Nanobubble flotation technology of flake graphite

Flake graphite is an emerging strategic resource in the 21st century and is widely used in aerospace, medical, electrical and other fields. With the continued mining of large-scale easily mineable graphite ores, fine-scale graphite will become the main graphite resource utilized in the future. Due to the fine particle size of fine flake graphite, it is more difficult to recycle than large flake graphite 

Nanobubble flotation is one of the technologies that enhances fine particle flotation. In flotation, hydraulic cavitation is used to generate nanobubbles. This method is currently widely used in mineral flotation.

The fixed carbon content of a certain flake graphite is 29.8%, and the gangue minerals are mainly quartz, muscovite, pyrite, garnet and kaolinite. The particle size distribution of graphite is uneven, with +150 μm graphite accounting for about 13%, −75 μm particle size range accounting for about 75%, and −38 μm particle size accounting for about 52%. In flotation, lime is used as a regulator, sodium hexametaphosphate is used as an inhibitor, diesel is used as a collector, and MIBC is used as a frother.

When the slurry passes through the bubble generator, the water pressure decreases as the flow rate increases, causing the air dissolved in the water to precipitate in the form of air nuclei or nanobubbles (<1 μm) on the particle surface or in the liquid phase.

Nanobubbles usually refer to spherical bubbles smaller than 1 μm. There is "capillary force" in the nanobubbles on the surface of the two graphite particles, which can promote the hydrophobic agglomeration of fine flake graphite in the slurry and form particles with larger apparent sizes. This agglomeration of fine flake graphite particles has a great impact on flotation. The performance of flotation is determined by the collision probability of bubbles and particles, the adhesion probability of bubbles and particles, and the shedding probability of bubbles and particles. The apparent size of the hydrophobic agglomeration of fine flake graphite increases, which can effectively increase the probability of collision and adhesion between particles and bubbles. Regarding the probability of shedding, when the mineral particles are too large and exceed the load capacity of the bubbles, the probability of shedding will increase.

Nanobubbles can effectively recover fine flake graphite, especially in the range of −10 μm. There are almost no particles in this size range in traditional flotation concentrates, while the −10 μm particle size in nanobubble flotation concentrates accounts for approximately than 5%. It shows that the introduction of nanobubbles into the fine flake graphite slurry system can improve the recovery effect of fine flake graphite.