Latest advances and progress in the microbubble flotation of fine minerals: Microbubble preparation, equipment, and applications

In the past few decades, microbubble flotation has been widely studied in the separation and beneficiation of fine minerals. Compared with conventional flotation, microbubble flotation has obvious advantages, such as high grade and recovery and low consumption of flotation reagents. This work systematically reviews the latest advances and research progress in the flotation of fine mineral particles by microbubbles. In general, microbubbles have small bubble size, large specific surface area, high surface energy, and good selectivity and can also easily be attached to the surface of hydrophobic particles or large bubbles, greatly reducing the detaching probability of particles from bubbles. Microbubbles can be prepared by pressurized aeration and dissolved air, electrolysis, ultrasonic cavitation, photocatalysis, solvent exchange, temperature difference method (TDM), and Venturi tube and membrane method. Correspondingly, equipment for fine-particle flotation is categorized as microbubble release flotation machine, centrifugal flotation column, packed flotation column, and magnetic flotation machine. In practice, microbubble flotation has been widely studied in the beneficiation of ultrafine coals, metallic minerals, and nonmetallic minerals and exhibited superiority over conventional flotation machines. Mechanisms underpinning the promotion of fine-particle flotation by nanobubbles include the agglomeration of fine particles, high stability of nanobubbles in aqueous solutions, and enhancement of particle hydrophobicity and flotation dynamics.