Bubble Loading in a Fluidized Column: Effects of Bubble Size, Particle Size, Contact Angle and Particle Density

Abstract

ABSTRACT The size of bubbles and particle properties (including particle size, density and contact angle) play an important role on the degree of particle loading on bubbles and this has been studied extensively. However, experimental results on the influence of these properties on bubble loading under fluidized-bed flotation conditions (where the probability of detachment is expected to be negligible) are scarce. In this work, the loading fraction (L) of individual bubbles was studied using a high-speed video camera (Phantom Miro LC111). Particles of silica (−75 + 53 µm to −1018 + 850 µm) and magnetite (−425 + 300 µm) were fluidized in a specially designed perspex column. Specific sizes of air bubbles were generated using a combination of a syringe pump and nozzles with different internal diameters. The generated bubbles rose through a bed of fluidized particles, which resulted in bubble loading. The results indicate that fractional bubble loading decreased with an increase in both bubble and particle size. With a 2 mm bubble, the loading fraction of silica declined from circa 0.9 to circa 0.1. However, with coarse particles (−850 + 600 µm and −1018 + 850 µm), bubble loading increased with an increase in bubble size, until an optimum bubble size of 2 mm and then started to decrease as bubble size increased. An increase in particle contact angle showed a corresponding increase in loading fraction, while the density of the material seemed to play no role in terms of the loading fraction. An increase in loading fraction had a negative effect on bubble rise velocity.