Effects of Oxygen Element and Oxygen-Containing Functional Groups on Surface Wettability of Coal Dust with Various Metamorphic Degrees Based on XPS Experiment.

Gang Zhou,Wen Nie,Weimin Cheng,Cuicui Xu,Qi Zhang

doi:10.1155/2015/467242

Abstract

To investigate the difference of surface oxygen element and oxygen-containing functional groups among coal dusts with different metamorphic degrees and their influence on surface wettability, a series of X-ray photoelectron spectroscopy experiments on 6 coal samples are carried out. The result demonstrates that the O/C ratio of coal surface shows an overall increasing trend compared with the result of its elements analysis. As the metamorphic degree increases, the O/C ratio on the surface gradually declines and the hydrophilic groups tend to fall off from coal surface. It could be found that different coals show different surface distributions of carboxyl and hydroxyl which are considered as the greatest promoter to the wettability of coal surface. With the change of metamorphic degree, the distribution of ether group is irregular while the carbonyl distribution keeps stable. In general, as the metamorphic degree goes higher, the content of oxygen-containing polar group tends to reduce. According to the measurement results, the contact angle is negatively related to the content of oxygen element, surface oxygen, and polar groups. In addition, compared with surface oxygen content, the content of oxygen-containing polar group serves as a more reasonable indicator of coal dust wettability.

Highlights

As a serious threat to safety of mine production and health of miners, coal dust is deemed to be one of the major hazards in coal production process
Explosions by coal dust will cause severe accidents; on the other hand, miners exposed to the environment directly, which was contaminated by coal dust, are highly susceptible to pneumoconiosis
For a long time most of the studies on coal dust wettability are focused on the macroscale content, such as contact angle and settlement test [6]

Summary

Introduction

As a serious threat to safety of mine production and health of miners, coal dust is deemed to be one of the major hazards in coal production process. The main reason is that most of the coal dust in China has poor wettability, which leads to a limited effect of the wet dust removal method applied to underground work place. X-ray photoelectron spectroscopy (i.e., XPS), which was widely used in chemical structure analysis for its ability to efficiently observe elemental composition and functional group information on coal surface within 10 nm, is one of the most effective methods for element investigation. The investigation on the relation between coal dust wettability and its oxygen-containing functional group is helpful to uncover the characters of wettability from a microscopic view. The influence of surface element and oxygen-containing functional group on coal surface wettability is analyzed, and our results explain and demonstrate the wettability mechanism of coal dust

Experimental Procedure

XPS Experiment of Different Coal Samples

Results and Discussion

Content Analysis of Oxygen-Containing Functional Groups on Coal Surface

Conclusions