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.