Dr Ai Wang

Fluidized-bed flotation is a novel process with combined features of flotation and density separation. The application of fluidized-bed flotation in grinding circuit to reject coarse gangues for sulfide ores has been increasingly attracting attentions. Previous studies have focused on the effect of mineral liberation on coarse particle separation. Little work has yet been conducted to simultaneously investigate the effect of mineral liberation, particle and bubble sizes on the fluidized-bed flotation efficiency. The lack of this work has hindered the process optimization to some extent. In this study, three sizes of bubbles (498 µm, 1200 µm, 1952 µm) were generated to separate molybdenite ores under three particle size fractions (150¿450 µm, 450¿700 µm and 700¿1000 µm) in a fluidized-bed flotation column (80 mm in diameter). For the 150¿450 µm and 450¿700 µm particles, small bubbles of 498 µm could achieve separation by effectively reducing the particle density. For the 700¿1000 µm particles with greater mass, intermediate bubble of 1200 µm was required to reduce the particle density for separation. No separation was observed for the three particle size classes with the oversized bubbles of 1952 µm due to high bubble detachment probability. It was concluded that fluidized-bed flotation is a consequence of matched bubble and particle sizes affected by the exposure rate of hydrophobic mineral and its distributing discreteness, the underlying mechanism for which was discussed. It is believed that the outcomes of this work could facilitate the optimization of fluidized-bed flotation in coarse gangue rejecting for sulfide ores.

In this study, we report the rising behaviour of the millimetric size ellipsoidal shaped particle-laden bubbles (particle diameter dP ~ 114 µm, bubble diameter dB ~ 2.76 and 3.34 mm) in the range of bubble surface loading (BSL) from 0 to 0.6 both in absence and presence of a surfactant (Sodium Dodecyl Sulphate, 20% CMC). High-speed imaging was used to capture the trajectory of the particle-laden bubble and an image processing methodology was developed to quantify the bubble surface loading. Three different regimes were observed - bubble shape transition (nearly spherical to ellipsoidal), particle detachment (at bubble rear end), and steady (for high BSL) or expansion (for low BSL) of the particle surface covered zone. A threshold for bubble surface loading (BSL ~ 0.40) was determined which had reasonable agreement with the experimental observations. Bubble rise velocity was observed to decrease with bubble surface loading but this trend was less steep in presence of surfactant. It was noted that loss of bubble surface mobility was higher in presence of surfactant, however in absence of surfactant, bubble surface loading contributed significantly to surface immobility. Finally, a correction factor to Schiller-Naumann drag coefficient model was proposed accounting for the bubble surface loading both in presence and absence of surfactant.