Characterization of coal particles wettability in surfactant solution by using four laboratory static tests

Coal dust is a health threat to underground coal miners, and the current common practice is to use water spray to control it. The coal wettability plays a significant role in studying the effectiveness of coal dust suppression, and the addition of surfactant to water can greatly improve the coal wettability. The aim of this paper is to evaluate the reliability of four methods that are commonly used to quantify the coal wettability in presence of surfactant, they are the sessile drop measurement, the sink test, the capillary rise test and the drop penetration test. The advantages and disadvantages of these four methods were detailed. The results indicated that the sink test is the most reliable method in terms of its simplest operation and the highest accuracy. It also has the ability to quantitatively compare the wettability of different coal particle sizes, which the other three methods failed to identify. The addition of surfactant resulted in smaller contact angles, less sink time, less drop penetration time and more capillary rise weight gains compared with using water only, which indicated that the coal wettability is improved by surfactants. Of the two studied surfactants, SDBS performed better than SDS. This study provided a guideline on both evaluation method and surfactant selection when studying the wettability of coal particles