Applications of micro-FTIR technique in studying hydrophobicity of coal

This paper investigates the application of micro-FTIR technique in predicting hydrophobicity of coal inferred from contact angle measurements. Two ranks of coal were selected: Pennsylvanian high-volatile bituminous coal from the Illinois Basin, USA (Ro 0.59-0.63%) and Cretaceous medium-volatile bituminous coal from British Columbia, Canada (Ro 1.19-1.50%). Sessile drop and captive bubble techniques were used to measure contact angle on coal surfaces, and those surfaces were then analyzed with micro-FTIR to correlate contact angle with chemistry. In addition, an image analysis system was used to add the maceral composition effect on chemistry and hydrophobicity. The results show that low- and high-rank coal samples have distinct and opposite trends between functional groups semi-quantitative ratios and contact angle, reflecting rank-dependent effects of chemistry on coal surface hydrophobicity. This work demonstrates that micro-FTIR can be a valuable tool to investigate the hydrophobicity of coal and shows that tracking correlations between chemical groups on the surface of individual macerals, and relating them to hydrophobicity is an effective way to build understanding of the effects of coal chemistry on flotation.