Enhancement of liquid-solid mixing and particle hydrophobization by an impeller-less flotation pulp conditioning device

Abstract

An impeller-less device was proposed to employ opposite rotational jet flows conditioning pulp before flotation. The flow field characteristics and relevant effects on the liquid-solid mixing performance were investigated by the numerical simulation of computational fluid dynamics that was proved effective by the particle image velocimetry technique. The outcome of particle surface modification was clarified by variations in the contact angle and surface species of quartz particles. Results showed that the increase of turbulent kinetic energy induced by the opposite rotational flows remarkably improved the dispersion of mineral particles. Smaller particle size and larger circulation rate were conductive to a more uniform distribution of particles. In the case of a volume flow of 3.6 m3/h and a feed volume fraction of 7 % with an average particle size of −45 μm, nearly 4/5th of the whole device area exhibits a particle volume fraction within the range of 6 % and 7 %, and the coefficient of variation was as low as 0.151. Meanwhile, strong turbulence and high shear induced by opposite rotational flows provided favorable conditions for the collector adsorption and particle hydrophobization, which was responsible for the increase in contact angle under relatively higher volumetric flow rates. However, when the volume flow exceeded 3.0 m3/h, over-increasing shear stresses and excessive turbulence caused the desorption of adsorbed collectors, reflected as the decreased nitrogen content on quartz surfaces from 0.85 % to 0.51 %, thereby accounting for the declined contact angle of conditioned quartz particles. This study highlighted the dominant effect of turbulence and shear strain on particle surface modification, and the significance of proper parameter control.