Changes of coal dust characteristics: correlation between grinding degree, functional group contents, and wettability

The wettability of coal dust with different particle sizes varied significantly in underground coal mines. To analyze the chemical reasons in the wettability differences of coal dust (from the same coal sample) with various particle sizes, this paper investigated the changes of functional group structures and surface electrochemical properties under different grinding degrees based on the infrared spectroscopy, XPS, and surface potential experiment. Experimental results exhibited that with the increase of grinding degrees, the functional group peak positions remained unaffected by grinding degrees, but their peak values were remarkably changed, i.e. the contents of aliphatic hydrocarbon and aromatic nucleus were significantly increased while the contents of −C=O and –C–O– remarkably decreased. The content changes of functional groups were also quantitatively confirmed through XPS experiments, which was showed that with the increase of grinding degrees, the content of hydrophilic functional groups decreased significantly, while the content of hydrophobic functional groups increased. Additionally, the surface charge of coal dust also exhibited an elevated trend with the grinding degree increased, reducing the agglomeration possibility among dust particles. From the contact angle experiments, it was found that the wettability of coal dust with smaller size was poorer, due to the increased hydrophobic group content. The above conclusion would provide some information for optimizing the wetting property of the dust suppression solution, further achieving a better matching relationship between the dust suppression solution and coal dust.