Effect of Nanobubbles on the Slime Coating of Kaolinite in Coal Flotation

Understanding the coating behavior of fine gangue slimes in the presence of nanobubbles (NBs) is important for the application of NB technology in flotation. In this study, slime coating of kaolinite in the flotation of a low-ash coal using deionized (DI) water and NB water was investigated. Kaolinite was found to depress coal flotation by the formation of coating on coal surfaces, but its deleterious effect was less pronounced in the NB water with mitigated slime coating. Setting tests, Brunauer–Emmett–Teller surface area measurements, and dynamic light scattering were conducted to understand the underpinning mechanism. In comparison with DI water, the degree of kaolinite aggregation was enhanced in the NB water. The intensified self-aggregation of kaolinite platelets which appears to be induced by the presence of NBs reduces the solid–liquid interfacial area as well as the number of free kaolinite particles in the suspension, mitigating the coating of kaolinite on coal surfaces in NB water flotation.