Industrial application of microbubble generation methods for recovering fine particles through froth flotation: A review of the state-of-the-art and perspectives

The depletion of high-grade and coarse-grain ores has led to an increasing demand for the development of efficient separation technologies for low-grade and fine-grain ores. However, conventional froth flotation techniques are not adequate to efficiently recover fine and ultrafine particles (typically <10-15 μm) due to the low collision probability between these particles and the relatively large bubbles used in the process. The introduction of microbubbles has shown promise in enhancing particle recovery, making it a subject of significant interest. Thus, this review focuses on microbubble generation methods that have the potential to be scaled up for industrial applications, with a specific emphasis on their suitability for froth flotation. The methods are categorized based on their scalability: high-hydrodynamic cavitation, porous media/medium-dissolved air, electrolysis/low-microfluidics, and acoustic methods. The bubble generation mechanisms, characteristics, advantages and limitations of each method and its applications in froth flotation are discussed to provide suggestions for improvement. There is still no appropriate technology that can optimize bubble size distribution, production rate and cost together for industrial froth flotation application. Therefore, novel approaches of combining multiple methods are also explored to achieve the potential synergic effects. By addressing the limitations of current microbubble generation methods and proposing potential enhancements, this review aims to contribute to the development of efficient and cost-effective microbubble generation technologies for fine and ultrafine particles in the froth flotation industry.

Numerical and experimental investigations on the jet and shock wave dynamics during the cavitation bubble collapsing near spherical particles based on OpenFOAM

The interaction between cavitation bubbles and particles is essential for the operational performance many kinds of fluid machineries. In the present paper, jet dynamics and shock waves induced by the cavitation bubble collapsing near two spherical particles are numerically investigated based on OpenFOAM. The numerical scheme is validated by the experimental data obtained based on our high-speed camera cavitation system. Our results reveal that bubble split induced by annular jet is the primary feature during bubble collapsing with four typical cases defined. For the jet formation, the localized high pressure produced at the bubble split point is the main reason and the split point also serves as the source of the shock waves shown by the numerical schlieren. Furthermore, the nondimensional bubble-particle distance is the most paramount parameter influencing the jet phenomenon (e.g. jet velocity).

Theoretical investigation and experimental support for the cavitation bubble dynamics near a spherical particle based on Weiss theorem and Kelvin impulse

In the present paper, the laser-induced cavitation bubble dynamics near a fixed spherical particle is comprehensively investigated based on the Weiss theorem, the Kelvin impulse theory and the high-speed photography experiment. Firstly, the applicability range of the theoretical model in the time and the space is statistically obtained based on sufficient experimental results. Then, the in-depth theoretical analysis is carried out in terms of the liquid flow field and the bubble Kelvin impulse with the corresponding experimental results as the reasonable support. In addition, the theoretical prediction model of the bubble movement is established and experimentally fitted from the analytic expression of the Kelvin impulse. Through our research, it is found that: (1) the applicability range of the Kelvin impulse theory for the bubble near the spherical particle is approximately the dimensionless distance between the bubble and particle (γ) greater than 0.50. (2) The effect of the particle on the liquid velocity between the bubble and the particle is mainly manifested in the form of the image bubble, which always causes the liquid velocity in this region to be significantly lower than other surrounding regions. (3) The average movement velocity of the bubble centroid can be reasonably predicted by establishing a directly proportional function between the Kelvin impulse and the velocity with the relationship constant (α) equal to 3.57×10^-6 ± 1.63×10^-7 kg.