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Yaowen Xing - One of the best experts on this subject based on the ideXlab platform.
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Role of molecular simulation in understanding the mechanism of low-Rank Coal flotation: A review
Fuel, 2020Co-Authors: Rui Zhang, Yaowen XingAbstract:Abstract Flotation is the main method for recovering and reusing fine low-Rank Coal by taking advantage of the difference in physicochemical properties of the mineral surface, but its efficiency has not yet reached a satisfactory level. Particles, flotation reagents, and air bubbles are highly dispersed and interact with each other in a flotation cell. Therefore, a basic understanding on the fundamental mechanism of the above interactions involved in a low-Rank Coal flotation system is the prerequisite for improving low-Rank Coal flotation recovery. In recent years, with the development of theoretical chemistry and computational chemistry, molecular simulation has gradually become a powerful tool for studying low-Rank Coal flotation, which has shed new light on the molecular structure of low-Rank Coal and the interfacial interaction in low-Rank Coal flotation at the molecular or atomic levels. In this paper, we first review the basic theory of molecular simulation, and then we review the recent advances in the molecular structure of low-Rank Coal. Coal-water, Coal-reagent, Coal-bubble, and Coal-clay interactions are discussed comprehensively from the viewpoint of molecular simulation. This review is closed with a brief conclusion and perspective discussion.
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enhancement of flotation response of fine low Rank Coal using positively charged microbubbles
Fuel, 2019Co-Authors: Longwu Wang, Zili Yang, Rui Zhang, Yaowen XingAbstract:Abstract This study investigates the possibility of using positively charged (PC) microbubbles in pulp conditioning to improve the flotation response of fine low-Rank Coal. The surface properties of the Coal are characterized by means of a zeta potential analyzer, scanning electron microscopy, and X-ray photoelectron spectroscopy. Batch flotation tests are conducted with the use of PC microbubbles, cetyltrimethylammonium bromide (CTAB) solution, and tap water in pulp conditioning. The roles of PC microbubbles in the Coal flotation are illustrated by combining observations of particle–particle and particle–bubble interactions and extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory calculations. The results indicate that fine low-Rank Coal is negatively charged and contains a large amount of oxygen. In addition, the rough structure and the presence of numerous impurity mineral particles on the surface of low-Rank Coal afford adsorption sites for water molecules. These features of the Coal render traditional collectors ineffective, whereas the presence of PC microbubbles significantly enhances flotation recovery. However, increasing CTAB concentration cannot continuously improve flotation performance with the use of PC microbubbles, possibly because the excess CTAB molecules can form bilayer or micelle adsorption structures on the Coal surface, particularly on the mineral surface. The presence of PC microbubbles promotes particle–particle agglomeration and particle–bubble attachment by providing an additional attractive electrical double-layer force and enhancing hydrophobic interactions. The extended DLVO theory calculations agree well with the experimental results.
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Effects of pore compression pretreatment on the flotation of low-Rank Coal
Fuel, 2019Co-Authors: Zili Yang, Zijian Ma, Ming Li, Yaowen XingAbstract:Abstract The poor flotation efficiency of low-Rank Coal in the flotation process is due to the large and rich pore structure on its surface. In this study, the changes in the pore structure before and after pore compression pretreatment were analyzed by a scanning electron microscope and Brunauer–Emmett–Teller analysis. The effects on the flotation were then evaluated by analyzing the results of collector adsorption experiments and flotation kinetics tests. After pore compression, the pore state on low-Rank Coal surface was from open to half-closed and then closed. Further, the pore volume, specific surface area, and average pore diameter of the particles decreased from 0.02497 to 0.01214 cm3/g, 17.383 to 5.006 m2/g, and 9.6992 to 5.7466 nm, respectively. In addition, the adsorption rate of the collectors improved and the equilibrium adsorption time of n-dodecane decreased from 436 s to 250 s, whereas the adsorption rate of water decreased with the porosity of the Coal after pore compression. Meanwhile, according to the flotation results, the maximum clean Coal yield (74.44%) was obtained within 400 MPa of pressure pretreatment using n-dodecane as a collector; this value is 20.46% points higher than that of raw Coal flotation using n-hexane as the collector. Furthermore, it was also found that a collector with too high a viscosity or too short a carbon chain causes the total cumulative yield of the low-Rank Coal to decrease. It is anticipated that the results of this work can provide guidance in low-Rank Coal flotation applications.
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enhancement of the surface hydrophobicity of low Rank Coal by adsorbing dtab an experimental and molecular dynamics simulation study
Fuel, 2019Co-Authors: Zili Yang, Rui Zhang, Yaowen XingAbstract:Abstract This study investigated the mechanism of improving the surface hydrophobicity of low-Rank Coal by adsorbing dodecyltrimethylammonium bromide (DTAB). Experimental tests were conducted to analyze the adsorption characteristic of DTAB on the Coal surface including the adsorption amount, Zeta potential, wetting heat, and X-ray photoelectron spectroscopy measurement. Furthermore, the adsorption configuration, spatial location of the simulation systems, and the Coal–water interaction were investigated by molecular dynamics (MD) simulation at the atomic scale. Experimental results indicate that the hydrophobicity of the low-Rank Coal first increased, then decreased as the DTAB concentration increased. The electrostatic force plays a dominant role in the adsorption of DTAB on low-Rank Coal surface. The adsorption of DTAB reduced the wetting heat between water and low-Rank Coal because the oxygen-containing groups were covered. The decrease in hydrophobicity at high DTAB concentration was due to the formation of a bilayer or micelle adsorption. MD simulation results show that the adsorption of DTAB reduced the thickness of the water adsorption layer. The nitrogen atoms of DTAB were oriented toward the Coal surface, such that the alkyl chains were oriented to the water phase, thereby producing an additional repulsive effect and subsequently inhibiting the adsorption of water molecules. As a result, the number of hydrogen bonds and the interaction energy between water molecules and low-Rank Coal decreased, indicating that the hydrophobicity of low-Rank Coal was enhanced.
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Waste colza oil used as renewable collector for low Rank Coal flotation
Powder Technology, 2019Co-Authors: Mengdi Xu, Yaowen XingAbstract:Abstract The high cost of low Rank Coal flotation using diesel as the collector significantly restricts the improvement in economic efficiency of the Coal plant. Waste colza oil (WCO) from the catering industry was used as a renewable and alternative collector for ultrafine low Rank Coal flotation in this investigation. Scanning electron microscopy (SEM) test was carried out to check the surface morphologies of the Coal sample. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) tests were performed to examine the Coal chemical compositions. The flotation yield using WCO was always higher than that of using diesel, especially at a high dosage. When 6 kg/t dosage was used, 35.68% yield was obtained with WCO, 5.54% higher than that with diesel. The mechanism of WCO used as an alternative collector was discussed based on the induction time, FTIR, and XPS tests. The induction time of the low Rank Coal after conditioning with 6 kg/t diesel and WCO were 200 ms and 100 ms, respectively, indicating that WCO was a more effective collector for improving the floatability of low Rank Coal compared with traditional diesel. XPS tests confirmed the adsorption of WCO on Coal surface as the WCO has a large amount of C O groups according to FTIR results. The hydrogen bonding between oxygen-containing groups in WCO and low Rank Coal surface was responsible for the improvement of floatability and flotation recovery.
Rui Zhang - One of the best experts on this subject based on the ideXlab platform.
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Role of molecular simulation in understanding the mechanism of low-Rank Coal flotation: A review
Fuel, 2020Co-Authors: Rui Zhang, Yaowen XingAbstract:Abstract Flotation is the main method for recovering and reusing fine low-Rank Coal by taking advantage of the difference in physicochemical properties of the mineral surface, but its efficiency has not yet reached a satisfactory level. Particles, flotation reagents, and air bubbles are highly dispersed and interact with each other in a flotation cell. Therefore, a basic understanding on the fundamental mechanism of the above interactions involved in a low-Rank Coal flotation system is the prerequisite for improving low-Rank Coal flotation recovery. In recent years, with the development of theoretical chemistry and computational chemistry, molecular simulation has gradually become a powerful tool for studying low-Rank Coal flotation, which has shed new light on the molecular structure of low-Rank Coal and the interfacial interaction in low-Rank Coal flotation at the molecular or atomic levels. In this paper, we first review the basic theory of molecular simulation, and then we review the recent advances in the molecular structure of low-Rank Coal. Coal-water, Coal-reagent, Coal-bubble, and Coal-clay interactions are discussed comprehensively from the viewpoint of molecular simulation. This review is closed with a brief conclusion and perspective discussion.
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enhancement of flotation response of fine low Rank Coal using positively charged microbubbles
Fuel, 2019Co-Authors: Longwu Wang, Zili Yang, Rui Zhang, Yaowen XingAbstract:Abstract This study investigates the possibility of using positively charged (PC) microbubbles in pulp conditioning to improve the flotation response of fine low-Rank Coal. The surface properties of the Coal are characterized by means of a zeta potential analyzer, scanning electron microscopy, and X-ray photoelectron spectroscopy. Batch flotation tests are conducted with the use of PC microbubbles, cetyltrimethylammonium bromide (CTAB) solution, and tap water in pulp conditioning. The roles of PC microbubbles in the Coal flotation are illustrated by combining observations of particle–particle and particle–bubble interactions and extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory calculations. The results indicate that fine low-Rank Coal is negatively charged and contains a large amount of oxygen. In addition, the rough structure and the presence of numerous impurity mineral particles on the surface of low-Rank Coal afford adsorption sites for water molecules. These features of the Coal render traditional collectors ineffective, whereas the presence of PC microbubbles significantly enhances flotation recovery. However, increasing CTAB concentration cannot continuously improve flotation performance with the use of PC microbubbles, possibly because the excess CTAB molecules can form bilayer or micelle adsorption structures on the Coal surface, particularly on the mineral surface. The presence of PC microbubbles promotes particle–particle agglomeration and particle–bubble attachment by providing an additional attractive electrical double-layer force and enhancing hydrophobic interactions. The extended DLVO theory calculations agree well with the experimental results.
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enhancement of the surface hydrophobicity of low Rank Coal by adsorbing dtab an experimental and molecular dynamics simulation study
Fuel, 2019Co-Authors: Zili Yang, Rui Zhang, Yaowen XingAbstract:Abstract This study investigated the mechanism of improving the surface hydrophobicity of low-Rank Coal by adsorbing dodecyltrimethylammonium bromide (DTAB). Experimental tests were conducted to analyze the adsorption characteristic of DTAB on the Coal surface including the adsorption amount, Zeta potential, wetting heat, and X-ray photoelectron spectroscopy measurement. Furthermore, the adsorption configuration, spatial location of the simulation systems, and the Coal–water interaction were investigated by molecular dynamics (MD) simulation at the atomic scale. Experimental results indicate that the hydrophobicity of the low-Rank Coal first increased, then decreased as the DTAB concentration increased. The electrostatic force plays a dominant role in the adsorption of DTAB on low-Rank Coal surface. The adsorption of DTAB reduced the wetting heat between water and low-Rank Coal because the oxygen-containing groups were covered. The decrease in hydrophobicity at high DTAB concentration was due to the formation of a bilayer or micelle adsorption. MD simulation results show that the adsorption of DTAB reduced the thickness of the water adsorption layer. The nitrogen atoms of DTAB were oriented toward the Coal surface, such that the alkyl chains were oriented to the water phase, thereby producing an additional repulsive effect and subsequently inhibiting the adsorption of water molecules. As a result, the number of hydrogen bonds and the interaction energy between water molecules and low-Rank Coal decreased, indicating that the hydrophobicity of low-Rank Coal was enhanced.
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improving the adsorption of oily collector on the surface of low Rank Coal during flotation using a cationic surfactant an experimental and molecular dynamics simulation study
Fuel, 2019Co-Authors: Rui Zhang, Yaowen XingAbstract:Abstract The effect of a cationic surfactant, dodecyltrimethylammonium bromide (DTAB), on low-Rank Coal flotation using an oily collector (dodecane) was investigated by a combination of experimental tests and molecular dynamics simulations. Flotation results showed that the addition of DTAB during pulp conditioning increased the clean Coal yield, while a high concentration of DTAB exerted a negative influence. To explain the flotation behavior and analyze the interaction between low-Rank Coal, DTAB and dodecane, a series of experimental tests were conducted and the results indicated that a relatively lower concentration of DTAB is beneficial for the adsorption of dodecane on low-Rank Coal surface. In addition, by measuring the induction time, it was found that low-Rank Coal particles were easily adhered to bubbles in the presence of suitable concentration of DTAB. However, a high concentration of DTAB brings about an adverse effect. Later, molecular dynamics (MD) simulations were carried out to illustrate the positive effect of DTAB on the adsorption reaction between low-Rank Coal and dodecane. The results showed that the abundant number of oxygen-containing groups in low-Rank Coal are responsible for the limited adsorption of nonpolar dodecane molecules on its surface, while the pre-adsorption of DTAB on the surface of low-Rank Coal enhances dodecane adsorption. This can be ascribed to the exposed hydrophobic structure of the Coal-DTAB complex. As a result, dodecane molecules were more easily adsorbed on the surface of low-Rank Coal and the attraction of low-Rank Coal to dodecane in the presence of DTAB resulted in a lower mobility of dodecane molecules, and a larger interaction energy between dodecane and low-Rank Coal. The simulation results are in good agreement with experimental results.
Kalinka Markova - One of the best experts on this subject based on the ideXlab platform.
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structural study of the autoxidation processes in asphaltenes from low Rank Coal lithotypes
Oxidation Communications, 2003Co-Authors: Kalinka Markova, Maya Stefanova, Stefan MarinovAbstract:Proton NMR spectroscopy and "number average structural analysis" have been successfully applied to the identification of probable structural fragments in asphaltenes from low Rank Coal lithotypes (xylain, humovitrain, semifusain, fusain and liptain) of Bulgarian Coal basins and deposits (Maritza Iztok and Chukurovo). An attempt was made to relate the structural transformations in each separate lithotype to the dominant oxidation processes (oxidative destruction, thermal oxidation, and direct oxidation) that occur during the petrographic processes (gelification, fusainization, liptainization), respectively. The influence of the autoxidation processes in low Rank Coal lithotypes (both in deposit and during their storage and exploitation) on the structural parameters of the isolated asphaltenes has been assessed in a model oxidation reaction (150°C and 45 h).
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study of the effect of autoxidation processes on the generation of low Rank Coal lithotypes from some bulgarian basins
Oxidation Communications, 2003Co-Authors: Kalinka Markova, I J KostovaAbstract:Low Rank Coal lithotypes (xylain, humovitrain, semifusain, fusian and liptain) from two Bulgarian Coal provinces (Trakiya and Sofia) and three basic Coal basins in them (Maritza East, Chukurovo and Stanyantzi) have been studied. The purpose of the present work was to establish the concentration and distribution of the iron ions (Fe 2 + and Fe 3 + ) in the lithotypes of low Rank by applying Mossbauer spectroscopy. On the bases of the changes in the transformation of these ions, the characterisation of the type, continuation and intensity of the autoxidation processes (destructive oxidation, thermooxidation and direct oxidation), which take place in the peat bog and related with them petrological processes of disintegration (gelization, fusenization and liptization) which form the low Rank Coal lithotypes, has been done.
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investigation of low temperature autooxidation processes of low Rank Coal lithotypes by dta and tg
Journal of Thermal Analysis and Calorimetry, 1993Co-Authors: Kalinka Markova, N ShopovaAbstract:The autooxidation processes in the temperature range 50 o -150 o C in the low Rank Coal lithotypes (xylain, humovitrain, semifusain, fusain and liptain) were studied. The activation energy of the processes for the investigated temperature range was calculated by Coats and Redfern method. The established differences between the activation energies of the initial and oxidized lithotypes are connected with the structure peculiarities of the lithotypes, and with the varieties in the mechanism of the autooxidation processes
Zili Yang - One of the best experts on this subject based on the ideXlab platform.
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enhancement of flotation response of fine low Rank Coal using positively charged microbubbles
Fuel, 2019Co-Authors: Longwu Wang, Zili Yang, Rui Zhang, Yaowen XingAbstract:Abstract This study investigates the possibility of using positively charged (PC) microbubbles in pulp conditioning to improve the flotation response of fine low-Rank Coal. The surface properties of the Coal are characterized by means of a zeta potential analyzer, scanning electron microscopy, and X-ray photoelectron spectroscopy. Batch flotation tests are conducted with the use of PC microbubbles, cetyltrimethylammonium bromide (CTAB) solution, and tap water in pulp conditioning. The roles of PC microbubbles in the Coal flotation are illustrated by combining observations of particle–particle and particle–bubble interactions and extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory calculations. The results indicate that fine low-Rank Coal is negatively charged and contains a large amount of oxygen. In addition, the rough structure and the presence of numerous impurity mineral particles on the surface of low-Rank Coal afford adsorption sites for water molecules. These features of the Coal render traditional collectors ineffective, whereas the presence of PC microbubbles significantly enhances flotation recovery. However, increasing CTAB concentration cannot continuously improve flotation performance with the use of PC microbubbles, possibly because the excess CTAB molecules can form bilayer or micelle adsorption structures on the Coal surface, particularly on the mineral surface. The presence of PC microbubbles promotes particle–particle agglomeration and particle–bubble attachment by providing an additional attractive electrical double-layer force and enhancing hydrophobic interactions. The extended DLVO theory calculations agree well with the experimental results.
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Effects of pore compression pretreatment on the flotation of low-Rank Coal
Fuel, 2019Co-Authors: Zili Yang, Zijian Ma, Ming Li, Yaowen XingAbstract:Abstract The poor flotation efficiency of low-Rank Coal in the flotation process is due to the large and rich pore structure on its surface. In this study, the changes in the pore structure before and after pore compression pretreatment were analyzed by a scanning electron microscope and Brunauer–Emmett–Teller analysis. The effects on the flotation were then evaluated by analyzing the results of collector adsorption experiments and flotation kinetics tests. After pore compression, the pore state on low-Rank Coal surface was from open to half-closed and then closed. Further, the pore volume, specific surface area, and average pore diameter of the particles decreased from 0.02497 to 0.01214 cm3/g, 17.383 to 5.006 m2/g, and 9.6992 to 5.7466 nm, respectively. In addition, the adsorption rate of the collectors improved and the equilibrium adsorption time of n-dodecane decreased from 436 s to 250 s, whereas the adsorption rate of water decreased with the porosity of the Coal after pore compression. Meanwhile, according to the flotation results, the maximum clean Coal yield (74.44%) was obtained within 400 MPa of pressure pretreatment using n-dodecane as a collector; this value is 20.46% points higher than that of raw Coal flotation using n-hexane as the collector. Furthermore, it was also found that a collector with too high a viscosity or too short a carbon chain causes the total cumulative yield of the low-Rank Coal to decrease. It is anticipated that the results of this work can provide guidance in low-Rank Coal flotation applications.
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enhancement of the surface hydrophobicity of low Rank Coal by adsorbing dtab an experimental and molecular dynamics simulation study
Fuel, 2019Co-Authors: Zili Yang, Rui Zhang, Yaowen XingAbstract:Abstract This study investigated the mechanism of improving the surface hydrophobicity of low-Rank Coal by adsorbing dodecyltrimethylammonium bromide (DTAB). Experimental tests were conducted to analyze the adsorption characteristic of DTAB on the Coal surface including the adsorption amount, Zeta potential, wetting heat, and X-ray photoelectron spectroscopy measurement. Furthermore, the adsorption configuration, spatial location of the simulation systems, and the Coal–water interaction were investigated by molecular dynamics (MD) simulation at the atomic scale. Experimental results indicate that the hydrophobicity of the low-Rank Coal first increased, then decreased as the DTAB concentration increased. The electrostatic force plays a dominant role in the adsorption of DTAB on low-Rank Coal surface. The adsorption of DTAB reduced the wetting heat between water and low-Rank Coal because the oxygen-containing groups were covered. The decrease in hydrophobicity at high DTAB concentration was due to the formation of a bilayer or micelle adsorption. MD simulation results show that the adsorption of DTAB reduced the thickness of the water adsorption layer. The nitrogen atoms of DTAB were oriented toward the Coal surface, such that the alkyl chains were oriented to the water phase, thereby producing an additional repulsive effect and subsequently inhibiting the adsorption of water molecules. As a result, the number of hydrogen bonds and the interaction energy between water molecules and low-Rank Coal decreased, indicating that the hydrophobicity of low-Rank Coal was enhanced.
N Shopova - One of the best experts on this subject based on the ideXlab platform.
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investigation of low temperature autooxidation processes of low Rank Coal lithotypes by dta and tg
Journal of Thermal Analysis and Calorimetry, 1993Co-Authors: Kalinka Markova, N ShopovaAbstract:The autooxidation processes in the temperature range 50 o -150 o C in the low Rank Coal lithotypes (xylain, humovitrain, semifusain, fusain and liptain) were studied. The activation energy of the processes for the investigated temperature range was calculated by Coats and Redfern method. The established differences between the activation energies of the initial and oxidized lithotypes are connected with the structure peculiarities of the lithotypes, and with the varieties in the mechanism of the autooxidation processes
