Bubble size distributions in gas–liquid-solid systems and their influence on flotation separation in a bubble column

Abstract Measurements of bubble size distributions are very important in flotation which is widely used in different chemical industries such as the recovery of valuable minerals, wastewater treatment, deinking of waste paper, and oil recovery from tar sands. Although numerous authors determined bubble size distributions (BSD-s) in gas–liquid systems, BSD-s have been rarely determined in gas–liquid-solid systems. Moreover, the influence of BSD-s on flotation has not been quantified under a wide range of experimental conditions. Thus, this paper is focused on measurements of bubble size distributions by changing surfactant dosage, solid percentage, air velocity and particle size as well as establishing the relationships between bubble size distribution properties and flotation performances. It was found that the experimental bubble size distributions are successfully fitted by using the log-normal distribution model in which the two model parameters (µ and σ) are used. The results showed that the most important factors affecting the Sauter mean diameter (d32), the model parameters and the flotation recoveries are the surfactant dosage and the solid percentage. The increase in the surfactant dosage decreased d32 probably due to the decrease in liquid surface tension. The increase in solid percentage resulted in an increase in d32 perhaps due to the increase in the pulp viscosity at high solid percentage. The lower the d32, the lower the flotation recovery. The results show that d32 and the model parameters represent the true BSD-s. However, a thorough understanding of bubble size distributions is needed to better understand flotation performances.