Presence Of Frother Research Articles

Effect of ultrasound pre-treatment on carbonaceous copper-bearing shale flotation

Although numerous studies have been implemented on identifying the impact of acoustic waves on mineral beneficiation, its fundamental aspects remain unclear in the literature. The present work, for the first time, systematically investigates the role of ultrasound pre-treatment (UPT) in the carbonaceous copper-bearing shale flotation. To this end, conditioning was carried out at different powers of applied ultrasound. Non-treated and UPT shale flotation tests were performed in the presence of frother (MIBC) and collector (KEX). To analyse particle surface charge variation and collector adsorption properties after application of UPT, zeta potential and ultraviolet–visible spectroscopy measurements were implemented, respectively. The generation of sub-micron bubbles due to the acoustic cavitation was characterised by laser-based particle size measurements. Shale hydrophobicity was determined using the sessile drop and captive bubble techniques.The micro-flotation results showed that the mass recovery increased by 40% at 20 W of applied ultrasonic power. The positive effect of UPT on the copper-bearing shale flotation was related to: i) generation of ultrafine bubbles due to the acoustic cavitation phenomenon and ii) the cleaning effect through transient bubble collapse. However, rigorous ultra-sonication diminished the recoverability of the sample owing to the less intensified number of ultrafine bubbles on the particle surfaces and formation of free H and OH radicals, which led to the oxidation of particle surfaces. These statements were correlated well with the observations of the zeta potential, particle size analysis and quantified ultrafine bubbles. Finally, we briefly highlighted fundamental knowledge gaps in flotation and ultrasound-related issues for future work.

Nanobubble assisted flotation separation of complex Pb–Cu–Zn sulfide ore – Assessment of process readiness

ABSTRACT A considerable difference exists between the flotation separation of artificial minerals and real low-grade ores processing where selectivity would be the main issue. Nanobubble-assisted (NB) flotation investigations have been mostly examined with pure materials and a narrow particle size range, less on complex sulfide ores. This study considered NB flotation for processing complex Pb-Cu-Zn sulfide ore in two different size ranges and various conditions to assess the process readiness. Metallurgical NB flotation responses (recovery, grade, kinetics, and selectivity index) were determined, compared to conventional tests. Outcomes revealed that an inclusive size fraction (−150 µm) could result in a higher selective process than a fine fraction (- 38 µm). In contrast, mass recovery and kinetics were higher for the fine one. In general, adding NBs compared to the conventional (CB) could improve the flotation metallurgical responses; however, the way NBs were generated would be key. NBs generated in the presence of frother (NBF) could produce higher mass and water recoveries while decreasing selectivity. In general, different setups’ flotation products showed the following selectivity order of Pb-Cu sulfides: NB>NBF>CB. These results opened a new approach for considering different NB generation conditions when they are going to use in various flotation stages.

Bubble Size in a Flotation Column with Oscillatory Air Supply in the Presence of Frothers

ABSTRACT Oscillatory air supply has demonstrated advantages over conventional steady air supply in froth flotation with diffused aeration, but the interaction between oscillatory air supply and frother in determining bubble size remained unclear. In the present work, we measured the size of air bubbles in a laboratory scale flotation column with common frothers such as MIBC, Dowfroth 250, and polypropylene glycol with an average molecular weight of 425 (PPG 425), with conventional steady air supply and with oscillatory air supply. The oscillatory air supply was converted from steady airflow using a fast-switching solenoid valve with the main operating parameters being switching frequency and on/off time ratio. In the absence of frother, the Sauter mean bubble diameter (d 32) remained the same with oscillatory air supply replacing steady air supply, but the d 32 decreased by 13–35% in the presence of frother. It was also found that the critical coalescence concentration (CCC) of each frother were reduced by 11–69% using oscillatory air supply to replace steady air supply. The degree of reduction in d 32 or the CCC appeared to be dependent on the oscillatory airflow condition (i.e., frequency and on/off time ratio) and frother type. The present work also confirms the recent findings by others that the CCC is not solely a material property of frothers.

Evaluation of kinetics and thermodynamics of a naturally hydrophobic coal flotation in the presence of frother and regulated with pH

ABSTRACT Zeta potential of coal particles and kinetics of flotation along with the maximum recovery after a long time of fractionated flotation of naturally hydrophobic coals, both as a function of pH, were investigated. Empirical relations between the 1st order rate constant of flotation and zeta potential as well as the maximum recovery and zeta potential were established. Since fractionated flotation has features similar to chemical reactions, thermodynamic relations between maximum recovery and zeta potential as well as between rate constant and zeta potential were found. It was determined that the 1st order rate constant depends on two constants: flotation equilibrium constant and activity coefficient of surface electrical potential. It also depends on two variables: surface electrical potential (approximated with zeta potential) and the rate constant of the particle-bubble aggregate (flotulas) disintegration being a function of surface electrical potential. The values of the flotation equilibrium constant, activity coefficient of surface electrical potential and reverse process rate constant were determined. These parameters (especially flotation constant and activity coefficient of surface electrical potential) can be used for comparison of different flotation systems. Also useful for comparison purpose are kinetico-thermodynamic limits (Rmax vs k1) and Arrheniusan-type (ln k 1 vs ξ) plots.

The synergistic interaction between dithiophosphate collectors and frothers at the air-water and sulphide mineral interface

Dialkyl dithiophosphates (DTP) are commonly used as primary or secondary collectors in base metal sulfide and platinum group mineral flotation. However, evidence in the literature suggests that, under basic conditions, DTP does not adsorb onto certain minerals. The purpose of this study was to investigate the interactions between DTP or xanthate collectors and frothers at the solid-liquid and air-liquid interfaces. Microflotation and contact time tests showed that DTP synergistically improved recoveries and attachment probabilities of galena and pyrite in the presence of frother. These improvements were not seen for any of the single reagents or, most importantly, for mixtures of a xanthate collector and frother. By measuring the residual collector concentration in solution, it was shown that no DTP adsorbed onto the galena surface and only minimal amounts onto the pyrite surface, either in the presence or absence of frother. In contrast, all of the xanthate collector adsorbed onto both pyrite and galena. Investigations at the air-water interface included surface tension and bubble size measurements. These showed that DTP, unlike xanthate, was weakly active at the air-water interface, but did not show evidence of synergistic interaction with frother. It was concluded that DTP can have an alternative mechanism of flotation enhancement to conventional collectors by adsorbing at the air-liquid interface and not the solid-liquid interface. Various theories of the detailed mechanism are discussed in the paper.

Contribution of particle shape and surface roughness on the flotation behavior of low-ash coking coal

ABSTRACTIn 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.

Surface roughness in bubble attachment and flotation of highly hydrophobic solids in presence of frother – experiment and simulations

Surface roughness in bubble attachment and flotation of highly hydrophobic solids in presence of frother – experiment and simulations

Break-up in formation of small bubbles: an energy consideration

ABSTRACTThe formation of small bubbles in flotation is usually accomplished by the use of frothers, or sometimes is due to the presence of inorganic salts in the process water. The effective mechanism associated with the presence of these solutes is generally considered to be coalescence inhibition. However, recent work has demonstrated that the presence of frothers and salts also reduces the size of bubble at the initial formation stage. In this paper, we adapt the same experimental setup to investigate the time that it takes for a bubble to form; for a known system power input, the energy to form a bubble can then be estimated from the time. The hypothesis is that the presence of frother and salt will reduce the time for a bubble to form, which can be interpreted as an added energy component being derived from the solute. Testing different types and concentrations of frothers and salts, the hypothesis is supported: the mechanical energy required to form a bubble decreases by about 10% in the presence of these solutes.

Break-up in formation of small bubbles: Break-up in a confined volume

Small bubbles play the critical role in flotation of providing the large interfacial area for collecting and transporting selected (hydrophobic) mineral particles. The generation of these bubbles is a physical process chemically assisted by addition of surfactants (frothers). The prime action of frothers is commonly considered to be coalescence inhibition. In contrast, the possible role of frothers in the initial air break-up has attracted little attention. In this paper, we investigate the effect of frothers on break-up. An experimental setup was designed to isolate break-up from coalescence. Single bubbles were produced through mechanically-induced deformation of a trapped air volume, the design aiming to mimic the break-up of the air cavity behind an impeller blade in a mechanical flotation machine. The results show that the bubble size produced at break-up is strongly affected by the presence of frother, but weakly by the input mechanical energy and the volume of trapped air. The proposed mechanism is that frothers induce surface tension gradients which increase the instabilities along the air/water interface. For a finite air volume, increasing the number of instabilities means that more and smaller bubbles will break away. Frothers of different types and concentrations were tested.

MEASUREMENT OF CONTACT ANGLE OF COPPER- BEARING SHALES USING THE CAPTIVE BUBBLE METHOD

This paper describes the measurement of contact angle of the natural surface of copper-bearing shales immersed in solutions of selected reagents of various concentrations using captive bubble method. It demonstrates that the copper-bearing shales coming from Legnicko-Glogwski Copper Region develop natural hydrophobic properties in surfactant (frother) solutions and its hydrophobicity decreases from 82⁰ contact angle in distilled water, 78⁰ in C4E1 solutions, 76⁰ in C4E2 solutions, to 75⁰ in dodecylphenol solutions. These data show that the addition of frother causes a decrease of shale hydrophobicity but it can reduce stability of the thin film between the grain and air bubble. It means that flotation of copper- bearing shales in the presence of frother will only be possible provided specific concentrations.

The role of frother on the detachment of particles from bubbles

The influence of frother on the coalescence dynamic of bubbles coated with particles was investigated. Two bubbles grown at the tips of adjacent capillaries were loaded with methylated glass particles and pushed against each other to provoke coalescence. The event was recorded by a high speed camera and the change in the bubble shape at the moment of coalescence was analysed using an image analyser. Trends in oscillation behaviour and particle detachment in the absence and presence of frother were presented.

A test of the Tate equation to predict bubble size at an orifice in the presence of frother

Air bubbles of uniform size (ca. 1 mm diameter) were generated at a submerged orifice (glass capillary) under controlled frequency (down to ca. 0.06 s − 1 ) in aqueous solutions of frother (Dowfroth 250). The bubbles were sized with an imaging technique. One objective was to establish whether the Tate equation (static balance between buoyancy and capillary forces) could be used as a standard sizing calibration method. Another aim was to verify whether with decreasing surface tension (due to increasing frother concentration) the anticipated decrease in bubble size agreed with the equation prediction. An effect of frother was detected compatible with the role of surface tension but divided into two concentration regions, seemingly the result of a gradual change in bubble shape and wetting: > 6 ppm the bubble holds a spherical shape and the capillary appeared to be completely wetted while at ≤ 6 ppm a degree of non-wetting and bubble distortion (neck formation just prior to detachment) were apparent, supported by qualitative observations. In addition, at > 6 ppm the Tate value was only approached by decreasing the bubble frequency but not attained. Plausible causes for the failure to reach the predicted size are discussed.

Axial velocity profiles of single bubbles in water/frother solutions

The axial velocity profile (local velocity versus time or position) of single bubbles in the presence and absence of frother (Dowfroth 250, MIBC and pine oil) was measured in a water column over a distance of 4 m. Temperature along the column was maintained uniform and constant at 30°C by a temperature-controlled water jacket. Single bubble sizes 0.9, 1.5, 2.2 and 2.7 mm in diameter, covering a range of interest in flotation, were studied. A bubble generation frequency was selected such that velocity was independent of frequency. To follow the bubble during its rise, a video camera supported on a track and capable of moving vertically at adjustable speeds was employed. In the absence of frother, the profiles showed two stages: first the velocity increased rapidly and then decreased continuously over the 4 m. In the presence of frother, a third stage was reached, a constant (terminal) velocity. The terminal velocity was not dependent on frother concentration but, was a function of frother type. The shape and motion (path) of the bubble were also recorded. The observations are qualitatively explained in terms of time-dependent adsorption of surfactants, either present as contaminants in tap and distilled water or deliberately added in the case of frother.

Effect of fine solids and frother on gas hold-up and liquid mixing in a flotation column

The effect of fine solids and frother addition on gas hold-up and average bubble rise velocity in bubble swarm, and liquid phase mixing intensity has been studied in a 0.06 m flotation column. The variables studied were frother (pine oil) addition, feed solid concentration, gas and slurry velocities. The gas hold-up was estimated from the static pressure method, while the liquid phase mixing intensities were estimated using the pulse technique. In comparison with our previous air-water study [1], frother addition has a drastic effect on bubble characteristics, while the effect of solids is negligible except at low gas velocities for which complete suspension of solids from the gas distributor were not observed. The presence of small quantities of solids on the gas distributor resulted in bubble coalescence even in the presence of frother. In general, frother addition resulted in an increase in the liquid mixing intensity while the presence of solids had the opposite effect. Our results indicate that in the presence of frother, the bubbly flow regime is maintained over a wider gas velocity range.

硫化鉱物の浮選におけるα-テルピネオールとシネオールの作用に関する基礎的研究

The present investigation was undertaken in order to make clear the adsorption property of α-terpineol and cineol onto the mineral surface and to clarify these influences on the floatability of mineral particles surface-chemically.The gas chromatographic method was successfully used to analyze the concentration of a frother in the solution to determine the adsorption of α-terpineol and cineol on galena surface. The wettability of galena to frother was determined by capillary penetration tests. The floatability of galena was measured with a bubble pick up tube.The adsorption density of frother molecules on galena increased with increasing the concentration of a frother in the solution. The adsorption quantities of cineol on galena were larger than those of a-terpineol in either case with or without xanthate addition in the solution. The critical flotation curves of galena were determined when xanthate was used alone and also was used together with one of the frothers. The floatability of galena with xanthate increased greatly in the presence of frother, and decreased in the following order: cineol+ xanthate>α-terpineol+xanthate>xanthate.From these results, it was confirmed that the adsorption property of frother molecules onto the mineral related closely with the floatability of mineral and consequently the frother adsorption should play an important role in flotation.