A CFD study of the flow characteristics in a packed flotation column: Implications for flotation recovery improvement

The instalment of packed fluid guiding media in the cyclonic-static micro-bubble flotation column (FCSMC) has been experimentally tested for improving flotation efficiency. This paper presents calculations of the hydrodynamics of the continuous phase only in the FCSMC columns, obtained using computational fluid dynamic (CFD) with a single-phase model. The flow characteristics in the open and packed FCSMC columns are compared and interpreted in relation to the enhancement in the flotation recovery. In the open column, a mono-turbulent circulating flow pattern formed in the whole column. In comparison to the flow field in the open FCSMC, the flow pattern in the FCSMC packed with the fluid guiding media changed from a strong cyclonic flow to a mild upward flow in the column separation part so as to avoid particle-bubble detachment. The packed media is capable of maintaining a strong cyclonic flow in the cyclone separation part so that the particles collide with, and attach to, the bubbles, while stabilizing the liquid flow in the column separation part so that the attached particles stay attached to the bubbles. The influence of the rotating flow on the particle-bubble detachment was quantified by considering a particle-bubble couplet in the flotation column. The probability of particle detachment is substantially decreased in the packed column as the rotating velocity is dramatically decreased due to the hindrance effect of the packed media. The Bond number of the couplet in the open and packed columns is 0.59 and 0.15 individually, corresponding to the probability of particle detachment 51% in the open column and 0.34% in the packed column. In particular, we have connected the hydrodynamics to particle-bubble detachment in order to understand the mechanism for the improvement of the flotation recovery in the packed FCSMC flotation column. Computer simulation and modeling is proved to be a powerful tool in mineral processing research where experimental techniques are restricted due to the limitations of experimental conditions.