Haijun Zhang

Kerosene is a widely used nonpolar collector in fine coal flotation. However, its poor dispersion in water and weak interaction with polar oxygen-containing sites on the coal surface limit its collecting efficiency. In this study, kerosene was separately mixed with glycerol monooleate (GMO), methyl oleate (MO), and 4-dodecylphenol (4-DDP). The effects of these mixed collectors on the flotation behavior and interfacial properties of lean coal were systematically investigated. Contact angle and surface tension measurements were combined with density functional theory (DFT) calculations to elucidate the underlying mechanism. Flotation results showed that the effects of the mixed collectors depended strongly on the molecular structures of the polar components. At a dosage of 400 g/t, K-GMO achieved a clean coal yield of 40.41% and a combustible recovery of 55.59%, slightly higher than those obtained with pure kerosene (39.82% and 54.66%, respectively). In contrast, K-MO and K-4-DDP exhibited lower flotation performance than pure kerosene. Contact angle measurements showed that the mixed collectors significantly increased the surface hydrophobicity of coal. Surface tension measurements indicated that the addition of polar components effectively reduced the surface tension of the mixed systems. K-GMO showed the largest reduction, which favored the dispersion of kerosene in the aqueous phase. DFT calculations further showed that the polar functional groups of GMO, MO, and 4-DDP could favorably interact with oxygen-containing sites in representative coal structures. GMO showed the strongest interaction, with binding energies of −38.2 and −39.1 kJ/mol for acetophenone and phenol, respectively. Overall, the polar components reduced the surface tension and strengthened the interaction of the collector with polar sites on the coal surface. Meanwhile, the long hydrophobic chains cooperated with kerosene to form a hydrophobic layer. These effects improved the surface hydrophobicity and flotation performance of lean coal.

The production process of hot-rolled seamless steel tubes often needs secondary heating for tempering treatment, resulting in high energy consumption and low production efficiency. Controlled cooling technology has been introduced into the production process. By controlling the self-tempering temperature, the residual temperature of the steel tubes is used to realize self-tempering, so as to achieve the purposes of energy savings, emissions reduction, cost reduction, and efficiency increase. This study investigated the evolution of temperature and stress fields in a seamless steel tube during temperature-controlled quenching. The size of the steel tube is 140 mm × 20 mm × 200 mm. The outer-wall cooling intensity and the self-tempering temperature were selected as the main variables, and the other process parameters remained constant. The temperature distribution and stress variation curves under different cooling intensities were obtained. The results showed that the greater the cooling intensity of the outer wall, the higher the temperature recovery of the outer wall. Under the fixed cooling intensity, the lower the self-tempering temperature, the lower the return temperature. In the thickness direction of the steel tube, there is a stress distribution of “internal tension and external compression”. Moreover, the greater the cooling intensity, the lower the self-tempering temperature and the greater the residual stress.

Coal gasification fine slag (CGFS), a major solid by-product of coal gasification, contains substantial unburned carbon. However, efficient carbon–ash separation during CGFS flotation is often restricted by its complex surface properties. This study aims to enhance the flotation performance of CGFS by introducing a confined-turbulence pulp conditioning system. To clarify the role of conditioning pretreatment, the coupled effects of conditioning time and hydrodynamic intensity were systematically investigated. Flotation experiments were conducted to compare the separation performance under different conditions. Additionally, collector adsorption tests, wrap-angle measurements, zeta-potential analysis, and X-ray photoelectron spectroscopy (XPS) were performed to reveal the underlying interfacial modification mechanisms. The results indicate that within an appropriate time window, the intensified turbulence and high shear forces can effectively remove surface impurities and strengthen particle–reagent collision and adhesion, thereby improving flotation selectivity and combustible recovery. Specifically, an optimal conditioning time of 80 s achieves the maximum combustible recovery. Conversely, excessive conditioning induces an over-shearing effect, which leads to reagent desorption and a subsequent deterioration in flotation performance. In conclusion, the confined-turbulence pulp conditioning strategy successfully restructures the surface properties of CGFS and enhances its flotation efficiency. These findings provide fundamental data and a feasible technical approach for intensifying the carbon–ash separation of CGFS.

Constrained by the low grade and poor floatability of the run-of-mine ore, the beneficiation of porphyry-type copper–molybdenum sulfide ores generates large quantities of molybdenum tailings, leading to significant environmental risks and resource losses and necessitating urgent recovery and reutilization. In this study, a representative sample of molybdenum tailings with a Mo grade of 0.354% was investigated to analyze its process mineralogy. The results show that molybdenite predominantly exists as fine, flaky particles intimately intergrown with quartz, pyrite, and aluminosilicate minerals, exhibiting an extremely low degree of liberation and an overall ultrafine particle size. Laboratory flotation tests show that the flotation kinetics conform to a first-order model; however, a considerable amount of molybdenum remains in the tailings, indicating that the mineralization process needs to be intensified. Through structural optimization and confined-space design, a vortex-based mineralization reactor was developed. Computational fluid dynamics simulations demonstrate that the mineralizer can generate flow fields with high turbulence intensity and dissipation rates and can induce high-energy, small-scale micro-vortices. On this basis, a semi-industrial rougher flotation system was established by coupling the developed mineralizer with a flotation column. Under optimized operating conditions, namely a feed pressure of 0.06 MPa and an impeller frequency of 20 Hz, single-stage treatment of the tailings produced molybdenum concentrates with a grade of 1.90% and a recovery of 81.29%, while the Mo grade of the tailings was reduced to 0.08%. The results are markedly superior to those obtained using a conventional laboratory flotation cell, demonstrating a substantial enhancement in mineralization efficiency and molybdenum recovery. The proposed approach, therefore, provides a practical reference for the flotation recovery of molybdenum tailings as well as other micro-fine, low-grade metal tailings.

Processes such as flotation and multiphase chemical reactions are typically carried out in turbulent aqueous environments, however, the coupling mechanism between the solution environment and turbulence during bubble-particle attachment remains unclear. This study systematically investigates the thinning dynamics of liquid films between bubbles and solids in flow systems using high-speed microinterferometry. Results indicate that an increase in interfacial approach velocity significantly affects liquid film formation and drainage by enhancing hydrodynamic effects. This leading to pronounced thickness differences between the film center and rim, along with concave deformation, that increases the retained liquid volume. Simultaneously, however, the steeper center-rim pressure gradient effectively speeds up drainage. Conversely, raising surfactant concentration markedly suppresses drainage: at high concentrations, the overall film thickness and deformation increase, thinning slows, and drainage time extends by more than an order of magnitude. This behavior is due to surfactant adsorption, which changes the interface toward an immobile state, increases viscous resistance, reduces bubble internal pressure, and maintains a higher equilibrium film thickness. Furthermore, investigations on hydrophilic surfaces confirm that the above conclusions can be extended to hydrophilic systems. Kinetic analysis further uncovers a coupled effect between interfacial approach velocity and surfactant adsorption: high-speed flow can cause nonuniform adsorption layers on the bubble interface, partly restoring local interfacial mobility and thereby weakening the inhibitory effect of surfactants on drainage. These findings clarify the individual and combined roles of hydrodynamics and surfactant adsorption in liquid film thinning, offering valuable theoretical insights for optimizing mineralization processes and enhancing bubble-solid attachment efficiency.

As a solid mixture discharged during coal production, coal gangue possesses comprehensive utilization potential. Efficient sorting and pre-enrichment of its classification are crucial for green mining practices. This study categorizes coal gangue into four types—residual coal (RC), gray gangue (GG), red gangue (RG), and white gangue (WG)—based on their apparent color and utilization properties. The research systematically analyzed how different light sources and illumination intensities affect the visual characteristics of these gangue types. The results indicate that white light sources most accurately reproduce the real coloration and texture features of coal gangue, with optimal textural clarity achieved at moderate illumination levels. Different colored light sources selectively enhance spectral reflectance, and red light significantly improves RG recognition. Support vector machine (SVM)-based classification experiments demonstrate that white light sources achieve optimal performance under moderate illumination (23,000 Lux) with Macro-F1 = 0.90, representing a 15.38% improvement over other conditions. These findings reveal that reasonable matching of light source and illumination intensity can substantially enhance the accuracy of the visual recognition of coal gangue, providing valuable optimization guidance for future precise classification applications.

The electrode materials from spent lithium-ion batteries consist of graphite and lithium cobalt oxides (LCO), which cannot be efficiently separated by the conventional flotation technique due to the fine size distributions of graphite and LCO. In this work, nanobubbles were introduced to the flotation system of electrode materials. Nanobubbles were produced with the method of temperature difference. Different degrees of gas oversaturation in the water/slurry were achieved by raising the temperature of cold water (stored at 4 °C for at least 72 h) to target values of 20 °C, 25 °C, and 30 °C. It was found that the height and lateral distance of nanobubbles increased with the degree of gas oversaturation of water. In addition, the larger graphite agglomerations were observed to form in the presence of nanobubbles. The D₅₀ (chord length) of graphite agglomerations increased by 8 μm, 11 μm, and 21 μm, respectively, compared with the D₅₀ of graphite in natural water. More graphite agglomerations adhered to a captive bubble with the aid of nanobubbles than in the case of no nanobubbles, which was indicated by increased wrapping angles of graphite (agglomerations) adhering to a captive bubble. Furthermore, the maximum adhesion force between a captive bubble and substrate increases to 220, 270, and 300 μN as cold water temperature increases to 20, 25, and 30 °C, respectively. The frost of nanobubbles on a graphite surface and the resulting graphite agglomerations through the bridging effect of nanobubbles are thought to be responsible for the improved flotation performance of electrode materials. The present results indicate that the flotation performance of fine minerals can be regulated by regulating the gas oversaturation degree of the slurry.

Coal gangue, the primary bulk solid waste generated during coal utilization, requires decarbonization and the enrichment of valuable components such as calcium and magnesium through methods like hydrocyclone separation for comprehensive utilization. This study observed the free-settling behavior of coal gangue particles using a high-speed dynamic image analysis system and analyzed their kinematic characteristics to guide the hydrocyclone separation process. The results indicate that particle size and density significantly influence settling behavior. Fine-grained, low-density particles exhibited more pronounced directional deflection and velocity fluctuations, while high-density coarse particles demonstrated higher settling velocities. Based on terminal velocity, the drag coefficient of fluid resistance acting on particles was calculated. The findings show that high-density coarse particles have larger drag coefficients, likely due to fluid disturbances and the hydrophobic nature of particle surfaces. Additionally, the mechanical properties of settling motion were analyzed, indicating that gravity dominates the settling process of coarse particles, while fine particles are subjected to relatively balanced forces. Furthermore, density variations primarily affect hydrodynamic drag, which is related to the surface properties of particles. Therefore, enhancing the centrifugal force field through cyclone structural optimization is necessary to improve separation precision for fine coal and gangue particles.

The electrode materials from spent lithium-ion batteries consist of graphite and lithium cobalt oxides (LCO), which cannot be efficiently separated by conventional flotation technique due to fine size distributions of graphite and LCO. In this work, nanobubbles were introduced to the flotation system of electrode materials. Nanobubbles were produced with the method of temperature difference. The different degrees of gas over-saturation in water/slurry were created by increasing temperature of cold water stored in a 4℃ environment at least 72 h to the terminal 20℃, 25℃, 30℃ respectively. It was founded that height and lateral distance of nanobubbles increased with the degree of gas oversaturation of water. Besides, the larger graphite agglomerations were observed to form in the presence of nanobubbles. The D50 (chord length) of graphite agglomerations increased by 8 μm, 11 μm and 21 μm respectively compared with the D50 of graphite in natural water. More graphite agglomerations adhered to a captive bubble with aid of nanobubbles than the case of no nanobubbles, which was indicated by increased wrapping angles of graphite (agglomerations) adhering to a captive bubble. Furthermore, the maximum adhesion force between a captive bubble and substrate increases to 220, 270, 300 μN as cold water temperature increases to 20, 25 and 30℃. The frost of nanobubbles on graphite surface and thus resulting in graphite agglomerations by bridging effect of nanobubbles together should be responsible for the improved flotation performance of electrode materials. The present results indicate that flotation performance of fine minerals can be regulated by regulating gas oversaturation degree of slurry.