Bubble Attachment Research Articles

Use of “oily bubbles” and dispersants in flotation of molybdenite in fresh and seawater

Molybdenite - as all inherently hydrophobic minerals – is floated with the use of water-insoluble oily collectors. Such collectors can be used in flotation either after emulsification in water, but can also be brought to the point of particle-to-bubble attachment on the surface of bubbles (as oily-bubbles). In this paper we are testing the effect of oily-bubbles and the dispersants sodium hexametaphosphate (SHMP) and sodium silicate (SS) on the flotation of moleybdenite in seawater in alkaline environment. The results show that molybdenite recovery increases when kerosene is supplied on the surface of bubbles which was particularly important in the flotation of molybdenite at pH > 9.5 in seawater. SHMP dispersant had a strong positive effect on the recovery of molybdenite at pH > 9.5, the pH range known to cause depression of the molybdenite flotation when pH is raised to depress pyrite and magnesium species precipitate as hydroxo-complexes/hydroxide. The combined effect of the oily bubbles and dispersants allows for the molybdenite recoveries to reach to similar values to those achieved when using fresh water. The results of induction time measurements indicate that the attachment of bubbles to molybdenite is significantly improved when the bubbles are coated with a layer of kerosene.

Stochastic induction time of attachment due to the formation of transient holes in the intervening water films between air bubbles and solid surfaces

HypothesisBubble attachment to hydrophobic solid surfaces is influenced by the liquid film instability. Inclusion of transiently formed holes within the film rather than the so-called hydrophobic force in the theory is expected to better describe and explain film rupture and triple contact line formation in the bubble–surface attachment process. The significance of surface hydrophobicity and hole formation renders the stochastic nature of the induction time of attachment. ExperimentsA combination of high-speed video microscopy and theoretical analysis was applied to investigate the induction time of attachment and critical film thickness of air bubbles rising freely perpendicularly to silica surfaces of different hydrophobicities. FindingsFilm rupture occurred statistically for shorter induction times and thicker films on the more hydrophobic surface, rejecting the conjecture of hydrophobic force. Computed results of the critical base radius of the transient holes causing film rupture were merged together nicely, independently of surface hydrophobicity. The paper sheds light on the significance of hydrophobicity on the attachment process by means of a novel and easily implemented methodology, without relying on the debatable hydrophobic force.

The effect of carbon dioxide and nitrogen on pyrite surface properties and flotation response

In 1997 Newmont USA Ltd. introduced the N2TEC process for the flotation recovery of auriferous pyrite and other sulfide minerals in Carlin type ores, using nitrogen as the flotation gas, and low pH to prevent oxidation and hydrolysis of the pyrite surface. However, increased amounts of carbonate gangue minerals in certain Carlin type ores adversely affect the flotation recovery due to difficulties with pH control in the presence of carbonate minerals, i.e. calcite, dolomite, etc. Subsequently, it was discovered that by using CO2 for flotation, the pH of the system can be more effectively controlled, and consequently the recovery and rate of pyrite flotation can be improved significantly.In our current laboratory research on pyrite flotation chemistry these results were confirmed, as both fresh and oxidized pyrite particles exhibited an increased flotation response in CO2 saturated solution. It was found that the water contact angle at the pyrite surface increased in CO2 and N2 saturated solutions, while surface oxidation and bubble attachment time decreased. In addition to decreased surface oxidation and the influence of pH on surface hydrolysis, the significance of bubble attachment phenomena in these CO2 flotation systems helps to explain the improved flotation response.

Differences in dry and wet grinding with a high solid concentration of coking coal using a laboratory conical ball mill: Breakage rate, morphological characterization, and induction time

This study explored the influence of wet and dry grinding conditions on breakage rate, shape factor and surface roughness of ground particles, induction time (the threshold for particle–bubble attachment to occur), and flotation recovery. The experimental results indicated that the dry grinding breakage rate was much higher than the wet grinding one. The first-order region was limited to a relatively short grinding time, where it was considered that little or no secondary breakage occurred. With the increasing time, the dry grinding breakage rate increased, while it decreased for wet grinding (solid concentration of 70 vol.%). The differences in shape factor and surface roughness of the wet- and dry-ground samples were attributed to different breakage mechanisms and grinding energy amounts generated by those two types of procedures. The wet-ground particles were characterized by more irregular shape factors and smoother surfaces, and thus presented shorter induction times and higher floatation recoveries compared to the dry-ground ones.

Crude oil-bubble attachment in aqueous solutions of Deep Eutectic Solvents (DESs)

Flotation technology can be employed as a soil remediation technique in the removal of oil from contaminated soil. Studies have demonstrated that the efficiency of flotation technology can be significantly improved by using surfactants. Today, Deep Eutectic Solvents (DESs) which are referred to as “green” solvents are increasingly used as a replacement to traditional surfactants. In this study, the attachment of bubbles to crude oil was investigated in various molar ratios (1:2, 1:3 and 1:4) and concentrations (1000, 8000, 15,000, 18,500 and 22,000ppm) of DES. Characteristics of DESs including surface tension, interfacial tension and pH were initially measured. The attachment between bubble and crude oil was then investigated by measuring the contact angle and zeta potential in DES. These experimental results were then verified using the Derjaguin-Landau, Verwey-Overbeek (DLVO) theory. Results showed that DES is able to reduce the IFT of the crude oil-water system. DES 1:2 demonstrated the highest reduction in IFT at a concentration of 22,000ppm (32.4 mN/m) compared to DES 1:3 (35.3 mN/m) and DES 1:4 (35.8 mN/m) at the same concentration. This is hypothesized to be due to the decreasing proportion of cations (choline) to hydrogen bonds. Although the contact angle showed a decreasing trend with increase in DES concentration, the contact angle displayed good attachment (more than 90°) at all concentrations. Based on zeta potential measurements, the optimum attachment is suggested to occur at concentrations between 18,500 and 22,000ppm for all molar ratios of DESs. The DLVO theory further demonstrated that DES 1:2 exhibited the lowest energy barrier for all concentrations in comparison to DES 1:3 and DES 1:4. This theory also verified that DES concentrations above 18,500ppm are preeminent for optimum attachment between crude oil and bubble.

Improvement of hybrid jig separation efficiency using wetting agents for the recycling of mixed-plastic wastes

We have developed the hybrid jig which combines the principles of jig separation and flotation. However, the selectivity of bubble attachment in water was poor because most plastics have inherently hydrophobic surfaces; so, development of surface modification techniques for plastic particles would expand the application of hybrid jig to the material recycling of plastics. In this study, hybrid jig separation of polypropylene using glass fiber and high impact polystyrene having similar specific gravities and surface wettability were investigated with three wetting agents [Di-2-ethylhexyl sodium sulfosuccinate (Aerosol OT, AOT), sodium lignin sulfonate, and tannic acid]. The results showed that the probability of bubble attachment was influenced by wetting agents because of their strong effects on the surface tension of solution and surface wettability of plastics. The results also suggest that wetting agents could be utilized to control the selectivity of bubble attachment and improve the hybrid jig separation efficiency. In addition, since the hybrid jig separation of polyvinyl chloride and polyamide (nylon-66) using AOT was imperfect, a two-step approach, composed of a pre-wetting step (first step) in a solution containing the wetting agent (AOT) and hybrid jig separation in water (second step), is proposed.

Intensification of interfacial adsorption of dodecylamine onto quartz by ultrasonic method

Besides being a versatile mineral resource, quartz is also a common gangue mineral in mineral separation. The separation and enrichment of quartz minerals are particularly important in industrial production. Cationic surfactants of dodecylamine (DDA) is mainly used as collector in the quartz flotation as it consists of hydrophilic amino group which attach to the quartz surface, and the hydrophobic carbon-chain groups which make the quartz hydrophobic. So the adsorption behaviour of DDA is vital to the quartz flotation. In this paper, we examine an ultrasonic method for enhancing the adsorption of DDA in the froth flotation of quartz. The adsorption mechanism of the DDA collector onto quartz is systematically investigated via Fourier transform infrared spectroscopy (FTIR) measurements, adsorption heat measurements, adsorption amount tests, contact angle analysis, and induction time tests, and X-ray photoelectron spectroscopy (XPS) analysis. Our results indicate that ultrasonication does not change the functional groups of the DDA, however, the adsorption intensity with an adsorption heat of −26.56 J/g between ultrasonically treated DDA and quartz is fairly large. The adsorption amount of DDA onto quartz significantly increases after ultrasonically treated without increasing its concentration, and the maximum contact angle of quartz particles after conditioning by the ultrasonically treated DDA increase from 53.07° (for untreated DDA) to 66.13° at the concentration of 8 × 10−5 mol/L. In bubble attachment tests, the induction time between quartz particles and a bubble is observed to decrease from 30 ms to 20 ms compared to that without ultrasonic treatment, and coupled with a greater attachment performance of the DDA solution with ultrasonic treatment. And the XPS analysis confirms the adsorption of ultrasonically treated DDA onto quartz surface. Further, we perform micro-flotation tests to verify the enhanced adsorption of the ultrasonically treated collector onto the quartz surface for different initial concentrations; the results indicate that ultrasonication of DDA significantly improves the flotation recovery of quartz, particularly at moderate collector concentrations. This study is beneficial for understanding the interfacial adsorption and the ultrasonic intensification of DDA onto quartz particles.

Development of suitable product recovery systems of continuous hybrid jig for plastic-plastic separation

A modified jig called the hybrid jig was recently developed to separate mixed-plastics with similar specific gravities effectively using the concepts of bubble attachment, surface wettability and gravity separation. This method was effective in a batch-type jig setup, but when applied to a continuous-type jig setup, the efficiency of the process dramatically decreased. This drop in efficiency was attributed to the unintended negative effects of air bubbles on separation especially close to the screw-type extractor at the product end though this type of product recovery system was successfully applied to the RETAC and reverse jigs. To address this problem, a better product recovery system for continuous-type hybrid jig is proposed in this study, and the effects of air injection rate at different positions of the hybrid jig separation chamber were evaluated. The results showed that fluidization behavior of particles in the hybrid jig was influenced by not only water pulsation but also the rising motion of air bubbles. To improve the purity of heavy materials in the bottom layer products, two product recovery systems are proposed: (1) a screw-type extractor with one “separating” single-screen, and (2) a screw-type extractor with modified air injection and water pulsation (i.e., upward flow period was shortened).

Rupture of Wetting Films Formed by Bubbles at a Quartz Surface in Cationic Surfactant Solutions

AbstractExperimental studies were performed on the kinetics of the three‐phase contact formation and bubble attachment to a quartz surface in solutions of a cationic surfactant of various concentrations. By tuning the distance between the single‐bubble formation point and the quartz surface immersed in the solution, the influence of the state of the dynamic adsorption layer over a rising bubble on the mechanism of rupture of a wetting film formed was elucidated. Based on the unique methodology, allowing precise control over the initial degree of adsorption coverage at the detaching bubble, new evidence was found confirming the electrostatic character of the wetting film rupture in cationic surfactant solutions of low concentrations.

Enhancement of flotation response of fine low-rank coal using positively charged microbubbles

This study investigates the possibility of using positively charged (PC) microbubbles in pulp conditioning to improve the flotation response of fine low-rank coal. The surface properties of the coal are characterized by means of a zeta potential analyzer, scanning electron microscopy, and X-ray photoelectron spectroscopy. Batch flotation tests are conducted with the use of PC microbubbles, cetyltrimethylammonium bromide (CTAB) solution, and tap water in pulp conditioning. The roles of PC microbubbles in the coal flotation are illustrated by combining observations of particle–particle and particle–bubble interactions and extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory calculations. The results indicate that fine low-rank coal is negatively charged and contains a large amount of oxygen. In addition, the rough structure and the presence of numerous impurity mineral particles on the surface of low-rank coal afford adsorption sites for water molecules. These features of the coal render traditional collectors ineffective, whereas the presence of PC microbubbles significantly enhances flotation recovery. However, increasing CTAB concentration cannot continuously improve flotation performance with the use of PC microbubbles, possibly because the excess CTAB molecules can form bilayer or micelle adsorption structures on the coal surface, particularly on the mineral surface. The presence of PC microbubbles promotes particle–particle agglomeration and particle–bubble attachment by providing an additional attractive electrical double-layer force and enhancing hydrophobic interactions. The extended DLVO theory calculations agree well with the experimental results.

The Influence of Polysaccharides on Film Stability and Bubble Attachment at the Talc Surface

The wetting characteristics and water film stability at the talc surface have been studied, particularly the effect of polysaccharides such as guar gum, starch, and dextrin. Talc is a gangue mineral in the flotation of base metal sulfide ores, precious metal sulfide ores, and platinum group metal (PGM) sulfide ores. Talc surfaces were investigated using surface analysis techniques including atomic force microscopy, high-speed video bubble attachment measurements, and wetting film stability measurements using a synchronized tri-wavelength reflection interferometry microscope (STRIM). In the presence of polysaccharides, there is a significant increase in bubble attachment time at the talc surface, but only a slight change in contact angle, which suggests that polysaccharide depression of talc is due primarily to the slow rate of bubble attachment and not due to a change in contact angle. The critical rupture thickness (hc) for a hydrophobic talc surface was found to be 56 nm, while the hydrophilic phlogopite surface of similar structure has an equilibrium film thickness (he) of 25 nm. At low polysaccharide concentrations, the wetting films formed on the talc surfaces were unstable, but at high concentrations the wetting films became stable with similar thickness values as the critical rupture thickness, and bubble attachment did not occur. However, it was found that the critical and equilibrium film thickness values do not change significantly with the polysaccharide type or concentration. The results from this research help us understand further details of film rupture and displacement during bubble attachment.

Attachment, Coalescence, and Spreading of Carbon Dioxide Nanobubbles at Pyrite Surfaces.

Recently, it was reported that using CO2 as a flotation gas increases the flotation of auriferous pyrite from high carbonate gold ores of the Carlin Trend. In this regard, the influence of CO2 on bubble attachment at fresh pyrite surfaces was measured in the absence of collector using an induction timer, and it was found that nitrogen bubble attachment time was significantly reduced from 30 ms to less than 10 ms in CO2 saturated solutions. Details of CO2 bubble attachment at a fresh pyrite surface have been examined by atomic force microscopy (AFM) measurements and molecular dynamics (MD) simulations, and the results used to describe the subsequent attachment of a N2 bubble. As found from MD simulations, unlike the attached N2 bubble, which is stable and has a contact angle of about 90°, the CO2 bubble attaches, and spreads, wetting the fresh pyrite surface and forming a multilayer of CO2 molecules, corresponding to a contact angle of almost 180°. These MDS results are complemented by in situ AFM images, which show that, after attachment, CO2 nano-/microbubbles spread to form pancake bubbles at the fresh pyrite surface. In summary, it seems that CO2 bubbles have a propensity to spread, and whether CO2 exists as layers of CO2 molecules (gas pancakes) or as nano-/microbubbles, their presence at the fresh pyrite surface subsequently facilitates film rupture and attachment of millimeter N2 bubbles and, in this way, improves the flotation of pyrite.

The hydrophobic surface state of talc as influenced by aluminum substitution in the tetrahedral layer

Talc is both an important industrial mineral product recovered by flotation, and also in other cases, a gangue mineral of concern in the flotation of certain sulfide ores, such as the PGM ores from South Africa and from the United States. The talc face surface is naturally hydrophobic with a water sessile drop contact angle of nearly 80°, which accounts for its flotation recovery in one case, and its contamination of sulfide mineral concentrates in other instances. Due to the presence of impurities in the talc structure the surface properties change. One such effect is the presence of aluminum, which can replace silicon in the silica tetrahedral layer of the talc structure. This results in a charge imbalance on the face surface because Si+4 is replaced by Al+3. Sessile drop contact angle and bubble attachment time measurements were made, and these results were compared to the results from molecular dynamics simulations (MDS). The extent of aluminum substitution in the silica tetrahedral layer was considered, and the sessile drop contact angle was found to decrease with increased aluminum content, decreasing from about 80° for no substitution (talc) to 0° for extensive substitution (phlogopite). The water film was found to be stable at the surface of highly aluminum substituted crystals due to the interaction between water molecules and the increased polarity of the surface state. This stable water film restricts the air bubble from attaching to such face surfaces. However, in the absence of aluminum substitution, no interactions between the water molecules and the face surface were observed and the air bubble readily attached to the face surface. This study provides additional understanding of how aluminum substitution in the tetrahedral layer affects the fundamental surface properties of talc, paving the way for the design of improved reagents for talc flotation as an industrial mineral product, and for talc depression in the recovery of sulfide mineral concentrates.

The detachment of particles from bubbles at various locations in a turbulent flotation cell

In a mechanical flotation cell, turbulence is required to suspend particles, to disperse the air flow into small bubbles, and enhance the attachment of bubbles and particles. However, turbulent eddies may also cause particles to detach from bubbles. This paper describes experiments in which particle-laden bubbles were observed at various locations in a turbulent flotation cell. Two different types of particles were used for the flotation experiments: irregular silica particles, and smoothly spherical glass particles, both of Sauter mean diameter 180 µm. A specially designed flotation cell was constructed in which particles were attached to bubbles in an external fluidized bed. Bubble-particle aggregates were carried into the vessel by a stream of liquid rising through its base. Agitation was provided by a Rushton turbine impeller of standard design. The cell was configured so that bubble-particle aggregates could be introduced at a range of radial distances from the axis of the impeller shaft. The data were analysed with reference to the theory of Schulze (1982) for detachment of particles in a turbulent field, using the data of Lee and Yianneskis (1998) for the local energy dissipation rate. The detachment of particles at different locations was observed experimentally and compared with the Bond number calculated using local energy dissipation rates. No single critical Bond number was observed, the fractional detachment increasing gradually with increasing Bond number. Detachment was highest nearest the impeller as expected. The results generally followed the theory over a fourfold reduction of the dissipation rate. As the bubble size increased, particles were observed to detach more easily. For a given Bond number, the fractional detachment of particles was higher for the irregular silica particles, relative to that of the spherical glass particles under the same conditions. The relevance of existing detachment models in expressions for flotation kinetics is questioned.

Wetting characteristics of spodumene surfaces as influenced by collector adsorption

The selective flotation separation of spodumene from other aluminosilicate minerals remains a challenging problem in flotation chemistry, and the surface chemistry features are of fundamental importance. In this study, the interfacial chemistry features, particularly the wetting characteristics of selected spodumene surfaces (1 1 0, 0 0 1, 0 1 0, and 1 0 0 crystal surfaces), in the absence and presence of collectors, were studied by water contact angle and bubble attachment measurements, molecular dynamics (MD) simulation, and sum-frequency vibrational spectroscopy (SFVS). The experimental results revealed the interfacial water structure at spodumene surfaces. Contact angle, bubble attachment measurements, and MD simulation results showed that the four spodumene surfaces were naturally hydrophilic, whereas in the presence of collectors, preferential adsorption of sodium oleate on the (1 0 0) and (1 1 0) surfaces was found to create a hydrophobic surface state. Detailed analysis of the interfacial water structure was conducted in order to understand the wetting characteristics at the molecular level, and SFVS was used to study the state of collectors at selected surfaces. The MD simulation and SFVS results revealed that the natural state of the surfaces contributes to the distinct interfacial water structure and the adsorption state of collectors. It seems that unsaturated Al sites at the spodumene surface and their spatial locations account for chemisorption of sodium oleate, while electrostatic attraction appears to be the main driving force for dodecylamine adsorption.

A comparative study of turbulence models for non-premixed swirl-stabilized flames

ABSTRACTThe accuracy of turbulent swirl-stabilized flame simulation strongly depends on the choice of turbulence model. In this study, four 3D unsteady turbulence closures, including large eddy simulation, scale-adaptive simulation, and two detached eddy simulation variants, along with four RANS models, including RNG k−ϵ, SST k−ω, transition SST, and RSM, are examined for moderate- and high-swirl case studies. It is observed that the scale-adaptive simulation provides the most accurate results for almost all variables and both swirl conditions in the reactive flow. Only the 3D unsteady models predict the vortex breakdown bubble and flame attachment state correctly. However, based on our error analysis, the flow and composition fields predicted by the RANS models are in acceptable agreement with the experimental fields, especially the ones of transition SST when higher swirl number cases or minor species concentration are of interest. Moreover, it is concluded that the viscosity ratio criterion is a better measure of the local LES quality than the turbulent kinetic energy ratio, and the accuracy of a hybrid simulation may be much more dependent on the ability of the model to operate close to the RANS mode where the grid resolution is not sufficient for a resolving simulation than the fraction of the resolved kinetic energy. Finally, the propriety of the base (RANS) model of a DES for the application of interest is important, such that DES with realizable k−ϵ outperforms the commonly used DES with SST k−ω model.

Interpretation of Hydrophobization Behavior of Dodecylamine on Muscovite and Talc Surface through Dynamic Wettability and AFM Analysis

In this study, a new approach, “dynamic wettability”, and atomic force microscopy (AFM) imaging analysis techniques were successfully used to characterize the hydrophobization mechanism of the collector dodecylamine (DDA) on muscovite and talc surfaces. The attachment of bubbles to the minerals was studied through the dynamic contact angle to gain a detailed understanding of the hydrophobization mechanism of DDA on a muscovite and talc surface. AFM imaging and interaction forces were performed to explain the DDA adsorption mechanism on both minerals. Finally, flotation tests were performed to verify the effectiveness of these techniques. After treatments with DDA, the contact angles became much larger compared to initial angles, particularly for muscovite, and the attachment of bubbles on the talc surface was much easier than muscovite due to its natural hydrophobicity. From AFM imaging, both the muscovite and talc showed a similar tendency; the higher the DDA concentration, the more the adsorbed amount. However, the adsorbed amount of DDA on talc surface was obviously more than that on muscovite. As far as interaction forces are concerned, the maximum attractions occurred at certain different concentrations respectively for muscovite and talc and agreed well with the AFM-imaging results. Moreover, results obtained from flotation tests were promising and quite in agreement with the phenomenon of these techniques.

Anisotropic Polymer Adsorption on Molybdenite Basal and Edge Surfaces and Interaction Mechanism With Air Bubbles.

The anisotropic surface characteristics and interaction mechanisms of molybdenite (MoS2) basal and edge planes have attracted much research interest in many interfacial processes such as froth flotation. In this work, the adsorption of a polymer depressant [i.e., carboxymethyl cellulose (CMC)] on both MoS2 basal and edge surfaces as well as their interaction mechanisms with air bubbles have been characterized by atomic force microscope (AFM) imaging and quantitative force measurements. AFM imaging showed that the polymer coverage on the basal plane increased with elevating polymer concentration, with the formation of a compact polymer layer at 100 ppm CMC; however, the polymer adsorption was much weaker on the edge plane. The anisotropy in polymer adsorption on MoS2 basal and edge surfaces coincided with water contact angle results. Direct force measurements using CMC functionalized AFM tips revealed that the adhesion on the basal plane was about an order of magnitude higher than that on the edge plane, supporting the anisotropic CMC adsorption behaviors. Such adhesion difference could be attributed to their difference in surface hydrophobicity and surface charge, with weakened hydrophobic attraction and strengthened electrostatic repulsion between the polymers and edge plane. Force measurements using a bubble probe AFM showed that air bubble could attach to the basal plane during approach, which could be effectively inhibited after polymer adsorption. The edge surface, due to the negligible polymer adsorption, showed similar interaction behaviors with air bubbles before and after polymer treatment. This work provides useful information on the adsorption of polymers on MoS2 basal/edge surfaces as well as their interaction mechanism with air bubbles at the nanoscale, with implications for the design and development of effective polymer additives to mediate the bubble attachment on solid particles with anisotropic surface properties in mineral flotation and other engineering processes.

Three-phase contact line expansion during air bubble attachment to hydrophobic solid surface – experiment and modeling

Three-phase contact line expansion during air bubble attachment to hydrophobic solid surface – experiment and modeling

The enhanced flotation of coal by nanosilica particles

ABSTRACT It is well known that the stability of hydration film on the particle surface affected the particle-bubble attachment in a flotation process. In this paper, the effect of attached nanosilica particles on the stability of liquid film around the coal particles was investigated by measurements of viscosity of the coal pulp and the bubble attachment time for coal particles. The interaction energy between a nanosilica particle and a coal particle was calculated using the EDLVO theory. Results showed that the nanosilica-coal attachment was driven by hydration attraction. And the stability of liquid film was weakened with the attachment of nanosilica particles, which is probably due to the change of surface roughness. In this case, the bubble-particle attachment time was reduced and further improved the flotation recovery of coal.