotation (DAF) discussed include: bubble formation and size, bubble-particle interactions, measures of supplied air, and modeling of the reaction and clarification zones of the flotation tank. Favorable flotation conditions for bubble attachment or adhesion to particles requires a reduction in the charge of particles and production of hydrophobic particles or hydrophobic spots on particle surfaces. A conceptual model for the bubble-particle reaction zone based on the single collector collision efficiency is summarized and discussed. An alternative modeling approach is considered. Clarification or separation zone modeling is based on particle-bubble agglomerate rise velocities. The application of DAF in drinking water treatment is addressed beginning with summaries of design and operating parameters for several countries. DAF should not be considered as a separate process, but integrated into the design and operation of the overall treatment plant This concept shows that flocculation ahead of DAF has different requirements regarding floc size and strength compared to sedimentation. The efficiency of DAF in removing particles and reducing particle loads to filters needs to be integrated into DAF plant design. The impact on filtration performance is illustrated. Finally, fundamental and applied research needs are addressed.

A simple algorithm for the calculation of the terminal velocity of a single solid sphere in water

A method for predicting the terminal settling velocity of a single solid spherical particle in water is described. The terminal velocity is a function of, among others, particle size and the Archimedes number of 0 to 512000. The prediction is in agreement with that by using Stokes law or Allen law or Newton law for drag force and is useful for the modeling of the flotation elementary processes of the particle-bubble interaction.

What is the role of hydrophilic/hydrophobic surface forces and/or polar interfacial interactions in the interaction between bubbles and minerals?

It is known that the hydrophilic/hydrophobic surface forces operating between hydrophilic/hydrophobic colloids and surfaces strongly affect the particle-bubble interaction. The van Oss surface thermodynamics of interfacial interactions between two identical surfaces has been extended to particle-bubble attachment. A very simple formula for the hydrophilic/hydrophobic surface force component has been derived on the basis of the Lewis acid-base (AB) contribution to the work of adhesion. The applicability of the formula has been verified using the theory of thin wetting films.

A flotation column simulator based on hydrodynamic principles

Based on the hydrodynamic principles of bubble-particle interactions, a simulation package has been developed to predict the performance of flotation columns for sulfide flotation. The input variables to the simulator include particle size, bubble size, particle hydrophobicity, feed rate, feed composition, aeration rate, wash water rate, column height, etc. The problems associated with carrying capacity limit and froth overloading have also been considered in the model development. The simulation results show that operating a column considerably beyond this limits creates a circulating load between the froth and pulp phases, which is helpful for improving the product grade. Since the simulator is based largely on first principles, it can be useful for scale-up, control, optimization and trouble-shooting.

Hydrophobic interaction in flocculation and flotation 3. Role of hydrophobic interaction in particle—bubble attachment

In this paper, the particle—bubble interaction in flotation is analyzed and the potential energies of interaction are calculated. It is found that the hydrophobic interaction plays a predominant role in particle—bubble attachment. The so-called contactless attachment occurs only in the case of hydrophilic particle—bubble systems under proper conditions and is detrimental to flotation.

On the kinetics of froth flotation

The problem of froth flotation kinetics is treated as a transport phenomenon. Two coupled equations of balance are formulated which concern the particles attached upon the bubbles and the free particles in the pulp. The combined equations are solved and an analytical expression for the recovery as a function of time is obtained. The correctness of the theoretical derivation is checked by way of laboratory flotation experiments with glass ballotini (160–200 μm) in a wide pH range (pH 3–13) and collector dodecylamine hydrochloride (C 12H 25NH 2, HCL). The authors demonstrate that the recovery of glass possesses a well-defined maximum at pH 11.2. The cause of this maximum is sought for in the strong dependence of the three-phase contact (TPC) rate of expansion on pH. The role of the kinetic characteristics: time of TPC formation and TPC expansion rate are discussed with the help of the well-known criterion of floatability “attachment forces greater than the detachment forces” which is applied locally in any moment of the particle-bubble interaction.