Effect of Ultrasonic Pretreatment on Flocculation Filtration of Low-Rank Coal Slurry.

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.

Energy Feature of Air Bubble Detachment from a Low-Rank Coal Surface in the Presence of a Dodecane-Oleic Acid Collector Mixture.

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.

Combined Column and Mechanical Flotation Cell Process for the Beneficiation of Sanshandao Gold Ore.

Semi-industrial tests were conducted to investigate the feasibility and efficiency of a combined column and mechanical flotation cell process for the beneficiation of Sanshandao low-grade gold ore. The results showed that the performance of the combined flotation process of the cyclonic-static microbubble flotation column (FCSMC) and mechanical flotation cells was superior to that of the mechanical flotation cell, while the flowsheet was simplified. FCSMC is efficient when used on fine particles, whereas a mechanical flotation cell is effective for coarse particles. Thus, the combined flotation process exhibited a better separation performance by employing the strengths of both methods. The use of the combined FCSMC and cell flotation process showed promising results for a producing grade of 48.24 g/t gold with 96.13% recovery. The combined column and cell flotation process introduces a new approach for the separation of low-grade gold ore.