Surface Of Coal Particles Research Articles

Effect of the advancing contact angle on coal particle–bubble detachment at the mesoscopic scale

Improving particle–bubble adhesion stability and reducing particle–bubble detachment are crucial in froth flotation processes. In this study, a nonequilibrium molecular dynamics approach is applied to investigate the dynamic detachment process of low-rank coal particles adhering with/without a collector from bubbles under different pull forces at the mesoscopic scale. Results indicate that a collector oil film on the surface of a low-rank coal particle can considerably increase the advancing contact angle and counteract the contraction of the three-phase contact line, enabling the particle to withstand a greater detachment force. Conversely, the residual water clusters on the particle surface tend to cause contraction of the contact line. Force analysis of the liquid surrounding the particle and the contact line indicates that the maximum static capillary force between the particle and the bubble is equivalent to the capillary force when the bending angle of the liquid surface reaches the advancing contact angle. When the bending angle of the liquid surface exceeds the forward contact angle, the force on the liquid around the contact line becomes unbalanced, causing the contact line to move to decrease the bending angle of the liquid surface and restore balance to the surrounding liquid. Hence, on mesoscopic scales of ten to tens of nanometers, the advancing contact angle still determines particle–bubble detachment. The study of particle–bubble detachment mechanisms at the mesoscopic scale is expected to establish a relation between microscopic mechanisms at the molecular scale and macroscopic experimental studies at the micrometer to millimeter scale

Effectiveness and mechanism of microbial dust suppressant on coal dust with different metamorphosis degree.

The extraction of coal from open-pit mines significantly contributes to environmental degradation, posing grave risks to human health and the operational stability of machinery. In this milieu, microbial dust suppressants leveraging microbially induced carbonate precipitation (MICP) demonstrate substantial potential for application. This manuscript undertakes an exploration of the dust mitigation efficiency, consolidation attributes, and the fundamental mechanisms of microbial dust suppressants across coal dust samples with varying metamorphic gradations. Empirical observations indicate that, in resistance tests against wind and rain, lignite coal underwent mass losses of 7.43g·m-2·min-1 and 98.62g·m-2·min-1, respectively. The production of consolidating agents within the lignite dust, attributable to the microbial suppressants, was measured at 0.15g per unit mass, a value of 1.25 and 1.07 times greater than that observed in bituminous coal and anthracite, respectively. Scanning electron microscopy coupled with X-ray energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) analyses illuminated that the consolidating products within the coal dust predominantly constituted calcite and vaterite forms of calcium carbonate. The consolidation mechanism of coal dust via microbial suppressants is articulated as follows: Subsequent to the application on coal dust, the suppressants induce the formation of carbonate precipitates with inherent adhesive properties. These carbonates affix to the surfaces of coal dust particles, progressively encapsulating them. Furthermore, they play a pivotal role in bridging and filling the interstices between adjacent dust particles, thereby culminating in the genesis of a dense, cohesive mass capable of withstanding erosive forces.

Natural polymers and electrolytes enhanced coal dust suppression and explosion prevention: New insight from experimental and molecular dynamic simulations

This paper expressed a new insight including experimental and molecular dynamic simulations to illuminate multi-scale mechanisms of coal dust suppression and explosion prevention when applying natural polymers and electrolyte. Results reveals that the addition of natural polymers and electrolyte achieve a maximum 11.85% improvement on dedusting rate and 36.36% improvement on suppression speed when compares with the individual application of SDBS, the MIE and MITC also receives a maximum 1.5 times and 23.58% improvement as well. This achievement is jointly affected by the wetting and agglomerating behaviour between suppressant and coal particles. The chain-like ionic structure and two benzene rings offer LS-Na exhibits good planarity in space and can vertically embed into the surface of coal particles. The lower diffusion coefficient and larger wetting area brings LS-Na stronger ability to help SDBS adsorbing on the coal particles and therefore exhibit better wettability. However, higher electrostatic potential difference endows CMC-Na stronger ability to absorb H2O molecules to form more viscous liquid environment. More hydrogen bond and higher bond energy of CMC-Na could promote the agglomeration of coal particles. The kinetic analysis reveals that the activation energy of coal particles treated by ternary suppressant is higher than that of binary ones. With the help of neutralization reactions between Na· and Cl· generated by molten NaCl and H· and OH· generated by the combustion, the reactivity of coal particles has been diminished and the combustion chain has been interrupted.

Development of a micro-infrared thermometry method for surface temperature distribution and variation of millimeter particle during high-temperature reaction

Temperature strongly affects the conversion efficiency, local reactivity, and particle stabilization of the reactions, particularly at high temperature. This study integrated infrared thermography with a high-temperature hot stage reactor to develop a methodology of continuous temperature measurement for a single particle reaction at high temperatures. The external optical transmission transmittance and temperature field core were corrected, and the relationship between the measured temperature (Tr) and true temperature (T0) was obtained by adjusting the sample emissivity. Sample temperature with known emissivity at elevated temperature was measured with 1% deviation. The instantaneous temperature measurement for the gasification process was carried out and the overall emissivities of coal particles were corrected. Temperature distribution and variation on the coal particle surface during the gasification process were further obtained and consistent with the previous research results. The proposed online temperature measurement method provides a new approach for gaining insights into particle reaction states.

Study on the effects of inorganic salts and ionic surfactants on the wettability of coal based on the experimental and molecular dynamics investigations

Through the evaluation and preparation of a novel inorganic salt composite solution consisting of sodium dodecyl benzene sulfonate (SDBS), the nonionic surfactants polyethylene glycol pisooctyl phenyl ether (Triton X-100), and inorganic salt Na2SO4, based on surface tension, contact angle, settling time, wetting rate, and changes in the surface microstructure and functional groups of coal, this study analyzed the wetting behavior of the solution on coal dust and its adsorption capacity on the surface of coal particles. The results demonstrate that the composite solution of inorganic salts can significantly enhance the wettability of coal samples, reducing the contact angle to 21.54° and lowering the surface tension to 26.10 mN/m. After treatment with the solution, the relative content of oxygen-containing functional groups in the microscopic structure of the coal sample increased to 59.6 % and pores more prominent than 25 nm increased to 34.63 %. Molecular dynamics (MD) simulations of the water-inorganic salt composite solution-coal system are conducted using Materials Studio software, revealing that after the addition of the composite solution, the self-diffusion coefficient (D) of water molecules is 6.3 × 10-9 m2/s, the starting point of the composite solution is 15 Å, and the system's interaction energy increase to 14000 kcal/mol. It further elucidated the modification of the surface molecular structure of coal dust by the inorganic salt composite solution, increasing hydrogen bonds, enhancing wetting, and demonstrating a solid adsorption capability of the inorganic salt composite solution on the surface of coal dust.

Flow Field Characteristics and Flotation Efficacy in a Pulse Jet Flotation Machine: A Comprehensive Investigation

The design and optimization of flotation machines hold significant importance in enhancing the industrial-grade coal beneficiation process. In this research, the flow field characteristics and flotation performance of a novel pulse jet flotation machine (PJFM) were investigated. The results showed that a PJFM equipped with an innovative pulse cavity can improve the mineralization efficiency of coal due to the coupling of multiple jet shapes. The aeration performance of this PJFM also exceeds the usual desired targets of coal flotation machines, which are characterized by an aeration uniformity coefficient higher than 70% and dominant bubbles of 100~200 μm and 200~300 μm, including a small amount of −100 μm bubbles. The cavitation of the pulse jet achieved the modification of the coal particle surface, and subsequently, the electric potential of the coal largely decreased in absolute value, and the floatability of the coal significantly improved. The concentrate yield of step release flotation increased by 12.42%, while the ash content was only 0.45% higher. Furthermore, in the early stage of flotation, the flotation rate of 0~0.074 mm coal slurry is the fastest and is preferentially floated; in the later stage, the flotation of 0.25–0.5 mm particles dominates. The PJFM demonstrates enhanced particle size selectivity and superior performance in selective flotation.

Polyaspartic acid, an eco-friendly regulator for the improvement of coking coal flotation: applications and mechanism

ABSTRACT In this study, a novel approach is to apply polyaspartic acid (PASP) as an eco-friendly regulator for the flotation of coking coal, which is different from the conventional use of oil collectors only. Flotation trails showed that adding PASP contributes to a two-way improvement in the yield and ash content of clean coal. SEM-EDS observations directly revealed that adding PASP significantly reduces the coating of high-ash fine slimes on the surface of low-ash coal particles. Contact angle detections and zeta potential analysis presented that the preferential adsorption of PASP hardly affects the adsorption of sodium oleate (NaOL) on the surface of low-ash coal particles but significantly weakens the adsorption of NaOL on the surface of high-ash fine slimes, leading to a remarkably hydrophobic difference. Particle interaction energy calculations verified that adding PASP enlarges the energy barrier between low-ash coal particle and high-ash fine slime. Hence, it can be arrived that the preferential adsorption of PASP affects the adsorption of NaOL on the surface of high-ash fine slime, widens the hydrophobic difference, enlarges the energy barrier between low-ash coal particle and high-ash fine slime, reduces the high-ash fine slime coating, therefore leading to a better flotation performance of lean coal.

Reduction of slime coating: effects of sodium silicate and sodium carbonate on lean coal flotation in sodium oleate system

High-ash fine slime has an adverse effect on coal flotation. In this study, the roles of sodium silicate (SS) and sodium carbonate (SC) in the facilitating effect on lean coal flotation (a type of coking coal) were studied when sodium oleate (NaOL) was used as a collector through flotation tests, Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) observations, turbidity measurements, and particle interaction energy calculations. The flotation tests found that SS has a stronger capacity than SC for the improvement of flotation performance of lean coal. Moreover, SEM-EDS observations and turbidity measurements showed that SS presents a stronger weakening effect for the coating of high-ash fine slime on the surface of low-ash coal particles than SC. Furthermore, the particle interaction energy calculations verified that the increase in the energy barrier for the attachment between low-ash coal particle and high-ash fine slime caused by SS is larger than SC, providing theoretical supports for the experiments. Compared to kerosene as a collector, based on the similar ash content, the yield of clean coal increases greatly with the synergistic effect of SS and NaOL. In summary, SS is an appropriate dispersant for lean coal flotation in sodium oleate system.

Experimental study on metal removal characteristics of Zhundong coal to produce ultra-clean coal using acid-alkali method

The large-scale application of coal-based deash carbon materials has put forward growing requirements for the removal technology of ash within coal. Extensive research has demonstrated that the contents of ash and metal elements have a large influence on the performance of the coal-based electrodes made from ultra-clean coal. However, there is a lack of research on the ash and mental elemental removal characteristics of Zhundong coal. In the present study, one kind of Zhundong coal characterized by a comparatively low ash content, was utilized to examine the characteristics of ash and metals removal during the acid-alkali ash removal process. An inductively coupled plasma optical emission spectrometer (ICP-OES) was utilized to analyze the metal element concentrations in the solution during ash removal and the metal element contents within the coal samples. The removal characteristics of metal elements were further analyzed based on the detection results. The experimental results indicate significant improvements in the removal of ash and metals through acid-alkali multi-stage leaching. Under the specific experimental condition here, a two-stage acid-alkali ash removal process achieves coal with the lowest ash content of 1.6% and the removal of 98.0% of Fe, 95.2% of K, and 94.6% of Na, with the removal of Al reaching up to 40%. In addition, the Fe removed in the acid leaching step accounted for 95% of the total amount removed, and adding an acid pretreatment step based on acid-alkali leaching can remove 90.2% of Fe within coal. Both the acid leaching and alkali leaching steps exhibit a certain removal proportion for Al, K, and Na elements, which are closely related to the existing form of these elements within the coal. Iron-containing minerals are mostly acid soluble and distributed on the surface of coal particles. Potassium-containing minerals are mainly alkaline soluble, resulting in a removal rate of over 60% in the alkali leaching step of acid-alkali leaching combined with acid pretreatment. The low removal rate of Al (∼40%) is due to the wide variety of Al-containing minerals, such as kaolin, illite, and aluminates, which are less removed during the reaction with alkali due to temperature limitations. The present study can offer improved knowledge on mineral removal to obtain ultra-clean coal for utilization as function materials.

Enhancement of magnetic activation on the backfilling performance of coal gangue-based composite materials

ABSTRACT The large accumulation of coal gangue has resulted in significant environmental contamination and detrimental impacts. Utilizing it as a filler material in coal mining operations may successfully address this issue. It may be used to efficiently alleviate this issue by filling up coal mines. The wettability of magnetized solution on the coal gangue surface and the phase composition, microstructure, and pore structure of hydration products of coal gangue-based composite material (CGCM) at different ages were analyzed by means of contact angle (CA), X-ray diffraction (XRD), thermogravimetry (TG/DTG), mercury intrusion (MIP), and scanning electron microscopy (SEM) in order to control the fluidity and mechanical properties of backfilling materials. Simultaneously, an investigation was conducted on the slump expansion, setting time, and compressive strength of composite filler materials derived from magnetized coal gangue. The findings indicate that the application of a magnetic field reduces the interaction force among the molecules in the mixing water. Consequently, this leads to an improvement in the wettability of the coal gangue particle surface. Thus, the fluidity of the backfilling slurry is improved. The permeability and diffusion characteristics of magnetized water surpass those of regular water, The rate of dissolving and hydration reactions of the cementitious active material in the slurry is increased, resulting in a noticeable reduction in the setting time of the slurry. In the backfilling body, magnetized mixing water can encourage the formation of dicalcium silicate (C2S), tricalcium silicate (C3S), and Ca (OH)2. Higher amounts of C-S-H gel and Aft are produced by the pozzolanic action with SiO2, which enhances the pore structure. Thus, the mechanical qualities of the filler body are enhanced. The study findings provide novel insights into the coal gangue backfill mining and offer an environmentally friendly and efficient approach for the large-scale processing and exploitation of coal gangue.

Ignition behavior of a mixture of brown coal and biomass during the movement of fine particles in a hot air flow

The combustion of brown coal, biomass and their mixtures was studied experimentally and analytically. The experimental research was conducted using a laboratory setup that reproduced the conditions of combustion of pulverized solid fuel in a boiler furnace. Thermogravimetric analysis was employed as part of the analytical study to determine the key characteristics of combustion of solid fuels, such as temperatures at which the ignition and burnout occur, as well as the combustion index. Scanning electron microscopy was utilized to analyze the surfaces of coal and wood particles to detect pores, cracks and channels. To determine the tendency of the solid fuel mixture to slag heat exchangers in boiler furnaces, the ash residue characteristics (iron oxide deposits, active alkali, calcium sulfate compounds) were obtained. Biomass is more reactive than brown coal. Its ignition delay times at 500 °C and 750 °C are 57 % and 25 % lower, respectively, than those for coal. The higher the biomass content in the solid fuel mixture, the lower the ignition delay time. The heating source temperature at which the coal/biomass fuel mixture ignites corresponds to the temperature at which biomass ignites. With a larger proportion of biomass, the temperature during the fuel mixture combustion goes down, while the combustion index increases. On the basis of the findings of the conducted research, optimal proportions of solid fuel components were found (80 % brown coal, 20 % biomass). Also, fuel preparation and feeding systems for pulverized fuel combustion and fluidized bed combustion of optimal fuel mixtures in a coal-fired boiler furnace were proposed.

A fundamental study of flotation separation of mineral particles using ultrasound-induced bubbles

This paper describes the flotation separation of naturally hydrophobic coal particles and hydrophilic quartz particles in water (free of any reagents) using ultrasound-induced bubbles only, without any additional air supply. A laboratory-scale flow tubing system with an ultrasound transducer was designed and used. The experiments were conducted for coking coal, quartz and their mixture, respectively, over a broad range of particle size. Results showed that using ultrasound with a relatively high energy input, acoustic cavitation occurred in water and on the surface of coal particles, and different behaviours of coal particles and quartz particles under this condition were observed: coal particles formed larger aggregates and most of them were trapped in the slurry or floated to the surface of the slurry, while quartz particles had very slight aggregation and settled down. This difference enabled good separation of coal particles from quartz particles, with high combustible recoveries and product grade over a broad particle size range tested (including 250–500 µm for coal particles). When the energy input of ultrasound was relatively low, however, no cavitation bubbles were visible, with slight aggregation and trapping of coal and quartz being observed and explained by the acoustic radiation force.

Cottonseed oil biodiesel used as a renewable collector for coking coal flotation

ABSTRACT Hydrocarbon oil collectors used in coking coal flotation are nonrenewable resources, and their collecting performance is difficult to meet current industry needs. In this study, cottonseed oil biodiesel (CSOB) was prepared from cottonseed oil by alkali-catalyzed transesterification, and experimental studies on flotation of 1/3 coking coal were carried out. The results showed that the clean coal yield was about 75% when the use of CSOB was 2000 g t−1. The results of contact angle, FTIR and XPS tests showed that the oxygen-containing groups of CSOB were adsorbed on the hydrophilic spots on the surface of coal particles, and the surface hydrophobicity of coal particles was increased. The ash level of the clean coal with the addition of CSOB during flotation was essentially the same as with the addition of an equivalent amount of diesel oil.

Chemical additive based on sodium oleate and linseed oil for preparation coal dust suppression composition

The mining, transportation, and processing of coal involve the formation and emission of significant amounts of particulate matter, which includes coal dust. The most commonly employed method for controlling coal dust in an air is water spray dust suppression (hydrodedusting). This method is founded on water’s capacity to moisten dust particles and bond them to both each other and the surfaces where the dust settles. One notable limitation of this method is the coal’s hydrophobic nature, which hinders water from wetting coal dust particles. In order to overcome this, surfactants are introduced into the water to increase the wettability of the hydrophobic coal particle surface. In this paper, we proposed a dust suppressant composition consisting of oleic acid, sodium hydroxide, and linseed oil in water. We examine its properties and evaluated its ability to enhance the wettability of coal dust. We have identified the most effective concentration, resulting in a working solution that improves the wettability of coal dust by 87 % compared to water, surpassing the wettability of most known reagents. The proposed composition contains 140 mg/L oleic acid, 100 mg/L sodium hydroxide, and 70 mg/L linseed oil in water. The simplicity of this composition, its minimal impact on the environment and human health, and its negligible influence on the further use of coal raw materials make this wetting agent composition highly promising for application in coal industry technologies of water spray dust suppression.

Influencing effects of different types of dispersants on the permeability levels of Coal-Bearing propped fractures in coalbed methane reservoirs

This study investigated how to effectively discharge deposited pulverized coal particles in coal-bearing propped fractures and improve the permeability levels of the propped fractures in order to enhance coalbed methane production. Four types of dispersants were selected to carry out wettability and permeability tests, including sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), dodecyl dimethyl betaine (BS-12), and alkyl poly glycoside dodecyl glucoside (APG). The results showed reductions in surface tension of 63.71 to 69.75 %, and reductions in contact angles of 40.08 to 60.46 %, when compared with water injections alone. In addition, under the same closure pressure conditions, the dispersant solutions had increased the permeability of the propped fractures by 76.67 to 123.34 % when compared with that of the water injections, and the pulverized coal discharge rates were increased by 1.44 to 2.41 times. The decreases in closure stress also contributed to the enhancement of the permeability of the propped fractures, with increases of between 11.24 and 29.18 % observed. This study found that for the four tested dispersants, the order of the effective wetting of the pulverized coal particles and enhancement of the permeability of the propped fractures were (from strong to weak) as follows: SDS > BS-12 > APG > SDBS. Among the tested dispersants, the 6 mmol/L SDS dispersant solution was found to be the most effective for improving the wettability of the pulverized coal particle surfaces and achieved the highest permeability improvement of the propped fractures.

Flotation of lean coal using trisodium citrate dihydrate as a dispersant in the presence of sodium oleate

Flotation is a highly efficient method for purifying low-ash coal particles from high-ash fine slimes. Herein, the dispersion effect of trisodium citrate dihydrate (TCD) on the reduction of slime coating on low-ash lean coal particle surface was studied using flotation tests, scanning electron microscope–energy Dispersive Spectroscopy (SEM–EDS) observation, turbidity measurements, and extended Derjaguin–Landau–Verwey–Overbeek (E-DLVO) calculations. Flotation tests revealed that after adding of 2000 g/t TCD, the yield of clean coal increased by 1.09 % and the ash content of clean coal decreased by 1.45 % with 1000 g/t NaOL at pH 7.0, thereby increasing the combustible recovery and flotation perfect index by 2.50 % and 6.42 %, respectively. The SEM–EDS observation and turbidity measurements indicated that the coating of the high-ash fine slimes on the low-ash coal particle surface was significantly weakened in the presence of 2000 g/t TCD. Furthermore, the E-DLVO calculations verified that the addition of 2000 g/t TCD increased the energy barrier between the low-ash coal particles and high-ash fine slimes, providing theoretical evidence for flotation tests and SEM–EDS observation. Therefore, TCD served as an effective dispersant for the high-ash fine slimes to improve the flotation performance of lean coal.

Characteristics of OH formation during single coal particle ignition and volatile combustion in O2/N2 and O2/CO2 atmospheres

The behaviors of volatile combustion and ignition of lignite coal were assessed on a concentrating light heating platform using hydroxyl-Planar laser-induced fluorescence (OH-PLIF) over a range of 21–60% O2 in both N2 and CO2 diluent gases. The results indicated that when the O2 concentration was below 40%, substituting CO2 for N2 delayed the ignition delay time (tign). This was evident as no ignition occurred in the 21% O2/CO2 mixture, and a nearly 1.0 s difference in tign emerged when substituting CO2 for N2 in 30% and 40% air atmospheres. Additionally, the weaker flame luminosity and the shorter volatile flame duration time (tvol) were also observed in O2/CO2 compared with that in O2/N2. Correspondingly, a significantly lower OH signal intensity was observed in O2/CO2 compared to O2/N2, which was primarily due to physical and chemical effects of CO2. Firstly, the higher heat capacity and lower diffusion rate of O2 in O2/CO2 leads to a lower volatile release rate and decreasing flame temperature, as evidenced by the closer proximity of the flame front to the coal particle surface. The lower flame temperature and volatile release rate would reduce the number of hydrocarbon molecule (RH) and the reaction rate of RH→hydrocarbon radical (R) + H, leading to a decrease in the concentration of OH radical from the reaction: H + O2→OH + O. Secondly, CO2 participates directly in H + OH + three-body (M)→H2O + M reaction, competing with the primary OH formation pathway, H + O2→OH + O, for H radicals, thus suppressing the OH generation. However, when O2 concentration exceeded 40%, the tign was shorter in O2/CO2 by about 1.2–1.4 s than in O2/N2 with the same O2 concentration. Simultaneously, compared to the O2/N2, similar flame luminosity and tvol were observed in the O2/CO2. An obvious increase in OH intensity was also observed in O2/CO2. With higher O2 concentrations in the O2/CO2, the absorption and emission radiation characteristics of CO2, increased O2 diffusivity and the decreased specific heat capacity in the O2/CO2 gas mixture, synergistically facilitate temperature rise and volatile release, which promotes the generation of RH, and then increases the H concentration due to the reaction RH→R + H. This would lead to a substantial increase in concentration of OH produced by the reaction H + O2→OH + O, which was detected by OH-PLIF.

Micro-scale study of mineral transformation and coverability at single coal char particle surface during high-temperature gasification process

During the high-temperature coal gasification process, mineral transformation is essential to the formation of residual carbon and ash/slag discharge. The current work investigated the mineral transformation and coverability of the single coal char particle with various ash content during gasification, as well as established the correlation between the ash layer and carbon conversion. Three stages of the gasification process at 1350 °C were defined by the quadratic difference method based on the interaction between the char and the liquid slag, and the two critical points that distinguish the three stages were between 15%–20% and 71%–90% respectively. Further investigation showed that the melting behavior of coal char during gasification was affected by the inhomogeneous distribution of elements. Ca showed a tendency to migrate from the unmolten area to the molten area. The migration behavior was attributed to the eutectic formation between silica-aluminate in the molten area and calcium salts in the unmolten area, leading to a reduction in melting point and gradual melting of minerals in the unmolten area. Eventually, a homogeneous gehlenite phase was formed and covered on the residual char surface. Besides, the relationship between liquid slag coverage and carbon conversion was established, and for SF, YL, and XLT chars, the maximum coverage of liquid product occurs at the conversion of 0.86, 0.78, and 0.66, respectively. This paper provides an in-depth understanding of the slag melting behavior and residual carbon formation in the entrained gasifiers.

Synergistic improvement of the fine size coal dewatering performance by using binary surfactant mixtures

In this study, gemini surfactants and binary surfactant mixtures were used in order to enhance the dewatering performance of fine size coal particles. Compared to three single gemini surfactants, binary surfactant mixtures presented a better dewatering performance of fine size coal particles, especially the binary surfactant mixture composed of Gemini − 1 surfactant and sodium dodecyl benzene sulfonate (SDBS). Meanwhile, the binary surfactant mixture composed of Gemini − 1 surfactant and sodium dodecyl sulfonate (SDS) was further used in the experimental test as a comparison and showed better dewatering performance than that of the binary surfactant mixture composed of Gemini − 1 surfactant and SDBS. The lowest cake moisture content (20.72 %) was gained when the dosage of Gemini − 1 surfactant and SDS was 400 g/t at the molar ratio of 6 to 7. Surface functional groups of the prepared coal samples were characterized by a Fourier transform infrared spectroscopy (FTIR). Wetting heat values of coal samples before and after adsorbing surfactants were measured by a microcalorimeter. The adsorption capacity of surfactant on coal surface was investigated for studying the difference between three single surfactants and the binary surfactant mixture. Intermolecular interaction calculation and thermodynamics of micellization for the judgment of synergistic effect indicated that the synergistic interaction was formed in the binary surfactant mixture and the binary surfactant mixture of Gemini − 1 surfactant and SDS showed a stronger synergistic interaction. A possible hydrophobic mechanism was supposed that the water molecules were displaced by the binary surfactant mixture for the improvement of hydrophobicity of coal particle surface.

Investigation on coal dust prevention by biomimetic mineralized dust suppressant with polyacrylic acid modifier

Coal dust prevention is crucial for the environment and the safety of coal miners. This study proposed a biomimetic mineralized dust suppressant (BMDS) with polyacrylic acid (PAA) modifier, based on calcium carbonate precipitation technology. The consolidation effect of BMDS on coal dust was evaluated through wind erosion resistance tests, unconfined compressive strength tests, and microscopic characterizations. The results show that the consolidation effect of the BMDS on coal dust heavily depends on the PAA concentration. When the PAA concentration is 4 g/L and the concentration of calcium chloride and sodium carbonate is 0.5 mol/L, the BMDS presents the best dust suppression effect and could realize the practical application requirements. The generated calcium carbonate is mainly calcite type, and the efficiency of cementing coal dust particles is the highest. Moreover, similar to bacteria in biological dust suppressants, it confirms that PAA could effectively modify the nucleation and growth of calcium carbonate, promote the adhesion of calcium carbonate to the surface of coal dust particles, and enable the generated calcium carbonate to effectively bond coal dust particles. Accordingly, the BMDS with PAA modifier can be effectively used in the prevention of secondary coal dust pollution.