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This is an article in the field of mineral processing engineering. Three samples of 5#, 9# and Mugua coal from Coal Preparation Plant of Lyulin Energy & Chemical Co., Ltd. were collected as the research objects. Screening, proximate analysis and ultimate analysis of the three coal samples were carried out. The mineral composition and surface functional groups of the three coal samples were analyzed by XRD, FT-IR and XPS. Kerosene, on-site reagent and TY6 developed in the laboratory were used for flotation tests. The collecting effect of the three reagents on different types of coal samples was compared. The results showed that 5# coal sample was easy to float, 9# coal sample showed less floatability than 5# coal, while Mugua coal showed the poorest floatability owing to high oxidation and strong hydrophilicity. For the three coal samples, TY6 and the on-site reagents both showed much better collective ability than kerosene and consume less as well. For easy-to-float coal, TY6 showed better selectivity, while for difficult-to-float coal, TY6 showed better collectivity. Smaller particle size dispersed in water, higher viscosity, and containing oxygen-bearing organic substances were the main characteristics of TY6 and the on-site reagents that made them stand out as compared with kerosene, which resulted in better reaction with coal surface, bigger contact angle and better hydrophobicity. In this point of view, TY6 behaved even a little better than the on-site reagents.

The conversion of coal to a hydrophilic state presents a significant challenge for process engineers, especially when treating oxidized coals in flotation-based beneficiation plants. Flotation of oxidized coal often requires a substantial consumption of oily collectors, resulting in unacceptably low yields. To address this, several pre-processing methods have emerged for coal deoxidation, including mild grinding, surface activation, and ultrasonic or microwave treatment. However, their effective application depends on a thorough understanding of the degree of oxidation in the coals. Therefore, it is crucial to gain insights into the nature of oxidized coal before initiating the deoxidation process. This present study provides various characterization techniques such as XRD, SEM-EDS, FTIR Spectroscopy, Raman Spectroscopy, TGA, and Zeta Potential Analysis employed on oxidized low-grade coals. The study revealed that the proximate analysis of low-grade coals KC, DC, RC, and PC contains varying ash percentages of 32.65%, 44.47%, 25.44%, and 37.53%, respectively, with SiO2 and Al2O3 comprising over 80% of the total ash. XRD characterizations identified quartz and kaolinite as major mineral phases in all samples, while SEM-EDS confirmed rough coal surfaces with peeling, off-white aggregations, and surface pores. HGI value ranging from 80 to 91 was attributed to partial decomposition and surface cracking due to oxidation. FTIR spectra revealed pronounced oxidation behavior, with strong −OH peaks in the 3600–3700 cm−1 range. Zeta potential analysis affirmed the oxidized nature of the coals with a pH below 3.1 and an extremely negative zeta potential beyond 3.1. The findings mentioned above showcase the distinct characteristics of oxidized low-grade coals, which serve as crucial indicators for exploring coal beneficiation, especially through the flotation process. [ABSTRACT FROM AUTHOR]

Copyright of Multipurpose Utilization of Mineral Resources / Kuangchan Zonghe Liyong is the property of Multipurpose Utilization of Mineral Resources Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To explore the surface properties of oxidized coal and reduce its risks of spontaneous combustion, the pore structure development of oxidized coal and its effect on oxygen adsorption capacity were studied by using liquid nitrogen adsorption and oxygen adsorption analysis techniques. The results show that the pore structure development of oxidized coal increases the pore volume and specific surface area. Micropore surface area is the main component of the specific surface area of coal. The mesopores of oxidized coal break into micropores and small pores. Among them, micropores are the most developed to generate more active adsorption sites, and the order of micropore growth is Coal 1 lignite>Coal 3 fat coal>Coal 2 gas coal. A deeper oxidation degree of coal corresponds to a greater number of active adsorption sites generated on the oxidized coal surface, which promotes the adsorption of oxygen on the surface. The order of oxygen adsorption capacity growth is Coal 1 lignite>Coal 3 fat coal>Coal 2 gas coal. The specific surface area is positively correlated with the maximum oxygen adsorption capacity. The order of sensitivity of the maximum oxygen adsorption capacity to the growth of specific surface area is Coal 1 lignite>Coal 2 gas coal>Coal 3 fat coal. The pore structure development could promote the generation of active adsorption sites and enhance the oxygen adsorption capacity of the oxidized coal surface. [ABSTRACT FROM AUTHOR]

Oxidized and unoxidized coal samples of various ranks are compared, as well as the humic and fulvic acids derived from those materials. Petrographic analysis shows that macerals of the vitrinite group predominate in the coal samples; the oxidized samples belong to oxidation group OK II. B coal (lignite) and D coal (long-flame coal) undergo more profound changes than G coal (gas coal) on oxidation (weathering). Compared to their unoxidized counterparts, the oxidized coal samples are characterized by higher ash content, yield of volatiles, and content of oxygen, nitrogen, and sulfur. The elemental composition of fulvic and humic acids from oxidized and unoxidized B and D coal varies widely but may be regarded as typical. Compared to fulvic acid, all the samples of humic acid are higher in carbon and lower in oxygen, nitrogen, and sulfur. Given the high yield of fulvic and humic acids from oxidized B and D coal, they may be regarded as promising raw materials for humic production. The yield of fulvic and humic acids from oxidized G coal is minimal. [ABSTRACT FROM AUTHOR]

This is an essay in the field of mineral processing engineering. During the mining and storage process of coal resources, a large amount of oxidized coal is formed, resulting in waste of coal resources and environmental pollution. Extracting humic acid from oxidized coal can achieve the goal of high-value utilization of oxidized coal resources. In order to further improve the content and utilization efficiency of humic acid in oxidized coal, this article uses three methods: H2O2 oxidation, concentrated H2SO4 oxidation, and reverse flotation to pretreat oxidized coal samples. The influence of these methods on the content of humic acid in oxidized coal was investigated, and the changes in oxygen-containing functional groups were analyzed using Fourier transform infrared spectroscopy (FTIR). The experimental results show that both oxidation and reverse flotation can improve the utilization efficiency of humic acid. After using H2O2 oxidation, the humic acid content in coal samples increases from 21.58% to 43.62%; After oxidation with concentrated H2SO4, the content of humic acid reached 48.51%, and the extraction rate of humic acid reached 81.08%. Extracting humic acid through reverse flotation treatment can remove some minerals, and humic acid is enriched in sediment. The extraction rate of humic acid is also improved. After oxidation treatment, the extracted humic acid has an increase in oxygen-containing groups and enhanced hydrophilicity.

With the deterioration of the high-grade coal seams and the inadequate adsorptions noticed with the oily collectors, along with the cost escalations in petroleum-based products, there is a potential for alternative collectors. For this cause, bio-based green flotation reagents and their conjugations are gaining more concern on account of their reduced cost and sustainability. In this paper performance efficiency of oily collectors, Vegetable oil (Crude Palm Oil), and their combinations are compared for high-ash oxidized Indian coal considering their fatty acid adequacies and availability in the local markets. The adsorption mechanisms of both single and mixed collectors on coal surfaces were conducted with the aid of Fourier Transform Infrared Spectroscopy, Gas Chromatography-Mass Spectrometry, X-ray photoelectron spectroscopy, and contact angle measurements. Different surface characterization results divulged that the arrangement of more oxygenated functional groups in the POC and KP could ameliorate flotation efficiency through dipole attraction or hydrogen bonding, in addition to the Van der Waals forces. A maximum yield of 72.84% could be obtained with KP collectors with reduction ash of up to 20.44% (from feed ash of 35.63%). The present biodegradable collector and the mixtures lay an essential pathway for the effective separation of oxidized medium volatile coking coals. [ABSTRACT FROM AUTHOR]

Copyright of Multipurpose Utilization of Mineral Resources / Kuangchan Zonghe Liyong is the property of Multipurpose Utilization of Mineral Resources Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Revealing the characteristics of spontaneous combustion and re-combustion of oxidized coal is of great significance for the coal fire prevention and control. Synchronous Thermal Analyzer (STA) and Fourier Transform Infrared Spectrometer (FTIR) were used to measure the thermal kinetics and microscopic characteristics of coal samples with different oxidation degrees (unoxidized, 100 ℃, 200 ℃ and 300 ℃ oxidized coal). It is found that the characteristic temperatures decrease first and then increase with the increasing degree of oxidation. The ignition temperature of 100 ℃-O coal (oxidized at 100 ℃ for 6 h) is relatively the lowest at 334.1 ℃. Pyrolysis and gas-phase combustion reactions dominate the weight loss process, while solid-phase combustion reactions are relatively minor. The gas-phase combustion ratio of 100 ℃-O coal is the highest at 68.56%. With the deepening of coal oxidation degree, the relative content of aliphatic hydrocarbons and hydroxyl groups gradually decreases, while that of oxygen-containing functional groups (C-O, C = O, COOH, etc.) increases first and then decreases, reaching the highest value of 42.2% at 100 ℃. Moreover, the 100 ℃-O coal has the minimum temperature at the point of maximum exothermic power of 378.5 ℃, the highest exothermic power of -53.09 mW/mg and the maximum enthalpy of -18,579 J/g. All results show that 100 ℃-O coal has the highest risk of spontaneous combustion than the other three coal samples. This suggests that there is a maximum point of spontaneous combustion risk in the range of pre-oxidization temperatures of oxidized coal. [ABSTRACT FROM AUTHOR]

The existing research on the spontaneous combustion characteristics of oxidized coal is mostly based on the coal samples prepared under the conditions of lower oxidation temperature and air. It lacks the analysis of the kinetic characteristics during the oxidation process of oxidized coal. In order to solve the above problems, the C80 microcalorimeter is used to study the exothermic and kinetic characteristics of low-temperature oxidation reaction of preoxidized coal prepared under different oxidation temperatures (100, 200, 300 ℃) and oxygen volume fraction (21%, 15%, 5%). The effects of oxidation temperature and oxygen concentration on the activation energy of low-temperature oxidation reaction of preoxidized coal are discussed. The analysis results of low-temperature oxidation exothermic characteristics of preoxidized coal are shown as follows. ① The low-temperature oxidation process of preoxidized coal lags behind that of raw coal. The degree of lag increases with the increase of oxidation temperature and oxygen concentration. ② The heat release of low-temperature oxidation reaction of preoxidized coal is lower than that of raw coal. The heat release gradually decreases with the increase of oxidation temperature and oxygen concentration. When the oxidation temperature is 100 ℃, t1 (the temperature at which the heat flow value starts ＞0), t2 (the temperature corresponding to the maximum growth rate of heat flow value) and the reaction heat of low-temperature oxidation of preoxidized coals with different oxygen concentrations are basically equal. ③ With the increase of oxidation temperature, the effect of oxygen concentration on t1, t2 and the reaction heat of low-temperature oxidation is gradually obvious. The results show that the effect of oxygen concentration on the low-temperature oxidation reaction of preoxidized coal is only reflected at higher oxidation temperatures. However, too high oxidation temperature will lead to a serious lag of the low-temperature oxidation reaction process of pre-oxidized coal and the reaction heat release is less than 0. The analysis results of kinetic parameters (activation energy and pre-exponential factor) of low-temperature oxidation of pre-oxidized coal are shown as follows. ① The activation energy of the low-temperature oxidation reaction of pre-oxidized coal in the accelerated oxidation stage is higher than that of raw coal. The activation energy of the rapid oxidation stage is lower than that of raw coal. The results show that the threshold of the oxidation reaction of pre-oxidized coal entering the accelerated oxidation stage is increased, but it is easier to enter the rapid oxidation stage. ② The pre-exponential factor data show that the low-temperature oxidation reaction of pre-oxidized coal is more rapid than that of raw coal. ③ The changes of oxidation temperature and oxygen concentration have no obvious regularity with the activation energy of the low-temperature oxidation process of preoxidized coal. In the accelerated oxidation stage, the activation energy increases with the increase of oxidation temperature. The activation energy first decreases and then increases with the increase of oxygen concentration. In the rapid oxidation stage, when the oxidation temperature is 100 ℃, the activation energy first decreases and then increases with the increase of oxygen concentration, while 200 ℃ is the opposite.

In order to explore the low-temperature oxidation characteristics and evolution law of oxidized coal, this paper adopted a temperature-programmed experiment system. Firstly, the low-temperature oxidation temperature-programmed experiment was carried out on the oxidized coal formed by N2 anaerobic cooling after the coal samples were pre-oxidized to 60 ℃, 90 ℃, 120 ℃, 150 ℃, 180 ℃ and 210 ℃ respectively. At the same time, in order to further reveal the characteristics of low-temperature oxidation behavior of oxidized coal formed under different fire extinguishing conditions, the low-temperature oxidation temperature programmed test was carried out on the oxidized coal formed after fire extinguishing with three different volume fractions of N2 when the coal sample was pre-oxidized to 120 ℃. This reveals the changes of oxygen consumption rate, production rate of signature gases (CO, CO2) and heat release intensity of these two kinds of oxidized coals during low temperature oxidation process. The results show that the oxygen consumption rate, signature gas generation rate and heat release intensity of oxidized coal are all lower than those of raw coal. Furthermore, the spontaneous combustion characteristic parameters of coal samples pre-oxidized to 90 ℃ are closer to that of raw coal, indicating that coals pre-oxidized to critical temperature are more likely to reignite. When pre-oxidized to 120 ℃, the higher the volume fraction of N2, the closer the spontaneous combustion characteristic parameters of this oxidized coal are to the original coal, indicating that the coal with higher volume fraction of N2 has stronger recrudescence ability. Therefore, it is necessary to prevent the recurrence of coal when mining the coal body in the near coal seam group, the recrudescence working face and the unsealing fire area.

The results of a study of the effect of mechanical energy on the properties of humic acids in the course of mechanical processing of oxidized coal in a planetary mill are presented. It is shown that, upon the mechanical action on coal in the presence of alkaline and oxidizing alkaline reagents in a planetary-type mill with steel balls used as grinding bodies, the yield of humic acids increased by 25–33%; the molecular weight decreased and the concentration of functional groups increased in comparison with those of humic acids obtained by mechanical processing with ceramic balls. A change in the density of balls affects the mechanics of their motion and the amount of energy during the fall. [ABSTRACT FROM AUTHOR]

In order to master the relationship between the key active groups of weathered coal and oxidized coal at the characteristic temperature of coal spontaneous combustion, this paper takes the fresh coal as the reference coal to compare and analyze the microstructure of weathered coal and oxidized coal. Firstly, the relative content of active functional groups and characteristic structural parameters of weathered coal and oxidized coal in the initial state were analyzed by Fourier transform infrared spectroscopy, the variation laws of four main active functions under characteristic temperature were determined, and the differences of different active groups between weathered coal and oxidized coal were semi quantitatively analyzed. The key active groups affecting the difference of natural ignition between weathered coal and oxidized coal are revealed. Through the programmed temperature rise experiment of coal spontaneous combustion, the release characteristics of index gas concentration of weathered coal and oxidized coal were analyzed, and the evolution and migration of key functional groups at characteristic temperature were verified. The results show that the content of CO produced by oxidized coal was higher than that of weathered coal due to the different content of C-O-C in oxygen-containing functional groups, while the content of C2H6 produced by weathered coal was higher than that of oxidized coal due to the different asymmetric stretching vibration of methyl and methylene in aliphatic hydrocarbons.

It is necessary to study the thermophysical properties and heat transfer mechanism of coal for underground coal gasification (UCG). The long-flame coal from Ningtiaota coal mine was pyrolyzed and oxidized at different temperatures (200, 250, 300, 350 °C in nitrogen, and 100, 150, 200, 225, 250, 275, 300, 325 °C in air), respectively. The influence of pre-treatment temperature and real-time temperature on thermal diffusivity, specific heat capacity, and thermal conductivity of coal was studied by laser-flash method. The results show that there are strong correlations between temperatures and thermophysical properties. During the real-time testing, with the rise of real-time temperature, the thermal diffusivity of different pre-treated coal decreases and the change rate gradually decreases. Meanwhile, specific heat capacity and thermal conductivity increase, and obvious stage characteristics are shown around 210–240 °C. Pyrolysis and oxidation can significantly degrade the thermal diffusivity and thermal conductivity of coal samples, and the degradation degree of oxidized coal is higher. The specific heat capacities of pyrolyzed and oxidized coal are normally higher than raw coal, and the effect of oxidation on the specific heat capacity increases with real-time temperature. The results can provide an important reference for exploring coal's thermophysical properties change mechanism during the process of UCG. [ABSTRACT FROM AUTHOR]

Numerous oxygen elements are present on the oxidized coal surfaces, resulting in the difficulties for flotation. In this study, the enhancement of oxidized coal flotation using the impact flow conditioning pulp was investigated, and the impact flow velocity was optimized. The enhancement mechanism of the impact flow conditioning pulp was investigated via a series of experiments. The results showed that the use of impact flow conditioning pulp could improve the cumulative combustible recovery and flotation kinetics of oxidized coal, and these increased with the increasing impact flow velocity. In the experimental range, an optimum flotation result was obtained at an impact flow velocity of 5 m/s. The SEM analysis showed that the impact flow conditioning pulp could remove the aggregations on the oxidized coal surface, exposing a fresh surface. The XPS analysis confirmed that the impact flow conditioning pulp could increase the carbon contents and decrease the oxygen contents on the oxidized coal surface. Further, the impact flow conditioning pulp could significantly enhance the hydrophobicity and floatability of oxidized coal. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An increase in the concentration of acidic surface groups, the sorption exchange capacity of oxidized coal, and the yield of humic acids by 20–40% due to mechanical action with alkaline and oxidizing alkaline reagents was found. According to the IR-spectroscopic data of coals and the potentiometric titration of acidic groups, a decrease in the concentration of carboxyl groups in aliphatic fragments due to their maximum sorption capacity for metal ions was noted. Humic acids were characterized by a significant increase in the number of oxygen-containing groups and stable polyconjugated heteroaromatic fragments as a result of mechanochemical action. [ABSTRACT FROM AUTHOR]

The effect of pH on zeta potential, combustible matter recovery, and Fourier transform infrared (FTIR) spectrum of oxidized coal was studied, and also the effects of Na+, Mg2+, and Fe3+ on oxidized coal flotation at different pH were investigated. The optimal floatability of oxidized coal was explored through the conditions of pH and inorganic salt ion. Both combustible matter recovery and zeta potential decreased as pH increased. The maximum combustible matter recovery and approximate isoelectric points (IEP) were obtained at pH 3. The adsorption peaks of oxygen-containing functional groups and hydrophobic groups in FTIR spectrums were, respectively, lowered and enhanced while pH varied from 7 to 3. Oxidized coal flotation was improved by Na+, Mg2+, and Fe3+ in acidic condition but depressed in alkaline condition. Compared with the combustible matter recovery in the absence of inorganic salt ion, Na+ presented the maximum increase rate of combustible matter recovery at pH 6 but also the minimum at pH 12. The combustible matter recovery for Na+ gradually increased while that for Mg2+ and Fe3+ generally decreased with the increase in ion concentration. The optimal floatability was gained at pH 3 and in the presence of Na+ with a concentration of 1600 g/t. [ABSTRACT FROM AUTHOR]

After rock burst and spontaneous combustion, a coal seam is exposed, and this form of compound disaster shows new characteristics. Therefore, basic research on oxidized coal is important to the theoretical research and prevention of compound disasters. Based on temperature-programmed and mechanical experiments and the first law of thermodynamics, as the degree of the oxidation of coal increases, the volume expands slightly and then shrinks, and the mass, density and wave speed decrease. Raw coal and 70 ℃ oxidized coal have a strong impact, 135 ℃ oxidized coal and 200 ℃ oxidized coal have a weak periodic impact, and 265 ℃ oxidized coal has no impact. Additionally, wave velocity is positively correlated with compressive strength and the elastic strain energy index but is negatively correlated with the dynamic fracture duration. Compressive strength is positively correlated with the elastic strain energy index and negatively correlated with the dynamic fracture duration. As the degree of oxidation increases, the post-peak dissipated energy release of coal changes from linear to stepped, and its release intensity basically corresponds to the results of bursting liability. Finally, high stress is likely to cause coal fractures to develop, thereby inducing the spontaneous combustion of coal. Spontaneous coal combustion further weakens the bursting liability of coal, but the danger of rock burst increases significantly. [ABSTRACT FROM AUTHOR]

High-rank coals are generally more floatable than low rank or oxidized coals due to their higher hydrophobicity. Surface oxidation of coals due to the exposure to atmospheric oxygen renders the surface some hydrophilic character. As a result, the low rank or oxidized coals do not effectively attach to air bubbles and result in lower flotation yields. Nonpolar collectors like diesel and other commercial collectors when used in a flotation process do not effectively attach to the hydrophilic sites of the oxidized coal surface leading to lower yields. Researchers have generally tried pre-treatment with reagents to improve the floatability of these types of coals. In the present work, we have synthesized two collectors, tetrahydrofurfuryl oleate based (C1) and tetrahydrofurfuryl ether based (C2), which contain both hydrophilic and hydrophobic components in some rationale so that they can attach to hydrophobic as well as hydrophilic sites of the oxidized coal. The attachment of synthesized collectors to the oxidized coal can provide better particle-bubble attachment which was evident from the improvement in contact angle from 73.4° to a maximum of 88.54°. Flotation results showed that the yield increased from 8% in absence of any collectors to 40% in presence of collector 1. The flotation performance was further enhanced by the synthesis of a novel frother and the synergistic effect of developed collectors and frothers produced higher yield (53%) and lower ash (10%) clean coal fines compared to some of the well-known collectors like diesel, polyethylene glycol and frothers like Methyl Isobutyl Carbinol (MIBC) used in the study. [ABSTRACT FROM AUTHOR]

Nowadays, the flotation of oxidized coal attracts more and more attention in China. In this study, a conventional flotation column with a novel of forth feed was used to beneficiate the oxidized coal. Exploratory experiments showed that the froth feed flotation can improve the overall combustible recovery by 22.25% with only 1.19% increase in ash content compared to conventional pulp feed flotation. Box-Behnken design (BBD), a response surface method, was used to design the flotation tests and model the effect of variables on responses. Four operating parameters, including frother concentration, superficial gas velocity, feed height and wash water rate as well as two response factors, namely ash content and combustible recovery were investigated. Meanwhile, their interactions were also described with three-dimensional response surface. Results showed that the models obtained for both ash content and combustible recovery were statistically significant. Additionally, the effect of wash water rate on ash content was found to be more significant than those of other parameters, while the combustible recovery depended more on the frother concentration. At last, the predicted optimal results were obtained within the experimental ranges, which well responded to the verification experiments. [ABSTRACT FROM AUTHOR]

In this study, coal tar, an industrial by-product of the carbonization/gasification of coal, was adopted as an economical flotation collector for recovering clean oxidized coal. The characteristics of high-temperature coal tar (HTCT), its performance as a flotation collector, and the interaction mechanism between HTCT and oxidized coal were analyzed by gas chromatography/mass spectrometry, flotation experiments, X-ray photoelectron spectroscopy, and dynamic contact angle measurements. The results revealed that HTCT has a strong selective collection ability because it contains a large number of aliphatic and aromatic compounds with oxygen-containing functional groups. At HTCT dosage of 3000 g/t, 79.23% of combustible matter with an ash content of 9.99% was obtained. The major mechanism responsible for the enhanced oxidized coal separation is that, with the adsorption of HTCT onto oxidized coal, the C–O hydrophilic functional groups were covered and an increased amount of the C–C/C–H hydrophobic functional groups of the oxidized coal surface was exposed, resulting in improved surface hydrophobicity and floatability of the oxidized coal. This study provides valuable guidelines for the re-utilization of coal tar and the flotation upgradation of oxidized coal. [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]

Spontaneous combustion of oxidized coal occurs frequently in mining and utilization process, which is influenced by the first oxidation conditions significantly. With a focus on the influence of pre-oxidation temperature on spontaneous combustibility of oxidized coal, oxidized coal samples were prepared by heating at preset temperature of 50 °C, 70 °C, 90 °C, 110 °C and 130 °C. Programmed heating tests on oxidized coal and raw coal samples were carried out in air atmosphere of 120 mL min−1, with the heating rate of 0.3 °C min−1. The gaseous mixture of O2, CO and CO2 at the outlet was identified by gas chromatography to analyze oxidizability and exothermicity of experimental coal samples. The results showed that, with the increasing pre-oxidation temperature, the oxidizability and exothermicity of oxidized coals decreased first and increased later, which were related with change of oxygen consumption rate, emission rate of CO and CO2 gas. The spontaneous combustibility order by pre-oxidation temperatures was 130 °C, raw, 50 °C, 110 °C, 90 °C and 70 °C. Being oxidized at 130 °C could promote coal to self-heat, and being oxidized below 110 °C would inhibit coal self-heating. [ABSTRACT FROM AUTHOR]

Copyright of Archives of Mining Sciences is the property of Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is well-known that ultra-fine particles, especially those with oxidized surface, are difficult to float using conventional methods. Flotation of oxidized ultra-fine particles has been a serious problem which should be well solved as the demand for energy is increasing. In this investigation, the flotation behaviors of fresh and oxidized fine coal (<45 μm) and the effect of mixing with coarse particles (250–500 μm) in equal proportions were discussed. Zeta potential and contact angle results indicated the surface hydrophobicity of oxidized fine coal was much lower than that of fresh fine coal. When floating alone, yields of fresh, moderately oxidized, deeply oxidized and very deeply oxidized fine coal were 77.88%, 62.36%, 34.66% and 16.67%, respectively. However, the yields for the above four fine coals were increased to 82.83%, 87.04%, 82.72% and 50.07%, respectively when mixed with coarse particles. The yield improvement indicator values for the four fine coals were 4.95%, 24.68%, 48.06% and 33.40%, respectively. Obviously, the yield improvement indicator values for oxidized fine coals were much higher than fresh fine coal. A similar trend was also observed in the experiments without collector. Throughout this research, mixing with hydrophobic coarse coal is proved to be an effective method to improve the flotation behavior of oxidized fine coal. [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]

Spontaneous combustion of coal is one of the main problems in coal mine safe production. The oxidized coal recrudescence should be paid enough attention at the unsealing stage. To reveal the re-ignition characteristics of coal with different oxidation levels, the research was conducted on the development of coal spontaneous combustion at each stage. The test system for spontaneous index gases was developed to analyze the occurrence and development of index gases produced by coal with different oxidation levels, and Fourier transform infrared spectroscopy was used to investigate the characteristics of functional group by the qualitative analysis of absorbance and the quantitative analysis of peak area. The results show that the determination index for coal spontaneous combustion tendency is Iym

Abstract: The use of natural rubber, phenol, polyvinyl alcohol, and water-soluble melamine-formaldehyde resin as antioxidants for Donetsk Basin Zh and K coal proves highly effective. With increase in grain size of the coal, its oxidation rate falls. Similar experiments should be conducted on an industrial scale. [ABSTRACT FROM AUTHOR]

Abstract: The flotation of low-quality Russian and Mongolian coal by means of spent motor oil is investigated. Ozonization is used to improve the flotational properties of the spent oil. The optimal ozonization depth of oil used to enrich coal of poor metamorphic development is 5-6 g/kg. Ozonization increases the oil's content of oxygen-bearing heteropolar compounds, which determine its flotation properties. In addition, the viscosity declines. The use of ozonized spent oil improves the flotation of gas coal by 24%. Flotation of naturally oxidized gas coal by spent oil, before and after ozonization, is poor and requires large quantities of reagents. [ABSTRACT FROM AUTHOR]

Abstract: The influence of preliminary demineralization of coal by aqueous solutions of hydrochloric and hydrofluoric acid on the texture of sorbents produced by thermolysis in the presence of potassium hydroxide is investigated (when the mass ratio of the KOH and the coal is 2.0). The results show that successive treatment of coal with 10% hydrochloric and 10% hydrofluoric acid decreases the coal's ash content to a residual value of about 0.6%. In thermolysis, a sorbent with an ash content of 1.5% is obtained on thermolysis. In comparison with sorbent from untreated coal, the sorbent from the demineralized coal is characterized by higher specific surface and total pore volume. In the treated coal, more than 70% of the pore space consists of micropores. [ABSTRACT FROM AUTHOR]

This paper compares FTIR (Fourier Transform Infrared Spectroscopy) and contact angle measurements to characterize surface properties of the oxidized coals with different ash contents. FTIR analysis was employed to investigate functional chemical groups of the oxidized coals. Contact angle measurements were utilized to characterize the hydrophilicity of the oxidized coal. The results showed that contact angle measurements were the same regarding of the type of the oxidized coal. However, FTIR results show that the coal samples with lower ash content had more hydrophobic groups and less hydrophilic groups than the coal samples with higher ash content. This paper demonstrated that FTIR technique is more sensitive than contact angle measurements in studying surface properties of oxidized coal samples. [ABSTRACT FROM AUTHOR]

The influence of oxidation of long-flame coal pieces (at 100-250°C for 5-40 h) on the yield and composition of the pyrolytic products, the emission dynamics of volatiles, and the properties and porous structure of the semicoke is studied. [ABSTRACT FROM AUTHOR]

In this study, the combined effect of chemical composition and spreading velocity of collector on flotation performance of oxidized coal was investigated. Oxidized coal samples were prepared using the H 2 O 2 solution oxidation method. The contents of oxygen-containing groups on the coal surface increased with the oxidation degree by X-ray photoelectron spectroscopy (XPS) analysis and the coal surface became more hydrophilic by water contact angle measurement. The chemical composition and the spreading velocity of three oily collectors, including diesel collector, novel collector a (NCA), and novel collector b (NCB), were compared. The content of oxygen-containing groups was the order of NCB > NCA > diesel by FTIR analysis. The spreading velocity determined from the interfacial tension, viscosity and coal-oil-water contact angle measurement results showed the order of diesel > NCA > NCB. With more oxygen-containing groups to induce adsorption and higher spreading velocity to achieve spreading rapidly on the coal surface, NCA kept the fastest flotation rate all along by flotation kinetics experiment, while the flotation rates of diesel and NCB depend a lot on the oxidation degree of coal surface. This can be explained by a combined interaction mechanism from chemical composition and spreading velocity of collector. During the oxidized coal flotation, oxygen-containing groups of collector played a leading role in the collector-particle adhesion process which determined whether the collector can adsorb on the oxidized surface, while the spreading velocity acted as a dominant part in the spreading process which affected the final flotation rate. [ABSTRACT FROM AUTHOR]

The objective of this study is to explain the different flotation responses observed in oxidized coal flotation when using a nonpolar flotation collector, dodecane, versus a polar flotation collector, oleic acid. Particularly, the effect of each flotation collector on bubble--coal particle attachment was investigated. Colloidal probe atomic force microscopy (AFM) was used to directly measure the force between a model coal surface and a model bubble in the presence of either dodecane or oleic acid. Pyrolytic graphite (PG) treated with oxygen plasma and a polymethylmethacrylate (PMMA) particle were selected to represent the model oxidized coal surface and model bubble. High speed visualization for bubble--oxidized coal attachment was used to monitor the attachment behavior between bubble and oxidized coal in presence of dodecane and oleic acid, respectively. It was found that the force between the oxidized PG and the PMMA particle in Milli-Q water was monotonically repulsive, illustrating that oxidized coal particles attach onto bubble surface with difficulty. The flotation recovery using a traditional hydrocarbon oil, dodecane, was always lower than when oleic acid was used at a low dosage (300-1100 g/t). The force measurements showed that an attractive hydrophobic force was introduced when a 0.01 mM oleic acid solution was used, while the force was still repulsive in presence of a 0.01 mM dodecane solution. The minimum contact time for successful attachment between oxidized coal surface and bubbles in the presence of 0.01 mM oleic acid is much shorter than that in 0.01 mM dodecane. However, a high flotation recovery of 85.81% was obtained when dodecane concentration was further increased to 1700 g/t. The significant jump into contact effect observed in the AFM force curves and the short induction time in the presence of 1 mM dodecane solution was responsible for this high flotation recovery. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile pore-regulating strategy to integrate large specific surface area and suitable mesopore volume in interconnected porous carbons. • The optimal sample shows a high specific capacitance of 345 F g−1 at 1 A/g. • High energy density of 56 Wh kg−1 at 741 W kg−1 is obtained in ionic liquid electrolyte. The porous structure and specific surface area (SSA) of porous carbon are important factors affecting the performance of supercapacitors. However, it is still a great challenge to leverage the tradeoff between the SSA and mesopores to achieve both excellent capacitive and rate performance. Herein, we develop a facile pore- regulating strategy to integrate interconnected porous structure, large SSA and suitable mesopore volume in porous carbons. The co-pyrolysis of cotton stalks and oxidized coal can generate more defect sites, which is conducive to form a honeycomb-like morphology and reasonable porous structures in the following activation process. The integration of large SSA (1510 m2 g−1) and abundant mesopore volume (0.24 cm3 g−1) endow the optimal sample with a high capacitance (345 F g−1 @ 1 A/g), superior rate performance (69 % capacitance retention @ 50 A/g), and excellent long cyclic stability in 6 M KOH electrolyte. Moreover, the assembled symmetric supercapacitor exhibits a high energy density of 56 Wh kg−1 @ 741 W kg−1 in EMIM BF 4. This work provides a simple strategy to tailor the morphology and structure of coal and biomass-derived porous carbon, and offers new insights into the tradeoff between SSA and mesopores for high performance supercapacitors. [ABSTRACT FROM AUTHOR]

Coal plays an important role in energy supply. However, low rank/oxidized coals are difficult to float with the common oily collectors, and hence effective collectors are urgently needed to be found or created. The difficult-to-float reason of low rank/oxidized coals primarily includes two aspects, i.e. abundant oxygen-containing groups on coal surface and porous surface of coal particle. The common oily collectors are difficult to adsorb on hydrophilic sites on low rank/oxidized coals surface and a porous structure of coal surface needs large consumption of collectors. This review is to highlight recent advances in the effective collectors for enhancing the flotation of low rank/oxidized coals, especially an overview of effective collectors proposed in the past decade. The effective collectors are achieved through the emulsion of common oily collectors, the mixture of several collectors/surfactants, the special collectors and bio-collectors. Throughout this review, the mechanism of the effective collectors enhancing the flotation of low rank/oxidized coals is discussed and the development directions of effective collectors in the future are also recommended. [ABSTRACT FROM AUTHOR]

The activation of carbon sorbents in CO is investigated. The sorbents are produced by the thermolysis of naturally oxidized SS coal steeped in potassium hydroxide, with an alkali/coal ratio R = 0.01 and 0.05 g/g. The influence of CO activation on the texture of the sorbents obtained is established. After 10-min activation, the increase in specific surface area of the sorbents is a maximum (about 100%). Longer activation increases the loss of material. The pore volume formed on activation is proportional to the proportion of carbon-bearing material removed. The volume of adsorbing pores formed in the sorbents is greatest when the loss of material is 25-35%. [ABSTRACT FROM AUTHOR]

Oxidized coal is difficult to float with common oily collectors because oxidation processes occurring on the coal surface reduces the surface hydrophobicity of coal. Grinding pretreatment has been widely applied in the improvement in the floatability of oxidized coal. However, there is no sufficient investigation into the optimization of grinding conditions for the effective flotation of oxidized coal. This paper is to reveal the effects of grinding conditions, such as grinding time, pulp density, and feed amount on the flotation behavior of oxidized coal. The optimum grinding conditions are as follows: the feed amount is 70 g, the pulp density is 40%, and the grinding time is 15 min. Under the optimum grinding conditions, 62.53% combustible matter recovery with 12.99% clean coal ash content is obtained. [ABSTRACT FROM PUBLISHER]

Colloid mill attrition can remove the oxidized layer from oxidized coal surface. The effects of colloid mill gap space and milled pulp density were investigated according to the flotation response. It was found that both particle size reduction and flotation recovery enhancement were higher at higher pulp density and smaller gap space. When colloid mill worked at higher pulp density and smaller gap space, oxidized layers of coal particles could be removed more thoroughly. In addition, the greater reduction in particle size at higher pulp density and smaller gap space should be conductive to the flotation of oxidized coal because large particle size of oxidized coal is considered not suitable for its flotation. Because colloid mill was successfully applied in improving oxidized coal flotation, the results of this paper will promote the industrial application of colloid mill into effective flotation of oxidized coal in coal preparation plants. [ABSTRACT FROM AUTHOR]

The influence of coal oxidation in the bed on the structural features and basic properties of the coal is analyzed. Unoxidized and oxidized coal samples are compared. [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]

The beneficiation of oxidized coal is difficult to achieve by conventional flotation with oily collectors. Oxidized coal samples were prepared by the peroxide solution oxidation and a new type of oxygenated polar compound collector (CC) and a powerful blending frother (BF) were used to intensify oxidized coal flotation in the present study. The effects of the CC and BF on the froth stability and flotation performance (i.e., recovery and selectivity) were investigated. The results show that only 44.51% recovery with 9.71 s dynamic froth stability index (DFS) was obtained for oxidized coal flotation by using conventional diesel and octanol as the collector and frother, respectively. Lots of oxygen functional groups (− OH and C-O) were introduced after peroxide oxidation indicated by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis, leading to poor hydrophobicity and low flotation recovery. An optimal separation result with 76.24% oxidized coal recovery and 19.43 s DFS was obtained using the CC combined with octanol, which was attributed to the hydrogen bonding between the hydrophilic sites on coal surface and polar oxygen functional groups in CC. An identical DFS (19.43 s) was obtained using conventional diesel combined with the BF, while with only 21.38% recovery. Diesel did not sufficiently render the coal hydrophobicity and as a result only a small amount of coal particles was collected by attaching to bubble surface in pulp phase. The Fuerstenau upgrading curves show that both the maximum recovery and the best flotation selectivity could be obtained using the CC combined with octanol. [ABSTRACT FROM AUTHOR]

The objective of this study is to explain the different flotation responses observed in oxidized coal flotation when using a nonpolar flotation collector, dodecane, versus a polar flotation collector, oleic acid. Particularly, the effect of each flotation collector on bubble–coal particle attachment was investigated. Colloidal probe atomic force microscopy (AFM) was used to directly measure the force between a model coal surface and a model bubble in the presence of either dodecane or oleic acid. Pyrolytic graphite (PG) treated with oxygen plasma and a polymethylmethacrylate (PMMA) particle were selected to represent the model oxidized coal surface and model bubble. High speed visualization for bubble–oxidized coal attachment was used to monitor the attachment behavior between bubble and oxidized coal in presence of dodecane and oleic acid, respectively. It was found that the force between the oxidized PG and the PMMA particle in Milli-Q water was monotonically repulsive, illustrating that oxidized coal particles attach onto bubble surface with difficulty. The flotation recovery using a traditional hydrocarbon oil, dodecane, was always lower than when oleic acid was used at a low dosage (300–1100 g/t). The force measurements showed that an attractive hydrophobic force was introduced when a 0.01 mM oleic acid solution was used, while the force was still repulsive in presence of a 0.01 mM dodecane solution. The minimum contact time for successful attachment between oxidized coal surface and bubbles in the presence of 0.01 mM oleic acid is much shorter than that in 0.01 mM dodecane. However, a high flotation recovery of 85.81% was obtained when dodecane concentration was further increased to 1700 g/t. The significant jump into contact effect observed in the AFM force curves and the short induction time in the presence of 1 mM dodecane solution was responsible for this high flotation recovery.

Some physicochemical properties of carbon adsorbents produced by chemical activation with alkali are determined: specifically, their total ash content, the content of water-soluble ash, the total iron content (recalculated for Fe), and the content of water-soluble iron compounds. Their content of water-soluble ash and the total iron content are minimal; no water-soluble iron compounds are observed in the sorbents. However, the total ash content in the sorbents is impermissibly high. With increase in potassium content in the initial content, the total ash content of the sorbents is reduced to 16.5%. [ABSTRACT FROM AUTHOR]

[Display omitted] • AAS adsorption on OC was investigated through experiments and DFT calculation. • AAS can enhance the hydrophobicity and reduce the electronegativity of OC surface. • AAS cannot effectively promote the hydrophobic aggregation settlement of OC. • Intermolecular force dominates the adsorption of AAS on OC surface. To clarify the hydrophobic modification mechanism of AAS (alkyl amine/ammonium salts) on OC (oxidized coal) surface, four different AAS on OC was investigated through experiments and DFT calculations. Adsorption of AAS on OC enhances its surface hydrophobicity and reduces its surface electronegativity, which further promote its aggregation sedimentation, but the overall effect is poor. Polar head groups of AAS adsorb on coal oxygen structural units of OC through hydrogen bonding, while the carbon ring structural units of OC can be adsorbed by both polar head group and non-polar carbon chain of AAS through intermolecular forces, but the adsorption state of AAS on OC particle is not steady in aqueous environment. The main adsorption mechanism of AAS on OC is hydrogen bonding and weak intermolecular forces, with intermolecular forces dominating. Results can provide theoretical support for efficient separation and separation of coal slime water and its pharmaceutical design. [ABSTRACT FROM AUTHOR]

[Display omitted] • We simulate the wettability of oxidized coal surface using MD simulation. • We investigate the synergetic adsorption of DDC and DDA on oxidized coal. • Adsorption of DDC can promote the effective adsorption of DDA cations on oxidized coal through dispersion interaction. • Synergistic adsorption of DDC and DDA is beneficial to the efficient separation and settlement of oxidized coal. In order to explore the synergetic adsorption mechanism of nonpolar hydrocarbon oil and cationic amine on OC (oxidized coal) surface, the MD (Molecular Dynamics) simulations were used to simulate the wettability of OC surface and the dynamic characteristics of DDC (Dodecane)/DDA (dodecylamine) adsorption on OC/water interface under different complex conditions. Water molecules in a nano water droplet have strong hydrogen bond adsorption with the OC surface, which is easy to be wetting and spread along the surface to occur strong hydration of OC surface. DDC can adsorb on OC surface well, while DDA cations can not. When DDC and DDA are co-adsorbed on OC surface, can have a synergistic adsorption effect. The synergistic adsorption mechanism is mainly that, after DDC adsorbed on OC surface, its carbon chain will adsorb partial DDA cations through dispersion interaction, thus promoting the effective adsorption of DDA cations on OC surface. Synergistic adsorption of DDC and DDA can not only improve the surface hydrophobicity of OC, but also reduce the surface negative electricity through the adsorption of DDA cations, to achieve the effect of effectively promoting the agglomeration of particles, which is very beneficial to the efficient separation and settlement of oxidized coal. [ABSTRACT FROM AUTHOR]

H 2 O 2 solutions of different concentrations were added to a bituminous coal to obtain samples of different oxidation degrees. Flotation and concentrate screening experiments were conducted. It was found that the yield and ash content of the concentrate both decrease after oxidation and particles finer than 0.074 mm are more likely to be oxidized. Grinding flotation experiments were conducted at grinding time of 10, 20 and 30 min. The size distribution and Zeta potential of samples after grinding were detected. The results showed that grinding can effectively improve flotation performance. The optimum grinding time increases with the oxidation degree. And the relative extent of external and internal oxidation changes with the oxidation degree. [ABSTRACT FROM AUTHOR]

Oxidized coal is usually difficult to float using common oily collectors in a traditional flotation process. In order to float oxidized coal efficiently, this paper proposed a novel flotation process which was named zero-conditioning flotation process. Samples of oxidized anthracite coal were used in flotation tests throughout the paper. Fourier transform infrared spectroscopy (FTIR) was used to indicate the chemical properties of coal samples. A comparison of traditional and zero-conditioning flotation performances of oxidized anthracite coal was investigated. It was found that the zero-conditioning flotation process was suitable for the upgrading of oxidized anthracite coal. Combustible matter recovery in the zero-conditioning flotation process was much higher than that in the traditional flotation process. In addition, concentrate ash content in the zero-conditioning flotation process was a little lower than that in the traditional flotation process. [ABSTRACT FROM AUTHOR]

XPS was used to indicate the difference in surface properties between fresh and oxidized coals. XPS results showed that fresh coal had much more C C and C H groups than oxidized coal. In contrast, oxidized coal had much more C O, C O and O C O groups than fresh coal. Oxidized coal had higher ash content than fresh coal and oxidized coal surface had more ash minerals than fresh coal surface. The contact angle of fresh coal was much higher than that of oxidized coal, and hence oxidized coal was more hydrophilic than fresh coal. Flotation behavior of different size fractions of fresh and oxidized coals at different collector dosages were investigated in an experimental flotation cell. Flotation results showed that combustible matter recovery of oxidized coal was much lower than that of fresh coal. Combustible matter recovery decreased with the increase of particle size. Oxidation processes had much more negative effect on the flotation of coarser coals than the flotation of finer coals. The flotation behavior of oxidized coal may be enhanced by the increasing of collector dosage. Furthermore, a lower hydrophobic property makes larger oxidized coals (especially for the coal size more than 0.125 mm) more difficult to float. Reducing coal particle size should be suitable for oxidized coal flotation. [ABSTRACT FROM AUTHOR]