Floatability Of Coal Particles Research Articles

Effect and mechanism of microemulsion on low-rank coal flotation by mixing AEO-3 and diesel oil

ABSTRACT Low-rank bituminous coal has a low degree of metamorphism, a high oxygen content, and poor hydrophobicity. When using a conventional collector, it renders a low yield of clean coal, making it difficult to improve the quality via flotation. In this work, a type of diesel microemulsion (C1) was prepared using primary alcohol ethoxylate (AEO-3), which was adopted to conduct flotation. The results demonstrated that compared with a conventional diesel collector, the yield of clean coal was increased by 44.37%; the content of tailing ash was increased by 37.60%; the combustible recovery rate was improved by 55.65%, respectively; and the flotation kinetic constant was increased by 0.505. The addition of AEO-3 could significantly reduce the surface tension and generate smaller emulsion droplets, which could also adhere to coal particles, easily enhancing their hydrophobicity. An X-ray photoelectron spectroscopy analysis and its contact angle verify a significant enhancement in the hydrophobicity of the coal surface. More importantly, a molecular dynamic simulation revealed that adding AEO-3 could augment the electrostatic interaction between the collector (diesel) molecules and coal particles, as well as reduce the mean square displacement, i.e., the adsorption strength between the collector molecules and coal particles. On the other hand, the microemulsion could improve the hydrophobicity and floatability of coal particles and enhance the wrap angle of particle-bubble. And accelerating the generation of stable mineral flocculation, which was the main reason for the faster flotation process.

Effect of microemulsion on low-rank coal flotation by mixing DTAB and diesel oil

It is difficult to recover low-rank coal using traditional oily collectors because a large number of oxygen-containing functional groups and pores exist on its surface. In this study, a microemulsion was prepared by mixing dodecyl trimethylammonium bromide (DTAB) and diesel oil; its effect on low-rank coal flotation was studied via water contact angle and wrap angle measurements. The results show that the clean coal could not be effectively recovered using a single reagent of DTAB or diesel oil. However, the microemulsion can improve the clean coal recovery with a small amount of diesel oil. The recovery of clean coal was greatest when the mass ratio of DTAB and diesel was 1:2. The addition of DTAB could act as a dispersant in the oily collector, and thus increased the contact area between coal and reagent. More importantly, DTAB and diesel oil could be adsorbed on the low-rank coal surface because of their synergistic effect. On the one hand, DTAB can improve the dispersion of diesel oil. On the other hand, the combination of diesel and DTAB promoted the spread of diesel on the particle surface. The microemulsion could improve the hydrophobicity and floatability of coal particles and enhance the stability of particle-bubble adhesion. The relationship between wrap angle and time could be well fitted by the first-order kinetic equation and the results show that the attachment rate gradually increased and reached its maximum when the mass ratio of DTAB and diesel was 1:2.

The relationship among contact angle, induction time and flotation recovery of coal

ABSTRACT Flotation is used to separate valuable minerals from gangue minerals based on the differences in their natural or induced hydrophobicity. Flotation recovery is a direct indicator of flotation performance. Similarly, induction time and contact angle are often used to characterize floatability. In order to measure the correlation of these indicators, contact angle measurements, induction time measurements and flotation tests were performed. The bubble-particle induction time measurements were performed with a homemade induction timer. Fourier translation infrared spectroscopy analysis was used to characterize the surface functional groups of different coals. The results showed that shorter induction times and greater contact angles resulted in higher flotation recoveries. However, induction time measurements can reveal the floatability of individual particle size fractions, which cannot be realized in traditional contact angle measurements. Moreover, the contact angle is measured in an equilibrium system while the induction time represents a dynamic measurement. For a dynamic flotation system, it would be more appropriate to describe floatability of coal particles by induction time rather than traditional contact angle.

Investigation of the effect of particle size, petrographic composition, and rank on the flotation of Western Canadian coals

ABSTRACT Coal is one of the most crucial natural resources used for steel and energy production. To improve its utilization properties, the run-of-mine coal is processed to remove undesirable impurities such as mineral matter and sulfur. The fine coal is usually processed by flotation, and the efficiency is highly dependent on the particle size, maceral composition, and the rank. The effect of particle size and reagent dosages are usually the most commonly studied parameters for flotation, whereas optimization through the study of the response of the petrographic components and the rank based on the vitrinites’ reflectance of coal particles (V-types) are rarely investigated. This paper studied the floatability of coal particles in terms of their physical and compositional attributes including particle size, petrographic composition, and rank (V-types) from coal blends representing different feeds to the plant. The results showed that the higher content of inertinite macerals and a high quantity of ultra-fines contributed to a poor floatability for the studied coals. On the other hand, the coal sample containing vitrinite particles from a higher rank exhibited a much better flotation response, despite the presence of significant amounts of ultra-fine.

Role of surface roughness in the attachment time between air bubble and flat ultra-low-ash coal surface

Surface roughness plays an important role in the floatability and wettability of mineral and coal particles. However, the role of surface roughness in the floatability of coal particles has not been sufficiently investigated because coal consists of organic and inorganic materials. This paper is to obtain some insights into the role of surface roughness in the coal surface wettability. In this investigation, Taixi ultra-low-ash coal particles, with ash content of 1.55%, were polished and the polished flat coal surfaces with various roughness were obtained. The attachment time between air bubble and flat coal surface were tested at the water solution without flotation reagents. Throughout this paper, it was found that the attachment time increased with the increase of roughness of coal surface. The attachment area between bubble and flat coal surface was decreased with the increase of surface roughness. The attachment between bubble and flat rough coal surface was unstable, compared to the attachment between bubble and smooth coal surface. The rougher coal surface makes the detachment between bubble and coal surface easier than the smoother coal surface. The higher the roughness of coal surface is, the more pores and grooves the coal surface has. The pores, gaps and grooves are filled up with the water in the slurry and have negative effects on the attachment between bubble and flat coal surface.

Enhancing flotation performance of low rank coal by improving its hydrophobicity and the property of oily bubbles using 2-ethylhexanol

In this paper, the influence of 2-ethylhexanol used as a modifier/emulsifier on the surface chemical property of low rank coal and its flotation performance was investigated. According to the FTIR analysis, it showed an obvious decline in the hydrophilic groups while an increase in the hydrophobic groups on the surface of coal after pretreatment by 2-ethylhexanol solution for 12 h, resulting in the increase of contact angle from 74.9° to 95.4°. Whereas the induction time showed a significant decrease from 246.0ms down to 85.4ms, which meant the better hydrophobicity and floatability of coal particles after the pretreatment. As a result, a better flotation efficiency of low rank coal was attained after the pretreatment. Additionally, the oily bubble flotation combining 2-ethylhexanol was employed to enhance the flotation of coal samples. The results indicated that the mixture of diesel oil and 2-ethylhexanol improved the collecting power and selectivity of oily bubbles, with the oil contact angle for coal samples decreasing from 17.8° to 14.5° and the induction time from 50ms down to 19.7ms. The performance of oily bubble flotation, especially using the mixed diesel oil bubbles, was much better than that of conventional flotation, and the recovery of combustible matter and flotation efficiency index increased from 43.42% and 29.52% up to 89.27% and 59.91% respectively. Consequently, the flotation performance of low rank coal may be enhanced by the surface modification of 2-ethylhexanol as well as the novel oily bubble flotation technology.

Effect of low-temperature pyrolysis on surface properties of sub-bituminous coal sample and its relationship to flotation response

Coal spontaneous combustion makes coal suffer a high-temperature heating process (similar to a low-temperature pyrolysis). Additionally, low rank coal is considered to be friendly utilized through two steps, i.e. low-temperature pyrolysis of low rank coal to gain gas/liquid components and then coal char forwarded to the burning or other chemical applications. Therefore, it is necessary to investigate the effect of low-temperature pyrolysis on the surface properties of low rank coal and its role in the floatability of coal particles because coal already suffering spontaneous combustion should be upgraded before usage. In this investigation, SEM, XPS, attachment time and flotation tests were employed to reveal the changes of surface properties and floatability of sub-bituminous coal before and after the pyrolysis. After the pyrolysis, a significant mass loss was observed and many pores/cracks were newly created as well as the content of hydrophobic functional groups on coal surface was increased whereas the content of hydrophilic oxygen-containing functional groups was reduced. The attachment time of coal-bubble was significantly decreased after the pyrolysis, which directly made an increase in the hydrophobicity and floatability of sub-bituminous coal. The findings of this paper may be useful for a better use of sub-bituminous coal resources because sub-bituminous coal is well known as difficult to float and sub-bituminous coal fines are usually wasted in coal preparation plants. This paper proposes that coal char from sub-bituminous coal may be forwarded to a further upgrading process (i.e. flotation) because the floatability of sub-bituminous coal is significantly improved by the pyrolysis.