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A stable attachment between bubbles and solid particles is essential for flotation. Therefore, it is particularly necessary to study the dynamic process that occur in the attachment of bubbles to a solid surface. In this paper, Teflon and plexiglass plates were used as hydrophobic and hydrophilic solid surfaces, respectively, and solid surfaces with roughness of 0.018 μm to 5.33 μm were prepared by polishing with sandpaper. The influence of roughness on the dynamic process in bubble attachment to solid surfaces with different hydrophobicity was studied via a high-speed camera (750 frames per second). It was found that roughness played a positive role in the attachment to the hydrophobic Teflon surface while a negative role in the attachment to the hydrophilic plexiglass surface in terms of the bubble's attachment to the solid plates. For a smooth Teflon surface, the formation of three–phase contact (i.e., the drainage of wetting film) took up to 95 ms, whereas for a very rough Teflon surface it took only 5 milliseconds. On the contrary, the high roughness prevented the bubble from attaching to the hydrophilic plexiglass surface. It was concluded that the increased roughness of Teflon plates was conductive to air entrapment in surface irregularities, inducing the rapid rupture of the wetting film on a very rough Teflon surface, while the increased roughness of the plexiglass plates resulted in "water pockets" in surface grooves, making the wetting film on the plexiglass surface stable. [ABSTRACT FROM AUTHOR]

In this study, the influence of particle shape and surface roughness on the flotation behavior of +0.25-0.5 mm low-ash coking coal particles was investigated. The low-ash coking coal particles with different particle shape and surface roughness obtained through grinding or crushing were measured, calculated, and analyzed using an optical microscope associated with Image J software. The flotation kinetics tests were conducted in a 0.75 L XFD flotation cell with the presence of frother and in the absence of collector in order to investigate the natural floatability of the low-ash coking coal particles. The flotation kinetics constant of low-ash coking coal particles was calculated through the first-order rate equation. The experimental results illustrated that the flotation kinetics constant increased with increasing the aspect ratio and roughness, while the particle owning high roundness and circularity value led to smaller flotation kinetics constant. Finally, the quantitative contributions of particle shape and roughness of low-ash coking coal particles on flotation performance were established. [ABSTRACT FROM AUTHOR]

• Hematite and quartz surfaces with different roughness were conditioned with starch and DDA. • Snap-in force of water droplets on the surfaces of the conditioned minerals was measured. • The largest variation in snap-in force was presented on the roughest surface. • Increasing roughness could enlarge the snap-in force difference for the two minerals. • There is a liner correlation between snap-in force and advancing contact angle. Surface roughness plays a vital role in flotation, because it has a pronounced impact on colloidal interactions, i.e., solid-liquid adhesion. In the previous studies, the natural mineral surfaces with various roughness were mainly taken as research object and the adhesion force of liquid on mineral surfaces with various roughness after conditioning with surfactants remains unknown. To fulfil this gap, in this study, the role of surface roughness in the snap-in force (An attractive force when the water droplet sharply and instantaneously spreads on the mineral surface in less than 0.1 s) of water droplets on hematite and quartz surfaces after conditioning with soluble starch and dodecylamine (DDA) was investigated using a high-sensitivity microelectronic mechanical balance. Results revealed that the effect of surface roughness on the snap-in force of water droplets on hematite surfaces was distinctly affected by the concentrations of both DDA and soluble starch, while the effect of surface roughness on the snap-in force of water droplets on quartz surfaces was only significantly affected by DDA concentration. After conditioning with 2 × 10−4 mol/L soluble starch and 4 × 10−4 mol/L DDA under pH value of 8.75, increasing surface roughness increased the snap-in force of water droplets on hematite surfaces and decreased the snap-in force of water droplets on quartz surfaces, suggesting that increasing surface roughness could enlarge the difference in the snap-in force of water droplets on the surfaces of the two minerals. In addition, the snap-in force was found to be a linear correlation with the advancing contact angle, providing evidence that surface roughness could affect the wettability and thereby the snap-in force. [ABSTRACT FROM AUTHOR]

Surface roughness of solid affects its interactions with gas bubbles in water. Here, we investigate the effect of surface nano-scaled (random) roughness, quantified with the root-mean-square (RMS) roughness from about 3 to 260 nm, on the adhesive strength of air bubble with natural hydrophilic hematite and pyrite surfaces using a microelectronic balance-camera system. The recorded values include bubble-mineral adhesion forces, water contact angles, and bubble base diameters during stages of air bubble attachment and spreading, maximum adhesion, and detachment. The results confirm weakening of adhesive forces for air bubble with hydrophilic surfaces of increasing nano-scale roughness. The study reveals a linear dependency between adhesion force and RMS roughness. The adhesion force was also found to be in a linear correlation with contact angle and its sine function, providing evidence for the surface tension force dominance in adhesion of bubble to hydrophilic surface with nano-scaled surface roughness characteristics of random nature. [ABSTRACT FROM AUTHOR]

• Quartz particles having nano-scaled surface roughness were produced in disc and ball mills. • Higher adsorption capacity of Ca2+and NaOL were observed for particles having higher roughness. • Both the wettability and floatability were affected by surface roughness. Surface roughness affects both the adsorption capacity of collector and mineral flotation separation. To investigate the role of surface roughness in quartz flotation, in this study, quartz particles were ground by different mills to produce two quartz samples with different nano-sized roughness, which was quantified with atomic force microscopy (AFM). Flotation experiments were carried out using CaCl 2 as an activator and sodium oleate (NaOL) as a collector. The results of flotation experiments showed an excellent performance with high recoveries for the rough quartz particles in contrast to the case with the smooth ones. Surface chemical aspects for the role of surface roughness in flotation were investigated through measurements of X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscope-Energy Dispersive Spectrometry (SEM-EDS), collector adsorption capacity and contact angle analysis. Both XPS and SEM-EDS results demonstrated larger adsorption capacity of Ca2+ for the rough quartz particles due to more adsorption sites provided by larger specific surface area. The NaOL adsorption capacity results also confirmed that larger surface roughness corresponded to higher adsorption capacity of NaOL. Subsequently, the contact angle results revealed that after interacting with NaOL the rough quartz particles presented more hydrophobic. Combined with flotation tests and surface chemical analysis, it might be arrived that surface roughness affected the adsorption capacity of both Ca2+ and NaOL, therefore impacting the wettability and floatability of quartz particles. [ABSTRACT FROM AUTHOR]

• Magnesite surfaces having RMS = 2 to 240 nm roughness were produced via polishing. • Attachment, adhesion and detachment of water droplets and air bubbles were recorded. • Induction time increased and adhesion force decreased for bubbles on rough magnesite. • Nano-roughness enhances the adhesive strength of water with magnesite surface. Surface roughness affects the interactions of solids with droplets and bubbles. In this study, natural magnesite lumps were polished by a series of sandpapers and diamond to produce four magnesite specimens having 2 to 240 nm root-mean-square roughness. The dynamic measurements of attachment, spreading, adhesion, and separation with a high-sensitivity microelectronic mechanical balance revealed the effect of surface nano-scaled roughness on the induction time and forces of spreading, adhesion and separation for both water droplets and air bubbles. It was found that the increasing nano-scaled roughness enhances the spreading of water on hydrophilic magnesite and strengthens the water-magnesite adhesive contact. Nano-roughness also causes delays in attachment of air bubbles to magnesite surface, inhibits displacement of water by adhering air bubbles, and reduces the adhesive strength of air bubbles to the magnesite surface, factors that might slow down the flotation separation. [ABSTRACT FROM AUTHOR]

Higher surface roughness not only benefits the aggregation of particles, but also facilitates the attachment between bubble and particles, resulting in a perfect flotation. Figure Possible mechanism of surface roughness affecting magnetite flotation. It is well known that surface roughness of mineral particles has a significant influence on their flotation behaviors. In this investigation, magnetite was ground in rod and ball mills to generate particles with similar dimension and shape but varying degree of surface roughness, which was quantified using Atomic Force Microscopy (AFM). The influence of surface roughness on the floatability of magnetite particles was performed by flotation tests using an XFG flotation machine. Flotation tests indicated magnetite particles possessed higher surface roughness had higher flotation recovery and larger flotation rate constant. The aggregation behaviors of different rough magnetite particles were compared for the first time via an optical microscopy. Results of the optical microscopic tests revealed that there were a large number of aggregations in the system of particles with higher surface roughness. A proposed model was deduced with the parameters carefully calculated (not arbitrarily selected) to analyze the bubble-particle interaction energy using an Extended DVLO (Derjaguin–Landau–Verwey–Overbeek) theory. The theoretical interaction energy points to lowering energy barrier when magnetite particles are covered with 28.03 nm asperities as compared to 9.47 nm asperities. The effect of surface roughness on mineral flotation was investigated from the view of both particle aggregations and energy barrier of bubble-particle attachment for the first time, which are the primary causes for differences in flotation performance. [ABSTRACT FROM AUTHOR]

• Magnesite particles having nano-scaled surface roughness were produced in disk and ball mills. • Both flotation recovery and kinetics were affected by size of surface nano-asperities. • The effect of surface roughness on flotation is diminished with increasing collector dosage. • A simple theoretical model shows that surface roughness benefits bubble-particle attachment. Roughness of mineral particles affects bubble-particle interactions and particle flotation separation. In this study, magnesite was ground in stainless-steel disc and ceramic ball mills to produce flotation feed material of different surface nano-roughness, which was quantified using atomic force microscopy (AFM). The effect of surface roughness on the floatability of magnesite particles was carried out by a micro-flotation kinetic test using an XFG flotation machine. The flotation results demonstrated both higher flotation recovery and larger flotation rate constant for particles having larger nano-asperities of rough particle surface. Additionally, the difference in cumulative flotation recovery between magnesite particles with different nano-roughness characteristics systematically decreased with increasing collector (sodium oleate) concentration from 25 to 150 mg/L. Contrarily, a difference in the value of flotation kinetics constant for particles with larger and smaller asperities remained at a level of 0.2–0.3 min−1 for the entire range of collector concentration. The interaction energy between bubbles and rough magnesite particles with different nano-roughness was estimated using an extended DLVO (Derjaguin–Landau–Verwey–Overbeek) theory. The theoretical interaction energy points to lowering energy barrier when the magnesite particles are covered with 12 nm asperities as compared to 2 nm asperities. It is therefore hypothesized that the energy barrier is a primary cause for differences in flotation performance of particles decorated with nano-asperities of different dimensions. [ABSTRACT FROM AUTHOR]

The surface roughness of mineral particles treated by different methods varies greatly, which will significantly affect flotation operations. In this investigation, magnesite particles with different surface roughness were obtained by ultrasonic treatment for different times. A new simplified mathematical model of rough particle-bubble interaction energy based on the extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory was formulated. Theoretical analysis shows that it is essentially consistent with the Wenzel wetting model. The parameters in the model were obtained by contact angle test, zeta potential test and AFM test. The interaction energy between a rough magnesite particle and a bubble at different NaOL concentrations was calculated. The results indicate that increasing the surface roughness of hydrophobic magnesite particles can significantly reduce the value of energy barrier (E m) that needed to be overcome for the adsorption between bubbles and magnesite particles. Meanwhile, it can push the location of energy barrier further away (that is, increase the critical hydration film thickness h cr when bubble-particle adhesion occurs), allowing magnesite particles to adhere to bubbles earlier and more easily, thereby improving the flotation performance of magnesite particles. However, the promoting effect of increasing surface roughness on the flotation of magnesite particles gradually weakened as the concentration of NaOL increased. [Display omitted] • A new simplified model of rough particle-bubble interaction energy was formulated. • The new mathematical model is essentially consistent with the Wenzel wetting model. • Surface roughness affects magnesite flotation especially at low NaOL dosages. [ABSTRACT FROM AUTHOR]

[Display omitted] • The surface roughness of quartz was increased by acid etching. • Acid etched roughness contradicts anionic and cationic flotation results of quartz. • Etched roughness increase active sites thus promote anionic flotation of quartz. • Etched roughness decrease negative charge thus impairs cationic flotation of quartz. Surface roughness has a significant effect on mineral flotation. In this study, the surface roughness of quartz was altered using HF etching and their values before and after acid etching were quantified using AFM. Anionic flotation experiments with CaCl 2 as activator and sodium oleate (NaOL) as collector, and cationic flotation experiments with dodecyl trimethyl ammonium chloride (DTAC) as collector were carried out for both the raw and acid-etched samples. The results showed that acid etching is beneficial to increase the surface roughness of quartz. The rougher quartz particle has higher recovery and quicker flotation rate during anionic flotation, while lower recovery and slower flotation rate during cationic flotation. The role of surface roughness in the discrepancy of these two flotations was investigated in terms of surface chemistry by X-ray photoelectron spectroscopy, UV spectrophotometer, surface force tensiometer, and zeta potential analyzer. The rougher sample was confirmed to have more unsaturated interfacial active sites, adsorbed more Ca2+ and NaOL, and exhibited higher hydrophobicity in anionic flotation. Differently, the rougher sample was verified to have less interfacial negative charge, adsorbed less DTAC, and exhibited weaker hydrophobicity in cationic flotation. Taken together, the surface roughness altered by acid etching has different effects on the adsorption capacity of NaOL and DTAC, thus affecting the wettability and floatability of quartz particles inconsistently in anionic and cationic flotation. [ABSTRACT FROM AUTHOR]