Factors involving the solids-carrying flotation capacity of microbubbles

• Dissolved air flotation (DAF) is a technique used extensively for separating fine particles.
• Efficiency of DAF in treating mineral particles is limited to slurries with less than 3% of solids.
• Particle size distribution, solids content and air superficial velocity were the studied variables.
• Microbubbles were found to be not selective with respect to particle size.
• Carrying capacity of microbubbles (<100 μm) increases with the average particle size.

Dissolved air flotation (DAF) is a technique used extensively for separating fine particles in water and wastewater treatment, but, unfortunately, its use is still limited for froth flotation of minerals. This appear to be due to the very low lifting power of the microbubbles (40–70 μm) and low airflow rate because of the low solubility of air in water. Thus, the efficiency of DAF in treating mineral particles has shown to be poor and as a solid/liquid separation technology is limited to slurries with no more than 3% solids. This work presents results showing (measuring) the limits of DAF as a function of particle size distribution, solids content and air superficial velocity. Interestingly, the microbubbles were found to be not selective with respect to particle size, floating both fine and coarse particles, which is most likely due to the existence of several mechanisms acting on the flotation of particles by these minute bubbles.