Nanobubble generation and its applications in froth flotation (part IV): mechanical cells and specially designed column flotation of coal

Coal is the world's most abundant fossil fuel. Coal froth flotation is a widely used cleaning process to separate coal from mineral impurities. Flotation of coarse coal particles, ultrafine coal particles and oxidized coal particles is well known to be difficult and complex. In this paper, the nanobubbles' effects on the flotation of the varying particle size, particle density and floatability coal samples were evaluated using a bank of pilot scale flotation cells, a laboratory scale and a pilot scale specially designed flotation column. The parameters evaluated during this study include the flow rate ratio between the nanobubble generator and the conventional size bubble generator, the superficial air velocity, collector dosage, frother concentration, flotation feed rate, feed solids concentration, feed particle size, and the superficial wash water flow rate, etc. The results show that the use of nanobubbles in a bank of mechanical cells flotation and column flotation increased the flotation recovery by 8%∼27% at a given product grade. Nanobubbles increased the flotation rate constants of 600∼355, 355∼180, 180∼75, and 75∼0 microns size coal particles by 98.0%, 98.4%, 50.0% and 41.6%, respectively. The separation selectivity index was increased by up to 34%, depending on the flotation feed characteristics and the flotation conditions.