Experimental investigation on the micro wettability of coal dust: considering the comprehensive effects of physical chemistry characteristics

Coal seam water injection technology plays an important role in the reduction of dust in the working face. To improve the wetting effect of low-permeability and difficult-to-wet coal seams and achieve dust control at the source, it is necessary to carry out quantitative research on the relationship between the wettability and physical chemistry properties in coal and to clarify the factors and mechanisms that affect the wettability of coal. In this study, six samples with different ranks were adopted to experimentally acquire the coal parameters, including the proximate compositions, ultimate contents, chemical bonds, pore-fracture structures, and nuclear magnetic resonance (NMR) T 2 -spectra peaks. Moreover, the molecular dynamic behavior of six coals with different metamorphic degrees was simulated to reveal the wettability from a microscopic view. A quantification coefficient was constructed to comprehensively represent the wettability of coal dust and was further verified by experimental data. Results demonstrated that a proposed coefficient was presented as the product among square root of moisture contents, square root of ratios of carbon contents, hydroxyl ratios, half to the third power of pore diameters, and reciprocal of the square of oxygen content ratios. This coefficient appeared a good correlation ( R 2 = 0.74) with the normalized T 2g (P 3 ), which signified that moisture contents, ratios of carbon contents, hydroxyl ratios, and pore diameters posed the positive relationships with T 2g (P 3 ). However, the larger T 2g (P 3 ) corresponded to the lower ratios of oxygen contents. Especially, the linear correlations between T 2g (P 3 ) and moisture contents/pore sizes presented higher accuracies of 0.86 and 0.84, respectively. The contents of ash, volatile matter, hydrogen/nitrogen, carboxyl/carbonyl groups, and surface area play weak roles in wettability, appearing the less than 0.5 fitting coefficients.