Role Of Bubble Size Research Articles

Bubble-particle detachment behavior during bubble coalescence: Role of bubble size

Studies have reported that bubble coalescence causes particle–bubble detachment in the flotation pulp and foam phases. Most coalescence experiments have been conducted using bubble pairs with the same diameter; however, this is not the case in real flotation. In this study, particle–bubble detachment behavior during the coalescence of two bubbles with different sizes was investigated using a high–speed camera, and the variation of the coalescing bubble area was fitted to a damped oscillatory equation and analyzed. To explore the intrinsic detachment mechanism of the bubble size effect, the flow field variation in the bubble periphery was simulated using COMSOL 6.1. Results show that the particle–bubble detachment probability decreased with increasing bubble size difference. The released energy is greatest when the two equal bubbles coalesced, thus leading to the strongest oscillation and highest detachment probability. The simulation results show that turbulent kinetic energy affects particle-bubble stability and is an important reason for inducing particle-bubble detachment. Notably, particle–bubble detachment did not occur at the maximum turbulent energy, because there was a delay due to the time required for the sliding contraction of the three–phase contact line. The research finding provides new insights into the mechanism of particle–bubble detachment.

Reply to “Comments on ‘Role of bubble size for the performance of continuous foam fractionation in stripping mode”’

Abstract A commenting letter on a recent publication challenges the measurement technique developed for optically determining bubble size distributions in foams of continuous foam fractionation in stripping mode. The author assumes an effect of bubble distortion at the glass wall leading to a misinterpretation of the experimental results. In this reply letter it will be shown that bubble distortion is of less relevance in the measurement technique considered confirming validity and reliability of the bubble size measurement method developed. Thus, the correlations between the bubble size and the liquid fraction in the foam and the operating conditions as well as the separation performance in the original publication are seen to be valid.

Comments on “Role of bubble size for the performance of continuous foam fractionation in stripping mode” by Hofmann et al.

Abstract A recent publication in this journal reported the effect of bubble size on foam fractionation performance. Whilst the bubble size is indeed an important parameter, bubble size measurement in the said article is likely affected by a well-known source of error, namely bubble distortion by the column wall which leads to an erroneous interpretation of the experimental phenomenon. Consequently, the authors resorted to empirical equations with little physical basis to correlate their experimental data, while established two-phase flow theories have been largely overlooked. This letter attempts to clarify such issues.

Role of Bubble Size in Flotation of Coarse and Fine Particles—A Review

Froth flotation is the dominating mineral beneficiation technique and has achieved great commercial success. This process has also found many applications in other industries where physical separation of materials is needed. However, its high process efficiency is often limited to a narrow particle size range of approximately 10–100 µm. Considerable efforts have been made to extend this size range to the lower limit of a few microns, even submicrons, and the upper limit of 1–2 mm, in response to increased needs for higher process efficiency and expanded applications of flotation. The particle–bubble collision, attachment, and detachment are the most critical steps in the flotation process. These individual elementary processes (microprocesses) and their effects on flotation efficiency are discussed and the most recent findings are reviewed. The low flotation recovery of fine particles is mainly due to the low probability of bubble–particle collision, while the main reason for poor flotation recovery of coarse particles is the high probability of detachment of particles from the bubble surface. Fundamental analysis indicated that use of smaller bubbles is the most effective approach to increase the probability of collision and reduce the probability of detachment.

Dynamics of gas–liquid flow in a rectangular bubble column: experiments and single/multi-group CFD simulations

Several flow processes influence overall dynamics of gas–liquid flow and hence mixing and transport processes in bubble columns. In the present work, we have experimentally as well as computationally studied the effect of gas velocity, sparger design and coalescence suppressing additives on dynamics of gas–liquid flow in a rectangular bubble column. Wall pressure fluctuations were measured to characterize the low frequency oscillations of the meandering bubble plume. Bubble size distribution measurements were carried out using high-speed digital camera. Dispersed gas–liquid flow in bubble column was modelled using Eulerian–Eulerian approach. Bubble population was represented in the model with a single group or multiple groups. Bubble coalescence and break-up processes were included in the multi-group simulations via a suitable population balance framework. Effect of superficial gas velocity and sparger configurations was studied using single-group simulations. Model predictions were verified by comparison with the experimental data. Role of bubble size in determining plume oscillation period was studied. Multi-group simulations were carried out to examine evolution of bubble size distribution. An attempt is made to understand the relationship between local and global (over all the dispersion volume) bubble size distribution. The models and results reported here would be useful to develop and to extend the applications of multi-group CFD models.

Foam/Froth Flotation

Abstract In this second part of the Review on foam and froth flotation, many other aspects of the flotation process are examined, referring mainly to the separation of particulate matter. The effect of particle size is analyzed, stressing the effect of the finer fractions; the role of bubble size is also examined. Among the flotation techniques investigated are those capable of treating fines, such as electrolytic flotation, dissolved-air flotation and column flotation. Operation and design are also discussed. The subject of mineral processing is finally addressed, since it is the main application of the process.