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1

Enhanced separation efficiency of low–rank coal using waste engine oil as a flotation collector

Li Ming, Xia Yangchao, Guo Fangyu, Rong Guoqiang, Li Guosheng, Xu Baolin, Xing Yaowen, Gui Xiahui

Physicochemical Problems of Mineral Processing

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2020

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Vol. 56, iss. 2

252--263

EN

Because of the rich oxygen-containing functional groups and developed pores on the Surface of low-rank coal, it is difficult to realize efficient separation during low-rank coal flotation using common oil collectors. Waste engine oil (WEO) is abundant in polar oxygen-containing functional groups and could be an alternative collector. In this study, the effect of WEO on low-rank coal floatation was assessed and engine oil (EO) was also used for comparison. The results show that the separation efficiency of low-rank coal can be significantly improved using WEO; additionally, 96.73% of the clean coal yield can be obtained when the WEO dosage was only 4 kg/t. Compared with EO, the bubble–particle induction time in the presence of WEO shortened from 430 to 220 ms. Moreover, more low-rank coal particles were captured and adhered to the bubble surface using WEO, which indicated a higher probability of bubble–particle attachment. Nonpolar components, polar components and metal ions synergistically promote the flotation separation enhancement of low-rank coal using WEO.

2

Tetrahydrofurfuryl-functionalized polystyrene nanoparticles as collectors for low rank coal flotation

An Maoyan, Liao Yinfei, Cao Yijun, Zhao Yifan, Qiu Yuliang

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 2

516--527

EN

In this paper, tetrahydrofurfuryl-functionalized polystyrene nanoparticles (TFPNs) were evaluated as collectors in low-rank coal flotation. A series of TFPNs were prepared by immobilizing tetrahydrofurfuryl groups onto the surface of polystyrene nanoparticles (PNs), and further characterized in terms of their size, shape, surface charge and surface functionalization group concentration (SFGC). The coal flotation performance using TFPNs was compared to that using PNs and diesel oil (DO). The interaction mechanisms between TFPNs and low-rank coal were also discussed. The results show that TFPNs gave higher recovery than that given by PNs and DO. Smaller TFPNs were more effective flotation collectors. The recovery of TFPNs increased firstly and then decreased with SFGC. TFPNs can specifically deposit onto the low-rank coal particles with the hydrogen bonding function between tetrahydrofurfuryl groups and oxygen-containing functional groups, and promote low-rank coal flotation by increasing the hydrophobicity and roughness of coal particle surface with the adsorbed TFPNs. It was demonstrated that TFPNs introduced a new class of collectors for low rank coal flotation.

3

Structure and dynamics of water adsorbed on the lignite surface: Molecular dynamics simulation

You Xiaofang, He Meng, Cao Xiaoqiang, Lyu Xianjun, Li Lin

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 1

10--20

EN

The effects of oxygen-containing functional groups on the structure and dynamic properties of water molecules near a lignite surface were investigated through molecular dynamics (MD) simulations. Because of its complex composition and structure, a graphite surface containing hydroxyl, carboxyl, and carbonyl groups was used to represent the lignite surface model. According to X-ray photoelectron spectroscopic (XPS) results, the composing proportion of hydroxyl, carbonyl and carboxyl is 21:13:6. The density profiles of oxygen and hydrogen atoms indicate that the brown coal surface characteristics influence the structural and dynamic properties of water molecules. The interfacial water is much more ordered than bulk water. The results of the radial distribution functions, mean square displacements, and local self-diffusion coefficients for the water molecules in the vicinity of three oxygen-containing functional groups confirmed that carboxyl groups are the preferential adsorption sites.

4

Molecular simulation study on hydration of low-rank coal particles and formation of hydration film

Xia Yangchao, Yang Zili, Xing Yaowen, Gui Xiahui

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 2

586--596

EN

Water molecules in low-rank coal (LRC) significantly influence its upgrading and utilization. To investigate the hydration of LRC particles and the formation of a hydration film, molecular simulation techniques were innovatively used, including molecular dynamics (MD) simulations and density functional theory (DFT) calculations. The adsorption of water molecules on LRC and various oxygen-containing groups was analyzed. The results show that water molecules adsorb close to the LRC surface and form a large overlapping layer at the LRC/water interface. The radial distribution functions (RDFs) show that the adsorption affinity of water molecules on oxygen-containing sites is stronger than that on carbon-containing sites, and the RDF peaks indicate the existence of a hydration film. Moreover, the differences in adsorption between various oxygen-containing groups depend on both the number of hydrogen bonds and the adsorption distances. The calculated binding energies indicate that the adsorption capacity follows the order carboxyl > phenolic hydroxyl > alcoholic hydroxyl > ether linkage > carbonyl. Experimental results show that a high sorption rate exists between water vapor and LRC samples at the beginning of sorption, which verified the simulation results.

5

Enhancing low-rank coal flotation using a mixture of dodecane and n-valeraldehyde as a collector

Liu Zechen, Liao Yinfei, An Maoyan, Lai Qingteng, Ma Longfei, Qiu Yuliang

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 1

49--57

EN

Low-rank coals are difficult to float using common hydrocarbon oily collectors, such as dodecane and diesel. In this investigation, a mixture of dodecane and n-valeraldehyde was used as a collector to enhance low-rank coal flotation. The changes of the contact angle and surface functional groups of low-rank coal were measured before and after different collectors’ adsorption to indicate its absorption mechanism. Surface tension of different collectors was also measured to identify its spreading performance. The results showed that the flotation performance using the mixture as a collector was much better than that using dodecane or n-valeraldehyde solely. When used the mixture of dodecane and n-valeraldehyde as collector, dodecane primarily covers the hydrophobic sites while n-valeraldehyde primarily covered the hydrophilic sites by hydrogen bond promoting adsorption of dodecane at these sites. There existed synergistic effect between dodecane and n-valeraldehyde. Additionally, n-valeraldehyde can reduce the surface tensions to improve the spreading performance of mixed collector on low-rank coal surface. The improvement both in adsorption and spreading was responsible for the enhancement of low-rank coal flotation by using the mixture.

6

Adsorption behavior and XPS analysis of nonylphenol ethoxylate on low rank coal

You Xiaofang, Ma Chuandong, Li Zhihao, Lyu Xianjun, Li Lin

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 3

721--731

EN

In this work, low rank coal was used for the removal of nonylphenol ethoxylate with fifteen ethylene oxide groups (NPEO15) from aqueous solutions at different contact times, temperatures, and initial adsorbent concentrations. The adsorption isotherms showed good fit with the Langmuir equation. Maximum adsorption capacities calculated at 308, 318, and 328 K were 23.64, 29.41, and 35.71 mg g–1, respectively. The changes in the free energy of adsorption (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were calculated in order to predict the nature of adsorption. The results of the thermodynamic analysis indicated that a spontaneous process took place, driven synergistically by both enthalpy and entropy. The adsorption kinetics of NPEO15 were consistent with a pseudo-second order reaction model. XPS results showed that the oxygen functional groups on the low rank coal surface were significantly covered by NPEO15. Furthermore, while the content of C–C/C–H functional groups increased significantly, that of C–O functional groups decreased after absorption. These results clearly indicate that low rank coal is more hydrophobic and displays better floatability.

7

Thermochemical utilization of low rank coal and flotation concentrate

Gąsior Rafał, Smoliński Adam

Journal of Sustainable Mining

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2019

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Vol. 18, iss. 2

109--111

EN

Flotation concentrates are waste material from coal mine operation. The process of steam gasification seems to be an attractive option for their economic utilization and an alternative to their potential combustion in boilers. The gasification process is characterized by both higher efficiency and lower emission of pollution than conventional combustion systems. In this paper the results of the steam gasification of low rank coal and flotation concentrate into hydrogen-rich gas at the temperature of 800 °C are presented. The reactivity for 50% carbon conversion as well as the maximum reactivity in this process were calculated for the samples studied.

8

Coal Enrichment Methods by Using Microorganisms and Their Metabolites

Deska M., Głodniok M., Ulfig K.

Journal of Ecological Engineering

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2018

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Vol. 19, nr 2

213--220

EN

The aim of this study is to review the literature on the methods of low-rank coal enrichment by using microorganisms and their metabolites. Effective bio-beneficiation technologies for low-rank coals in the future are also suggested throughout this paper. An extensive literature review highlights recent advances in bio-beneficiation technologies for low rank coals. This paper presents the state of the art in the field of the bio-beneficiation technology - carbon leaching with the aid of microorganisms, especially fungi. The knowledge of the low-rank coals leaching is an important step to meet the carbon eco-requirements and improve the economics of mining companies. There are several reasons to investigate microbial activities towards coal. This paper presents the current state of knowledge concerning bioleaching of coal. Thus, in view of the increasing importance of hard coal as a raw material and energy source, it seems hopeful to study the potential of microorganisms to modify the low-rank coal structure.

9

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

Wang S., Tao X.

Gospodarka Surowcami Mineralnymi

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2018

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T. 34, z. 1

69--82

EN

In this paper, flotation performances of low-rank coal were investigated in the 2-ethyl hexanol, DAH (dodecyl amine hydrochloride), and SDS (sodium dodecyl sulfate) solutions, respectively. In order to reduce the heterogeneity and hydrodynamic effects on the hydrophobicity and movement trajectory of low-rank coal particles, respectively, experimental coal samples with low ash content and 0.500–0.250 mm in size fraction were adopted. The XPS result demonstrated that the total silicium and aluminum content of 0.500–0.250 mm size fraction was 1.58%. It was also found that the ash content of the 0.500–0.250 mm size fraction was 1.91%. Therefore, it demonstrated that there were few hydrophilic mineral particles on the coal sample surface. Thus, the heterogeneity effect of hydrophilic mineral particles during sliding process measurements can be ignored. The XPS result also indicated that after the grinding process, the mineral content on the low-rank coal surface was very small, which would play a small role in the hydrophobicity of low-rank coal samples. The flotation results indicated that the hydrophobicity of the low-rank coal particles could be improved by nonionic 2-ethyl hexanol and cation DAH surfactants. Moreover, from the analysis of slip angle velocity, it demonstrated that the flotation responses of low-rank coal were depressed by anionic SDS. Furthermore, it was observed that the slip angle velocity can be used to evaluate the effect of surfactant agents on the flotation performance of low-rank coal while the surfactant concentration was more than 10–6 mol/L.

PL

W niniejszym artykule zbadano właściwości flotacyjne węgla niskiej jakości w roztworach 2-etyloheksanolu, DAH (chlorowodorku dodecylu) i SDS (dodecylosiarczanu sodu). W celu zmniejszenia niejednorodności i skutków hydrodynamicznych hydrofobowości i trajektorii ruchu cząstek węgla niskiej jakości przyjęto do doświadczeń próbki węgla o niskiej zawartości popiołu z klasy ziarnowej 0,500–0,250 mm. Wynik XPS wykazał, że całkowita zawartość krzemu i glinu w klasie ziarnowej 0,500–0,250 mm wynosiła 1,58%. Stwierdzono również, że zawartość popiołu w klasie ziarnowej 0,500–0,250 mm wynosiła 1,91%. W związku z tym wykazano, że na powierzchni próbki węgla znajduje się niewiele hydrofilowych cząstek mineralnych. W ten sposób można pominąć efekt heterogeniczności hydrofilowych cząstek mineralnych podczas pomiarów kąta poślizgu. Wynik XPS wskazał również, że po procesie mielenia zawartość minerałów na powierzchni węgla niskiej jakości była bardzo mała, dlatego też występuje słabe oddziaływanie na hydrofobowość tych próbek. Wyniki flotacji wskazują, że hydrofobowość cząstek węgla niskiej jakości można poprawić za pomocą niejonowego 2-etyloheksanolu i kationowych środków powierzchniowo czynnych DAH. Analiza prędkości kąta poślizgu wykazuje, że flotacja węgla niskiej jakości została obniżona przez SDS. Ponadto zaobserwowano, że prędkość kąta poślizgu może być wykorzystana do oceny wpływu środków powierzchniowo czynnych na sprawność flotacji węgla niskiej jakości, gdy ich stężenie jest większe niż 10–6 mol/L.

10

Flotation of long flame coal pretreated by polyoxyethylene sorbitan monostearate

Ni C., Xie G., Li Z., Bu X., Peng Y., Sha J.

Physicochemical Problems of Mineral Processing

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2016

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Vol. 52, iss. 1

317--327

EN

In this investigation, polyoxyethylene sorbitan monostearate (Tween 60) was used to improve flotation of fine long flame coal. The flotation recovery of long flame coal could be increased when long flame coal was either pretreated or conditioned with Tween 60 in a flotation cell for a period before the addition of collector. Fourier Transform Infrared (FTIR) technique was used to indicate surface properties of long flame coal. The results of FTIR show that there are many oxygen functional groups on the sur-face. Contact angle measurements were used to indicate changes in hydrophobicity of coal surface before and after Tween 60 and/or diesel pretreatments. The results of contact angle measurements show that hydrophobicity of coal can be increased by Tween 60. Tween 60 can also enhance adsorption of diesel on the coal surface, and hence floatability of long flame coal can be further improved. Tween 60 primarily enhances the flotation recovery of low density coal fractions (<1.5 and 1.5-1.8 kg/dm3). However, the increase in flotatation recovery is less significant with an excessive addition of Tween 60.

11

Determining optimal conditions for lignite flotation by design of experiments and the halbich upgrading curve

Sahbaz O.

Physicochemical Problems of Mineral Processing

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2013

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Vol. 49, iss. 2

535--546

EN

In this study conditions for flotation of low rank coal (lignite of Tuncbilek, Turkey) were investigated in detail. The experiments were performed using the 3-variable 2-level (23) full factorial experimental design with four base point replicates, and the results were analyzed by the regression model, Fischer test (F-test) and Halbich’s upgrading curve for the responses of ash content (or combustible matter grade) and the combustible matter recovery. The results obtained from the analysis indicated that while every factor considerably affected the combustible matter recovery, both collector (kerosene) and frother (AF65) significantly influenced the ash contents of the carbonaceous matter products. The only effective mutual interaction influencing recovery was caused by the kerosene-aeration interaction, while the interaction of kerosene-aeration and kerosene-AF65 and interactions of all factors (kerosene-AF65-aeration) were significant for the ash content of the products. Basing on the grade–recovery Halbich upgrading curve, regression model and a criterion for optimum of flotation results, it was found that a coal product with combustible matter grade of 91.09% and 71% combustible matter recovery can be obtained provided that it is processed at the higher level of kerosene (3 kg/Mg), higher level of frother AF65 (40 ppm) and lower aeration rate level of (0.16 cm/s).