Flotation Performance Of Low-rank Coal Research Articles

New insights for improving low-rank coal flotation performance via emulsified waste fried oil collector

A novel emulsified waste fried oil collector (EWFOC) of the oil-in-water (O/W) type was prepared via transesterification and ultrasonic emulsification, and to be used as an alternative collector to improve the flotation performance of low-rank coal while reducing the collector dosage. The preparation process of EWFOC was optimized, and its performance was compared to that of a common collector (diesel) and waste fried oil collector (WFOC) in the flotation of long-flame coal collected from two top coal-producing province (autonomous region) in China. The micrograph, particle size distribution and dispersion of EWFOC were observed under optical microscope. In addition, the functional groups and wettability were also analyzed. The optimized emulsification conditions for EWFOC were determined as HLB = 14.0, emulsifier dosage of 1 %, oil–water ratio of 3:7, ultrasonic time of 5 min, and a NaCl concentration of 0.02 mol/L. Compared to diesel, WFOC improved the recovery of clean coal and reduced the ash content of clean coal. EWFOC, on the other hand, demonstrated better flotation performance, resulting in up to a 70 % reduction in WFOC dosage. This significant improvement is attributed to the cavitation mechanism of phacoemulsification, which renders EWFOC stable in water with homogenous dispersion and enhances its attachment to coal particles. EWFOC showed better performance compared to diesel and WFOC in terms of improved contact angle as well as adherence to oxygen-containing functional groups (especially O=C–O and C–O) on the surface of long-flame coal, thus enhancing the hydrophobicity of the said coal.

Experimental study on the dispersion behavior of a microemulsion collector and its mechanism for enhancing low-rank coal flotation

As the poor dispersion of oily collectors and the inferior hydrophobicity of the mineral surface, the low-rank coal has an unsatisfactory flotation performance when using traditional collectors. In this paper, an ionic liquid microemulsion was used as a collector to enhance its floatability. Flotation test results demonstrated the microemulsion collector exhibited a superior collecting ability. A satisfactory separation performance of 78.66% combustible material recovery was obtained with the microemulsion collector consumption of 6 kg/t, which was equivalent to the flotation performance of diesel at a dosage of 25 kg/t. The dispersion behavior of the microemulsion collector was investigated using the Cryogenic-Transmission Electron Microscopy. The interaction mechanism of the microemulsion collector on enhancing the low-rank coal flotation was elucidated through the Zeta potential and contact angle measurements, the Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The microemulsion collector exhibited superior dispersibility, which was dispersed into positively charged oil droplets with an average size of 160.21 nm in the pulp. Furthermore, the nano-oil droplets could be more efficiently adsorbed on the low-rank coal surface through electrostatic attraction, resulting in the improvement of its hydrophobicity. Thus, the microemulsion collector shows great application potential in improving the flotation performance of low-rank coal.

Enhancing Flotation Performance of Low-Rank Coal Using Environment-Friendly Vegetable Oil

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.

Effect of ionic surfactants on flotation of low-rank coal: a DFT calculation and MD simulation study

ABSTRACT The poor flotation performance of low-rank coal is due to the large number of oxygen-containing functional groups on the coal surface. To improve the hydrophobicity of low-rank coal surface, dodecyl trimethyl ammonium bromide (DTAB) and sodium dodecyl benzene sulfonate (SDBS) were selected as cationic and anionic surfactants, and their promotion mechanisms were theoretically investigated using a combination of quantum chemical density functional theory (DFT) and molecular dynamics simulation (MD). The results of DFT calculations showed that the absolute value of the energy difference between the HOMO orbital of DTAB and the LUMO orbital of low-rank coal was the smallest compared with that of SDBS and water molecules, and the adsorption distance and interaction energy between low-rank coal and DTAB at adsorption equilibrium were the smallest, indicating that DTAB was able to replace the water molecules on the surface of low-rank coal. The MD simulation results showed that DTAB can adsorb directionally on the surface of low-rank coal, effectively covering the hydrophilic sites and inhibiting the adsorption of water molecules. The adsorption orientation and electrostatic repulsion of SDBS lead to a smaller degree of weakening of the interaction energy between coal and water. In the coal/DTAB/water system, the coal-water interaction was the smallest and the number of hydrogen bonds formed was the lowest. DTAB can promote the migration of water molecules, improve the hydrophobicity of low-rank coal surface and increase the flotation efficiency.

Effects of nonionic collectors with oxygen-containing functional groups on flotation performance of low-rank coal

This study aims to investigate the influence of nonionic collectors (diesel, methyl linoleate, oleic acid, and castor oil acid) on the flotation response of low-rank coal particles using X-ray photoelectron spectroscopy analysis, particle-bubble adhesion tests, and froth floatation measurements, in addition to density functional theory, molecular dynamics, and grand canonical Monte Carlo simulations. The results of the XPS analysis and the particle-bubble adhesion index showed that methyl linoleate, oleic acid, and castor oil acid could effectively adsorb onto the surfaces of low-rank coal particles and upgrade their surface hydrophobicity. The greatest content of hydrophobic functional group CC/CH and the flotation yield obtained by adding methyl linoleate during the flotation process were 78.88% and 86.95%, respectively. The electron-absorption induction effect of oxygen-containing groups and large π bonds of methyl linoleate considerably improved the wetting process on the surface of low-rank coal particles compared with that of dodecane, which contains a saturated bonding structure. The highest average adsorption capacity was obtained when methyl linoleate was applied to the surface of low-rank coal particles. The results suggest that ester surfactants such as methyl linoleate can substantially enhance the flotation response of low-rank coal.

Influence of Air Solubility on the Flotation Performance of Low-Rank Coal.

Low-rank coal (LRC) contains large amounts of harmful impurities that must be processed before utilization. Flotation is an effective means for separating fine particles, which can be influenced by air solubility in water. In this work, deaerated water (DW), ordinary water (OW), and pressurized water (PW) were prepared to research the underlying mechanism of the effect of air solubility on the flotation performance of LRC. The results show that PW dissolves the greatest amount of air in the three kinds of water (DW, OW, and PW). The flotation performance of LRC in different water types is directly proportional to air solubility in aqueous solutions. In addition, the induction time of LRC in PW (600 ms) is significantly shorter than those in OW (1200 ms) and DW (4000 ms). Atomic force microscopy (AFM) studies reveal that typical interfacial nanobubbles (NBs) only form on a highly oriented pyrolytic graphite (HOPG) surface in PW due to the supersaturated air in water. Furthermore, the interaction between LRC particles and HOPG in PW is significantly stronger than those in both OW and DW, which is attributed to the capillary force of rgw nanobubble bridge formed between particles. The hydrophobic interaction enhanced by NBs is critically important for the attachment of LRC particles to macrobubbles in flotation. Overall, air solubility in water has a great effect on LRC flotation performance, and PW flotation technology can be extended to LRC purification.

Effects of Nonionic Collectors with Oxygen-Containing Functional Groups on Flotation Performance of Low-Rank Coal

Effects of Nonionic Collectors with Oxygen-Containing Functional Groups on Flotation Performance of Low-Rank Coal

Enhanced floatability of low rank coal using surface functionalized polystyrene nanoparticles as collectors

Low rank coal (LRC) is difficult to be upgraded by flotation due to the rich oxygen-containing functional groups on its surface. The main objective of this study was to identify the feasibility of surface functionalized polystyrene nanoparticles as LRC flotation collectors. Tetrahydrofurfuryl-functionalized polystyrene nanoparticles (TFPNs) and hydroxyl-functionalized polystyrene nanoparticles (HFPNs) were prepared by emulsion polymerization, and their properties were characterized by X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), Zeta potential and particle size measurement. The effect of nanoparticles properties on the LRC flotation was investigated and the performance between TFPNs, HFPNs, polystyrene nanoparticles (PNs) and diesel oil (DO), was compared. The results show that the LRC flotation recovery of PNs was 2.82%–16.86% higher than that of DO, while that of TFPNs and HFPNs exceeded 28.30%–34.33% and 3.58%–18.92%, respectively, which indicated that the performance of PNs was improved by immobilizing tetrahydrofurfuryl or hydroxyl onto the surface. But surface functionalization degree (SFD) should be kept in an appropriate range, i.e. 5.78%–6.56% for TFPNs, 3.94%–5.62% for HFPNs. TFPNs and HFPNs can specifically deposit onto the LRC with the hydrogen bonding function. By improving the hydrophobicity and roughness with deposited nanoparticles, the flotation performance of LRC was significantly enhanced. The performance of TFPNs was superior to that of HFPNs, which resulted from the strong ability to form hydrogen bond for hydroxyl that reduced nanoparticle hydrophobicity. Effective nanoparticle collectors for LRC flotation were likely to be TFPNs with ∼50 nm diameter, positive Zeta potential and SFD around 6.56%. The balance among colloidal stability, hydrophobicity and selectivity of nanoparticles was an effective way to reduce the dosage of nanoparticle collector and promote its industrial application. The results of this study introduce a new class of special collectors for enhancing LRC flotation and put forward its path to commercial utilization.

Carrier Flotation of Low-Rank Coal with Polystyrene

The problem of low-rank coal flotation continues to be a challenge due to the poor hydrophobicity and abundant oxygenated functional groups on particle surfaces. In this study, carrier flotation was used to improve the flotation performance of low-rank coal with polystyrene as a carrier material. Kerosene was used as a collector and played a role in the adhesion of fine low-rank coal to polystyrene due to its hydrophobic properties. The carrier feature of polystyrene was demonstrated by Turbiscan Lab Expert stability analysis and scanning electron microscopy analysis. The flotation experiments revealed that the optimum conditions were: collector dosage 5000 g/t, pulp concentration 40 g/L, and the ratio of low-rank coal to polystyrene 100:10. Under these conditions, the combustible recovery by carrier flotation was obtained as 70.59% when the ash content was 12.32%, which increased by 25.68 points compared with the combustible recovery of conventional flotation under almost the same ash content. The fine coal particles coated the coarse polystyrene particles through hydrophobic interactions between the polystyrene and hydrocarbon chains of the kerosene adsorbed on coal particles. The results suggested that the flotation performance of low-rank coal was significantly improved by carrier flotation with polystyrene, especially for fine particles.

Adsorption behavior of mixed dodecane/n-valeric acid collectors on low-rank coal surface: Experimental and molecular dynamics simulation study

In this investigation, a mixed collector (MC) of dodecane and n-valeric acid was used to improve low rank coal flotation. Fourier transformation infrared spectroscopy (FTIR) measurements and contact angle measurements were conducted to explain flotation responses. Furthermore, using a molecular dynamics (MD) simulation, the changes of water/collector (dodecane or MC)/coal systems were studied before and after adsorption to indicate the absorption behavior and mechanism. The results showed that a better flotation performance of low-rank coal was obtained using the MC compared to a conventional collector of dodecane. The hydroxyl (OH) or carbonyl (CO) or carboxyl (COOH) migration of the coal with the MC was stronger than that with dodecane as a solo collector, and the MC can enhance the hydrophobicity and lipophilicity of the coal surface. MD simulation results revealed the adsorption behavior of the MC on low-rank coal surfaces. Dodecane was mainly adsorbed on the hydrophobic surface of coal, and n-valeric acid was more inclined to act on the oxygen-containing functional group of coal, i.e., a hydrophilic surface. The mobility of = dodecane molecules on the coal surface was reduced owing to the presence of n-valeric acid, which increased the lipophilicity and hydrophobicity of the low-rank coal surface, thus attracting dodecane molecules of the MC and restricting their movement, and accelerating the departure of water molecules from the low-rank coal surfaces. There was also a higher interaction energy between the MC and low-rank coal. The simulation results are in good agreement with the measured results; this effectively explains the flotation results.

Improving Coal Flotation by Gaseous Collector Pretreatment Method and its Potential Application in Preparing Coal Water Slurry

Low-rank coal is difficult to upgrade using conventional flotation methods due to its high hydrophilic properties. Thus, it is necessary to explore new methods for upgrading and utilizing low-rank coal. In this investigation, a gaseous dodecane pretreatment method was used to enhance the flotation performance of low-rank coal. Pore distribution analysis, FTIR (Fourier Transform Infrared Spectroscopy), and contact angle measurements were used to study the surface properties of the coal sample. Size distribution and float-sink test results indicated that the coal sample contained a lot of clean coal with low ash content, which could be used as a high quality raw material for making coal water slurry. FTIR, pore distribution analysis, and contact angle results showed that the coal was very hydrophilic due to the high concentration of -OH group and the large number of pores and cracks on the coal surface. The hydrophobicity of the coal sample was significantly improved by the gaseous dodecane pretreatment method. Clean coal with 67.2% combustible matter recovery and 10.5% ash content was obtained by gaseous dodecane pretreatment flotation method. Coal water slurry with 60% concentration was prepared using the flotation clean coal.

Effects of low-temperature air plasma pretreatment on the surface properties of low-rank coal

The surface topography, chemical composition, and pore size distributions of low-rank coal treated with RF (Radio Frequency) plasmas using various periods were investigated by the means of SEM-EDS, XPS, and BET to realize the potential of plasma technology for the surface modification of low-rank coal in the selective flotation. Moreover, the wettability and floatability of coal sample were studied after plasma pretreatment. The results showed that a large sum of stripes and polygonal pits were generated, which significantly increased surface roughness, gradually decreased the contents of CC and CH, and increased COO content through the plasma pretreatment. The contact angle of coal sample decreased from 75° to 0° with the increase of treatment time. The flotation tests indicated that the floatability of the low-rank coal sample sharply decreased through the plasma pretreatment. The remarkable differences in the contact angle and the flotation yields between the untreated coal and the treated coal under various treatment periods suggested that the reverse flotation performance of low-rank coal can be efficiently improved through modifying the surface properties of coal by plasma pretreatment.

Flotation Performance of Low-rank Coal in the Presence of Cetyltrimethyl Ammonium Bromide

ABSTRACT The flotation enhancement mechanism and flotation kinetics of low-rank coal in the presence of cetyltrimethyl ammonium bromide (CTAB) were investigated. The contact angle of the coal sample increased by 46.07% and the attachment time between coal particles and a single air bubble decreased by 85.79% with increasing the concentrations of CTAB from 0 to 1 × 10–4 M. Low concentrations of CTAB enhanced the flotation performance of low-rank coal, and the concentrate yield significantly increased by up to 8.59 percentage points with increasing the concentrations of CTAB from 0 to 1 × 10–5 M at the cost of a lower increase in the ash content. However, the selectivity was reduced at high CTAB concentrations (5 × 10–5 M and 10–4 M). Six kinetic flotation models were employed to fit the flotation test data using the 1stOpt analysis software; the flotation rate constant (k), the maximum combustible recovery (ε ∞), the correlation coefficient (R 2) and the modified flotation rate constant (k m) were calculated. Most models showed that the modified rate constant and the maximum combustible recovery of low-rank coal increased with the increasing concentrations of CTAB.

Effect of particle shape and roughness on the hydrophobicity of low-rank coal surface

ABSTRACT In this paper, a relationship between the roundness, roughness and induction time of low-rank coal particles was investigated. With the increase of grind time from 1 to 5 minutes, the roundness of low-rank coal particles slightly increased. The results of induction time measurements indicated that the particle surface roughness played a significant role in the surface hydrophobicity of low-rank coal particles. Moreover, it was also found that the roundness and roughness of low-rank coal particle surfaces presented a certain degree of change after both grinding and abrasion processes. Contrary to roundness change, during the grinding process, the roughness of low-rank coal particles significantly decreased. It was also observed that the roundnesses of low-rank coal samples after the grinding process significantly increased with the increase of abrading time. However, unlike the roundness increase with the abrading time increase, the roughness of low-rank coal samples significantly decreased. Therefore, the induction times of low-rank coal samples showed an increased trend after the grinding and abrading processes, which may be attributed to the difficult rupture of wetting film on the smooth solid surface. The grinding and abrading processes may result in a further decrease in surface hydrophobicity and adversely impact on the flotation performance of low-rank coal.

Effect of surfactants on the flotation performance of low-rank coal by particle sliding process measurements

Effect of surfactants on the flotation performance of low-rank coal by particle sliding process measurements

Combination of viscosity regulator and frother to enhance low-rank coal flotation performance

ABSTRACTThis study investigated the synergistic effect of viscosity regulators (polyethylene glycol, sodium carboxymethyl cellulose, and polyacrylamide) and frother (2-octanol) on upgrading the flotation performance of low-rank coal. The results of flotation tests were consistent with the analysis of induction time and supported by the results of SEM, viscosity, foaming ability, and foam layer stability. In the present work, it was observed that the highest combustible matter recovery was obtained by mixing the polyethylene glycol (PEG300) with 2-octanol, which increased from 32.9% to about 64.4% accompanied by a little increase of ash content (0.54%). Therefore, it demonstrated that the combination of PEG300 and 2-octanol provided the highest combustible matter recovery and better flotation selectivity.

Effects of magnetized 2-octanol on low-rank coal flotation

ABSTRACTIn this study, the effects of magnetized 2-octanol at different magnetization times and magnetic field intensities on the flotation performance of low-rank coal were investigated with the aim of recycling more concentrate. The mechanism of magnetized 2-octanol enhancing the floatability of low-rank coal was also elucidated in this investigation. After 2-octanol was subjected to the magnetized pretreatment, interfacial tension of 2-octanol and pulp conditioned with magnetized 2-octanol gradually decreased. The flotation results showed that clean coal yield was improved, while the clean coal ash barely changed. Therefore, magnetized 2-octanol have a significant effect on low-rank coal flotation.