Isotropic turbulence surpasses gravity in affecting bubble-particle collision interaction in flotation

Abstract

Turbulence and mechanical flotation cells have been the workhorse of the mining industry to process the high tonnage but low-grade ores for more than a century. However, our quantitative understanding of the effect of turbulence on flotation is still limited. Here we theoretically investigate the bubble-particle collision in flotation in homogeneous isotropic turbulence using the correlation method. We show a novel paradigm that isotropic turbulence can surpass gravity in affecting bubble-particle collision in flotation. Specifically, motions of particles of micrometer sizes and bubbles of millimeter sizes are described using the Basset-Boussinesq-Oseen equation. The drag forces on particles and bubbles are calculated using Stokes' law with a particle-size correction factor and Allen's law, respectively. The correlation method is applied to determine bubble and particle velocity variances and covariances. The collision kernel is then calculated, taking into account the effects of turbulence acceleration and shear, and gravity of the bubble-particle system. We compare our collision model with the available models and investigate the influence of bubble and particle sizes, particle density and dissipation rate of turbulent kinetic energy on the collision kernel. The results show that the bubble-particle collision kernel increases with increasing bubble and particle sizes, and dissipation rate of turbulent kinetic energy. Importantly, turbulence can significantly enhance the collision efficiency, exceeding the ideal rate of collision by gravity and leading to the turbulence collision efficiency greater than unity.