Combustible Recovery Research Articles

The flotation deashing separation performance of high-ash fine coal-slime using humic acid depressant and insights to its depressant mechanism

Effective inhibition of clay minerals remains a challenge in the flotation separation of fine coal with high ash content. The quest for efficient, environmentally friendly, and cost-effective depressants to improve the flotation efficiency of fine coal-slime has become a focus of current research. Humic acid (HA), a macromolecular organic compound widely present in nature, is known for its non-toxic, low-cost, and biodegradable properties. In this study, the potential selective depressant HA was utilized to enhance the recovery of low-ash clean coal in the coal-kaolinite system. Adsorption and inhibition mechanisms were explored through contact angle measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) methods. Flotation tests demonstrated that HA, at varying dosages, significantly increased combustible matter recovery while reducing ash recovery compared to conventional flotation. Optimal conditions, with an HA dosage of 750 g/t, resulted in a combustible matter recovery of 40.56 % and an ash content of 17.77 % in the clean coal. Contact angle measurements confirmed that high-dosage HA significantly reduces the coal surface hydrophobicity, resulting in a rapid decline in the recovery of combustible matter. It did not significantly alter the contact angle of kaolinite, however, across the entire range of HA dosages. Furthermore, XPS studies revealed that the reduction in hydrophobicity on the coal surface after HA adsorption is mainly attributed to the coverage of surface carbon–carbon/carbon-hydrogen groups (C–C/C–H) and the increased presence of carbonyl groups (C = O). Additionally, the study found that HA predominantly adsorbs on the Si-OH groups of kaolinite. Finally, AFM results showed that the primary mechanism underlying the altered heterocoagulation behavior between coal and kaolinite is HA’s effect on their interaction forces. The optimal flotation results achieved at the HA dosage of 750 g/t are primarily attributed to the consistent presence of repulsive forces during the approach process and weak adhesion forces during the retraction process between coal and kaolinite, thus reducing kaolinite coating on the coal surface. These findings provide a promising direction for utilizing HA to enhance flotation deashing of high-ash coal-slime.

Mechanism analysis on carbon-ash separation of coal gasification fine slag by high internal phase emulsion collector

ABSTRACT Coal gasification slag is a solid waste produced in modern coal chemical industry, its mixed characteristics of residual carbon and ash materials restrict its resource utilization. This study focused on improving the flotation effect of coal gasification slag and reducing the consumption of flotation reagents, a water in oil type high internal phase emulsion collector was prepared, and the microstructure, rheology, stability, particle size and other characteristics of the emulsion collector were analyzed. By comparing with the flotation effect of conventional kerosene collector, when the amount of organic liquid is basically equal, the ash content of the tailings increased by 4.02%, the yield of concentrate increased by 9.79% and the recovery of combustible matter increased by 11.11%. When the combustible matter recovery is similar, the emulsion collector can save 13.40% of kerosene. The flotation kinetics test shows that the emulsion collector can significantly improve the flotation speed. By analyzing the flocculating ability of emulsion collectors, emulsion collectors can significantly improve the flocculating ability of particles, thereby improving the flotation effect. The research results have certain guiding significance for improving the flotation efficiency of coal gasification slag.

Impact of grinding media shape on the dissociation characteristics and flotation behavior of coking coal middlings

The effective dissociation of feed materials has a major impact on the mineral flotation recovery performance in the mineral processing field. Coking coal middlings is difficult to be effectively dissociated due to its complex internal gangue distribution characteristics. The aim of this paper is to compare and evaluate the performance of ball versus hexagonal prism media for the coking coal middlings comminution by point contact and line-surface contact. The results of the grinding tests show that hexagonal prism could result in a more uniform coal particle size distribution, less over-grinding and better selective dissociation effect comparing with ball. The results of the particle shape coefficient indicate the hexagonal prism milled product has a sphericity (Rs) of 0.90 and an elongation (EW) of 1.69, which is more slender than the ball milled product (Rs = 0.94, EW = 1.47). Flotation tests showed that the hexagonal prism milled product was more hydrophobic with a wrap angle of 185° compared to the ball milled product at 121°. Meanwhile, the TSI value of the hexagonal prism milled product is 80.500, which is lower than the 82.608 TSI value of the ball milled product, indicating that the flotation system of the hexagonal prism mill product is more stable. Under the same flotation test conditions, the combustible matter recovery rate of the hexagonal prism milled product was 5.08 % higher than that of the ball milled product.

Exploration on the mechanism of enhancing flotation of long-flame coal by diesel modification via oxidation

Low-rank coal is naturally hydrophilic, and the traditional hydrocarbon collectors often have poor performance in its flotation. In this study, the modification of diesel was conducted using an instantaneous gasification-oxidation-condensation device for the expected improvement of collector’s performance. Experimental analyses and interfacial interaction calculation were performed to explore the mechanism of enhancing flotation of long-flame coal by diesel modification. It indicated that the flotation of coal sample can be greatly enhanced by the modified diesel, and a combustible matter recovery of 90.52 % could be attained only consuming 6 kg/t of modified diesel which was far better than the flotation effect consuming 100 kg/t of common diesel. The improved flotation effect of the coal sample could be attributed to the increased polarity of collector from 0.48 % to 9.76 % resulted from the newly added oxygenated functional groups after the oxidation of diesel, which significantly enhanced the adsorption capacity of the collector on the long-flame coal surface reflected by the FTIR and XPS analyses. Furthermore, the calculated results of interfacial interaction between the coal sample and the common/modified diesel suggested that the efficient adsorption of modified diesel on the coal sample was achieved through the bridging role acted by water molecules. This research may give some insight into enhancing flotation of low-rank coal.

Comparative analysis of cotton oil and fuel oil as collectors in hard coal flotation: Toward sustainable mining practices

ABSTRACT This study investigates cotton oil as an environmentally friendly alternative to fuel oil in the flotation of hard coal from the Zonguldak Kozlu Region, Türkiye. We compared their performance across various operational parameters using a Denver-type flotation machine. Results showed that cotton oil achieved superior combustible recovery in most scenarios. At 1000 g/t, cotton oil achieved 97% combustible recovery compared to fuel oil’s 90% at 2000 g/t. Cotton oil maintained high recovery (94–95%) over a broader pH range (2–10) compared to fuel oil’s stable 90% from pH 2–8. However, fuel oil demonstrated better ash rejection, achieving 50% rejection at 2% solids compared to cotton oil’s 36%. Both oils performed optimally at pH 8.25 and 10% solid ratio. Cotton oil maintained 93% recovery at 1050 rpm compared to fuel oil’s 89% and exhibited less sensitivity to frother concentration. FTIR and zeta potential analyses revealed distinct interaction mechanisms, with cotton oil showing stronger adsorption on coal surfaces. This research contributes to developing sustainable practices in coal beneficiation, highlighting the trade-offs between combustible recovery and ash rejection when choosing between these collectors for industrial applications.

Sustainable strategy for high-efficiency flotation of fine low-rank coal: Eco-friendly composite collector prepared from waste oil

This study prepared an innovative composite collector of waste oil (WO) in kitchen waste, suitable for fine low-rank coal (LRC) flotation. It systematically investigated the potential of the composite collector to recover clean coal from fine LRC by froth flotation. The flotation mechanism of fine LRC particles could be elucidated by the combination of FTIR and XPS. The flotation results demonstrated that the WO composite collector significantly increased the yield and combustible recovery of the fine LRC flotation concentrate. Notably, as the dosage of the WO composite collector increased from 200 to 1000 g/t, the clean coal yield rose from 20.08 % to 74.60 %, while the combustible recovery improved from 24.89 % to 91.19 %. FTIR and XPS analyses indicated that the WO composite collector containing C-H/C-C groups adhered to the surface of the coal particles, which enhanced the hydrophobicity of the particles and improved the flotation efficiency.

Exploration on performance of the oxidized collector in the low-rank coal flotation

ABSTRACT Low-rank coal can be concentrated by flotation process using oxidized kerosene, which can improve flotation performance. However, the difference between oxidized kerosene and conventional collector with the same dosage on flotation performance is little known. In this study, the FTIR spectrum, GC-MS analysis and surfaces tension of collectors were analyzed for comparison the physical and chemical properties. The results showed the kerosene appearance of the short hydrocarbon chains with oxygen groups. The surface tension of kerosene is reduced by 21.99 mm/m after oxidation process. The contact angle and flotation tests were used for the kerosene, mixture including oxidized kerosene and kerosene with a mass ratio of 1:1, as well as oxidized kerosene for evaluating the performance. The results showed that the order of coal surface contact angle is that kerosene > mixture > oxidized kerosene. In addition, flotation tests revealed that mixture had superior flotation performance compared with kerosene and oxidized kerosene. The oxidized kerosene could significantly diminish the ash content of flotation concentrates, and the combustible matter recovery of clean coal with mixture is nearly 16.50% higher than that with kerosene. These results constitute a substantial step forward in technical development for resource recycling of low-rank coal.

Deep recovery of clean coal from coking middlings: Pre-separation in liquid-solid fluidized bed and subsequent flotation

The coking middlings remaining after the production of coking coal contain a significant amount of clean coal, which has the high economic and environmental value if it can be effectively enriched. To improve resource utilization and avoid the negative environmental impacts of coking middlings, this study evaluated a new comprehensive separation process (i.e., pre-gravity separation in liquid-solid fluidized bed and subsequent flotation) to achieve high-yield recovery of clean coal from coking middlings. Preliminary enrichment by gravity separation achieved a combustible recovery rate, a clean-coal yield, and an ash content of 64.43 %, 49.62 %, and 15.89 %, respectively. This product was ground for 20 min to further dissociate clean coal and inorganic minerals and was further enriched by flotation separation. Under optimal flotation conditions (rotational speed, 2200 rpm; mass of collector, 2 kg/t; mass of frother, 200 g/t; and pulp concentration, 40 g/L), a clean-coal combustible recovery rate of 84.19 % was achieved. Overall, the comprehensive separation process achieved a clean-coal product with a high yield of 38.82 % and low ash content of 9.08 %, which is suitable for use as coking coal for steel plants. The tailings, with an ash content of 51.49 % and a yield of 61.18 %, are suitable as fuel for power plants. Therefore, the comprehensive separation process provides good economic benefits.

Investigation on the flotation of a mixed collector and its mechanism for enhancing low-rank coal flotation: Effect of micro adsorption and its interaction with gangue particle

The flotation effect of the association formed by dodecyl trimethyl ammonium bromide (DTAB) and dodecyl alcohol polyoxyethylene ether sodium sulfate (AES), and nonpolar kerosene mixed collectors on low-rank coal (LRC) was investigated. The results show that the combustible matter recovery was significantly improved compared with a single kerosene from 49.88% to 74.97% when the the mixed collector was used, while concentrate ash content decreased from 9.76% to 8.57% simultaneously. The utilization of the mixed collector not only enhanced the surface hydrophobicity of organic particles but also facilitated the intercoalescence among them, thereby reducing the ash content of concentrate during flotation. The molecular dynamics simulation (MDS) results show that the effect of the mixed collector on the surface of LRC is mainly the electrostatic interaction and hydrogen bonding between the collector molecules and the surface molecules of LRC, which makes the polar molecules in the collector closely adsorbed on the surface of LRC.

Flotation of ultra-low ash coal combined with ultrasonic pretreatment

ABSTRACT Ultra-low ash coal is an essential clean energy and material. The preparation of ultra-low ash coal by flotation is facing challenges due to the inherent drawbacks. This work aims to enhance the flotation efficiency of ultra-low ash coal by ultrasonic pretreatment. Timed-release flotation experiments were conducted with ultrasonic pretreatment before and after collector addition. The results showed that the recovery and combustible recovery and flotation perfect index of clean coal increased after ultrasonic pretreatment. Additionally, the flotation circuits can reduce from three to two times to obtain clean coal with ash content around 5%. The particle size distribution of coal varied from unimodal to bimodal after ultrasonic pretreatment no matter whether collector was added, indicating that ultrasonic had both dispersing and flocculation effects. Scanning electron microscope (SEM) analysis illustrated that the surface of coal was cleaned due to the ultra-fine gangue particles coated on coal surface was dispersed, and the flocculation of low-ash coal particles was promoted after ultrasonic pretreatment. Consequently, the ultra-low ash coal with higher recovery and quality could be obtained with simplified circuits.

Elaboration of an Economic and Efficient Pulp Conditioning Method for a Low-Quality Coarse Coal Slime

ABSTRACT The high energy consumption of high-intensity conditioning (HIC) limits the popularization of this technology although it has been validated as an effective way to improve flotation. In this study, an economic and efficient pulp conditioning method for a low-quality coarse coal slime was innovatively proposed by comparing four different conditioning-flotation processes. It is found that the energy consumption per unit combustible recovery of conditioning using emulsified diesel was reduced by 8.3% compared with that of the conventional conditioning. This is attributed to the energy reduction of the optimum conditioning speed decreased from 2100 rpm to 1300 rpm, and a negligible energy consumed in the preparation of emulsified diesel. Results showed that when using an emulsified diesel, flotation performance was further improved and less affected by conditioning speed but more by conditioning time. Moreover, flotation is no longer affected by the degree of surface cleaning. It was indicated that the dispersion of collector is crucial for HIC. This study provides a technical reference for the development of economic and efficient conditioning equipment.

Study of the effect of airflow rate and agitation speed on entrainment of ash particles in bottom ash flotation

To enhance the recovery and grade of the final product, reducing the entrainment of the hydrophilic particles during flotation is critical. We conducted the improvement of entrainment to reduce the amount of ash in the concentrate with the purpose of recovering high-quality unburned carbon from the bottom ash and reusing it as fuel in power plant. In this study, we investigated the effects of airflow rate and agitation speed on the entrainment of hydrophilic particles. In the self-aerating flotation machine, it was difficult to independently control the agitation speed and airflow rate, resulting in the degree of entrainment of 0.74. By independently controlling the airflow in which hydrophobic particles can float under conditions of the degree of entrainment with 0.7 (low agitation speed: 900 rpm), the combustible recovery and unburned carbon content of concentrate were 93.71% and 93.60%, respectively. The degree of entrainment was found to be 0.57, and entrainment could be minimized through independent control of airflow rate and agitation speed. To minimize entrainment, it is effective to inject air that can suspend hydrophobic particles in a low agitation speed condition.

Cleaning of fine-grained lignite by two-stage hydrophobic flocculation using different waste oils

ABSTRACT In this study, the conditions for obtaining clean coal from fine-grained lignite suspensions by two-stage hydrophobic flocculation using different waste oils were investigated. Waste vegetable oil, waste hydraulic oil and waste engine oil were chosen as bridging liquids for hydrophobic flocculation tests. During the studies, sodium silicate was used as the dispersant. Acetone was used at each stage to clean the floc obtained from the agglomeration process. The ash content (%) and combustible recoveries (CR, %) of the floc obtained at the end of each experiment were determined. In addition, contact angle (θ) and calorific values (kcal/kg) were measured and the results were evaluated in detail. At the end of the cleaning stages, low ash clean coal was obtained with a very high combustible recovery. In addition, it was observed that the calorific values increased considerably from 5128 to 5772,5558 to 6304 and 5447 to 5732 using waste vegetable oil, waste hydraulic oil and waste engine oil, respectively.

The impact of metal ions on flotation of coal gasification fine slag: an experimental study

ABSTRACT This study investigates the flotation performance of coal gasification fine slag in the presence of metal ions with different valences. The impact of metal ions on the surface topography, wettability, zeta potential, functional group, and particle size distribution of coal gasification fine slag were analyzed. The results demonstrated that K+, Ca2+, Mg2+, and Al3+ all have a positive effect on flotation, with Al3+ being particularly effective. At a concentration of 0.2 mol/L, Al3+ increased the recovery of combustible matter in coal gasification fine slag from 66.70% to 91.05% compared to deionized water. Metal ions reduce the absolute value of the gasification fine slag potential, compress its double layer while increasing its surface hydrophobicity. Higher ion concentration leads to a closer-to-zero potential and increased hydrophobicity. Additionally, Al3+ promote diesel adsorption onto coal gasification fine slag. This work explains the effects of metal ions on coal gasification fine slag flotation.

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

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

Performance Comparison of Waste Cooking Oil on Coal Slime Flotation with Sunflower Oil and Gas Oil

This study explores the potential use of waste cooking sunflower oil (WSO) as an eco-friendly collector for coal slime flotation. WSO and coal slime are both wastes and are hazardous to human health and the environment, if not disposed of properly. In this study, co-disposal of the two wastes was investigated; a gas oil (petroleum derived oil) and crude sunflower oil (CSO) were used for collector efficiency comparisons. This study also presents a green, low-cost and environmentally friendly alternative. Kinetic flotation tests were carried out to study the flotation selectivity, flammability and combustible recovery. Contact angle measurements were performed with 3 different oils (CSO, WSO and gas oil) by sessile drop technique to determine the hydrophobicity and surface properties of coal. Fourier-transform infrared (FTIR) spectroscopy was utilized to analyze the chemical composition of both waste oil and coal samples. 
 Keywords: Sunflower oil, waste cooking oil, gas oil, coal slime, flotation

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

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

Determination of carbon-14 in marine biota using oxidation combustion and gel suspension liquid scintillation counting

In this study, we report a new analytical method for determination of 14C in marine biota utilizing oxidation combustion separation combined with CaCO3 suspension of precipitates for liquid scintillation counting (LSC). The main factors affecting the oxidation combustion efficiency of tube combustion furnace and the counting efficiency of the LSC were systematically investigated and optimized. Under the optimal combustion conditions, the combustion recovery of carbon ranged from 85.6 % to 92.4 % for five marine samples. And the method achieved a detection limit of 0.13 Bq/g for 14C and repeatability of 3.9–9.1 %. The analytical turnover time was 6 h, and up to six samples could be processed simultaneously. Assessment of uncertainty components showed that the uncertainty in counting was the largest contributor, followed by combustion recovery and counting efficiency. The developed method enables reliable measurement of 14C in marine biota, providing valuable analytical tool for risk assessment purposes.

Recovery of residual carbon from coal gasification fine slag by a combined gravity separation-flotation process

Recovering inner residual carbon is important for fully utilizing coal gasification fine slag (CGFS) resources. In this study, we adopted a combined gravity-separation and flotation process to efficiently recover residual carbon by considering the characteristics of the CGFS and optimizing the operating factors of the process. CGFS is principally a mixture of residual carbon and ash, with low-density particles containing more of the former. Accordingly, residual carbon is preliminarily enriched by gravity separation, in which gas velocity (vg) and water velocity (vw) significantly impact separation efficiency, followed by feed volume (m). The residual carbon in the initial concentrate was preliminarily enriched (i.e., loss on ignition (LOI): 55.90%; combustible recovery (Ro): 72.36%) under appropriate operating conditions (i.e., vw = 0.04 m/s, vg = 3 m/s, m = 150 g). Moreover, the quality of the flotation concentrate was most influenced by collector dosage (mc), followed by aeration rate (η), frother dosage (mf), stirring speed (w), and grinding time (t) during flotation of the primary concentrate. The flotation concentrate exhibited LOI and Ro values of 90.95% and 50.34%, respectively, under the optimal flotation conditions (i.e., mc = 20 kg/t, mf = 15 kg/t, w = 2600 rad/min, η = 200 L/h, t = 360 s); it has a high residual carbon content and is an ideal raw material for preparing fuels or carbon materials.

Investigation on coal floatability and pore characteristics using acidification method

This paper investigated the relationship between coal floatability and pore characteristics from the perspective of froth flotation. Three types of coal samples with different ash contents were pretreated with HCl and acetic acid solutions to alter the pore features. The X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) measurements were conducted to specify the reactions that happened in acidification. The batch flotation and contact angle measurements were conducted to evaluate the floatability of the coal samples. The liquid nitrogen adsorption and mercury intrusion porosimetry (MIP) measurements were applied to measure the pore characteristics of the coal. The acidification treatment partially dissolved mineral components and organic functional groups on the coal surface but did not change the types of the major functional groups. The sedimentation of liberated fine minerals on coal pores caused the decrease in pore volume. The BET specific surface area of the three coal samples after acidification was found to have consistent negative relations with the flotation recovery and combustible recovery rate. This indicated the adverse impact of porosity in coal flotation. The floatability of coal is mainly influenced by the pores at the size fraction of 1–20 μm by pore volume. The nano-scale size pore and fine mineral inside the micron pore increased the water-wettability and resulted in the low floatability of coal.