Preparation of ultra-low ash coal from non-stick coal by using high-speed shear-selective agglomeration flotation

doi:10.21203/rs.3.rs-4869122/v1

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Preparation of ultra-low ash coal from non-stick coal by using high-speed shear-selective agglomeration flotation

https://doi.org/10.21203/rs.3.rs-4869122/v1

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Coal contains a large amount of ash, resulting in coal combustion of nitrogen oxides, sulfur dioxide and other heavy metal particles have a serious impact on the ecological environment. The preparation of ultra-low ash coal has become a major means to improve the utilization rate of coal resources. Therefore, this study takes a non-stick coal as the research object. The optimum flotation process and pharmaceutical regime were explored by high-speed shear hydrophobic agglomerate flotation. The results demonstrate that non-stick coal by high-speed shear hydrophobic agglomerate flotation can reduce the ash content of the original coal by 10.5–1.49%, with a yield of up to 54.93%. In addition, the experiment also found that high-speed stirring can overcome the energy barrier of particle interaction, making the hydrophobic particles more dense, which is more conducive to effectively separating clean coal and inorganic minerals. This study provides an effective way for high value-added utilization of coal, and provides reference for realizing the fine and clean utilization of coal resources.

non-stick coal

ultra-low ash coal

flotation

deep deashing

high-speed shear

selective agglomeration flotation

Coal is a significant contributor to the global energy mix, serving as a primary source of electricity generation. Coal accounts for about 25–35% of the world's fuel supply(Xia et al. 2015; Li et al. 2022a). In China, for example, more than 56.2% of China's energy comes from coal, and coal resources have always been dominant (Li et al. 2018; Li et al. 2022b). According to the storage conditions of coal and actual consumption demand, the amount of coal mining continues to increase, resulting in a gradual reduction in the quantity of high-quality coal reserves (Li et al. 2018; Yang et al. 2020). In light of the adjustment of national coal industry-related policies and the rapid expansion of the national economy, there has been a notable surge in the demand for high-quality coal resources.

Therefore, the importance of high value-added utilization of coal resources is becoming more and more prominent (Wang et al. 2020). The in situ production of ultra-low ash coal represents the most effective means to maximize the utilization rate of coal resources. Concurrently, this approach represents an efficacious methodology for the environmentally responsible utilization of coal resources (Yu et al. 2022; Zhang et al. 2023; Shen et al. 2022)..

Ultra-low ash coal has very low ash content and high chemical reaction activity. Its direct combustion can reduce the emission of soot, SO₂, CO₂ and other air pollutants. Ultra-low ash coal can not only replace petroleum as a chemical fuel, but also as a precursor of carbon materials such as coal-based carbon materials and chemical fuels(Ramudzwagi et al. 2020). It is widely used in oil-water coal slurry, high-grade activated carbon preparation, carbon black, coal-based carbon materials, chemical fuels, IGCC and other technologies. Consequently, it is imperative to purify coal in order to fully realize its potential as an industrial material (Juneja et al. 2018; Wang et al.). The most frequently employed preparation techniques for ultra-low ash coal are physical and chemical methods(Cheng et al. 2020; Singh et al. 2020), among which foam flotation is the most economical and reliable method for preparing ultra-low ash coal (Shi et al. 2018). Nevertheless, it is challenging to manufacture concentrators with a carbon content exceeding 95% through traditional flotation techniques (Aslan et al. 2008; Li and Liu 2014). One of the key reasons for this is that the presence of fine granular coal gangue (such as quartz, kaolinite, etc.) in the slime will reduce the floatation effectiveness through the floc coating or water entailing (Pascoe and Doherty 1997; Raju et al. 1991; Ozkan et al. 2006), which makes the secure separation of coal and gangue mineral particles a significant challenge. Accordingly, it is necessary to grind the coal mine into ultrafine particles before flotation to enable the separation of the gangue from the coal. In contrast, flotation is largely contingent upon the particle size of the mineral. If the particle size is too fine (< 10 µm), it will lead to a sharp decline in flotation performance. This explains why high grade ultra-low ash coal is not obtained by conventional flotation(Yoon 2000).

In order to resolve this issue, Warren initially proposed a shear flocculation method (Warren 1975; Bilgen and Wills 1991). This method separates the mineral from other impurities through a sufficiently large shear field. Additionally, the material is capable of selectively aggregating extremely fine particles to form flocs that are sufficiently stable to withstand in situ turbulent conditions in mineral processing applications. A large number of scholars have carried out research on shear flocculation experiments. For example, Ni put forth a methodology combining high-speed shear flocculation with flotation for the beneficiation of ultra-fine crystal ink. The impact of high-speed shear flocculation was examined in terms of its effect on the flotation kinetics of MG (Ni et al. 2022). Ozkan took lapis lazuli as the research object and compared the shear flocculation experiments of two different surfactants (sodium oleate and tallow amine acetate (TAA)) to explore the effects of pH value, dosage of active agent, stirring time and stirring speed on cations(Ozkan and Yekeler 2004). In order to ascertain the optimal process for enriching B₂O₃ in fine boron ore, containing coal colemanite, Ucbeyiay studied the effects of shear flocculation, two-stage shear flocculation, flotation and flocculation flotation. The results show that shear flocculation can effectively improve the recovery rate of concentrate, especially the two-stage shear flocculation can recover 38.65% of B₂O₃(Ucbeyiay and Ozkan 2014). In addition, it has been found that shear flocculation, especially high-speed shear, helps to improve flotation performance. However, most of the previous studies focused on the purification or flotation of graphite, scheelite, quartz and other minerals by shear flocculation. However, there appears to have been little scientific investigation of the preparation of ultra-low ash coal by shear flocculation. The mechanism of carbon-ash separation in ultra-low ash coal has not been explained.

Therefore, based on the traditional flotation production of ultra-low ash coal, this paper investigates the influence of high-speed shear flocculation flotation on the production of ultra-low ash coal. The effects of grinding system, chemical system, process flow and shear rate on flotation performance were discussed. The pulp was pretreated with high stirring speed and the flotation performance of the two processes was compared. Finally, according to the particle size dispersion of aggregates, the mechanism of shear flocculation to enhance the performance of ultra-low ash coal is explained, which provides an experimental basis for the future development of ultra-low ash coal.

2.1 Materials

Raw ore samples were taken from Dongsheng coal field in Shenfu, Shaanxi Province, China. The raw ore is crushed by a multifunctional mill (2500C, Yongkang Hongsun Electromechanical Co., LTD.), and further grinned by a disc vibration grinding instrument (SDPP3*100, Hunan Sande Technology Co., LTD.) and a planetary ball mill (JX-2G, Shanghai Jingxin Industrial Development Co., LTD.) to make its particle size around 0.074mm. The density of the crushed coal sample is < 1.4g/cm³ through the large float and sink experiment. Deionized water with pH = 6.9 was used for flotation experiment, laser force particle size test and contact Angle test.

Experimental agents include collector, foaming agent and electrolyte (as shown in Table 1). The collectors are diesel oil, kerosene, emulsified kerosene, and MJ. The foaming agent is MIBC. The flocculant is polyferric sulfate. The reagents are purchased from Haoxin Chemical Reagent Factory in Dongguan, Guangdong Province, China.

Table 1

The principal reagents employed in the experiment
Reagent Names	Chemical Formula	Purity	Usage
Diesel oil	Hydrocarbon mixtures	Industrial	Collector
Kerosene	Hydrocarbon mixtures	Industrial	Collector
Emulsified kerosene	Hydrocarbon mixtures	Industrial	Collector
MJ (Compound drug)	Hydrocarbon mixtures	Industrial	Collector
MIBC	C₆H₁₄O	Analytical Pure	Frother
Iron sesquisulfate	FeH₄O₅S	Analytical Pure	Flocculant

2.2 Flotation experiment

In this experiment, the stepwise desliming flotation experiment is used. One is conventional flotation, the other is high-speed shear flocculation flotation experiment. In conventional flotation, a certain amount of coal sample is weighed and poured into 1.0-L single-tank flotation cell (XDF1, Jiangxi Province Shicheng County Haoxin Mining Machinery Factory). First, the samples were mixed and stirred in the flotation cell for 2 min. Secondly, the appropriate amount of collector was added to the pulp and it was stirred for two minutes. Subsequently, the foaming agent was added and continued to be stirred for 40 seconds. Air was then introduced, and foam samples were collected for a period of three minutes. The foam sample scraped out is labeled as concentrate 1 and the material left in the flotation cell is tailings 1(as shown in Fig. 1).

On the basis of conventional flotation, high speed shear flocculation flotation is an experiment in which pulp is pretreated and then flotation separation is carried out. The pulp pretreatment process includes the fine dissociation of the feed, the mixing and mixing of the coal water slurry in the high-speed shear mixing and dispersing machine (ESFS-400, Shanghai Yishi Industrial Co., LTD.), and the addition of flotation drugs. The process of flotation separation is to pour the pretreated pulp into the flotation tank for flotation separation. The flotation process is described in the above paragraph and will not be repeated in this paragraph. The present study primarily examines the impact of mechanical stirring speed and stirring time on flotation tests (the experimental process is illustrated in Fig. 2).

The pulp pretreatment process includes the fine dissociation of the feed, the mixing and mixing of the coal water slurry in the high-speed shear mixing and dispersing machine (ESFS-400, Shanghai Yishi Industrial Co., LTD.) and the addition of flotation drugs.

2.3 Properties of non-stick coal samples

Table 2 shows the results of the chemical composition analysis of water, volatile matter and fixed carbon of the non-stick coal sample. The sample in Table 2 has low ash content (10.5%), high fixed carbon content (54.5%) and high volatile content (33.34%). The elements in coal are mainly carbon and oxygen, of which the content of carbon is (60.2%) and oxygen is (15.66%). Therefore, low ash, low sulfur and high carbon characteristics are present in the coal sample. The XRD pattern is shown in Fig. 3. The results show that the impurities in raw coal mainly consist of quartz, hematite, mica (aluminosilicate), calcite, etc. The content of quartz is high (40.4%), and the content of quick lime is low (4.61%).

Table 2

Industrial analysis and calorific value of bituminous coal samples
Samples	M_ad/%	A_d/%	V_d/%	FC_d/%	C_d/%	H_d/%	O_d/%	N_d/%	S_t,d/%
Contents	0.66	10.5	33.34	54.5	60.2	9.96	15.66	3.68	0.44

In addition, scanning electron microscopy and Fourier infrared spectrometer were used to observe the surface morphology, seam embedding characteristics and surface functional groups of coal samples, so as to analyze the flotability of coal (as shown in Fig. 3). (Hao Changsheng et al., 2022, Zhang Chao et al., 2022). From Fig. 4(a) it can be seen that the inorganic minerals in the raw coal are present in granular, lamellar or clump form on the particle surface or in fractures. Among them, inorganic minerals mainly include quartz and silicaluminate (the occurrence state is shown by the marks in the Fig. 4(a)).

The Fourier infrared spectrum is shown in Fig. 4(b). This shows that the absorption peak of the hydroxyl group of -OH is at wave number 3755 cm^− 1. The absorption peak of the H-bond stretching vibration of -OH is at wave number 3431 cm^− 1. The -CH₃ of cycloalkanes or aliphatic hydrocarbons is at 2860 cm^− 1. The wave number 1595 cm^− 1 is the vibration absorption peak of the stretching of the C-O-C bond. 1353 cm^− 1 is the absorption peak of the methylene stretching vibration or the anti-symmetric bending vibration of the methyl groups. The absorption peak of the C-H stretched vibration of the aromatic ring is around 769 cm^− 1. From the above analysis, it can be seen that there are hydrophobic functional groups of aromatic ring C-H and -CH₃ as well as hydrophilic mineral and -OH functional groups in the coal samples.

3.1 Effect of various conditions on the preparation of ultra-low ash coal by conventional flotation

Experimental studies of pulp concentration, agitation speed and flotation reagents were carried out for investigating the effect of various factors on the preparation of low ash coal. The initial flotation indicators are as follows: stirring speed of 2000 r/min, air charging capacity of 0.25m³ /h, pulp concentration of 60 g/L, diesel oil of 3 kg/t, and MIBC dosage of 1 kg/t. The results of the experiment are shown in Fig. 5 below.

In Figure (a), the yield of concentrate shows a different trend with the increase of pulp concentration. When the concentration of the pulp is 50 g/L, the yield of the concentrate reaches a maximum of 68.63% and the corresponding ash content is 3.1%. Figure (b) shows that at low stirring speed the concentrate yield increases significantly with increasing stirring speed and then decreases slightly. At the rotational speed of 2800 r/min, the lowest ash content of the concentrate is 3%, and the corresponding yield is 68.77%. In the flotation process, the chemical system has a crucial effect on the flotation effect. One of the important reasons is that flotation reagents are the most flexible, effective and convenient means to control mineral flotation behavior. A large number of stable bubbles obtained by flotation agents is also a prerequisite for efficient flotation. To ascertain the impact of collector type on flotation efficacy, diesel oil, kerosene, emulsified kerosene and MJ were selected for flotation experiment. The results demonstrated that the separation effect of kerosene was the worst under the same dosage of chemicals (as shown in Figure c). The ash content of the concentrate exhibits slight variations under the influence of the three types of collectors. In contrast, the yield displays considerable fluctuations. The yield of concentrates combined with MJ, emulsified kerosene and diesel oil are 82.86%, 79.63% and 68.77%, and the corresponding concentrates ash content are 3.22%, 2.92% and 3.31%. In summary, emulsified kerosene is the best collector.

Emulsified kerosene was selected as the collector in the experiment, and its dosage was tested with other parameters unchanged (As shown in Figure (d)). A As illustrated in Figure (d), an increase in the dosage of emulsified kerosene from 1 kg/t to 5 kg/t was accompanied by a notable enhancement in the yield of concentrate, accompanied by a reduction in the ash content of the concentrate, which fell from 3.23–2.89% and then rose to 3.53%. The ash content of concentrate should be given priority in preparing ultra-low ash coal. Therefore, emulsified kerosene dosage of 3 kg/t was selected in the experiment. In figure (e), it can be observed that the yield of the concentrate increases in direct proportion to the quantity of MIBC. When the dosage of MIBC was 1 kg/t, the yield of the concentrate reached the highest (80.17%) and the ash content reached the lowest (2.48%). Finally, in order to obtain better technical and economic indicators, a step-by-step release process is adopted (flotation effect is shown in (f)). As illustrated in Figure (f), with the increase of flotation times, the yield and ash content of concentrate continue to decline. After one roughing-three concentrates, the yield of ultra-low ash coal is 69%. This is accompanied by an ash content of 1.93%. This is the optimal flotation condition.

In summary, through the exploration of conventional flotation conditions, the optimal experimental parameters are as follows: The concentration of coal slurry is 50 g/L, the filling capacity is 0.25 m³/h, the stirring speed is 2800 r/min, the collector is emulsified kerosene and the dosage is 3 kg/t, and the dosage of MIBC is 1 kg/t. After one roughing-three concentrates, the ultra-low ash coal with yield of 69% and ash content of 1.93% can be obtained.

3.2 Effect of stirring speed and time on the preparation of ultra-low ash coal by high-speed shear flocculation flotation

Fluid flow can transport particles and provide an environment for flotation, which is one of the extremely important conditions. Strengthening fluid requires the input of external energy, which can be achieved through agitation(Ni et al. 2022; Chen et al. 2017). Stirring can strengthen the force between particles and particles, between agents and particles, so as to enhance the surface hydrophobicity of particles. The input of sufficient kinetic energy enables hydrophobic particles to easily overcome the potential energy barrier and adhere to each other, forming tight aggregates. In addition, the motion caused by the input of external forces can provide conditions for a reasonable balanced distribution of bubbles in the later stage (Yang et al. 2024). When the coal particles become finer, the collision efficiency between bubbles and particles becomes lower, and the recovery rate decreases. Consequently, it is of considerable importance to ascertain the optimal stirring intensity.

The optimal conditions of conventional flotation in the previous chapter are adopted. The results of stirring speed and stirring time on flotation are shown in Fig. 6 (a) and (b). Under high stirring speed conditions, the concentrate yield increases significantly with increasing stirring speed, but decreases slightly at 6000 r/min. The maximum yield (52.23%) and the minimum ash content (1.49%) were reached at 5000 r/min. Concentrate ash content decreased, then increased. Therefore, the aging is best when the pre-mixing time is 20 min.

Based on the above experimental conditions, the dosage of flocculant in the shear flocculation experiment was explored (as shown in Fig. 6 (c)). As the polyferric sulphate dose increased from 0 g/t to 25 g/t, the yield of concentrate increased from 56.78% to the maximum value (59.97%), and the concentrate ash content decreased to the minimum value (1.42%). One of the key findings of this study is the influence of stirring speed and flocculant addition on the preparation of ultra-low ash coal. Flotation performance is significantly better than conventional flotation under high-speed shear conditions. Specifically, under the condition of high stirring speed, coal particles and collectors collide with each other, the contact surface increases, and the small floc forms a dense large floc, thus reducing the adhesion and entrainment of high ash fine mud. However, when the stirring speed is too high, the formed flocs will be destroyed and reorganized, and the entrainment of fine minerals will be increased, resulting in the increase of ash (Nogueira et al. 2023). Appropriate addition of polyferric sulfate makes the impurities such as fine mud in the pulp tend to be stable, and improves the coating of fine mud particles on coal particles and the role of coal particles agglomeration. Thus, the apparent particle size of cleaned coal is increased and the hydrophobic effect of coal is improved.

3.3 Discussion

Scanning electron microscopy (SEM) was used to analyses and quantify the coal samples after conventional flotation and high-speed shear flocculation. The SEM micrographs of the samples are shown in Fig. 7. After high-speed shear flocculation, most of the inorganic minerals such as quartz and silicaluminate are removed. Among them, (a) and (b) are SEM images after conventional flotation. The content of quartz, alumina and calcium oxide in the sample is high (c) and (d) are SEM images after shear flocculation. After high-speed shear pretreatment, the ash component and clay particles in the concentrate are partially removed.

Figure 8 (a) shows the contact angle analysis of the high-speed shear flocculated coal sample. It is evident from the figure that the contact angles of the coal particles initially increase and then decrease as the mechanical stirring intensity increases. Stirring intensity increased from 2000 r/min to 6000 r/min, contact Angle increased from 55.50% to the maximum (80.5%). Subsequently, as the speed is too large, the contact Angle is reduced to 53.5%. This indicates that increasing the mechanical agitation speed can improve the effective collision adsorption of coal particles and chemicals, improving the hydrogen brittleness of the coal surface and facilitating the effective separation of concentrates and inorganic minerals (Yang et al. 2024).

In addition, the effect of increasing shear speed on the pulp will affect the particle size of the aggregate, and this effect difference can be quantified by the particle size distribution of the aggregate (as shown in Fig. 8(b)). When the stirring intensity is 2000 r/min, the maximum average particle size of coal particles is 242µm, and there is insufficient stirring. However, with the agitation intensity increasing to 6000 r/min, the average particle size of coal particles increases first and then decreases. This shows that in the process of hydrophobic agglomeration flotation, with the increase of stirring speed, the probability of effective collision and attachment between particles is increased, and the phenomenon of small particles adhering to large particles or clumping between large particles occurs, which increases the size of the coal particles and improves the recovery rate.

The adsorption of flotation agents is commonly influenced by the surface electrostatic properties of minerals during the flotation process. The examination and regulation of the change in surface electrical properties of minerals represents a significant methodology for the investigation of chemical processes, judge the floatability of minerals and realize the separation of different minerals. The double electric layer on mineral surface affects the separation effect of mineral in many aspects, especially the effect of electrokinetic potential. Therefore, the analysis of electrokinetic potential has practical significance in flotation research.

Figure (c) and (d) are respectively Zeta potential change and infrared analysis of coal. According to the variation trend of Zeta potential, upon increasing the dosage of polyferric sulfate from 0 g/t to 165 g/t, the Zeta potential first decreased from − 21.8mV to -23.5mV, and finally increased to -18.7mV. It shows that SO₄²⁻. FeOH²⁺ and Fe³⁺ plasma exist in the aqueous solution after the addition of polyferric sulfate, which will adsorb onto the surface of the emulsified kerosene or coal, thus changing the surface charge and changing the interaction between them (Cebeci et al., 2002). Specifically, the SO₄²⁻ ion is in equilibrium in an aqueous solution. The adsorption capacity of FeOH²⁺ and Fe³⁺ to coal becomes stronger when the dosage of chemical reagent continues to increase. The dominant role is the positive charge, these cations adsorb on the surface of emulsified kerosene and coal will neutralize part of the negative charge, making the Zeta value larger. As the amount of polyferric sulfate continues to increase, the double electric layer between minerals and coal is compressed, and the gravity becomes larger, resulting in an increase in the ash content of the concentrate (Dong Zilong et al., 2019).

To gain further insight into the impact of the flocculant, FT-IR comparative analysis was performed on PFS without PFS and PFS with different dosage (as illustrated in Fig. 8(d)). A broad absorptive peak associated with the -OH hydroxyl group is observed at a wave number of 3434 cm^− 1. However, after the addition of electrolyte, the peak gradually weakens to disappear, indicating that the addition of polyferric sulfate makes the impurities in the pulp tend to be stable, and the wide absorption peak of the hydrophilic functional group -OH gradually disappears. At the wave number of 1626cm^− 1 is the resonance absorption peak of hydroxyl > C = O or -OH hydroxyl group formed with the hydrogen bond. The wave number of 1035cm^− 1 is the absorption peak of inorganic minerals (Si-O-Si). These two absorption peaks decrease first and then increase. This phenomenon could be caused by the decrease of hydrophilic functional groups and the strong hydrophobicity of coal particles in the process of agglomeration. Upon increasing the dosage of polyferric sulphate from 25g/t to 165g/t, the absorption peaks at the three places were also slightly larger, which was due to the strong hydrophilicity and poor hydrophobicity of coal particles caused by excessive drug dosage. The conclusion obtained is consistent with the above.

Based on the above analysis, the shear flocculation mechanism diagram applied in the experiment in this paper is shown in 9. The turbulent environment of high-speed agitation promotes the dispersion of non-stick coal particles and gangue particles, and makes the flocculant aqueous solution displays selective adhesion to the surface of hydrophobic particles. The energy input from high-speed stirring makes the non-stick coal particles close to each other, increasing the actual collision probability between the particles, and eventually leading to the agglomeration of particles. In addition, high-speed stirring results in the crushing of minerals, which makes the coal particles effectively separate from gangue particles and other inorganic minerals, thereby improving the quality of the aggregates. It can be seen that, when high-speed stirring is employed, the size of the agglomeration formed by the hydrophobic particles increases continuously, and the quality of the agglomeration is also enhanced. The recovery rate of flotation concentrate is significantly influenced by the size of the aggregate particles. Accordingly, improvements in aggregate quality are also a significant contributing factor to the enhancement of concentrate grade.

(1) The averagedensity of raw coal is 1.4 g/cm³, and the averagedash content is 10.5%. Among them, the main inorganic minerals are quartz, hematite, silicaluminate, and calcite. Impurities in the form of 5 ~ 50 µm particles, lamellar or clusters occur on the exterior surface of coal particles or gaps. The coal sample has the characteristics of low ash and low sulfur.

(2) The optimum flotation parameters for preparing ultra-low ash coal by conventional flotation are: The concentration of coal slurry is 50 g/L, the filling capacity is 0.25 m³/h, the stirring speed is 2800 r/min, the collector is emulsified kerosene and the dosage is 3 kg/t, and the dosage of MIBC is 1 kg/t. After one roughing-three concentrates, the ultra-low ash coal with yield of 69% and ash content of 1.93% can be obtained.

(3) Based on the optimal conditions of conventional flotation, the ultra-low ash coal with yield of 54.93% and ash content of 1.49% was obtained when the rotational speed of shear flocculation flotation was 5000 r/min, stirring time was 20 min and the dosage of PFS was 25 g/t. In comparison with raw coal, the ash percentage has been reduced by 9.01%. It meets the requirements of the industry for ultra-low ash coal.

(4) The findings demonstrate that high-speed shear flocculation exerts a noteworthy influence on the preparation of ultra-low ash coal. An increment in the velocity of mechanical stirring can augment the effective collision adsorption of coal granules and chemicals, alter the contact angle of coal samples, improve the wettability of the coal surface, and facilitate the effective separation of concentrate and inorganic minerals. In addition, high-speed stirring can bring energy to the particles, overcome the ‘energy barrier’ of interparticle interaction or the medium resistance caused by particle collision, make the hydrophobic particles more dense, and increase the apparent particle size of coal particles. However, excessive strength will make the liquid film of coal particles attached to the bubble thin, the stability will decrease, the particle desorption rate will increase, and the apparent particle size will become smaller. The outcomes reveal that the preparation of ultra-low ash coal by shear flocculation is an effective beneficiation technology and has great potential for industrial application.

Conflict of interest

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.

Acknowledgments

This research was funded by the National Natural Science Foundation of China (51904096). We are grateful for the support of the National Natural Science Foundation.

Data availability statement

The raw/processed data required to reproduce these findings can’t be shared at this time as the data also forms part of an outgoing study.

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Preparation of ultra-low ash coal from non-stick coal by using high-speed shear-selective agglomeration flotation

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Abstract

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1 Introduction

2 Materials and Methods

2.1 Materials

2.2 Flotation experiment

2.3 Properties of non-stick coal samples

3 Results and Discussion

3.1 Effect of various conditions on the preparation of ultra-low ash coal by conventional flotation

3.3 Discussion

4 Conclusion

Declarations

References

Additional Declarations

Supplementary Files

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Version 1