Songjiang Chen

Coal gasification generates fine slag with high residual carbon, but its porous structure hinders efficient separation. This study investigates carbon–ash separation of gasification fine slag using a spiral chute. Particle size and pore structure jointly determine separation outcomes. Effective separation was achieved for +0.125 mm and 0.125–0.045 mm fractions, which exhibit developed porous carbon skeletons, yielding concentrate ash of 20.22% and 39.50%, respectively. Conversely, the −0.045 mm fraction (41.16% of feed) consists predominantly of mineral microspheres with poorly developed pores, leading to high feed ash (80.73%) and poor separation (concentrate ash 76.35%). Pore structure governs separation by reducing effective density through water absorption: high-porosity particles behave as light products and report to concentrate. Optimal conditions (10% concentration, 1.96 m³/h) achieved 64.67% carbon recovery and 52.92% concentrate ash. A Bagnold-based model reveals that radial particle position is co-determined by effective density and particle size, with fine particle entrainment limiting separation precision.

A stable attachment between bubbles and solid particles is essential for flotation. Therefore, it is particularly necessary to study the dynamic process that occur in the attachment of bubbles to a solid surface. In this paper, Teflon and plexiglass plates were used as hydrophobic and hydrophilic solid surfaces, respectively, and solid surfaces with roughness of 0.018 μm to 5.33 μm were prepared by polishing with sandpaper. The influence of roughness on the dynamic process in bubble attachment to solid surfaces with different hydrophobicity was studied via a high-speed camera (750 frames per second). It was found that roughness played a positive role in the attachment to the hydrophobic Teflon surface while a negative role in the attachment to the hydrophilic plexiglass surface in terms of the bubble’s attachment to the solid plates. For a smooth Teflon surface, the formation of three–phase contact (i.e., the drainage of wetting film) took up to 95 ms, whereas for a very rough Teflon surface it took only 5 milliseconds. On the contrary, the high roughness prevented the bubble from attaching to the hydrophilic plexiglass surface. It was concluded that the increased roughness of Teflon plates was conductive to air entrapment in surface irregularities, inducing the rapid rupture of the wetting film on a very rough Teflon surface, while the increased roughness of the plexiglass plates resulted in “water pockets” in surface grooves, making the wetting film on the plexiglass surface stable.

The comprehensive quality enhancement and grading of coal are crucial methods for unlocking the high value-added and low-carbon utilization of coal resources. In this work, the influence of oily bubbles on the flotation of Shendong Jurassic vitrinite-rich coal and inertinite-rich coal was studied via flotation tests, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle detection, and induction time measurements. FT-IR and XPS analyses demonstrated that the surface of inertinite-rich coal contains more hydrophilic oxygen-containing functional groups. Contact angle and induction time measurements showed that the vitrinite-rich coal is more hydrophobic than inertinite-rich coal, and that for both air and oily bubbles, the induction time on the surface of vitrinite-rich coal is shorter than that on the surface of inertinite-rich coal. In addition, rather remarkably, the induction times for both vitrinite-rich coal and inertinite-rich coal are significantly reduced by oily bubbles. Finally, a better flotation performance for oily bubble flotation of vitrinite-rich coal and inertinite-rich coal was found. It appears that oily bubble flotation is an efficient method for enhancing the recovery of vitrinite-rich coal and inertinite-rich coal.

The efficient utilization of lignite is a crucial area of research for the sustainable management of existing coal resources. One potential technique for cost-effective and environmentally friendly coal processing is the application of microbes or their derivatives to modify the surface of lignite for bioflotation. However, the precise process of surface modification between microbes and coal remains largely unknown. In this study, we focused on the use of a white-rot fungus called Hypocrea lixii AH and its various components, including spores, hyphae, extracellular polymer substances (EPSs), and culture solution, as biosurfactants for lignite modification. By employing techniques such as zeta potential analysis, induction time measurement, contact angle measurement, and Fourier infrared spectroscopy, we investigated the changes in the surface properties of raw and modified lignite. Furthermore, we conducted a preliminary bioflotation test using biosurfactants as collectors in order to explore the potential application of fungal modification in this context. Our results revealed that all biosurfactants were effective in improving the surface properties of lignite, with the EPS demonstrating the most prominent effect, followed by the culture solution, hyphae, and spores. The zeta potential and induction time of the modified lignite decreased, indicating enhanced hydrophilicity, while the contact angle exhibited a slight increase, suggesting a minor increase in hydrophobicity. Analysis of the Fourier infrared spectra indicated that EPS treatment resulted in the highest abundance of functional groups, including carboxyl, hydroxyl, and amidogen groups. Although fungal cells were found to improve the hydrophobicity of coal, they did not exhibit a significant effect on the flotation of lignite. Nonetheless, our findings suggest that fungal cells and their derivatives have the potential to remove or transform minerals present in lignite, particularly those containing sulfur. While they may not serve as effective bio-collectors in microflotation, their capability in mineral alteration makes them valuable candidates for lignite processing with a focus on mineral reduction.

The pH of flotation slurry directly affects the surface potentials of mineral particles and bubbles, and therefore the hydration of coal surface and the mineralization process of flotation. In this paper, the effect of pH on the surface potential, hydration degree, and floatability of lignite particles was studied, wherein Einstein’s dispersion viscosity theory was adopted to calculate the hydration degree, and DLVO theory was used to estimate the interaction between coal particles and oily bubbles. The effect of pH on the lignite floatability was evaluated in terms of induction time and oily-bubble flotation results. The results showed that with increasing pH, the zeta potentials of coal particles and oily bubbles decrease, causing a 37.89% increase in the coal surface hydration from pH 3 to pH 11. As a result, the energy barrier for attachment between the coal particles and oily bubbles reaches the maximum value of 2.669 × 10⁻¹⁶ J at pH 11, resulting in low attachment efficiency. Correspondingly, the combustible matter recovery of oily-bubble flotation is significantly decreased from 57.76% to 28.00%.

This study focused on the mechanisms of NaCl and CaCl₂ enhancing the oily-bubble flotation of lignite. The degree of surface hydration of coal particles before and after conditioning with NaCl/CaCl₂ was evaluated with the Einstein theory of dispersion viscosity, while the effect of these two electrolytes on lignite floatability was evaluated via attachment time and flotation tests. The results indicated the adsorption amount of Ca²⁺ on the coal sample was more than that of Na⁺ in the same electrolyte concentration. Owing to the cationic adsorption, the zeta potential of lignite particles increased with increasing NaCl and CaCl₂ concentrations, which thus decreased the electrostatic repulsion between coal particles and oily bubbles. Moreover, the hydration of the coal surface decreased when NaCl/CaCl₂ was added to flotation pulp, meaning the surface hydrophilicity of the coal sample was reduced. As a result, the attachment time between coal particles and oily bubbles decreased significantly, and the combustible-matter recovery correspondingly increased up to a maximum of 50.97% and 90.06% with increasing NaCl and CaCl₂ solutions concentration, respectively. However, it is necessary to keep the electrolyte solution concentration within a reasonable range for a good selectivity during the oily-bubble flotation.

This paper focuses on enhancing the flotation of coking coal with ultrasonic pretreatment and the corresponding improving mechanism. The effects of ultrasound on the coal surface properties and the dispersion of oil collector in flotation slurry were fully studied. The SEM, FTIR and XRF analyses indicated that, after the ultrasonic pretreatment, the fine particles covered on coarse coal particles were removed and the elements forming gangue minerals were decreased, which improved the surface hydrophobicity of the coal sample. What’s more, the optical microscope measurements for collector dispersion showed that the size of diesel oil droplets was greatly reduced after the ultrasonic treatment, suggesting the enhanced dispersion of collector in flotation pulp. As a result of synergistic effects of ultrasonic treatment on the coal surface cleaning and promotion of collector dispersion in pulp, a maximum combustible matter recovery of 79.79% was attained with the flotation process 2 (i.e., the ultrasonic treatment was performed after the addition of collector to the pulp). Furthermore, the enhanced collector dispersion in pulp caused by the ultrasonic treatment may be conducive to reduce the collector consumption in actual flotation practice.