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In this work, the assembly behavior and structure of a compound collector with different carboxyl group positions at the low-rank coal (LRC)–water interface were investigated through coarse-grained molecular dynamics simulation (CGMD) combined with sum-frequency vibration spectroscopy (SFG). The choice of compound collector was dodecane +decanoic acid (D-DA) and dodecane +2-butyl octanoic acid (D-BA). CGMD results showed that the carboxyl group at the carbon chain's middle can better control the assembly process between carboxylic acid and D molecules. SFG research found that the carboxyl group at the carbon chain's termination had a greater impact on the displacement of the methyl/methylene symmetric stretching vibration peak, while the carboxyl group at the carbon chain's middle had a greater impact on the displacement of the methyl/methylene asymmetric stretching vibration peak. The spatial angle calculation results revealed that the methyl group's orientation angle in the D-BA molecule was smaller and the carboxyl group's orientation angle in the BA molecule was bigger, indicating that D-BA spread more flatly on the LRC surface than D-DA. This meant that the assembled structure had a larger effective adsorption area on the LRC surface. The flotation studies also verified that the assembly behavior and structure of D-BA with the carboxyl group at the carbon chain's middle at the LRC–water interface were more conducive to the improvement of flotation efficiency. The study of interface assembly behavior and structure by CGMD combined with SFG is crucial for the creation of effective compound collectors. [ABSTRACT FROM AUTHOR]

The effect of mass proportions of fine slime on the flotation performance of coal was investigated in the present study. Generally, the presence of fine slime showed a negative effect on flotation, i.e. as the mass proportion of fine slime increased, both flotation yield and kinetics decreased, while ash content increased, which was attributed to slime coating and water entrainment. The sedimentation tests, adsorption amount measurements, and Cryo-SEM technique directly indicated the incidence of slime coating, which became more significant with the increase of slime mass proportion. Except for the higher collision efficiency between slime and coal particles, the increased pulp viscosity may also be the reason for the worse slime coating as scrubbing effect of turbulence was weakened. The froth drainage tests showed the occurrence of water entrainment was also correlated to slime mass ratio. However, the water recovery and froth stability showed an increase trend firstly and then a decrease. It may be attributed that high mass proportion of slime increased the pulp viscosity, leading to poor gas dispersion and froth stability. [ABSTRACT FROM AUTHOR]

Flotation is widely used for low-rank coal upgrading, although it is always inefficient due to its rough surface morphology and rich oxygen-containing functional groups. In this study, the environment-friendly vegetable oil 1030# was used to enhance the flotation performance of low-rank coal. The mechanism of 1030# enhancing the flotation of low-rank coal was revealed through surface property analysis of coal particles and bubble–particle adhesion tests. The flotation results showed that the flotation yield of low-rank coal increased with the increase in the collector dosage, and the flotation yield of 1030# as a collector is obviously higher than that of diesel. Scanning electron microscopy (SEM) and chromatography–mass spectrometry (GC-MS) were used to analyze the surface morphology of coal particles and components of the reagent. The SEM results showed that the surface of low-rank coal is loose and contains a large number of pores and cracks, which is not conducive to the spreading of chemicals on the coal surface and the mineralization of bubbles and particles. GC-MS results showed that 1030# mainly contained methyl oleate with more unsaturated double bonds than diesel. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the surface functional groups of the low-rank coal before and after reagent treatment. The results of FTIR and XPS showed that the coal surface of low-rank coal before reagent treatment contained a large number of oxygen-containing functional groups with poor surface hydrophobicity, while the surface of low-rank coal after reagent treatment had reduced oxygen-containing functional groups and increased hydrophobicity. The contact angle of the low-rank coal surface also showed the same variation trend as the FTIR and XPS results. The adhesion force between the bubble and coal surface in different collector solutions was measured. The maximum adhesion between the bubble and coal surface increased with the increase in the collector, and the maximum adhesion force with 1030# treatment was higher than that of diesel. This indicated that 1030# with a large number of polar components is more easily spread on the surface of low-rank coal, thus improving the hydrophobicity of low-rank coal. [ABSTRACT FROM AUTHOR]

Sedimentation of coal slime water (CSW) is an important process in coal processing plants. However, CSW is difficult to settle because of its high content of clay minerals and fine particles. In this paper, the effect of magnetization pretreatment on CSW flocculating sedimentation is investigated. The mechanisms of magnetization pretreatment were studied by measuring CSW's viscosity and zeta potential and calculating particle's hydration film thickness using Einstein's viscosity equation. The results show that the CSW flocculating sedimentation is enhanced by magnetization pretreatment. The optimum dosage of polyacrylamide was 6.0 mg/L and the best magnetic field strength and magnetization time was 0.3 T and 3 min, respectively. As the settling velocity was increased, the turbidity of the supernatant was reduced by magnetization pretreatment. Moreover, after magnetization pretreatment, the absolute value of the zeta potential and the viscosity were reduced, and the hydrated film thickness of coal particles was decreased from 305 nm to 155 nm. Magnetization pretreatment decreased the settling resistance and reduced the electrostatic repulsion and hydration forces between coal particles, thus promoting CSW flocculating sedimentation. It is demonstrated that magnetization pretreatment introduces a new path improve CSW settlement. [ABSTRACT FROM AUTHOR]

The efficient filtration of low-rank coal (LRC) slurry was significantly beneficial to the production process of wet coal beneficiation. However, relatively few studies have been reported on novel pretreatment methods for the efficient filtration of LRC slurry. In this paper, the mechanism of ultrasonic pretreatment to promote flocculation and filtration of slurry was studied. The hydrophobic variation of the slurry surface was measured by contact angle and XPS. The flocculation properties of slurry were characterized using zeta potential and FBRM. The effects of filter cake porosity and ultrasonic pretreatment on slurry filtration resistance were calculated by L-F NMR and Darcy's theory. The results showed that the ultrasonic pretreatment promoted the flocculation and filtration performance of LRC slurry, increased the filtration rate, and decreased the cake moisture content. Meanwhile, the contact angle of LRC increased significantly from 50.1° to 67.8° after ultrasonic pretreatment, and the surface tension of the filtrate decreased from 69.5 to 53.31 mN/m. Ultrasonic pretreatment reduced the absolute value of the zeta potential of coal slurry from 24.8 to 21.0 mV, and the average chord length of flocs increased from 5–10 μm to 25–30 μm, thus weakening the electrostatic repulsion between coals to promote floc formation. In addition, the pore tests and filtration theory calculations showed that the ultrasonic pretreatment significantly improved the permeability of the filter cake to water and reduced the resistance to slurry during filtration. In particular, the mesopore porosity increased by 9.18%, and the permeability increased by 2.937 × 108 m2. Therefore, this contributed to the reduction of slurry filtration resistance. This research provides an efficient method for promoting the efficient filtration of slurry. [ABSTRACT FROM AUTHOR]

Bubble–particle interactions are crucial in the flotation process, and the influence of adsorbed chemicals on bubble-surface collisions/attachment is important to fully understand the role of mixed collector in low-rank coal (LRC) flotation. In this paper, the process of rising bubble attachment to LRC surface in the presence of adsorbed dodecane (D)-oleic acid (OA) collector mixture was studied using high-speed video camera and molecular-kinetic (MK) model. The results showed that collector adsorbed on LRC surface reduced the collision times, the time for stopping collision and reaching standstill. Mixed collector showed more obvious advantages than single collectors in accelerating bubble-surface collisions/attachment and increasing contact line length. Only when OA and OA-D were adsorbed, the wetting film between bubble and LRC surface broke and a stable three-phase contact was formed. The molecular displacement length of D-OA was smaller than that of single collectors, indicating the adsorption sites of bubbles on LRC surface treated with D-OA were more dense, and the higher displacement frequency of D-OA meant that the molecular displacement rate and TPCL expansion velocity was faster. D-OA enhanced the hydrophobicity of LRC surface through the synergistic effect between OA and D, which promoted the kinetics of bubble interaction with LRC surface. [ABSTRACT FROM AUTHOR]

An oxidized coal surface is more negatively charged and hydrophilic than that of fresh coal because of the introduction of polar oxygen functional groups. During flotation, the decreased attractive hydrophobic force between bubbles and coal particles and the increased repulsive electrostatic force result in a low recovery for oxidized coal. In the present study, preconditioning with positive-charged microbubbles (PCMs), generated using a microbubbles generator and a cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB), was proposed to enhance oxidized coal flotation. Conventional column flotation tests were also carried out for comparison. The results show that many oxygen functional groups (-OH and C-O) existed on the oxidized coal surface as indicated by X-ray photoelectron spectroscopy (XPS). A flotation recovery of 84.33% with an ash recovery of 82.97% was obtained when PCM was used, much higher than that of conventional flotation (a recovery of 17.82% with an ash recovery of 9.64%). PCM preferably adsorbed at the negative-charged hydrophilic sites on oxidized coal in the preconditioning stage. An additional attractive electrostatic double-layer force between oxidized coal and negative flotation bubbles was introduced, enhancing PCM preconditioning. However, the worst flotation selectivity was observed using PCM compared with that of conventional flotation based on Fuerstenau upgrading curves analysis. [ABSTRACT FROM AUTHOR]

In order to study the fracture shape distribution and micromechanical properties of middling coal containing fracture fillings, the fracture information of coal samples was obtained using the morphological edge detection method. The results showed that the number of Y-shaped fractures was much greater than that of the X-shaped fractures, and the number of single fractures accounted for a larger proportion of the surface fractures. The micromechanical characteristics of the middling coals were analyzed qualitatively based on the nanoindentation load–displacement curve by the surface of middling coal containing fracture fillings. The mechanical properties of the fracture filling zone were nonuniform owing to the presence of multiple minerals, and the crack breaks along the interface or the side of the matrix having poor mechanical properties under an applied force. The difference in mechanical properties at the mineral–mineral interfaces was determined through the nanoindentation test to judge the fracture mode. [ABSTRACT FROM AUTHOR]

The developed pore distribution and large amount of oxygen functional groups have a detrimental effect on lignite flotation. The effect of mechanical thermal expression treatment (MTET) on lignite flotation performance was investigated in this study. The pore distribution and functional groups of the lignite before and after MTET were analyzed using static nitrogen adsorption method, mercury intrusion porosimetry, and Fourier transform infrared (FTIR) spectroscopy. The results showed that the clean coal yield after MTET at the 9 MPa and 200°C condition was 21.11% higher than that of untreated coal under the same flotation conditions. Both hydrophilic oxygen functional groups and porosity of the lignite decreased after MTET, increasing the absorption efficiency of oil collector on the lignite surface and the probability of bubble–particle attachment. The results of this study are expected to provide a basic understanding of the effect of MTET on lignite flotation. [ABSTRACT FROM AUTHOR]

Oxidized coal is difficult-to-float using conventional diesel as the collector due to the abundant oxygen-containing groups on coal surface. In this study, a short-chain cationic amine, n-octylamine, was added into diesel in 1:4 ratio for enhancing oxidized coal flotation. X-ray photoelectron spectroscopy (XPS) was used to identify the interaction mechanism between diesel-n-octylamine mixture (DO) and oxidized coal. The results showed that the flotation yield using 500 g/t DO mixture was much higher than that of using 2000 g/t diesel under a similar ash content of clean coal. The addition of n-octylamine was proven to be an effective way to lower the oily collector consumption in oxidized coal flotation. XPS showed that electrostatic bonding between n-octylamine and negative-charged hydrophilic sites on oxidized coal surface was responsible for the enhancement of flotation recovery using DO as the collector. [ABSTRACT FROM AUTHOR]

Six flotation kinetics models were applied to fit the flotation kinetics results of easy-to-float fine coal. It was found that, except for the second-order kinetic model, the rest models are well suited for fitting the experimental data. The rate constant decreased as flotation time increased, indicating that the particle floatability in the pulp decreased. However, only a slight decrease in the rate constant was observed within 100 s, indicating that the coal samples have good floatability in general. X-ray photoelectron spectroscopy results show that the small proportion of hydrophilic oxygen-containing groups is responsible for the good floatability and fast flotation kinetics. [ABSTRACT FROM AUTHOR]

Power input and flotation time are the two key factors influencing the efficiency of the fine coal flotation process. A new two-stage process is proposed in this investigation for intensifying fine coal flotation. The flotation process is divided into two parts: lowering energy input in the first stage and raising energy input in the second stage. Easily floated materials are recycled with low energy in the rapid floating section (first stage), and hard-to-float materials are compulsorily recycled using higher energy in the recycling section (second stage). A flotation energy consumption test system is established. Flotation tests were conducted in an XFD 0.75-L laboratory-scale flotation machine. The effects of energy input on the flotation rate constant in instantaneous flotation or flotation over a period of time were investigated. The results indicate that higher combustible matter recovery or lower concentrate ash content could be obtained using a two-stage process compared with a single-stage flotation process with the same energy consumption. Compared with energy input in the first stage of the flotation process, the energy added in the second stage of the flotation process would increase with flotation processing owing to the decreased rate of fine coal floatability in the first stage. The larger the floatability difference in the flotation process, the more energy must be used in the second stage of the flotation process. With the same energy input, the flotation tests indicate that lower ash content or higher combustible matter recovery could be obtained using the proposed two-stage flotation process. [ABSTRACT FROM AUTHOR]

The wettability of floc has a large effect on the selective flocculation flotation process of fine coal separation. The changes of thermodynamic characterization of coal and kaolinite have been investigated by Washburn dynamic method and Fourier transform infrared spectroscopy (FTIR) before and after the adsorption of anionic polyacrylamide. Lipophilic hydrophilic ratio (LHR), surface free energy, and its components were calculated by Washburn equation combined with Van Oss–Chaudhury–Good theory according to the wetting curves of coal and kaolinite samples wetted by n-hexane, α-bromonaphthalene, formamide, and water. After PAM A401 adsorption, the peaks of hydrophilic functional groups of coal (the amide group, free-NH2, secondary amide N–H, C–N) were increased, while the peaks of the hydrophobic functional group, including methyl (-CH3) and methylene (–CH2–), was decreased. The LHR value of coal decreased from 9.23 to 7.28. The polar components of coal were increased, the non-polar components were decreased, and the surface free energy was increased from 39.92 to 40.43 mN m−1. The coal surface became more hydrophilic. For kaolinite, both hydrophilic and hydrophobic functional groups were increased, while its LHR values increased from 1.44 to 1.65. The polar component was decreased from 58.27 to 55.05 mN m−2. Results of FTIR were corresponding to the surface property. [ABSTRACT FROM AUTHOR]

This study explored the effects of energy input and different energy increase patterns on the separation performance of a laboratory cyclonic–static microbubble flotation column in fine coal flotation. The energy input was changed by adjusting the circulating pump power and pulp residence time. Continuous flotation tests were designed by using five feed rates (i.e., different pulp residence time), which were 53.33, 80.00, 106.40, 133.60, and 160.00 g/min, and various useful power of the circulating pump (22.44, 30.14, 38.50, 46.86, 56.10, and 64.46 W). Results show that concentrate combustible recovery initially increased before reaching saturation distribution with increasing energy input absolute value. An ash content of 10.90% and combustible matter recovery of 92.84% were obtained at the energy input of 10098.00 J which is called the flotation saturation energyEs. Esis the essential condition and guarantee for a complete flotation process. A low ash content of clean coal was obtained with low energy input. With the increase of energy consumption, the additional coals recovered were coarse particles with low ash content and fine particles with high ash content. However, the ash content did not exhibit a significant change with the increase of energy input in this investigation. During the flotation process, a minimum critical flotation timeTand critical circulation pump useful powerPare required. If thePandTof a variable are less than the critical value, high combustible matter recovery could not be obtained by adding another variable to increase energy input. A reasonable mode of energy input was proposed that the absolute value of the energy input reachesEs; meanwhile, it ensures that each value of thePandTis greater than the critical values. [ABSTRACT FROM AUTHOR]

In order to improve the separation efficiency of fine oil droplets from oily wastewater, a new process utilizing coal adsorption and column flotation has been developed. In this work, anthracite from Jincheng, China was used as an adsorbent for oil removal from wastewater. The effects of adsorption time, coal particle size distribution, the value of pH, and the oil concentration in wastewater on the adsorption capacity of anthracite were investigated by static experiments. A novel device named a cyclone-static microbubble flotation column was developed for the separation of oily wastewater, which combines the conventional hydrocyclone with a conventional flotation column. Coal adsorption-column flotation tests were carried out and scaled-up from a lab-scale (1 m3/day), to a pilot scale (30 m3/day), and to a full-scale (2000 m3/day) unit. Different operating parameters, such as coal dosage, feed rate, circulation pressure, and gas flow rate were studied. In full-scale tests of 2000 m3/day, oil removal of 97.70% with the treated effluent containing an oil concentration of 23.39 mg/L was obtained. [ABSTRACT FROM AUTHOR]

Low flotation efficiency has always been a problem in the separation of low-grade molybdenum ores because of the finely disseminated nature and crystal anisotropy of molybdenite. In this study, a novel kerosene–coal tar collector (KCTC) was prepared and used to explore the feasibility of improving the recovery of fine molybdenite particles. The results showed that KCTC achieved better attaching performance than that shown by kerosene, and the surface coverage and attaching rate constant were improved significantly, especially for finer particles of −38 + 20 μm. Compared with kerosene, KCTC showed more affinity for molybdenite particles and greater adsorbed amounts of KCTC on molybdenite particles were achieved. Moreover, the composite collector was shown to float single molybdenite particles of different sizes, and it was found that the recovery of molybdenite particles of different sizes, particularly in the case of those at −20 μm, was improved dramatically by KCTC. The flotation results of actual molybdenum ores further confirmed that KCTC was beneficial to flotation recovery and the selectivity of molybdenite. This indicated that KCTC is a potential collector for the effective flotation of low-grade deposits of molybdenum ores, and more studies should be conducted on further use in industrial practice. [ABSTRACT FROM AUTHOR]

The mixed collector can improve low rank coal flotation efficiency, but its synergistic mechanism needs to be further explored. In this paper, oleic acid-dodecane (OA-D), oleic acid (OA), and dodecane (D) were employed to treat the low rank coal for revealing new synergistic mechanism of the mixed collector. First the surface free energy of the coal, the surface free energy of coal-water and coal-water-coal were calculated. Then wetting heat measurement, X-ray Photoelectron Spectroscopy (XPS) and FTIR were used to analyze synergistic mechanism of the mixed collector in depth. The results showed that OA-D obtained a higher combustible recovery than using OA and D, respectively. The essence of synergetic mechanism of OA-D was that they formed a relatively ordered "supramolecular structure" on the low rank coal surface, especially there were hydrophobic and van der Waals forces between the oleic acid chain and the dodecane chain that can promote the formation of a continuous collector film. [ABSTRACT FROM AUTHOR]

[Display omitted] • The desulfurization performances of medium–high sulfur coking coal via combined methods of flotation and oxidation were compared creatively. • The desulfurization mechanism of medium–high sulfur coking coal was analyzed by XPS, SEM, MD simulation, etc in detail. • After combined treatment of flotation and H 2 O 2 oxidation, inorganic sulfur is almost completely removed and its desulfurization performance is perfect. The presence of sulfur affects the clean utilization of coking coal. Inorganic sulfur in coal, which exists mainly in the form of pyrite, inherently pollutes clean coal during flotation, while organic sulfur, on the other hand, can only be effectively removed by chemical means. Here, the combined methods of flotation and oxidation were adopted for desulfurization, and the desulfurization mechanisms were analyzed via XPS (X-ray photoelectron spectrometer), SEM (Scanning electron microscopy), MD (Molecular Dynamics), etc. Results showed that the removal of inorganic sulfur was preferred compared to the removal of organic sulfur. The sulfur and ash contents in coal were reduced from 2.55% and 46.16% to 1.33% and 13.41%, respectively, via flotation-oxidation (FO) method. During the oxidation-flotation (OF) method, however, Fe 2 O 3 was observed to form on the surface of pyrite, while the content of oxygen-containing functional groups, adsorption capacity of water molecules and hydrophilicity were observed to increase. MD simulation was in agreement with experimental results, in which the diffusion coefficient of water molecules on the surface of oxidized coal was found to be lower than that of raw coal. As such, the oxidation process reduced the hydrophobicity of coal, resulting in a lower recovery of the products obtained via OF as compared to FO method. [ABSTRACT FROM AUTHOR]

This study developed a rapid and efficient graphite furnace digestion combined with inductively coupled plasma emission spectrometry (ICP-OES) method, enabling precise quantification of germanium (Ge) in coal and various coal-derived metallurgical byproducts across a broad concentration level (∼ppm-n%). The graphite furnace digestion conditions were examined intensively as a function of the acid amounts of HNO 3 and HF (5–10 mL), temperature (80–180 °C), time (1–5 h), and acid drive methods (H 3 BO 3 neutralization versus heating). Coal references including SARM 19, SARM 20, NIST SRM 1632e, and fly ash standard NIST SRM 2689 were tested. The optimum recovery of germanium was obtained when the HNO 3 dosage, HF dosage, solid sample mass, temperature, and duration time were 10 mL, 5 mL, 0.1 g, 80 °C and 1 h. Agreement of 95.15–96.54 % between the measured and certified value was obtained under the optimum conditions. The spiked recovery was 103.23–103.54 %, indicating the matrix-analytes interactions were negligible. Boric acid neutralization reduced the recovery rates to 47.2–49.3 % and was not be appropriate for driving HF. The optimal spectral line for determining Ge is at a wavelength of 265.117 nm, at which the limit of detect and the limit of quantification were 0.46 μg L−1 and 1.53 μg L−1, respectively. The applicability of the method was validated by quantifying Ge in Ge-rich lignite, fly ashes (FA), and chlorinated distillation residue (CR) samples. The concentration of Ge in coals was 44.75–225.41 μg g−1, the content in FA was 0.68%–2.3 %, and the content in CR was 0.18 %, with the uncertainty of the method obtained being less than 0.5 %. X-ray fluorescence spectrometer (XRF) was used to verify the results. The difference between XRF data and ICP-OES data was less than 5 %, confirming the accuracy and reproductivity of the analytical method. [Display omitted] • A rapid determination of Ge in coal and its metallurgical byproducts based on graphite furnace digestion was developed. • The optimum recovery (95.15–96.54 %) was obtained using 0.1 g sample digested with 10 mL HNO 3 plus 5 mL HF at 80 °C for 1 h. • H 3 BO 3 neutralization was found not to be appropriate for driving HF because it can significantly lower the detected value. • The optimal spectral line for determining Ge is at a wavelength of 265.117 nm with LOD and LQD of 0.46 and 1.53 μg L−1. • The method has wide applicability in various coal-derived solid byproducts with broad concentration level (∼ppm-n%). [ABSTRACT FROM AUTHOR]

[Display omitted] • The optimized combustion conditions can utilize the heating value in coal and transform REY to easily leachable forms. • REY greatly enriched in ash below 45 μm, caused by the small mineral grain size and extensive mineral fragmentation in boiler. • The enhanced acid leachability was related to thermal decomposition of flurocarbonates, aluminophosphates, and organic-bound REY in coal. • Different speciation transformation behavior of REY during combustion resulted in distinct REY leaching behavior for different ash types. The extraction of rare earth elements (REE) from coal ash has attracted significant attention, but satisfactory solutions have not yet been achieved. Indeed, the REE extractability is largely determined by the transformation behavior of REE during coal combustion. This study found that the controlled combustion conditions of circulated fluidized-bed boiler (CFB) can both utilize the heating value and enhance the recovery of REE from coal. Tests were conducted using a bituminous coal with REE concentration of approximately 149 ppm in an industrial 35 t/h CFB boiler with controlled boiler loads and coal sources. Advanced automated image analysis by scanning electron microscopy (AIA-SEM) and sequential leaching procedure were employed to clarify the speciation transformation behavior of REE in boilers and investigate the effects of these transformations on the leachability of REE. Approximately 75 % of REE partitioned into fly ash and enriched in particles < 45 μm (∼710 ppm) after combustion. Acid leaching tests under mild conditions (1 M HCl at 60 ℃ and S/L = 1:25) performed on coal, bulk ashes, and sieved ashes revealed an improvement in REE leaching ratio from coal (21.34 %) to fly ash (71.07 %). Particle size played a crucial role in acid extractability, particularly for middle and heavy REE in cyclone ash but had no influence on those in fly ash. The dominant forms of REE in coal including Ca-REE fluorocarbonates (36.7 %), aluminophosphates (12.0 %), and organic-bound REE (approximately 20 %) significantly decreased, contributing to the formation of leachable rare earth oxides (∼65 %) in ash. Furthermore, the small size of REE mineral grains in coal (over 50 % below 5 μm) and extensive mineral fragmentation occurring in boiler resulted in the enrichment and enhanced REY leachability in fine ash. [ABSTRACT FROM AUTHOR]

The enhancement of ultrasonic pretreatment on the flocculation filtration of coal slurry water has been reported. The structural characteristics of flocs are critical parameters in the flocculation and filtration process. In this paper, the effect of ultrasonic pretreatment on the flocs' characteristics during flocculation and filtration was investigated. The flocs size, number, strength, and fractal dimension in the microstate were characterized through a polarized light microscope, PVM, and FBRM. The changes in flocs characteristics on the filter cake's pore structure and moisture distribution were analyzed using L-F NMR. The results showed that the optimal condition was an ultrasonic frequency of 30 KHz, ultrasonic time of 3 min, and the dosage of cationic polyacrylamide (CPAM) with ionicity of 60 at 50 g/t, under which the filtration rate was 597.42 mL·(m2s)−1 and the moisture content of the filter cake was 27.03 %. Ultrasonic pretreatment increased the flocs' size, with a decrease in the proportion of small flocs and an increase in the proportion of medium and large flocs, mainly medium flocs. The increase in the fractal dimension and strength of the flocs structure made the filter cake deformed less under pressure, formed a porous skeleton structure, and increased the total porosity of the filter cake, with the most significant variation in mesopores. Moreover, ultrasonic pretreatment could decrease the proportion of adsorbed and bound water while increasing the proportion of free water and effectively reducing the filter cake's moisture content. This study revealed the essential relationship between floc characteristics and flocculation filtration efficiency, filter cake pore structure, and moisture distribution and provided a new perspective for exploring the application mechanism of ultrasonic technology in enhancing flocculation filtration performance. [Display omitted] [ABSTRACT FROM AUTHOR]

A series of coal-based hierarchical porous carbons with adjustable pores were successfully prepared with the assistance of the soluble salt Zinc chloride (ZnCl 2). During the carbonization process, ZnCl 2 , with a low melting point (238 °C), "in situ occupied" and "occupied" within the coal solids to generate interconnected pores, which acted as a template. Simultaneously, the activation of ZnCl 2 reduced the oxygen content of products and further improves their electrical conductivity. Optimization of the mass of the salt and the carbonization temperature resulted in targeted product with a suitable specific surface area (1581 m2 g−1) and unique pores (V meso /V total = 45%), which exhibited a high specific capacitance (470.7 F g−1 at 0.5 A g−1) in 6 M KOH electrolyte. The symmetrical supercapacitor of targeted product has favorable rate performance (256.7 F g−1 at 0.5 A g−1, 84.8% capacity retention at 30 A g−1) and excellent cycling performance (after 10000 cycles, the specific capacitance increases to 115% of the initial capacity at 10 A g−1). In the EMIMBF 4 electrolyte system, the energy density is 95.31 Wh kg−1 at 213.13 W kg−1. Therefore, this work provides an effective method to improve the green and efficient use of coal. [Display omitted] • The salt template method is used to synthesize the coal-based hierarchical porous carbons(CPCs) for the first time. •ZnCl 2 plays a dual function of template - activation in the carbonization process. •The materials obtained an interconnected hierarchical porous structure derived from the melting properties of ZnCl 2. •The material exhibits high specific capacitance (470.7 F g−1 at 0.5 A g−1) and excellent cycling performance. [ABSTRACT FROM AUTHOR]

In low-rank coal (LRC) mixed collectors, little attention has been paid to the structure-activity relationship of different carboxylic acids. In this study, the application effect and adsorption mechanism of the mixed collector composed of dodecane (D) and carboxylic acid with different carbon chain lengths (n-valeric acid (VA), n-decanoic acid (DA), myristic acid (MA)) for LRC were explored by using sum-frequency vibration spectroscopy (SFG) and molecular dynamics simulation (MD). SFG measured the groups orientation angle on the LRC surface treated with the mixed collector, revealing that during the interfacial assembly process of mixed collector molecules, D molecules and the main molecular axes of DA molecules with similar carbon chain length tend to be adsorbed parallel to the LRC surface. The MD results showed that adding D-DA could weaken the hydrogen bonding between the LRC surface and interfacial water to the greatest extent, thereby improving every component's diffusion ability. [Display omitted] • First time to use SFG and MD to study the adsorption and assembly of mixed collectors. • SFG strength calculation illustrated the overall interface adsorption conformation. • MD revealed the dynamic properties and the damage degree of the hydrogen bond network. • Note: SFG (Sum-frequency vibration spectroscopy); MD (Molecular dynamics simulation). [ABSTRACT FROM AUTHOR]

The recognition and quantification of rare earth and yttrium (REY) minerals in coal is extremely important for understanding their geological origin and developing high-efficiency extraction techniques. This study developed an automated image analysis by scanning electron microscopy (AIA-SEM) method for characterizing REY minerals in coal. Carbon and copper were used as grey-scale calibration standard to assure the consistency per experiment and differentiate organic matter and minerals with different brightness. Two critical issues in determining REY including rapid recognition of fine REY-bearing particles and accurate classification and quantification of REY minerals in coal are resolved by (1) establishing grey threshold standard to locate REY-bearing grains and a two-step image scan; (2) developing classification criteria supplemented with spot- and EDS-mapping analysis for questionable particles. By using the established method, a total of 166 REY-bearing mineral grains were identified from 12,930 particles in a medium-volatile bituminous coal (REY concentration: 149.21 ppm; ash yield: 21.25%). It is found that Ca-REE flurocarbonates, monazite, and (Sc, Y)-bearing zircon are the dominant REY species in the studied coal sample. REE-aluminophosphates are also important hosts for REE in coal, with total amounts being >10%. REY minerals are fine in particle size. Over 50% of monazite, xenotime, Ca-REE flurocarbonate, and REE-aluminophosphate have particle size below 5 μm and monazite occurs mostly as submicron particle. Most REY minerals (> 60%) are embedded into coal macerals as included minerals. About 80% of REY-bearing phosphates and zircon are partly or completely encapsulated in clay minerals, whereas more than half of Ca-REY-fluorocarbonates mineral grains is free of other minerals. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Froth stability is one of the most important factors in fine coal flotation as it significantly affects the separation efficiency. Diesel is always used as the flotation collector while the effect of diesel on the froth stability is less investigated. In this study, effect of diesel on the froth stability and its antifoam mechanism in fine coal flotation used MIBC as the frother was investigated. Three-phase and two-phase froth stability tests were first carried out and the negative effect of diesel on froth stability was further explained by the single foam film drainage and spreading pressure experiments. The results of the three-phase dynamic froth stability showed that the maximum froth height and half-life of froth first increased and then decreased with the increase in diesel concentration. When diesel concentration increased to 8 kg/t, the maximum froth height and half-life of froth increased to 7.7 cm and 19 s. Deforming effect was observed when further increasing diesel dosage. Two-phase froth stability tests showed that the foaming ability and foam stability gradually decreased as the diesel concentration increased. When the diesel concentration increased from 0 to 20 and 40 ppm, the foam half-life decreased from 19 to 2.84 and 1.42 s, respectively. Single foam drainage tests showed that the diesel droplets dispersed into the middle of the foam film resulting in the formation of oil-bridge and rupture of the foam film. Meanwhile, the oil-film spreading pressure was found increased as the diesel concentration increased, directly indicating the antifoam effect of diesel. MIBC molecules were competitively adsorbed at diesel droplets, which reduced the effective concentration of the frother at the gas-water interface. Throughout this study, a certain defoaming effect of diesel on the froth stability in coal flotation was identified. Unlabelled Image • Effect of diesel on froth stability in coal flotation was studied. • Froth stability first increased then decreased as diesel increased. • Oil-bridge was formed in foam film leading to film rupture. • Oil-film spreading pressure increased as diesel increased. [ABSTRACT FROM AUTHOR]

As a sub-process of flotation, the bubble-particle detachment plays a critical role in final flotation recovery. In this short communication, the effect of vibration mode, i.e., sine wave, triangle wave and square wave, on the detachment of low-rank coal particle from oscillating bubble was investigated using a home-made bubble-particle detachment measurement system. The critical detachment amplitude was used to evaluate the stability of bubble-particle aggregate. Three coal size fractions, i.e., 0.25–0.5, 0.5–1, and 1–1.5 mm, were used as the experimental samples, respectively. The results show that the critical amplitude decreased as particle size increased under different vibration modes due to the increased inertia. The critical amplitude at three different size fractions always decreased in the following order: sine wave, triangle wave and square wave, indicating the bubble-particle aggregate was the most stable under sine wave vibration. Square wave vibration has the most dramatic movement path changes, causing a highest instantaneous impulse and detachment force. Unlabelled Image • Effect of vibration mode on detachment of low-rank coal was studied. • The critical amplitude decreased with increasing particle size. • The critical amplitude decreased as follows: sine, triangle and square wave. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Use of positively charged microbubbles to improve coal flotation response is studied. • Properties of coal surfaces and positively charged microbubbles are characterized. • Positively charged microbubbles enhance particle–particle agglomeration and particle–bubble attachment. 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. [ABSTRACT FROM AUTHOR]

Abstract Surface roughness has a great impact on coal floatability, and usually the effect is found to be negative. In this paper, hypobaric treatment was introduced to improve the floatability of coal with varying surface roughness. The floatability was characterized by induction time, and the micro-bubble nucleation theory was proposed to explain the enhancement mechanism of hypobaric treatment. The results show that the induction time was increased with increasing surface roughness. However, hypobaric treatment was proven to be an effective method in mitigating the adverse effects of surface roughness on floatability. Under natural conditions, neither Wenzel nor Cassie model could be used to describe the wetting regime of coal surface. Instead, a mixed wetting state, where water partially wets the asperities on coal surface and partially sits on entrapped air pockets, was more appropriate. It was difficult to drain the entrapped water at the upper part of the grooves; hence, bubble-coal attachment was prevented, leading to the increased induction time at high surface roughness. After hypobaric treatment, the diffused gas molecules in water preferred to nucleate at the sites of air pockets, leading to the formation of micro-bubbles. These micro-bubbles would act as the bridge between macroscopic bubbles and the coal surface, significantly decreasing induction time and improving the coal contact angle and floatability. Graphical abstract Unlabelled Image Highlights • Effect of surface roughness on coal floatability was studied. • Hypobaric treatment was introduced to improve the floatability. • Hypobaric treatment can mitigate the adverse effect of roughness on floatability. • Microbubble nucleation theory was proposed to explain the mechanism. [ABSTRACT FROM AUTHOR]

Abstract The presence of clay minerals presents a great challenge to fine coal and mineral flotation due to the well-known phenomena of mechanical coating and water entrainment. In this paper, we study the effect of two different types of clay, kaolinite and montmorillonite, on the floatability of coal in de-ionized water (without flotation reagents) based on induction time and bubble-particle attachment kinetics. The bubble-particle attachment angle (BPAA) as a function of time was used as the kinetics raw data. We demonstrated how the presence of montmorillonite was detrimental to the floatability of coal in de-ionized water. This was not the case with kaolinite. The induction time and BPAA kinetics of coal particles only changed slightly after conditioning together with kaolinite. In contrast, the induction time increased considerably from 8.73 ms to 83.25 ms when montmorillonite was added. In addition, both the maximum BPAA and BPAA kinetics constant decreased, and hydrophilic montmorillonite coating occurred during the conditioning stage. These hydrophilic sites on the coal surface prevent the thinning-rupture of the water film between bubble and coal particles and thus decrease the floatability and recovery. Graphical abstract Unlabelled Image Highlights • Role of different types of clay in coal floatability was studied. • Kaolinite had little effect on coal floatability. • Montmorillonite was detrimental to coal floatability. • Hydrophilic montmorillonite coating occurred in DI water. [ABSTRACT FROM AUTHOR]

Diagram of the microemulsion collector and CO 2 nanobubbles on enhancing the low-rank coal flotation performance. [Display omitted] • An effective low-rank coal purification method combining the microemulsion collector with the CO 2 nanobubbles was innovatively proposed. • The positively charged CO 2 nanobubbles can be prepared using CO 2 as a gas source. • The hydrophobicity of the low-rank coal was significantly improved by the microemulsion collector. • The CO 2 nanobubbles were selectively adsorbed on the surface of hydrophobic coal particles and strengthened the particle agglomeration. As the inferior hydrophobicity and low probability of bubble-particle collision, the low-rank coal has poor flotation performance. In this paper, an effective purification method that innovatively combined the use of the microemulsion collector and the CO 2 nanobubbles was proposed. The procedure of the purification method and the reagent regime were established through flotation tests. And the flotation results showed that in the presence of the CO 2 nanobubbles, a satisfactory separation performance with 83.97 % of combustible matter recovery was obtained at a microemulsion collector consumption of 3.5 kg/t. The collector consumption decreased significantly compared with the diesel oil. The interaction mechanism was elucidated through the Zeta potential measurements, the rheological behavior tests, the fractal dimension analysis, and the extended Derjaguin–Landau–Verwey–Overbeek theoretical analysis. On one hand, the microemulsion collectors can reinforce the adsorption of the oily collectors on the low-rank coal surface to improve its hydrophobicity. On the other hand, the agglomeration of the coal particles was strengthened and the probability of bubble-particle collision was increased due to the selective adsorption of CO 2 nanobubbles on the hydrophobically modified surface of the low-rank coal. This research provided new insight into the improvement of the low-rank coal flotation. [ABSTRACT FROM AUTHOR]

The effect of kaolinite and montmorillonite on fine coal flotation in deionized water and calcium solution were studied through flotation experiments on a mixed coal–kaolinite/montmorillonite system in the present study, respectively. Fuerstenau upgrading curve was used to evaluate the whole flotation selectivity and the interaction force between kaolinite/montmorillonite and coal was measured using atomic force microscopy (AFM) colloidal probe technique. It was found that kaolinite and montmorillonite caused different issues in coal flotation process. In deionized water, the results show that a lower flotation recovery and worse selectivity were obtained for coal-montmorillonite system compared with that of coal-kaolinite. AFM results show that slightly jump-into-contact phenomenon was observed in coal–montmorillonite interaction while a repulsive force was always detected in coal–kaolinite interaction. The heterocoagulation between coal and montmorillonite was responsible for the low flotation recovery and bad selectivity in deionized water for coal-montmorillonite system. In presence of 0.1 mol/L calcium ion, the flotation recovery increased considerably while the selectivity of both systems was deteriorated. The jump-into-contact and high adhesion force were always found in coal-kaolinite/montmorillonite AFM force curves, indicating attractive force dominated the interaction between kaolinite/montmorillonite and coal. The electrostatic repulsive force between coal and clay particle or air bubble is fully suppressed by Ca 2+ , aggravating the kaolinite/montmorillonite coating and also leading to an increase of flotation recovery. [ABSTRACT FROM AUTHOR]

A traditional hydrocarbon collector dodecane and an oxygen-containing collector α-furanacrylic acid were selected for oxidized coal flotation in the present study, respectively. The changes of the surface functional groups and zeta potential of oxidized coal were measured before and after α-furanacrylic acid absorption and the electro-negativity of functional groups in α-furanacrylic acid was calculated to indicate its absorption mechanism on oxidized surface. Surface free energy and interfacial interaction energy were calculated to identify the interaction mechanism between coal and α-furanacrylic acid from the perspective of thermodynamics. Results show that 53.80% flotation yield with 14.03% ash content was obtained when 7000 g/t dodecane was used. In contrast, 69.17% yield with 11.98% ash content could be obtained only using 931 g/t α-furanacrylic acid. The high flotation recovery was attributed to the hydrogen bonding function between α-furanacrylic acid ( COOH and oxygen-containing five-memered rings) and oxidized coal surface. The interfacial interaction energy is 21.20 mN ∙ m − 1 for coal-water-α-furylacrylic acid system while − 23.09 mN ∙ m − 1 for coal-water-dodecane system. A repulsive hydration force was found between oxidized coal and α-furylacrylic acid via water phase. α-Furanacrylic acid could not form hydrogen bond directly with the oxygen-containing functional groups on coal surface. Instead, the water molecules in hydration film may act as the bridging role of hydrogen bond for α-furanacrylic acid absorption on oxidized coal surface. [ABSTRACT FROM AUTHOR]

A fundamental investigation was carried out on coal–coal, kaolinite–kaolinite, and coal–kaolinite interactions using the atomic force microscopy colloidal probe technique at different pH and calcium concentrations to explore the effect of kaolinite on fine coal flotation in the present study. The results showed that the kaolinite particles seem to be always detrimental to the flotation process. In deionized water, a repulsive force was always detected in the kaolinite–kaolinite interaction while kaolinite-coating phenomenon was not observed on a coal surface under the neutral pH. However, the repulsive force made it more difficult for the ultra-fine kaolinite particles to settle in the tailing thickener and the unsettled particles returned to the flotation flowsheet, which decreased the flotation efficiency because of the water entrainment. With the addition of Ca 2 + , the repulsive electrostatic force between kaolinite and kaolinite decreased. The attractive van der Waals force could dominate the kaolinite–kaolinite interactions, enhancing the sedimentation classification performance of fine kaolinite in tailing thickener. However, the interaction forces between coal and kaolinite changed from being weakly repulsive to strongly attractive and increased monotonously, resulting in the occurrence of the kaolinite-coating phenomenon during flotation. [ABSTRACT FROM AUTHOR]

[Display omitted] • High viscosity mixed collector had high detachment force. • Synergetic effect of ester-dodecane was showed in wetting and adsorption process. • Mixed collectors of long chain ester and dodecane showed short induction time. • The ester-dodecane mixed collectors obtained good flotation results. 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. [ABSTRACT FROM AUTHOR]

Abstract: To explore the laws of energy consumption in the fine coal flotation process, an energy consumption test system was established. In this investigation, it was discovered that fine coal with high ash content from Kailuan mine in China is difficult to float. The energy input in coal flotation process was changed by adjusting the shaft power and flotation time. A flotation rate test was conducted under different shaft speed conditions, and the characteristics of the flotation products with varying energy consumption were analyzed. The results showed that the floatability of the floating material decreased with the energy consumption increased. With the increase of energy consumption, the rate of increased yield of fractions is from higher to lower as following: 0.043–0.074mm, 0.074–0.124mm, −0.043mm, 0.124–0.246mm, 0.246–0.495mm, +0.495mm. Higher combustible matter recovery was achieved under high shaft speed conditions within the same flotation time. However, high energy input may increase the pollution of high-ash fine mud in the concentrate. The coarse intergrowth particles, such as coal and rocks were non-liberated and part of the micro-fine-grained coal particles, could be recovered by high energy input. For example, 18.74% concentrate yield was obtained for 1.5–1.6g/cm3 intergrowth particles at 144J energy input at the later stage of flotation process while the shaft speed is 1500r/min. [Copyright &y& Elsevier]

The effect of addition sequence for mixed collectors comprising of dodecane(D) and n-valeric acid(A) on low-rank coal flotation was explored by the following three sequences: D first and then A(D + A), A first and then D(A + D), D and A were added simultaneously(M). The total organic carbon, contact angle, zeta potential, and X-ray photoelectron spectroscopy results revealed that the coal had the highest adsorption capacity and the best hydrophobicity for the M, followed by A + D and D + A. The molecular dynamics simulation results indicated that for the M, the reagent molecules D and A worked together to facilitate the adsorption of the reagent molecules and solved some difficult-to-adsorb sites, not for the D + A and A + D. The M-type addition sequence would obtain the larger non-bonding interaction energy and more hydrogen bonds between collector molecules and the coal surface. Finally, the flotation experiments confirmed that the order of the flotation efficiency was M > A + D > D + A. [Display omitted] • The first attempt to use molecular dynamics simulation to study the addition sequence. • Adding two reagents simultaneously could solve some difficult adsorption sites. • Adding two reagents separately increased the diffusion of the reagent molecules. • Adding two reagents separately made the interface water layer tightly arranged. [ABSTRACT FROM AUTHOR]

[Display omitted] • The thermodynamics and kinetics of mixed collector spreading were explored. • Dodecane-oleic acid mixture performed the best wettability on low-rank coal surface. • Addition of oleic acid increased spreading force, but also spreading resistance. 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. [ABSTRACT FROM AUTHOR]

• Coal char was gasified by steam using microwave heating (MH) and conventional heating (CH). • Higher carbon conversion rate and better quality of gas product can be obtained in gasification using MH. • The kinetics of char steam gasification were described using SCM models. • The kinetics parameters of char steam gasification under MH and CH were obtained and compared. The behavior and kinetics of coal char steam gasification under microwave heating are investigated. The influence of the coal char particle size, water injection rate, and reaction temperature on the carbon conversion rate and gas product evolution during microwave heating gasification are considered and compared to the results from coal char steam gasification using conventional heating under the same conditions. The results show that microwave heating can accelerate the reaction rate of coal char steam gasification and improve the quality of the gas product. It was found that at temperatures varying from 600 to 900 °C, the coal char steam gasification reaction was well described using the shrinking core model (SCM). Activation energies of 82.8 kJ/mol and 114.3 kJ/mol were obtained for microwave heating and conventional electric heating, respectively. [ABSTRACT FROM AUTHOR]