Search Results (51)

High-ash coal slime water, characterized by its stable colloidal suspension of fine kaolinite particles, poses a significant challenge in the coal preparation industry because it is hard to achieve efficient solid–liquid separation. While traditional coagulants and flocculants often suffer from limited bridging capabilities and distinct pH sensitivity, novel molecular architectures offer potential solutions. In this study, a star-shaped inorganic–organic hybrid flocculant (Al-PAM) was synthesized via in situ polymerization. Its flocculation performance and interfacial adsorption mechanism on the specifically targeted aluminol basal plane of kaolinite were systematically investigated and compared with Polyaluminum Chloride (PAC), Non-ionic Polyacrylamide (NPAM), and their combination (PAC + NPAM). Settling tests revealed that Al-PAM exhibited superior performance at a significantly lower dosage (10 mg∙L⁻¹) compared to the PAC + NPAM binary reagent system. It achieved a rapid initial settling velocity and reduced the supernatant turbidity to 48.45 NTU, while maintaining a near-neutral pH favorable for water recycling. Furthermore, Quartz Crystal Microbalance with Dissipation (QCM-D) monitoring confirmed that Al-PAM forms a thick, viscoelastic, and irreversible adsorption layer on the Al₂O₃ substrate. The dissipation shifts (ΔD) revealed that the star-shaped architecture promotes distinct bridging and electrostatic adsorption, overcoming the limitation of linear polymers. This work elucidates the specific contribution of the alumina-surface interaction with flocculants and proposes an efficient strategy for treating refractory coal slime water. Full article

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. Full article

Spiral separators commonly face the issue of particle misplacement during fine particle separation, which severely limits separation accuracy. This study employs a coupled CFD-DEM numerical simulation method to systematically investigate the influence mechanism of transverse inclination angle (10°, 15°, 20°) on particle moving behavior. The results show that the separation process exhibits distinct stage characteristics, which can be divided into an initial stage (first 1/3 turn), a transition stage (1/3 to 2 turns), and a quasi-steady stage (after 2 turns). A steeper angle (20°) optimizes the flow field, reducing the inner low-velocity zone and widening the high-velocity core, which promotes inward migration of particles. This enhances the enrichment of high-density particles while effectively suppressing their mixing into the clean coal product at the outer edge. For difficult-to-separate fine particles below 0.1 mm, although complete separation is challenging, increasing the transverse inclination angle still shows a clear reduction in the misplacement of high-density particles, providing a controllable approach for improving the quality of the outer edge product. This study offers theoretical insights and design guidance for optimizing spiral separator structures and enhancing fine coal separation efficiency. Full article

Coal slime, a byproduct of coal processing with high ash content, poses significant challenges in terms of its efficient separation and resource utilization due to its fine particle size and complex composition. This study aims to optimize the oil agglomeration process for coal slime separation through systematic parameter investigation and predictive modeling. Response surface methodology (RSM) was employed to analyze the individual and interactive effects of pulp density, oil dosage, and agitation rate on three key performance indicators: combustible recovery, efficiency index, and ash rejection. Meanwhile, an artificial neural network (ANN) was developed to establish a robust prediction model for the efficiency index. The novelty of this work lies in the integration of thermodynamic analysis, multi-objective optimization, and machine learning approaches. The key findings include the identification of dodecane as the optimal bridging liquid due to its intermediate carbon chain length that balances interfacial tension and wettability. Under optimized conditions (14% pulp density, 22% oil dosage, and 1600 r/min), the process achieved a combustible recovery of 91.49%, ash rejection of 61.58%, and efficiency index of 53.07%. The ANN model demonstrated superior predictive capability with an overall R² of 0.9659 and RMSE of 1.12. This work provides comprehensive guidelines for the design, optimization, and scale-up of coal slime oil agglomeration processes in industrial applications. Full article

To improve fine particle retention in cyclone clarifiers for mine water treatment, we developed three baffle-structured cyclone clarifiers based on the traditional design: flat-baffle cyclone clarifier, convex-baffle cyclone clarifier, and concave-baffle cyclone clarifier. Using numerical simulation, a comparative analysis was conducted on the differences in flow field characteristics and particle separation performance between the traditional cyclone clarifier and the three types of baffle-structured cyclone clarifiers. The convex-baffle cyclone clarifier showed the highest pressure drop. At Section II-II, low tangential velocity minimized internal swirl, while Section I-I exhibited high axial velocity near the wall. The low upward axial velocity in the central region of Section II-II enhanced fine particle settling. The convex baffle also promoted uniform streamlines and efficient space utilization. The concave-baffle cyclone clarifier exhibited a larger flow angle relative to the baffle than the flat-baffle cyclone clarifier, causing stronger impingement and turbulence that transported particles to the overflow outlet. In contrast, the convex-baffle cyclone clarifier’s smaller flow angle yielded weaker impingement and more stable flow, reducing particle escape. Simulations confirmed that baffle-structured cyclone clarifiers improve particle removal. The removal efficiency of the convex-baffle cyclone clarifier reaches 78.19%, representing a 5.22% improvement compared to the traditional cyclone clarifier. Furthermore, the convex-baffle cyclone clarifier demonstrated the most effective removal of 5 μm particles compared with both the flat-baffle and concave-baffle cyclone clarifier. Full article

This study addresses the technical challenges of conventional coal slurry sedimentation equipment in handling fine coal particles, such as poor settling performance and strong dependence on chemical reagents, by designing a novel high-gravity sedimentation and dewatering device. Solid–liquid centrifugal separation was simulated on the CFD-Fluent platform using the Eulerian–Eulerian method, with the solid volume fraction and effective deposition thickness adopted as key indicators of particle settling performance. The settling behavior and flow field characteristics of particles with different sizes (0.045–0.5 mm) were elucidated under varying centrifugal radii (400–800 mm) and rotational speeds (400–1200 r·min⁻¹), thereby providing a solid theoretical foundation for the parameter optimization of centrifugal settling processes for fine particles. The results indicate that increasing the centrifugal radius and rotational speed strengthens the centrifugal field effect, markedly enhancing the dynamic pressure gradient and interphase slip velocity. Under high-speed (ω = 1200 r·min⁻¹) and large-radius (R = 800 mm) conditions, the dynamic pressure of fine particles (0.045 mm) reached 7.52 MPa with a radial velocity of 0.79 m·s⁻¹, effectively compensating for the settling disadvantage of fine particles, promoting solid–liquid separation, and ensuring the stable deposition of coal particles. Meanwhile, as particle size increases, a distinct deposition thickness can be formed under different operating conditions, demonstrating that particle size is the dominant factor governing deposition behavior. The study elucidates the intrinsic mechanism of how multiple parameters—rotational speed, centrifugal radius, and coal particle size—synergistically influence particle deposition characteristics. By regulating these parameters to accommodate different particle sizes, the findings provide valuable insights for the parameter optimization of centrifugal settling processes for fine particles. Full article

Low-quality fine-grained coal cannot be effectively separated in a conventional gas–solid fluidized bed. To enhance the density stratification and separation of low-quality fine-grained coal, this paper introduces a vibration force field to create a vibrating airflow composite force field. By investigating the force characteristics and sorting behavior of particles within this vibrating airflow composite force field, we reveal the mechanical properties of both high-density and low-density particles. An energy dissipation model for the vibrational energy among particles in the bed is established, clarifying how vibration acceleration varies between the front and rear sections of the bed. The experimental results indicate that acceleration at the feeding end is significantly greater than that at the discharging end. This higher acceleration at the feeding end facilitates the stratification and segregation of selected particles, while acceleration at the discharging end provides the necessary energy for the transport of gangue. The acceleration curve for low-density particles exhibits greater fluctuations compared to that for high-density particles; additionally, the forces acting on these particles along the y-axis direction promote density segregation. The forces tend to decrease gradually along the z-axis direction, which aids in particle migration and movement. The particle-sorting effectiveness within this vibrating airflow composite force field initially increases with rising vibration frequencies and gas velocities before subsequently decreasing. Under a frequency of 30 Hz and a gas velocity of 35 cm/s, the ash content and yield of the clean coal product from the bed are 7.1% and 52.6%, respectively, achieving the maximum degree of ash separation. Full article

Coal serves as a cornerstone and stabilizer for China’s energy security; utilizing it in a clean and efficient manner aligns with the current national energy situation. The moisture content of coal is a crucial factor affecting its calorific value and separation efficiency. Therefore, enhancing the drying rate while simultaneously reducing the moisture content in coal is essential to improve separation efficiency. This paper primarily investigates the drying and separation characteristics of wet fine coal particles within a gas–solid fluidized bed system. A hot gas–solid fluidized bed was employed to study the particle fluidization behavior, heat–mass transfer, and agglomeration drying properties under varying airflow temperatures. The results indicate that as the airflow temperature increases, the minimum fluidization velocity tends to decrease. Additionally, with an increase in bed height, the particle temperature correspondingly decreases, leading to weakened heat exchange capability in the upper layer of the bed. Faster heating rates facilitate rapid moisture removal while minimizing agglomeration formation. The lower the proportion of moisture and magnetite powder present, the less force is required to break apart particle agglomerates. The coal drying process exhibits distinct stages. Within a temperature range of 75 °C to 100 °C, there is a significant enhancement in drying rate, while issues such as particle fragmentation or pore structure collapse are avoided at elevated temperatures. This research aims to provide foundational insights into effective drying processes for wet coal particles in gas–solid fluidized beds. Full article

This study proposes considering the effective re–benefication of coal middlings and other such considered waste materials as a way to ensure that clean coal in coal by–products can be extracted and effectively utilized, saving costs and reducing coal waste. To quantify the clean–coal yield and ash reduction that can be achieved by re–beneficiating four typical by–product streams from the Guobei Coal Preparation Plant (6 Mt a⁻¹) were used for the study. Coking–coal middlings, flotation tailings, and pressure–filter cakes from preparation plants still contain 30–60% combustible matter. Re–beneficiation techniques have been considered to recover this often-wasted coal, reduce waste rock disposal, and cut greenhouse–gas emissions per ton of clean coal produced. Representative samples (n = 4) were collected, sample size–classified as (fine coal particles ≤0.5 mm and coarse particles ≥) and subjected to (i) magnetite removal, (ii) laboratory froth flotation (diesel 507 g t⁻¹, sec–octanol 103 g t⁻¹), and (iii) fine and large particle density separation at 1.3–1.8 g cm⁻³ ZnCO₃ media. Clean–coal yield and ash were measured for each stream and the coal’s particle liberation was examined by SEM. Crushing, grinding and liberation equipment and techniques that aid in the treatment of coal and the re–beneficiation of coal middlings and tailings. The key findings recorded during the experiment are as follows: Flotation of <0.5 mm fractions delivered 46.9–58.3% clean–coal yield at 10.3–17.0% ash. Density separation of 0.5–1.0 mm middlings peaked at 1.4–1.5 g cm⁻³, yielding 34.2% clean coal at 15–18.4% ash. Scanning Electron Microscope analysis confirmed partial liberation as results from re–grinding + second flotation which increased yield by a further 8–12%. A calculated theoretical examination of the preliminary cost–benefit analysis indicates ≈36 CNY t⁻¹≈9 million CNY a⁻¹ in saved disposal costs alone. savings in disposal and 0.25 Mt a⁻¹ additional clean coal for the Guobei plant. The research presented in this paper highlights the current work by Anhui University of Science and technology in collaboration with Guobei coal preparation plant and the results therein achieved. Full article

The high-hydrolysis reactivity cement clinker powder in cement plays a major role in cement’s cementation, while low-hydrolysis reactivity mineral admixture powders, such as slag, m mainly serve as a filler. Through optimizing the particle matching of cement clinker powder and slag powder, the mechanical properties of cement can be enhanced. In this study, clinker and slag with differing levels of fineness were obtained by separate grinding, and the particle gradation of clinker powder and slag powder in the cement was optimized. Fine clinker particles were mixed with coarse slag particles to systematically explore their effects on the rheology of cement paste, the formation of hydration products, the evolution of the pore structure, and the material’s mechanical properties. Through experimental tests and microscopic analysis, the mechanism whereby particle gradation is regulated by separate grinding was revealed. The findings of the study are as follows: with the same amount of cinder, finer clinker requires a higher water content of standard consistency. The addition of coarse cinder effectively reduces the standard-consistency water requirement of the blended cement. Fine grinding of coal cinder fails to enhance cement strength effectively but markedly raises the standard-consistency water demand. Thus, the specific surface area of coal cinder should be maintained at approximately 210 m²/kg. Full article

Developing resource-efficient technologies for producing ceramic materials with specific properties and performance characteristics is one of the most important tasks in modern materials science. As natural resources face depletion, the use of anthropogenic wastes, including fly ash from coal combustion, for the development of new compositions and the production of ceramics with an improved microstructure is of particular significance. The use of PM₁₀ fly ash microspheres in ceramic production will help to reduce particulate matter emissions. In this study, fine narrow fractions of PM₁₀ microspheres were successfully separated from coal fly ash using aerodynamic and magnetic separation. Glass–ceramic materials with a homogeneous microstructure, an open porosity of 0.4–37%, a compressive strength of 5–159 MPa, and acid resistance of up to 99.9% were obtained using narrow fractions. The materials obtained are promising for application as highly porous ceramics, effective microfiltration membranes, and fine-structured technical ceramics, which can be used in installations operating in aggressive media and/or at high temperatures. The ceramic membranes were characterised by high liquid permeability values up to 1194 L·m⁻²·h⁻¹·bar⁻¹. Filtration tests showed that the retention coefficient for dispersed microsilica particles with d_av = 1.9 μm is 0.99. Full article

In practical coal preparation processes, influenced by mining methods and mechanization levels, the proportion of fine and even ultrafine pulverized coal continues to increase. However, due to the small particle size, significant inter-particle interactions, and the low efficiency of conventional physical separation techniques, the efficient deashing of fine coal remains a significant technical challenge. Consequently, in the face of growing demand for fine coal processing, efficient and mature dry separation technologies are still lacking. To address this issue, a pulsating circulating airflow separation device was designed and developed in this study to deash and desulfurize pulverized coal with a particle size of less than 1 mm. The effects of gas velocity and pulsating airflow frequency on the deashing performance were investigated. Using Design-Expert software (version 13), an optimized formula for deashing efficiency was established, and the optimal operating parameters were evaluated. The separation results demonstrated that under the optimal conditions of fluidization, the number N = 1.2 and pulsating airflow frequency f = 2.375 Hz, the standard deviation of ash segregation (σ_ash) reached 25%, and the ash content in the cleaned coal was reduced from 37.28% to 22.32% in the cleaned sample. Furthermore, the sulfur content decreased significantly from 0.971% in the raw coal to 0.617% in the cleaned coal, indicating effective desulfurization. In addition, the concentrations of other harmful elements in the raw coal were also reduced to varying degrees. These findings demonstrate that the application of pulsating airflow can effectively enhance ash and sulfur removal from pulverized coal particles smaller than 1 mm. This approach offers a novel and promising method for the dry beneficiation of fine coal particles. Full article

Constanta port operations involving the handling of bulk minerals often lead to material losses, resulting in mineral waste, containing a mixture of iron ore, bauxite, and coal, amongst others. In order to recover these minerals, a processing plant was built, which successfully separates most of this waste into its constituents. However, a byproduct obtained from this process is a sludge containing fine particles below 0.5 mm, which are deposited in a reservoir that represents definitive tailings. Since this is a “rich” tailing material, which is difficult to be extracted by using conventional methods due to its small size, the selective flocculation procedure was tested as an alternative method. This paper presents the results obtained for standard methods of selective flocculation tests using polyacrylamide A 100 at a pH value of 10.5. SEM-EDS and XRD analyses were performed, and the chemical composition of the sample components was given. According to preliminary tests, using the selective flocculation procedure, the expected results were obtained in terms of separating the overflow between the content of impurities (with a reduced share of Fe in relation to the input) and sediment with an increased content of Fe (with a reduced share of impurities in relation to the entrance). Full article

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. Full article

Coal is expected to continue dominating the global energy landscape for a considerable period in the future. However, the depletion of high-quality coal resources and the increasing proportion of difficult-to-float coals are exacerbating environmental issues and leading to significant waste of carbon resources, making the clean and efficient utilization of such coals imperative. Enhancing the quality of coal through flotation is a prerequisite for the resource utilization of coal. Difficult-to-float coal, characterized by high hydrophilicity, complex pore structures, and fine particle size, poses challenges for efficient flotation using conventional collectors. Emulsions, owing to their exceptional surface and interfacial regulation capabilities and environmental adaptability, have been employed as flotation collectors for various minerals and have garnered significant attention in recent years for their application in the flotation of difficult-to-float coals. In the pursuit of green and cost-effective flotation technologies for such coals, this paper systematically reviews the causes of poor floatability in difficult-to-float coals and their latest research progress by emulsion flotation. It summarizes the impact of emulsion types and preparation methods on their properties and application areas, with a particular focus on the key mechanisms by which emulsion collectors enhance the flotation of difficult-to-float coals, including surface charge regulation, surface hydrophobicity modification, and interfacial tension control. Finally, this paper outlines future research directions on emulsion flotation, which will likely focus on the precise control of emulsion structure and size, the targeted separation of organic components by emulsion collectors under complex conditions, the development of low-cost and highly biocompatible synthetic reagents, and the development of efficient emulsion storage and transportation equipment. Full article