Hydrophobicity Of Coal Surface Research Articles

Influence of the carbon atom numbers and the structure of collectors on the coal fines flotation

AbstractThis paper highlighted measuring the contact angle, the wetting heat and the IR spectrum before and after interactions between eight alkanes and coals to investigate the influence of the alkane structure and the number of carbon atoms on the coal surface hydrophobicity. The coal fines flotation tests were conducted with alkanes as collectors. The results show that after different alkanes acted on the coal samples, when the carbon numbers are same, both the contact angle and the wetting heat of isoparaffins were higher than those of the normal alkane. When the number of carbon atoms was 12, the contact angle and the wetting heat reached the maximum values after alkanes interacted with coals. The yield of the clean coal, the combustible material recovery and flotation perfect indicators of the isododecane were higher than those of the dodecane by 3.62, 4.08 and 0.96% respectively under the same condition of flotation. The ash content of the clean coal was also higher than that of the dodecane by 0.9...

FLOTATION OF LONG FLAME COAL PRETREATED BY POLYOXYETHYLENE SORBITAN MONOSTEARATE

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/dm 3 ). However, the increase in flotatation recovery is less significant with an excessive addition of Tween 60.

Adsorption of collectors on model surface of Wiser bituminous coal: A molecular dynamics simulation study

Coal flotation makes use of the hydrophobicity of coal surface. To enhance the hydrophobicity of coal particles, oily collectors are usually added. Although collectors have been widely applied in coal processing, the microscopic collection mechanism remains a formidable task due to the complexity of coal surface structure. In this work, different combined systems formed by collectors, water and a model surface of Wiser bituminous coal have been studied using molecular dynamics calculations. We modeled the interaction of each collector oil droplet with the coal surface in aqueous phase. In addition, water/collector model systems were also considered in order to reproduce the interaction of the different collectors with water molecules in the collector adsorption process. The results indicate that all three collectors, i.e. dodecane, nonylbenzene and nonylphenol, form spherical insoluble oil droplet in aqueous phase. After the addition of collector droplet over coal surface, all these collectors could thermodynamically repel the interfacial water molecules and spread over the coal surface, thereby reducing roughness of coal surface. The adsorption of nonylphenol on coal surface via both π–π stacking and hydrogen bonds is most favorable, followed by that of nonylbenzene and dodecane. The presence of collector on the coal surface could improve the hydrophobicity. The number of hydrogen bond between water and modified coal surface decreases and the mobility of water molecules increases compared to the original coal surface. However, the extent of hydrophobicity of modified coal surface by these collectors is inconsistent with their adsorption capabilities. Nonylphenol is the worst collector to improve the surface hydrophobicity of coal as part of nonylphenol molecules orient away from coal surface to form hydrogen bonds via their hydroxyl groups with water molecules. Dodecane should be the most effective collector as the hydration energy of the modified surface and the number of formed hydrogen bond between this surface and water molecules are the lowest, whereas the mobility of water molecules on this modified surface is the highest.

Evaluation of the Role of Surfactant on the Surface Characterisation of Coal

The surfaces of three China coals varying widely in coal type(Baode,Xiangshan,Jincheng) have been modified by adsorption of three surfactants( Sodium dodecyl sulfate,Polyethoxylated fatty alcohols,Alkyl phenol gather oxygen vinyl ether).The impact about coals of the surfactant has been explored by correlating three chemical characterisation techniques.Changes in coal surface hydrophobicity were assessed using contact angle measurements at the coal/water interface.The largest variation in zeta potential resulting from addition of surfactants was seen for the higher rank coals.The Specific surface area decreased when surfactants were present.

Assessing the Hydrophobicity of Petrographically Heterogeneous Coal Surfaces

Wettability and hydrophobicity of coal surfaces are technologically important but their accurate determination as a function of coal composition still remains a challenge. In this paper, a new experimental methodology has been developed to characterize coal surface hydrophobicity. This methodology combines the assessment of the extent of the surface heterogeneity by semiautomated petrography and image analysis, with contact angle measurements, using the axi-symmetric drop shape analysis technique. The measured distribution of petrographic components of macerals and minerals and their fractional areas on the coal surface where contact angles had been measured were correlated with the contact angle measured at that position. Contact angles for vitrinite and minerals were estimated independently, and those of the finely dispersed inertinite and liptinite were estimated from the contact angles of the heterogeneous surfaces and the fractional areas of the maceral and mineral components via Cassie’s equation. The established link between the discrete petrographic components that define the coal heterogeneity and the coal surface hydrophobicity is significant for estimating the hydrophobicity of composite coal particles and for predicting the performance of the flotation process which is used for cleaning fine coal particles.

石炭表面の親水・疎水度がカラム浮選成績に及ぼす影響

Continuous column flotation is one of an economical coal cleaning processes. In this study, we exam-ined the effect of hydrophilicity and hydrophobicitiy of coal surface on the continuous column flotation processes. We found that Wallarah coal was most suitable coal for the coal cleaning by the column flotation. From a static separation of film flotation, we found that the floatability of coal particle strongly depended on the hydrophilicity and hydrophobicity of coal surface. On the other hand, the trend of demineralization and the ratio of carbonaceous recovery could be predicted by the observation of methylene-blue adsorption test.

The influence of surfactant adsorption on the surface characterisation of Australian coals

The surfaces of three Australian coals varying widely in coal type (Collie, Wongawilli and Norwich Park) have been modified by adsorption of three surfactants (sodium dodecyl sulphate, cetyl trimethylammonium bromide and Teric G12A8). The mechanism and impact of the surfactant adsorption has been explored by correlating three chemical characterisation techniques. Changes in coal surface hydrophobicity were assessed using contact angle measurements at the coal/water interface. Adsorption of surfactants did not increase the surface hydrophobicity for the lowest rank coal, however appreciable changes in contact angle were measured as the rank of the coal increased. As the coal rank decreased, the surfactant adsorption densities increased for all three surfactants under investigation. The largest variation in zeta potential resulting from addition of surfactants was seen for the higher rank coals. The results from this study have allowed a possible surfactant adsorption model to be postulated.

00/01191 A comparison of the influence of wetting heat with contact angle in flotation

Coal flotation yield is related to coal surface hydrophobicity. Contact angle is normally used as an index for floatability. This paper compares the influence of contact angle with wetting heat on flotation results from 16 Chinese coals with broad coalification range. It was found that the correlation of wetting heat is much better than that of contact angle in evaluation of coal floatability. Three levels of wetting heat values are proposed for classification of coal floatability.

95/04460 Film flotation - fractioned surface flotation (a new method for testing coal surface hydrophobicity)

95/04460 Film flotation - fractioned surface flotation (a new method for testing coal surface hydrophobicity)