An investigation of nanobubble treatment on fine particle flotation and associated mechanisms

Abstract

Flotation efficiency strongly depends on the collision and attachment probabilities of particles with bubbles, and ultrafine particles cannot easily float due to their low probability of collision. An innovative cavitation nanobubble treatment process was investigated for its enhancement performance on fine particle flotation by performing a series of column flotation tests with pure mineral and plant flotation feed samples. The associated enhancement mechanisms were explored using advanced characterization methods, such as nanoparticle tracking analysis and atomic force microscopy (AFM), and high-speed cameras. Flotation tests with coal samples showed that the nanobubble treatment process substantially improved the flotation recovery and reduced the clean coal ash content. The cavitation flow rate was an important parameter in the nanobubble treatment process. An increase in the cavitation flow rate promoted the agglomeration of fine particles and increased the nanobubble concentration on the hydrophobic particle surface and in the bulk solution. AFM measurements with highly oriented pyrolytic graphite (HOPG) demonstrated that the microscopic contact angle of surface nanobubbles (SNBs) on HOPG was approximately 164° to 166°, which was substantially greater than the macroscopic contact angle of 71°, and the presence of SNBs on the HOPG surface increased the macroscopic contact angle to more than 80°. Larger contact angles increase the attachment probability and contribute to the flotation enhancement performance of fine coal particles.