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With the increasing exhaustion of high quality coals, it is important to utilize lignite efficiently, which is a resource with abundant reserves. Flotation, as an efficient method for fine particles separation, however, is making slow progress for use with lignite, which basically remains in the laboratory stage. In this article, we briefly describ...
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... in the molecule mainly exists in the forms of phenolic/ alcoholic hydroxyl oxygen, ether oxygen, carbonyl oxygen and ester oxygen. The molecular structure was built and optimized using Materials Studio and is shown in Figure 1. In the literature, the molecular representations of coal have been described in detail. ...
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... significant effort, only 20% of feed ash could be removed. To restrain moisture re-adsorption of dried lignite, Liu and Liu (2017) (G12-2-12), to adsorb on the lignite surface for wettability modification. The hydrophilic heads of surfactants play an important role in the adsorption mechanisms and the structures of their adsorbed layers on the lignite surface, and the most favourable orientations of adsorbed surfactant molecules on the lignite surface over the whole adsorption region are shown in Figure 9. Four surfactants produce different effects on decreasing moisture readsorption of lignite. ...
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... in the molecule mainly exists in the forms of phenolic/ alcoholic hydroxyl oxygen, ether oxygen, carbonyl oxygen and ester oxygen. The molecular structure was built and optimized using Materials Studio and is shown in Figure 1. In the literature, the molecular representations of coal have been described in detail. ...
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... significant effort, only 20% of feed ash could be removed. To restrain moisture re-adsorption of dried lignite, Liu and Liu (2017) (G12-2-12), to adsorb on the lignite surface for wettability modification. The hydrophilic heads of surfactants play an important role in the adsorption mechanisms and the structures of their adsorbed layers on the lignite surface, and the most favourable orientations of adsorbed surfactant molecules on the lignite surface over the whole adsorption region are shown in Figure 9. Four surfactants produce different effects on decreasing moisture readsorption of lignite. ...
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The quality of lignite mined from the Lignite Centre of West Macedonia is characterized by an intensive variation, due to the nature of the deposit and dilution during the selective mining. Conventional coal processing and controlling techniques, that are possible to improve the lignite quality, by reducing its moisture and mineral matter contents,...
Citations
... Flotation is a commonly used technique for separating fine particles, relying on distinctions in the hydrophobic properties of particles to achieve their selective separation Cheng et al., 2020). The classical theory of flotation dictates that the separation of target minerals follows a prescribed sequence of three steps: particle-bubble collision, adhesion, and the formation of air flocs to assist in the flotation of particles (Yoon, 2000). ...
The adsorption and accumulation of gases at the solid-liquid interface facilitate the formation of nanobubbles, offering significant benefits to the separation of fine mineral particles in flotation processes. In this study, a synergy of experimental and molecular simulation (MD) simulations was employed to elucidate the effects of mineral surface hydration film characteristics on the behavior of gas adsorption and accumulation in aqueous environment. The research findings indicate that, in comparison to hydrophobic graphite, there is an improvement in both the thickness and stability of the surface hydration film subsequent to the oxidation of graphite. After graphite oxidation, the difficulty of gas adsorption, accumulation, and the formation of nano-bubbles in aqueous environments increases, with only a limited number of nanobubbles tending to accumulate within the hydrophobic regions of the oxidized graphite surface. MD simulations reveal that, despite N 2 molecules primarily experiencing Van der Waals forces on methylated-substrate and carboxylated-substrate, the difference in their adsorption strength is relatively minor. However, the substantial contrast in H 2 O molecule adsorption on methylated-substrate and carboxylated-substrate prevents N 2 molecules from penetrating the hydrophilic carboxylated-substrate's pre-adsorbed water layer, whereas adsorption and accumulation of N 2 molecules occur on the hydrophobic methylated-substrate surface.
... coal [1]. Currently the development of more mature coal gangue sorting methods are mainly flotation method [2], heavy media method [3], jigging method [4] and ray method [5]. Among them, flotation method, heavy media method and jigging method as wet coal beneficiation have problems such as water waste, environmental pollution and low coal utilization rate. ...
Aiming at the problems of misdetection, omission and low recognition accuracy of coal gangue recognition due to the harsh environmental factors such as low illumination, motion blur and large quantities of coal gangue mixing in coal mines, a coal gangue recognition method based on XBS-YOLOv5s is proposed.Simulate the actual underground production environment to build a machine vision platform, construct a coal gangue image data set, and provide a test environment for various target detection algorithms.In this paper, we construct a real-time detection model of coal gangue in the complex environment of coal mine by fusing SimAM parameter-free attention mechanism, BiFPN feature fusion network and XIoU loss function in YOLOv5s, so as to improve the model's ability of extracting, fusing and localizing key features of the target.The experimental results show that the recognition accuracy of XBS-YOLOv5s algorithm for coal gangue in the complex environment of low illumination, motion blur and large quantities of coal gangue mixed are effectively improved. Its mean average precision reaches 96%, which is 4.3% higher than the original YOLOv5s algorithm, meanwhile, compared with other YOLO series algorithms, it has the best comprehensive detection performance, which can provide technical support for intelligent and efficient sorting of coal gangue.
... With the depletion of highquality coal resources, the extensive use of low-rank coal (such as long-flame coal (LFC), non-caking coal, weakly caking coal and lignite) has become crucial to maintain regular energy supply, particularly in countries that are rich in low-rank coal, including China and Russia (Cheng et al., 2019b;Yu et al., 2022;Zang et al., 2020). However, low-rank coal contains developed porosity and a large number of oxygen-containing groups (Cheng et al., 2023c;Mao et al., 2022), which results in high consumption of oily collectors (kerosene, diesel) as well as poor flotation performances (Cheng et al., 2020b(Cheng et al., , 2022aMa et al., 2021;Wang and Tao, 2021). In addition, oil collectors are flammable and explosive, posing further environmental pollution risks when inappropriately discharged with slime water. ...
There is currently a need to develop efficient and environmentally friendly (green) collectors to improve the poor flotation performance of long-flame coal (LFC) due to its vast porosity and high oxidation degree. Herewith, this study introduces ozone (O 3) and ultraviolet (UV) oxidation methods to modify waste cooking oil collector (WCOC) and analyzes their effects on the LFC flotation performance. Furthermore, the separation efficiency (SE) of WCOC, O 3-WCOC, UV-WCOC and common collectors (diesel, kerosene, DEP) were compared. Fourier Transform Infrared Spectroscopy (FTIR) and Gas chromatography-mass spectrometry (GC-MS) were used to observe the effects of O 3 and UV oxidation on WCOC functional groups and chemical composition. The functional groups and wettability changes of LFC treated via common collectors, including WCOC, O 3-WCOC and UV-WCOC adsorption were analyzed. Results revealed that a shorter O 3 oxidation time resulted in better flotation performance and higher SE compared to UV oxidation. After O 3 (5 min) and UV (9 h) oxidations, C-H bonds in WCOC were oxidized and the content of oxygen-containing functional groups (particularly-OH) increased to 4.25% and 4.93% from 0.79%, respectively. Compared to common collectors, O 3-WCOC and UV-WCOC demonstrated better reactions with oxygen-containing functional groups (especially O = CO and CO) on the LFC surface. This phenomenon led to a substantial increase in contact angle. This novel oxidation method could potentially be applied in wastewater treatment, mineral processing, and other fields.
... The flotation effect evaluation system indicators based on flotation tests should be selected according to the characteristics of the effect and cost of the flotation collector when it is used [33,34]. The selection of the reagent effect index uses three indicators together, the yield of fine coal C26, the recovery of combustible body C27, and the flotation perfection index C28, to evaluate the flotation effect under different flotation conditions, and the ash is the ash required by the coal preparation plant. ...
The evaluation of flotation reagents performs an important role in the selection and green application of reagents. The green indexes and effect indexes of flotation collectors were selected by data literature method, system analysis method, mathematical model method, and qualitative and quantitative analysis method, and the green evaluation system of flotation collectors, flotation effect evaluation system, and comprehensive evaluation system of flotation collectors were established. The normalization method and expert evaluation methods were adopted to obtain the grade classification of quantitative and qualitative indicators, respectively. The analytic hierarchy process (AHP) was used to determine the weight of secondary indicators and tertiary indicators of the evaluation system and the weight of indicators at a lower level. Applying the fuzzy comprehensive evaluation (FCE), the trapezoidal function is selected to determine the index affiliation, the index system score is calculated according to the weighted average principle, and finally, the established evaluation system is applied in an example. The example application shows that the comprehensive evaluation system of flotation collectors can make a comprehensive evaluation of collectors from the aspects of the greenness of reagent, flotation effect, and cost, and it has a strong target and practicality for collectors evaluation. The establishment of the system has a guiding significance for the selection and use of flotation collectors.
... However, owing to its low calorific value and high content of ash and volatiles, low-rank coal must often be upgraded for efficient and environmentally friendly utilization [6]. Froth flotation is an effective method for upgrading lowrank coal slime [1,[7][8][9], but many factors affect the flotation of low-rank coal, including the type of flotation collector used and the molecular structure of coal [8,10,11]. ...
... However, owing to its low calorific value and high content of ash and volatiles, low-rank coal must often be upgraded for efficient and environmentally friendly utilization [6]. Froth flotation is an effective method for upgrading lowrank coal slime [1,[7][8][9], but many factors affect the flotation of low-rank coal, including the type of flotation collector used and the molecular structure of coal [8,10,11]. ...
... It is often difficult to separate low-rank coal using conventional flotation reagents [2] because the surfaces of low-rank coal particles contain numerous polar oxygen-containing functional groups, such as carboxyl (− COOH), hydroxyl (− OH), and carbonyl (C--O) groups [12,13]. The flotation performance of low-rank coal can be improved by using surfactants with different molecular structures [1,2,8,14] because the hydration film that forms on the surface of low-rank coal particles becomes thinner after the addition of a flotation surfactant. This permits interactions between the oxygen-containing functional groups of surfactant reagents and water molecules, which in turn enhances the surface hydrophobicity of low-rank coal [1,15,16]. ...
This study aims to investigate the influence of nonionic collectors (diesel, methyl linoleate, oleic acid, and castor oil acid) on the flotation response of low-rank coal particles using X-ray photoelectron spectroscopy analysis, particle-bubble adhesion tests, and froth floatation measurements, in addition to density functional theory, molecular dynamics, and grand canonical Monte Carlo simulations. The results of the XPS analysis and the particle-bubble adhesion index showed that methyl linoleate, oleic acid, and castor oil acid could effectively adsorb onto the surfaces of low-rank coal particles and upgrade their surface hydrophobicity. The greatest content of hydrophobic functional group C-C/C-H and the flotation yield obtained by adding methyl linoleate during the flotation process were 78.88% and 86.95%, respectively. The electron-absorption induction effect of oxygen-containing groups and large π bonds of methyl linoleate considerably improved the wetting process on the surface of low-rank coal particles compared with that of dodecane, which contains a saturated bonding structure. The highest average adsorption capacity was obtained when methyl linoleate was applied to the surface of low-rank coal particles. The results suggest that ester surfactants such as methyl linoleate can substantially enhance the flotation response of low-rank coal.
... [4][5][6] However, the flotation of micro-fine minerals which are smaller in size and have large specific surface area is hampered by their slow flotation rate, low recovery, poor selectivity, and high reagent consumption. [7][8][9][10][11] Process intensification, a process to improve interactions between particles and bubbles, is an efficient method to overcome the aforementioned difficulty in micro-fine mineral particles. The difficulties involved in the flotation mechanism of micro-fine particles and the strengthening paths are shown in Fig. 1. ...
Flotation process of micro-fine minerals have historically been hampered by slow flotation rate, poor selectivity, high reagent consumption, and low recovery. These disadvantages are mainly due to the large specific surface area attributed to the small-sized mineral particles. As such, research have revolved around enhancing their recovery by process intensification as one of the known effective methods. Micro/nanoparticles, on the other hand, possess many attributes, for instance, strong chemical activity, high reactivity, high surface free energy, and large adsorption capacity, all of which can contribute to improve the separation of micro-fine minerals. The mechanisms and preparation methods of nanoparticle collectors (NPCs) as well as ultrafine bubbles (UFBs) are described in this paper. Furthermore, the influences of NPCs and UFBs on the flotation of micro-fine minerals are also discussed. NPCs and UFBs are capable of providing hydrophobicity selectivity to the desired minerals to improve the flotation performance of mineral particles. This paper offers an overview of the underlying properties of NPCs and UFBs in intensifying flotation applications.
... With the continuous development and consumption of high-rank coal, like bituminous coal and anthracite, LRC beneficiation and utilization has become an urgent industrial demand, especially for countries rich LRC such as China or Russia. LRC is generally possessed rich and complex content of oxygencontaining groups (OCGs) and mineral impurities on the surface, hence even the widely applied froth flotation method is difficult to achieve satisfactory results [8][9][10]. ...
The interaction between oil collector drop and coal particle is important for low-rank coal (LRC) flotation. This paper investigated such interactions using dodecane (D), ethyl esters (E) and dodecane-esters mixed collector (MC). Measurements of oil drop-coal induction time and detachment force were conducted at a mesoscopic scale. The micro adsorption mechanism of oil collectors was revealed by wetting heats and FTIR measurements. Flotation results showed MC, especially dodecane-ethyl laurate, obtained high yield and low ash clean coal. There was a shorter induction time and higher adhesion strength between LRC particle and MC drop. The wetting heat of MC was greater than the sum of wetting heat of the two single collectors. FTIR analysis indicated that D validly adsorbed to the methyl or aromatic groups, and E bonded with the oxygen-containing groups. The macro flotation results was well interpreted by the interfacial interaction of collector-coal at the mesoscopic and micro scales.
... The microwaves modify the plastic surface by changing the roughness as well as type and concentration of the attached functional groups on the plastic surface [33]. Only limited previous research activities reported in the literature for the flotation of the plastics with the aid of the microwave irradiation [34][35][36][37][38]. The studies focused on the few plastics and depressants and no systematic study observed in related field. ...
The influential separation of an individual plastic from a mixture of waste plastics is a crucial factor for the quality evaluation of the recycled product. The selected engineering plastics available in municipal and industrial wastes including, acrylonitrile butadiene styrene, polycarbonate, and poly oxy methylene microwave irradiated for different microwave powers. The irradiated plastics conditioned with the selected dual depressants with different concentrations and after that, they introduced into the flotation tank with tap water as liquid media. The effects of microwave power and depressant concentration on the hydrophilic-hydrophobic (sink-float) properties of the plastic surface evaluated. It revealed, the microwave irradiation changed the capacity (the adsorbed depressant mono or multilayer molecules), numbers, and concentration of the plastic surface active sites. It resulted in different sink-float properties of the studied plastics. It was beneficial for the flotation of some plastics and depressants. The results evidenced by different techniques including, contact angles (θ), ATR-FTIR spectra, and AFM and SEM images. The driven equations by a design of experiment software (Design-Expert ®\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\circledR$$\end{document}) showed suitable conformity between the predicted and actual plastic flotation values.
... And nonpolar oil, such as diesel oil, kerosene, and fuel oil, are widely used as flotation collectors to improve the floatability of coal [14]. However, the surface of low-rank coal is rich in oxygen-containing functional groups (OCGs) [15], which are easy to form a hydrogen bond with water molecules, forming hydration membrane and hindering the adsorption of oil droplets [16][17][18][19][20]. And the high porosity of low-rank coal leads to the remarkable capillary phenomenon, in which is easy to absorb the oil into the pores, resulting in high collector consumption [9]. ...
... From Eq. (14) and Eq. (15), the decrease of the equilibrium contact angle, i.e. solid-liquid interaction enhancement, has two effects: increasing the driving force and reducing k 0 to increase the spreading resistance (reducing molecular flow in the three-phase contact area). Compared to D, D-OA can wet the low-rank coal surface better. ...
Spreading of water-insoluble collectors on the mineral surface is important in flotation. In this study, the spreading behavior of dodecane (D), oleic acid (OA), and dodecane-oleic acid (D-OA) mixture in low-rank coal flotation was investigated. The viscosity and oil/water interfacial tension was measured to calculate the spreading coefficient and speed. The relaxation of coal-oil–water contact angle and the movement of three- phase contact line during the collector droplet spreading process were interpreted using the molecular kinetic (MK) model. It was found that the order of absolute values of spreading coefficient were D-OA < OA < D, and the spreading speeds were in the order of OA < D-OA < D. D-OA had the smallest coal-oil–water contact angle and the longest contact line length. The addition of OA can enhance the interaction between D and the low-rank coal surface, but at the same time reduce the spreading speed. This was mainly because OA not only increased the spreading force of the droplet but also increased the spreading resistance. MK model fitting results showed that the length of molecular displacement increased in the order of D < D-OA < OA, indicating that the hydrophobic sites were more dense than hydrophilic ones on the coal surface and D-OA interacted with both sites simultaneously. The molecular substitution frequency and the free energy of wetting activation had an opposite order. High molecular substitution frequency meant fast-spreading velocity, and thus the MK model fitting parameters were consistent with the contact angle relaxation results.
... These include gasification, conventional combustion, fuel cells, and fuel efficiency enhancement. For instance, upgrading lignite by flotation enhances its heat content and reduces CO 2 releases during combustion [2,3]. ...
Safe transport of pressurized CO2 requires a profound knowledge of the processes' effect during the phase transition on catastrophic failure of a tanker filled with liquid CO2. This study presents experimental results and analyses associated with the characteristics of expansion waves during depressurization of liquified CO2 in a divergent cross-section vessel. It explores the rarefaction and evaporation waves velocities analyzed in different three vessel's regions based on the pressure records. Results showed that the evaporation wave velocity increased downward with decreasing cross-section and increased liquid volume fraction. Also, the upstream state properties after the isentropic expansion in the metastable region were determined. The results were compared with previously achieved outcomes of CO2 decompression from a constant cross-section rectangular duct.
Comparisons indicated significant differences in the wave pattern. So, expansion waves velocities varying in different vessel regions while they were nearly constant for the duct. The evaporation wave velocities were nearly identical for the duct and the upper conical vessel's regions. But their divergence increased as the evaporation wave propagated downwards. Furthermore, the downstream two-phase flow in the conical vessel propagated in an increased cross-section toward the exit. In comparison, there was non-spontaneous two-phase propagation behind the evaporation wave due to the small exit cross-section in the rectangular duct. Additionally, during the isentropic expansion, the degree of superheat was higher for the conical vessel than the duct, resulting in significant discrepancies in the upstream flow properties.
