Laboratory-scale Flotation Column Research Articles

Effects of agitation intensity and foam stability on the Floc-flotation of ultrafine minerals using a laboratory flotation column

In the present study flocculation flotation (floc-flotation) of ultrafine hematite and quartz was investigated in a laboratory-scale flotation column. A direct flotation scheme was used to float hematite using in-house synthesized n-octyl hydroxamic acid (OHA) as a collector. A polymer system containing tannic acid (TAN) and poly(ethylene oxide) (PEO) was used to flocculate quartz to reduce its entrainment. The effects of agitation intensity and foam stability on floc size distribution, entrainment reduction, and flotation kinetics/recovery were investigated. It was shown that the dual polymers TAN-PEO were effective in reducing quartz entrainment, and that the degree of entrainment reduction was affected by the intensity of agitation. A correlation was established between the mean floc size and a reduction in quartz entrainment. TAN-PEO dual polymer system also enhanced the flotation kinetics and recovery of hematite by OHA, originating from a synergistic effect between PEO and OHA. Therefore, higher separation efficiency was achieved from synthetic ultrafine hematite and quartz mixtures when TAN-PEO was added after OHA. The underlying mechanisms were studied by floc size distribution, surface tension, and foam height and decay time measurement. This work helps understand the relationship between hydrodynamic condition, flocs size, and mechanical entrainment when polymeric flocculation is used for entrainment reduction in fine and ultrafine minerals flotation.

Using Top-of-Froth Conductivity to Infer Water Overflow Rate in a Two-Phase Lab-Scale Flotation Column

The metallurgical performance of a flotation machine is largely defined by phenomena occurring in the froth zone. The water content in the froth affects recovery by influencing froth stability and mobility and, at the same time, reduces grade by mechanical entrainment of gangue particles in the overflow water. Efficient operation requires a compromise between the water carried by bubbles from the collection zone and that which overflows. It is believed that the most suitable operating strategy could be based on the measurement of froth water content, as a strong correlation with water overflow is anticipated. This work reports the testing results of an in situ electrical conductivity sensor continuously measuring the froth zone water content in a laboratory-scale flotation column. The test program included simultaneous measurement of froth conductivity and water overflow rates for changes in gas flow rate and frother concentration. The results show a stronger dependence of the measured top-of-froth water content on frother concentration than on the gas flow rate. A relatively linear trend was shown between top-of-froth water content and water overflow rate for a given air rate and frother.

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.

Optimization of flotation columns to provide added value of local sphalerite ore

Sphalerite is the most important mineral in the formation of zinc metal. According to regulation of Ministry ESDM No.5/2017 stated that the minimum grade of zinc concentrates to be exported is 51%. Therefore, it is necessary to do a beneficiation process for sphalerite ore to fulfil the requirements. Sphalerite is hydrophobic mineral, therefore it is the best way to processed sphalerite by flotation. Flotation is the process of concentrating valuable minerals from impurities based on the nature of the mineral surface. Column flotation is a flotation technology without an agitator as a producer of air bubbles like conventional flotation machines. Recovery is the most important factor in flotation and it shows the rate of acquisition of the flotation process. The purpose of this research was to determine the effect of air flow rates (2, 2.5, 3, 3.5, and 4 L / min.), percent solid (7.5%, 10%, 12.5%, and 15%), dose of reagent frother (10, 20, 30 and 40 ppm), and particle size of ore (-80 + 100 #, -100 + 140 #, -140 + 200 #, -200 #) on ZnS recovery. The research was carried out by using a laboratory scale flotation column with 4.6 cm in diameter and 150 cm column height. The flotation reagent used was activator (CuSO4), pH regulator (NaCO3), collector (PAX), and frother (dowfroth 1012). The highest recovery (90.29%) was achieved at a flow rate of 4.0 L/min, while on variation of particle size the highest recovery was 85.55% at (-100+140) #. The increase in percent solid or dilution of pulp is not always followed by an increase in recovery and the highest recovery ((71.26%) was achieved at 7.5% solid. In addition, recovery increases with increasing doses of frother, the highest recovery (86.04%) was achieved at 40 ppm doses of frother.

A Preliminary study of three-phase column flotation process monitoring using electrical capacitance volume tomography

A preliminary study of three-phase column flotation process using electrical capacitance volume tomography (ECVT) has been conducted. The purpose of this study is to investigate the possibility of ECVT method as a monitoring system by correlating the relative permittivity distribution (or three-dimensional image) with metallurgical performance (recovery of the process). Experiments were performed in a laboratory-scale flotation column with ECVT sensor embedded outside the pipe wall on the collection zone. The feed used was a synthetic ore consisting of sphalerite and silica with the purity of 99%. Process parameter used was air flow rate ranging from 2-4 l/m which each process was conducted for 10 minutes. The results showed that the ECVT method could observe the dynamic process of flotation, specifically in monitoring a feeding process and a separation process. They were indicated by increased and decreased relative permittivity distributions respectively. Relative permittivity signal and metallurgical performance have a good correlation and showed a positive correlation. These results show a prospect of ECVT method as the monitoring system in the flotation process, but further works need to be done for this monitoring system.

Development of a laboratory-scale flotation column with inlet bubble size measurement

This paper presents the development of a small-scale (1 in.) laboratory flotation column with online measurement of bubble size. In contrast to the systems that use sampling-for-image techniques and have the viewing chamber located at the top of the flotation device, the system employed here measures the bubble size via image analysis using a bubble size analyzer located at the bottom of the column using a well-referenced sloped viewing chamber. The main advantage of this configuration is that it allowed the measurement and monitoring of the bubble size during flotation experiments (three-phase system). This was possible because the sizes of the bubbles were determined before they entered the column; moreover, the “cloudy effect” caused by fine particles in the bubble viewing chamber was minimized owing to the use of an expansion chamber (named the bubble injection chamber). The image capture, processing, and analysis were automated, which rendered it possible to determine the bubble size distribution and mean bubble size (D32) of consecutive images every 5 s using a simple image analysis procedure. Two-phase experiments conducted to evaluate the system showed that the mean bubble size (D32) and gas holdup were within the ranges found in the literature. As expected, the holdup was dependent on the bubble size, which was strongly dependent on the frother concentration. Finally, some exploratory experiments were conducted to test the apparatus in a three-phase system. Recovery-particle size curves for different bubble sizes showed that mass recovery increases as the mean bubble size decreases, and the coarser the particles, the greater is the effect of the bubble size on the recovery.

On dealing with measured disturbances in the modifier adaptation method for real-time optimization

In this work, we propose the inclusion of the available information of measured or estimated disturbances in the modifier adaptation methodology for real-time optimization (RTO). The idea is to extend the applicability of this technique to processes wherein the disturbances affect the quantities involved in the necessary optimality conditions of the process. To do so, we include the estimation of process gradients with respect to both the decision variables and disturbances in the methodology. This approach was performed in a laboratory-scale flotation column, where the effects of changes in the feed characteristics on the economic performance of the process were analyzed. The influence of the availability of the disturbance information was also analyzed, considering immediate and delayed availability. In the latter case, the auto regressive integrated moving average model (ARIMA) was used as an estimator in each RTO iteration. The results show that the inclusion of the available disturbance information enables tracking of the optimum of the process under continuously changing feed conditions.

Improving column flotation of oxidized or ultrafine coal particles by changing the flow pattern of air supply

This paper proposes a simple method to improve the flotation performance of oxidized or ultrafine coals, that is, use of a solenoid valve to change the flow pattern of air supplied to a flotation column with a bubble diffuser/sparger. In the present work, the flotation tests were carried out at semi-continuous mode using a laboratory-scale flotation column to upgrade a coking coal in the absence of collector. An investigation of the effect of the frequency of oscillatory air on the flotation performance found that the preferred frequency was around 36 Hz. Further flotation tests for the coking coal with oxidation or without oxidation, at fine and ultrafine size fractions, were carried out with oscillatory air supply at 36 Hz, and the obtained results were substantially better than their counterparts with steady air flow.

Improving the performance of coal flotation using oscillatory air supply

Froth flotation is the most widely used method for beneficiation of fine coals. In flotation, the size of air bubbles is an important factor affecting the separation efficiency. The size of air bubbles generated by passing air through a bubble diffuser/sparger can be reduced by changing the air flow pattern from steady to oscillatory. In the present work, coal flotation with oscillatory air supply generated by a fluidic oscillator was investigated and the results were compared with those obtained with steady air flow. The flotation tests were carried out at semi-continuous mode using a laboratory-scale flotation column. The results suggest that use of the fluidic oscillator can lead to substantial reagent cost savings and help improve coal flotation efficiency. Further experiments were carried out to fundamentally understand the effect of different air flow patterns on the flotation performance. Compared to steady air flow, oscillatory air flow results in better gas dispersion, higher gas holdup, higher foam stability, and less axial mixing of fluid inside the flotation column.

Real-time optimization for a laboratory-scale flotation column

In this paper, a supervisory layer with real-time optimization (RTO) has been implemented in an experimental laboratory-scale flotation column for copper concentration. A two-stage and modifier adaptation (MA) methodology for RTO has been compared under structural, experimental and dynamic uncertainty. In addition, a gradient-free alternative for MA, called nested modifier optimization, has been proposed and tested. The results show that the KKT updates of the MA approach allow the process optimum to be determined under uncertain scenarios, unlike the two-stage approach. From the perspective of gradient modifiers, the performance of the nested methodology is comparable to the dual approach because previous past values are used to update the modifiers without requiring the gradient estimation step. In addition, the interaction of RTO with the regulatory layer must be considered to propose an optimal implementation.

Rebound and attachment involving single bubble and particle in the separation of plastics by froth flotation

Bubble–particle interaction is critical to the separation of particles by flotation which can be used in plastic recycling. The two particular processes of the interaction (rebound and attachment) are examined visually using high-speed photography in a laboratory scale flotation column. The effects of surfactant (concentration and type) and plastic material on these two stages are also studied quantitatively. The considered surfactants are Tea Saponin, SDBS and CTMAB, while the plastic materials are polyethylene, polypropylene and Teflon. A simple model of bubble attachment time is developed to analyse and interpret the experimental data. The results show that the presence of surfactant significantly affects the rebound process of a gas bubble, while the type of surfactant and plastic material seem to have slight effect. The bubble attachment process is a strong function of the surfactant and plastic material, which can be associated with the changing of bubble size and its hydrodynamic fluid resistance, contact angle on solid surface, as well as surface tension and viscosity of the solution. Such results are helpful for evaluation and analysis of the plastic flotation process, especially for the selection of reagents and objects at an early stage of design.

Visualized study on the interaction between single bubbles and curved solid surface in flotation separation process.

The present study has been devoted to bubble-curved solid surface interaction in water, which is critical to the separation of suspended particles by air flotation. For this purpose, two particular stages of the interaction (collision and attachment) have been examined visually using high-speed photography in a laboratory-scale flotation column. The effects of the surface material and surfactant concentration on these two stages have been also studied quantitatively. The considered solid materials are the cleaned glass as hydrophilic surface and Teflon as hydrophobic surface. The experimental results show that the presence of surfactant significantly affects the collision and rebound process of a gas bubble, while there is no obvious effect of the surface material on the rebound process. An increase in surfactant concentration has been observed to suppress the rebound number and maximal distance of the bubble from the surface. Moreover, the three-phase contact time of the bubble is a strong function of the surfactant concentration and surface hydrophobicity as well as of the bubble diameter. Another important finding is that the bubble attachment is only observed at the hydrophobic Teflon surface below the surfactant CMC (critical micelle concentration). Results of this study are relevant for deep understanding of the attachment mechanism and to determine the proper conditions for a selective flotation process.

Comparing the effect of biosurfactant and chemical surfactant on bubble hydrodynamics in a flotation column

Bubble hydrodynamics is fundamental to the performance of the flotation process widely used in the separation industry. To compare the effect of biosurfactants and chemical synthetic surfactants on bubble hydrodynamics in the flotation process, the motion of a single bubble and the size distribution of bubble swarms in various surfactants (rhamnolipid, tea saponin and Triton X-100) solutions were observed directly using a high-speed video camera in a laboratory scale flotation column. Bubble trajectory, dimensions, velocity and size distribution were then determined through image analysis. The results indicated that the addition of biosurfactants had the same significant effects on bubble motion and size distribution as chemosynthetic surfactants. The biosurfactant effect on bubble behavior was also found to depend on their type and concentration. In general, the effect of tea saponin was stronger than another biosurfactant (rhamnolipid) used in the present study. The present findings implied that some biosurfactants like tea saponin can replace chemosynthetic surfactants in controlling bubble behavior in flotation operation. This will contribute to promoting the use of green environmentally friendly flotation agents in the separation industry.

Biosurfactants as Alternatives to Chemosynthetic Surfactants in Controlling Bubble Behavior in the Flotation Process

AbstractTo examine the usage of biosurfactants as potential alternatives to chemosynthetic surfactants in controlling bubble behavior in the flotation process, a high‐speed photographic method was employed to measure the motion of single bubbles and the size distribution of bubbles in the presence of biosurfactants in a laboratory scale flotation column. Deionized water, rhamnolipid, tea saponin and t‐C8phenolethoxylateEO9 were used for making various surfactant solutions. Bubble trajectory, dimensions, velocity and size distribution were then determined from the recorded frames using the image analysis software. The results show that similar to chemosynthetic surfactants, the addition of biosurfactants has significant effects on bubble motion and size distribution. The addition of a small amount of tea saponin can significantly dampen bubble deformation, slow down terminal velocity, stabilize bubble trajectory, reduce bubble size and increase the specific surface area of bubbles due to the Marangoni effect. In addition, the biosurfactant effect on bubble behavior has been also found to depend on their type and concentration. The effect of tea saponin, fairly close to C8phenolethoxylateEO9, is stronger than rhamnolipid. The findings in the present study suggest that such biosurfactant as tea saponin may be good substitutes of chemosynthetic surfactants to control bubble behavior in flotation operation.

Effects of surfactant on bubble hydrodynamic behavior under flotation-related conditions in wastewater

Bubble behavior is fundamental to the performance of froth flotation operations used in wastewater treatment processes. To fully understand and characterize bubble behavior under flotation-related conditions in wastewater, the high-speed photographic method has been employed to examine the motion of single bubbles and size distribution of bubble swarms with intermediate sizes ranging from 1 to 4 mm in the presence of surfactants in a laboratory scale flotation column. Both distilled water and synthetic municipal wastewater have been used to make solutions as well as two types of common surfactants. The instantaneous bubble motion has been recorded by a high speed camera. Subsequently, bubble trajectory, dimensions, velocity and distribution have been determined from the recorded frames using the image analysis software. The experimental results show that the addition of surfactant into wastewater has similar effects on bubble hydrodynamic behavior as in pure water (e.g., improving trajectory stabilization, dampening bubble deformation, slowing down terminal velocity, reducing bubble size and increasing the specific surface area of bubble swarm) due to the Marangoni effect. However, it is interesting to note that surfactant effects on single bubble hydrodynamics in wastewater are slightly stronger than those in pure water while surfactant effects on size parameters of bubble swarms in wastewater are significantly stronger than those in pure water. This finding suggests that besides surfactant, inorganic salts present in synthetic wastewater have an important influence on bubble dispersion.

Nanobubble generation and its applications in froth flotation (part III): specially designed laboratory scale column flotation of phosphate

Froth flotation is used widely for upgrading raw phosphate. The flotation recovery of coarse phosphate (−1.18+0.425 mm) is much lower than that achieved on the −0.425+0.15 mm size fraction. Enhanced recovery of coarse phosphate particles is of great economic and environmental importance for phosphate industry. In this investigation, four different phosphate samples were aquired, characterized and tested in a specially designed laboratory-scale flotation column. Significant recovery improvement of coarse phosphate flotation was achieved using cavitation-generated nanobubble though its effects differ among the four testing phosphate samples. The laboratory-scale flotation column test results indicate that nanobubble increased P 2O 5 recovery by up to 10%∼30% for a given Acid Insoluble (A.I.) rejection, depending on the characteristic of phosphate samples. The improvement effect of nanobubble on the hard-to-float particles was more significant than that on easy-to-float particles, especially at lower collector dosages. Nanobubbles reduced the collector dosage by 1/3 to 1/2. Nanobubbles almost doubled the coarse phosphate flotation rate constant and increased the flotation selectivity index by up to 25%.

An experimental study of the recovery of hydrophilic silica fines in column flotation

This paper presents results of tests performed to investigate the effect of gas rate (1.2–2.5 cm/s), hydrophilic fines content (5–20% w/w silica) and froth depth (10–30 cm) on fines recovery in a laboratory-scale flotation column operating without wash-water addition and absence of floatable particles. A model was developed based on the entrainment coefficients presented by [Trahar, W.J., 1981. A rational interpretation of the role of particle size in flotation. International Journal of Mineral Processing 8, 289–327], which describes the mass contribution of the different size classes to the solids recovered in the concentrate. The entrainment model of [Zheng, X., Johnson, N.W., Franzidis, J.P., 2006. Modelling of entrainment in industrial flotation cells: water recovery and degree of entrainment. Minerals Engineering 19, 1191–1203] was also tested. The results show both models described well the dependence of the mass flow rate of hydrophilic solids in the concentrate.

A Study on Picobubble Enhanced Coarse Phosphate Froth Flotation

Effects of picobubbles on froth flotation of coarse phosphate particles (−1180 µm+425 µm) have been investigated with a specially designed flotation column. Cavitation generated picobubbles are characterized by inherently high probability of collision, high probability of attachment, and low probability of detachment during froth flotation due to their tiny size and high surface activity. Test results obtained with a 5 cm in diameter laboratory scale flotation column indicate that picobubbles are effective in enhancing the flotation of coarse phosphate particles, and increasing the flotation recovery by 10 to 23 absolute percentage points under various conditions. The required collector dosage and frother dosage for a given flotation performance were reduced by one‐half to two‐thirds.

Laboratory baffled-column flotation of mixed Lower/Middle Kittanning seam bituminous coal

The separating efficiency of a flotation column is largely limited by the degree of back mixing of tailings into the froth zone, and the recovery is limited by the degree of short-circuiting of feed to the tailings. Current columns are typically constructed very tall (30 to 40 ft) to limit the effects of back mixing and short-circuiting. These effects can also be reduced in a much shorter column, provided that the flow in the column approaches plug-flow. In this work, horizontal baffles were shown to improve the performance of a 6-ft laboratory-scale flotation column treating a poorly floatable coal. Tests with variations in the baffle positions showed that baffles are needed both above and below the feed inlet to achieve the greatest benefit. Tracer tests with a fluorescent dye in water showed that baffles reduce the amount of feed water entrained in the froth at any given coal recovery.

A Study of Flotation Column Performance for the Recovery of Fine Particles

The performance of a laboratory-scale flotation column has been experimentally investigated for the recovery of fine particles (-200 mesh). The column operation has been found to be exceptionally stable, and the solid particles (calcite) recovery to depend upon the pulp, gas, and washwater flow rates. An optimum performance can be achieved for a range of operating variables which depends upon the physical-chemical characteristics of the mineral system and also the geometrical features of the particular column in use.