Effective Separation of High-Ash Fine Coal Using Water Containing Positively Charged Nanobubbles and Polyaluminum Chloride.

The coal industry is facing the challenge of treating high-ash fine coal. In this study, we proposed an effective method to handle high-ash fine coal using water containing positively charged nanobubbles (PCNBs) and polyaluminum chloride (PAC). For comparison, normal nanobubble (NB) water was tested in parallel. Flotation results of a modeled high-ash fine coal showed that compared to the use of NBs alone, an enhanced combustible recovery with a simultaneous reduction in ash recovery was obtained when using water containing PCNBs and PAC. Particle size distribution together with particle video microscopy (PVM) and the degree of entrainment analysis were conducted to understand the underpinning mechanism. It was found that the presence of PCNBs intensified the aggregation of fine coal particles, which accounted for the boosted combustible recovery. It was interesting that PAC could disrupt coal flocs induced by NBs, leading to the release of trapped kaolinite particles with alleviated clay recovery by entrapment.

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.