Enhanced selective recovery of fine minerals in flotation by the oscillatory turbulence

Flotation is an effective method to recover fine minerals based on surface hydrophobicity differences. In flotation processes, the concentrate grade is a critical metric for assessing separation efficiency and concentrate quality. It quantitatively represents the mass fraction of the target mineral in the concentrate. Enhancing the concentrate grade not only reduces impurity levels but also improves the economic value and utilization efficiency. To effectively improve the concentrate grade of minerals, the oscillation method is proposed to enhance the detachment of non-target fine particles selectively. Turbulent dissipation rate and turbulent kinetic energy of the oscillatory flow field were studied by Particle Image Velocity measurement and numerical simulation. The turbulent field can be modulated effectively by changing the grid oscillation frequency. In experiments, by injecting the mineralized bubbles into the turbulent region, the detachment probability of the glass beads was obtained under different conditions such as grid oscillation frequency, particle diameter, particle hydrophobicity and bubble size. The increased turbulent kinetic energy and dissipation rate significantly promoted the separation efficiency between particles and bubbles. By high-speed dynamic cameras measurement, the bubble centrifugation, oscillation and coalescence caused by turbulence increased the probability of particle detachment. Moreover, stronger hydrophobic particles showed a lower detachment probability under the same turbulent conditions. Finally, a pair of oscillating grids were installed in the separation area of the vortex flotation column to float the coal. It was observed that the oscillatory turbulence effectively reduced the ash content of recovered coal at an oscillation frequency of 3 Hz. The results reveal the effect of oscillatory turbulence on the selectivity of fine minerals flotation. © 2024