The efficient filtration of low-rank coal (LRC) slurry was significantly beneficial to the production process of wet coal beneficiation. However, relatively few studies have been reported on novel pretreatment methods for the efficient filtration of LRC slurry. In this paper, the mechanism of ultrasonic pretreatment to promote flocculation and filtration of slurry was studied. The hydrophobic variation of the slurry surface was measured by contact angle and XPS. The flocculation properties of slurry were characterized using zeta potential and FBRM. The effects of filter cake porosity and ultrasonic pretreatment on slurry filtration resistance were calculated by L-F NMR and Darcy’s theory. The results showed that the ultrasonic pretreatment promoted the flocculation and filtration performance of LRC slurry, increased the filtration rate, and decreased the cake moisture content. Meanwhile, the contact angle of LRC increased significantly from 50.1° to 67.8° after ultrasonic pretreatment, and the surface tension of the filtrate decreased from 69.5 to 53.31 mN/m. Ultrasonic pretreatment reduced the absolute value of the zeta potential of coal slurry from 24.8 to 21.0 mV, and the average chord length of flocs increased from 5–10 μm to 25–30 μm, thus weakening the electrostatic repulsion between coals to promote floc formation. In addition, the pore tests and filtration theory calculations showed that the ultrasonic pretreatment significantly improved the permeability of the filter cake to water and reduced the resistance to slurry during filtration. In particular, the mesopore porosity increased by 9.18%, and the permeability increased by 2.937 × 108 m2. Therefore, this contributed to the reduction of slurry filtration resistance. This research provides an efficient method for promoting the efficient filtration of slurry.
It has been generally
proved that mixed collectors can enhance
the flotation of low-rank coal (LRC). However, the inhibition effect
of mixed collectors on the detachment between particles and bubbles
is still unclear. In this paper, the energy feature of air bubble
detachment from the LRC surface in the presence of dodecane (D), oleic
acid (OA), and the mixture of dodecane and oleic acid (OA–D)
was studied. The effect of collectors on the LRC surface property
was analyzed using contact angle measurement, X-ray photoelectron
spectroscopy, and wetting heat measurement. The force and displacement
during the detachment process were measured synchronously using microforce
balance. The results showed that the collector treatment increased
the C–C/C–H content and decreased the content of oxygen-containing
groups on the LRC surface. The synergistic effect between OA and D
enabled the mixed collector to exhibit higher contact angle and wetting
heat. Bubble detachment from the LRC surface can be divided into two
stages: bubble stretching and bubble sliding, which corresponded to
activation energy and detachment work, respectively. The activation
energy and detachment work decreased in the same order of OA–D
> OA > D, indicating that the mixed collector OA–D increased
the energy of bubble detachment from the LRC surface and enhanced
the adhesion strength. The theoretical detachment work was calculated,
and the calculated results were in agreement with the measured results.
This research provides a new perspective on the mechanism of LRC flotation
being improved by mixed collectors.
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