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.
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.
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