Low-rank Coal Surface Research Articles

Effect of NaNO2 Reductant Pretreatment on Low-Rank Coal Flotation.

As the reserves of high-quality coal resources in China are decreasing, it is imperative to improve the processing and comprehensive utilization of low-rank coal. In this study, NaNO2 was used for the flotation pretreatment test of the low-rank coal obtained from Majialiang, and the mechanism was discussed by contact angle analysis, zeta potential measurements, and XPS peak fitting analysis. The results showed that when the dosage of NaNO2 was 2000 g/t and the pretreatment time was 5 min, the flotation effect was the best, the ash contents of concentrate ash and tailings and the combustible recovery were 17.15, 37.12, and 42.23%, respectively; the combustible recovery increased by 12%. The contact angle, surface functional group content, and zeta potential measurements showed that with the change of NaNO2 dosage, the content of the hydrophobic functional group and the zeta potential value were consistent with the change of combustible recovery. The increase of hydrophobic functional groups can effectively enhance the hydrophobic interaction on the surface of the coal, which is conducive to the combination of collector and coal, and improve the efficiency of the collector. The NaNO2 pretreatment test can promote flotation efficiency, and the addition of reductant is an effective method for the flotation efficiency of low-rank coal in reducing oxygen-containing functional groups on the surface of low-rank coal to improve the poor floatability. In this study, the method of chemical pretreatment is put forward to provide a new idea for slime flotation.

Molecular dynamics simulation of fatty acid collectors with different carbon chain lengths on the surface of low-rank coal

The adsorption behaviors of fatty acid molecules with different carbon chain lengths as polar collectors on the surface of Longdong coal model in the presence of water were investigated by molecular dynamics simulation. The simulation results show that the interaction strength of short-chain fatty acid collectors is greater than that of long-chain fatty acid collectors at the same mass dosage, and the short-chain fatty acid collectors have stronger electrostatic interaction energy. Based on the results of mean square displacement and radial distribution function analysis, it was found that the diffusivity of short-chain fatty acid collectors was stronger than that of long-chain fatty acid collectors in aqueous environment, and long-chain fatty acid collectors had stronger hydrophobic ability. Considering the interaction energy of collector between coal, contact area, roughness, and diffusion coefficient of water molecules, caprylic acid is most suitable as a collector. This agrees with the experimental results.

Enhanced Flotation Separation of Low-Rank Coal with a Mixed Collector: Experimental and Molecular Dynamics Simulation Study.

The efficient flotation separation of low-rank coal is still a difficult problem. The development of a collector is the key to solve the problem. In this study, a kind of mixed collector scheme with a practical value is proposed. The effects of the single collector dodecane (D) and methyl oleate (MO) and mixed collector D–didodecyl dimethyl ammonium bromide (DDAB) and MO–DDAB on flotation separation of low-rank coal were investigated. The flotation test results show that when the molar ratios of the mixed collector D–DDAB and MO–DDAB are 9:1 and the flotation time is 4 min, the cumulative combustible recovery of low-rank coal flotation is 71.49 and 76.73%, respectively, and the cleaned coal ash is 15.26 and 13.03%, respectively. The mixed collector significantly improves the flotation effect of low-rank coal compared with the single collector. According to the analysis results of the contact angle, wetting heat, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy, the hydrophobicity of the low-rank coal surface is enhanced under the action of the mixed collector, and the adsorption between the mixed collector and coal surface is stronger. In addition, molecular dynamics (MD) simulation results show that compared with D or MO, DDAB tends to adsorb on the surface of low-rank coal, and the diffusion coefficients of water molecules on the surface of coal increase. The mixed collector first repels water molecules through its double hydrophobic carbon chain to weaken the binding of the coal surface to water molecules and then uses D or MO to further repel water molecules, thus effectively enhancing the surface hydrophobicity of low-rank coal.

Clariant[StQuote]s SynDane catalyst chosen for Wanhua[StQuote]s new world-scale maleic anhydride plant

Flotation is used to separate inorganic impurities and improve the quality of fine coal. However, the flotation of low-rank coal (LRC) is challenging due to the presence of many oxygen-containing functional groups (OCFG) on the LRC surface. In this work, the effect of a novel collector prepared by hot melting of plastic waste into diesel (XJD-2021-6) on LRC flotation and its interaction mechanism for improving the LRC flotation performance was investigated. The flotation results found that compared with diesel, XJD-2021-6 as a collector significantly improved the combustible matter recovery and effectively decreased the refined coal ash. The results of XPS and FTIR showed that XJD-2021-6 was better than diesel in masking OCTG of LRC surface, especially O=C-O and C-O. The contact angle and zeta potential results indicated that after XJD-2021-6 masking OCTG on the LRC surface, it not only strengthened the adsorption of DO on the LRC and enhanced LRC hydrophobicity, but also significantly reduced the electro-negativity of coal particles, weakened the electrostatic repulsion between the air bubble and coal particle, and improved the LRC mineralization effect.

BASF introduces PuriCycle portfolio of catalysts and adsorbents to enable plastics recycling

Flotation is used to separate inorganic impurities and improve the quality of fine coal. However, the flotation of low-rank coal (LRC) is challenging due to the presence of many oxygen-containing functional groups (OCFG) on the LRC surface. In this work, the effect of a novel collector prepared by hot melting of plastic waste into diesel (XJD-2021-6) on LRC flotation and its interaction mechanism for improving the LRC flotation performance was investigated. The flotation results found that compared with diesel, XJD-2021-6 as a collector significantly improved the combustible matter recovery and effectively decreased the refined coal ash. The results of XPS and FTIR showed that XJD-2021-6 was better than diesel in masking OCTG of LRC surface, especially O=C-O and C-O. The contact angle and zeta potential results indicated that after XJD-2021-6 masking OCTG on the LRC surface, it not only strengthened the adsorption of DO on the LRC and enhanced LRC hydrophobicity, but also significantly reduced the electro-negativity of coal particles, weakened the electrostatic repulsion between the air bubble and coal particle, and improved the LRC mineralization effect.

Improving the low-rank coal flotation performance using a novel collector prepared by hot melting of plastic waste into diesel

Flotation is used to separate inorganic impurities and improve the quality of fine coal. However, the flotation of low-rank coal (LRC) is challenging due to the presence of many oxygen-containing functional groups (OCFG) on the LRC surface. In this work, the effect of a novel collector prepared by hot melting of plastic waste into diesel (XJD-2021-6) on LRC flotation and its interaction mechanism for improving the LRC flotation performance was investigated. The flotation results found that compared with diesel, XJD-2021-6 as a collector significantly improved the combustible matter recovery and effectively decreased the refined coal ash. The results of XPS and FTIR showed that XJD-2021-6 was better than diesel in masking OCTG of LRC surface, especially O=C-O and C-O. The contact angle and zeta potential results indicated that after XJD-2021-6 masking OCTG on the LRC surface, it not only strengthened the adsorption of DO on the LRC and enhanced LRC hydrophobicity, but also significantly reduced the electro-negativity of coal particles, weakened the electrostatic repulsion between the air bubble and coal particle, and improved the LRC mineralization effect.

Adsorption process and mechanisms of AEO-3/dodecane mixed collector on low-rank coal surface driven by water flow: A non-equilibrium molecular dynamics simulation study

During coal slime flotation, the collector is adsorbed to the coal in the form of fine oil droplets in the turbulent slurry. And understanding the adsorption behavior of collector oil droplets on the coal surface is important for the development of efficient collector. In this study, the adsorption process and mechanism of triethylene glycol dodecyl ether (AEO-311triethylene glycol dodecyl ether.)/dodecane mixed collector oil droplet (MCOD22mixed collector oil droplet.) on the surface of low-rank coal driven by water flow were investigated by non-equilibrium molecular dynamics simulations. The changes of the mass center velocity of MCOD, contact area and interaction energy between MCOD and coal during the simulation were analyzed, and the adsorption process was divided into the adhesion stage, spreading stage and equilibrium stage. The kinetic reason for the adsorption of AEO-3 molecules at the interface was found. The pushing of oil droplet by the water flow caused the AEO-3 molecules to be slowly pressed into the contact interface between the oil droplet and coal, and the adsorption occurred. The presence of polar oxygen-containing functional groups on the AEO-3 molecule makes it much more strongly adsorbed on low-rank coal than dodecane. Water molecules play an important role in the adsorption process of AEO-3 with coal, and the bridging action of water molecules that enables indirect adsorption of collector with coal was proposed. The water molecule connects AEO-3 and coal molecules, which cannot form hydrogen bond due to the distance, through hydrogen bonding, and inserts between alcohol oxygen, ether oxygen and carbonyl oxygen, which are originally mutually exclusive, so that the three of them (OAEO-3, H2O and Ocoal) are connected together through hydrogen bonding (OAEO-3…H-O-H…Ocoal), and the stability of AEO-3 adsorption on coal surface is greatly enhanced. The presence of strong indirect electrostatic interactions between polar collector and coal generated by the bridging action of water molecules proves that it is the strong electrostatic interactions that are the reason for the strong flotation performance of polar collector on low-rank/oxidized coals.

Simulation study of the mechanism of mesoscopic adsorption and the evolution of molecular dynamics of a surfactant/polymer composite on the surface of low rank coal

In this paper, the head group, tail group, and main chain of a single type of surfactant were constructed by a mesoscopic simulation, and the interaction between the simulated surfactant and coal dust both on its own and in a composite with polyacrylamide (PAM) was studied. The molecular adsorption behavior of cetyltrimethylammonium chloride (CTAC) surfactant mixed in different ratios with PAM was also experimentally characterized. The results showed that. From the above results, we can see that CTAC and PAM can form spherical, rod-shaped, and wormlike aggregates and a network structure as their volume fraction increases in an aqueous solution. The energy spectrum showed that when CTAC adsorbed on the surface of the coal, the content of carbon on the surface decreased from 63.8 to 50.4%, and the content of oxygen increased from 35.2 to 41.8%. The study on the adsorption mechanism of surfactants and polymers on the surface of low rank coal and the hydrophilicity of low rank coal is of great significance in developing efficient dust prevention technology for low rank coal to reduce coal dust pollution.

Energy Feature of Air Bubble Detachment from a Low-Rank Coal Surface in the Presence of a Dodecane–Oleic Acid Collector Mixture

It has been generally proved that mixed collectors can enhance the flotation of low-rank coal (LRC). However, the inhibition effect of mixed collectors on the detachment between particles and bubbles is still unclear. In this paper, the energy feature of air bubble detachment from the LRC surface in the presence of dodecane (D), oleic acid (OA), and the mixture of dodecane and oleic acid (OA–D) was studied. The effect of collectors on the LRC surface property was analyzed using contact angle measurement, X-ray photoelectron spectroscopy, and wetting heat measurement. The force and displacement during the detachment process were measured synchronously using microforce balance. The results showed that the collector treatment increased the C–C/C–H content and decreased the content of oxygen-containing groups on the LRC surface. The synergistic effect between OA and D enabled the mixed collector to exhibit higher contact angle and wetting heat. Bubble detachment from the LRC surface can be divided into two stages: bubble stretching and bubble sliding, which corresponded to activation energy and detachment work, respectively. The activation energy and detachment work decreased in the same order of OA–D > OA > D, indicating that the mixed collector OA–D increased the energy of bubble detachment from the LRC surface and enhanced the adhesion strength. The theoretical detachment work was calculated, and the calculated results were in agreement with the measured results. This research provides a new perspective on the mechanism of LRC flotation being improved by mixed collectors.

Investigation on mechanism of the oleic acid/methyl oleate/diesel ternary compound collector in low-rank coal flotation

Polar and compound collectors are current research hotspots in the field of low-rank coal (LRC) flotation. However, most studies only focus on the collecting ability of collectors while ignoring its selectivity. This study presents the design for a novel high-efficiency ternary compound collector (oleic acid (OA), methyl oleate (MO) and diesel) with great selectivity, strong collecting and spreading ability for Sujiagou LRC. In comparison to diesel, the clean coal yield is increased by 41.40%, and its ash content is reduced by 0.91% at optimal dosage of 2000 g/t. And we propose some new insights on the mechanism of ternary compound collector through density functional theory (DFT) calculations, focused beam reflectance measurement (FBRM), and molecular dynamics (MD) simulations. OA has the strongest collecting ability with the shortest adsorption distance and smallest frontier orbital gap, which ensures the flotation efficiency and collecting ability of ternary compound collector. The great selectivity of ternary compound collector owing to these two reasons: MO adsorbs more strongly on the LRC surface through the flat-lying adsorption at the junction of hydrophilic and hydrophobic parts; the “wasteful adsorption” on the gangue surface is prevented as the nonpolar parts of ternary compound collector attract polar collectors. Finally, a firm oil film with strong spreading ability is formed on the LRC surface, which can achieve a spread across the hydrophilic area even without the adsorption of polar collectors. The synergistic adsorption not only improves the collecting ability of the ternary compound collector but also ensures its selectivity.

Understanding the Role of Polyvinylpyrrolidone on Ultrafine Low-Rank Coal Flotation.

Effective regulation reagents are essential in low-rank coal flotation for improving the floatability of ultrafine particles. Polymer regulators have great potential in the surface modification of ultrafine coal particles. A novel nonionic polymer, polyvinylpyrrolidone (PVP), is evaluated in this study to determine its effectiveness as a regulator in floating ultrafine low-rank coal. Laser particle size analysis is used to discern both the size distribution of coal particles and the change in size distribution. Contact angle tests are carried out to evaluate the wettability of low-rank coal. Surface functional groups of low-rank coal are analyzed by Fourier transform infrared spectroscopy, and the surface interaction energy is tested by X-ray photoelectron spectroscopy. The results show effective adsorption of PVP and demonstrate the effects of PVP at the coal surface. The adsorption of PVP changes the proportion of exposed carbon and oxygen-containing functional groups on the surface of low-rank coal, regulating the size distribution of low-rank coal particles in suspension. The success of polyvinylpyrrolidone as a regulator in low-rank coal flotation is demonstrated, and the mechanisms by which PVP can affect ultrafine low-rank coal flotation are elucidated.

Effect of bio-based surfactant on wettability of low-rank coal surface and its mechanism.

In this study, the effect of a bio-based environment-friendly surfactant, cardanol polyoxyethylene ether (BGF), on the wettability of the surface of low-rank coal (LRC) and its mechanism were studied. The adsorption experiment showed that the adsorption of the surfactant conformed to the Langmuir adsorption model and the pseudo-second-order kinetic model. The adsorption was mainly affected by hydrogen bonding, and the adsorption rate was affected by intraparticle diffusion and liquid film diffusion. The wettability experiment showed that the influence of BGF on the wettability of the surface of LRC followed the given order: BGF-7 > BGF-10 > BGF-15. The investigation of adhesion work showed that the adhesion work and the stability of the coal-water system decreased after adsorption. Fourier transform infrared and X-ray photoelectron spectroscopy analyses showed that after adsorption, the peak strength of vinyl ether, the content of elemental carbon, and the content of C-C/C-H groups increased.

Effect of mixed collector addition sequence on the adsorption behavior of low-rank coal surface: Experimental and molecular dynamics simulation study

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.

Spreading behavior of dodecane-oleic acid collector mixture in low-rank coal flotation

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.

Composition characteristics of siloxane derived waste lubricating oil and its effect on low-rank coal flotation

Waste motor oil/lubricating oil (WMO) is a hazardous and important resource. The waste siloxane-based motor oil/lubricating oil (WSMO) has a special composition based on siloxane. The WSMO has a large and increasing production worldwide. In this paper, the feasibility of WSMO as a collector for low-rank coal (LRC) flotation was discussed with a comparison to diesel oil (DO). The gas chromatography-mass spectrometry (GC/MS) and thermal gravimetric analysis (TGA) were used to analyze the chemical composition of WSMO. The flotation experiment was conducted to investigate the collectivity and selectivity of WSMO as an LRC collector. The interaction between WSMO and LRC was systematically analyzed using X-ray photoelectron spectroscopy (XPS), contact angle, zeta potential, and induction time measurements. The results indicated that WSMO majorly contained dimethylsiloxane and cyclodimethysiloxane with various chain lengths. High concentrates yield and low ash content was obtained in the flotation using WSMO. The adsorption of WSMO can mask the oxygen-containing groups (OCGs) on the LRC surface, leading to an increase of C content and a decrease in O content. This was beneficial to improve the hydrophobicity of the LRC surface so that the water-coal contact angle increased from 35.6° to 57.85° after WSMO treatment. Moreover, a significant increase in zeta potential was observed in the pH range of 4 to 10. LRC particles pretreated with WSMO were more easily adhere to the bubble surface in a short induction time of 40 ms. It was demonstrated that WSMO was an effective collector to promote LRC flotation.

Micro-mechanism of improving low-rank coal flotation by using carboxylic acid collector: A DFT calculation and MD simulation study

The poor flotation behavior of low-rank coal is mainly caused by the high content of functional oxygen groups present on the coal surface. Polar collectors, especially oxygenated collectors, play a significant role in the flotation enhancement of low-rank coal. In this study, to improve the low-rank coal flotation performance, octanoic acid was selected as a polar collector and the corresponding promotion mechanism was investigated at the molecular scale theoretically. The flotation results showed that an increased low-rank coal flotation response can be obtained by using an octanoic acid collector compared to a nonpolar dodecane collector. To obtain a molecular-level explanation of this phenomenon, a method of density functional theory (DFT) combined with molecular dynamics simulation was employed to explore the involved micro-mechanism. DFT calculation results suggested that the octanoic acid collector can interact with benzoic acid and phenol (representatives of oxygen-containing groups on the low-rank coal surface) through hydrogen bonding and repel water molecules present on benzoic acid and phenol. Based on theoretical calculations, in the presence or absence of water molecules, hydrogen bonding and electrostatic interactions are responsible for the strong affinity of octanoic acid to carboxyl group and hydroxyl group on the low-rank coal surface. Therefore, it was favorable for octanoic acid to form a stable adsorption layer on the low-rank coal surface, thus contributing to low-rank coal flotation significantly.

Kinetics of bubble interaction with low rank coal surface in the presence of adsorbed dodecane-oleic acid collector mixture

ABSTRACT 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.

Effect of mixing ratio on the adsorption behavior of low-rank coal surface using mixed collectors: Experimental and molecular dynamics simulation study

ABSTRACT The effect mechanism of mixing ratio on the adsorption behavior of low-rank coal surface using mixed collectors has not been systematically studied. In this study, dodecane (D) and n-valeric acid (N) were mixed into different collectors in different ratios, and their adsorption mechanism on the surface of LRC was studied by experiment and simulation calculation. The flotation results indicated that the sequence of the flotation clean coal yield was 8:2 > 6:4 > 5:5 > 7:3 > 9:1. The measurement results of the heat of adsorption, total organic carbon, and liquid phase contact angle all responded to the flotation results as a whole. The molecular dynamics simulation results revealed that when an appropriate ratio was used to form a mixed collector, the N molecules could make the D molecules form oil molecular layer thicken, thus increasing the hydrophobicity of the surface of the LRC molecules. The optimal mixing ratio could also create a large interaction energy between the mixed collector and LRC. Therefore, D and N need to be mixed at a proper ratio to maximize the LRC flotation efficiency.

Detachment Force of Air Bubbles Detached from Low-Rank Coal Surface in the Presence of Adsorbed Oleic Acid-Dodecane Collector Mixture.

It is well known that mixed collectors can effectively strengthen the flotation of low-rank coal. However, less concern has been paid to the detachment of low-rank coal flotation using mixed collectors. In this study, the force of air bubble detachment from low-rank coal surface treated by oleic acid (OA), dodecane (D), and oleic acid–dodecane (OA–D) collector mixture was investigated using microforce balance. The results showed that the process of bubble detachment from the low-rank coal surface was divided into three stages: relaxation stage, stretching stage, and sliding stage. The equilibrium contact angle and critical contact angle were the transition points between different stages. The order of detachment force required for bubble detachment from the surface of low-rank coal was OA–D > OA > D, indicating a synergistic effect between OA and D. Based on the three parameters of equilibrium contact angle, critical contact angle, and contact line length, a theoretical model was proposed to calculate the detachment force. The calculated results were in agreement with the measured results.

Surface Chemical Heterogeneity of Low Rank Coal Characterized by Micro-FTIR and Its Correlation with Hydrophobicity

Micro-Fourier transform infrared (micro-FTIR) spectroscopy was used to correlate the surface chemistry of low rank coal with hydrophobicity. Six square areas without mineral impurities on low rank coal surfaces were selected as testing areas. A specially-designed methodology was applied to conduct micro-FTIR measurements and contact angle tests on the same testing area. A series of semi-quantitative functional group ratios derived from micro-FTIR spectra were correlated with contact angles, and the determination coefficients of linear regression were calculated and compared in order to identify the structure of the functional group ratios. Finally, two semi-quantitative ratios composed of aliphatic carbon hydrogen, aromatic carbon hydrogen and two different types of carbonyl groups were proposed as indicators of low rank coal hydrophobicity. This work provided a rapid way to predict low rank coal hydrophobicity through its functional group composition and helped us understand the hydrophobicity heterogeneity of low rank coal from the perspective of its surface chemistry.