Surface pore characteristics of original coal dust produced in underground mining sites and their impact on the moisture content

In underground coal mines, the efficiency of water-based dust suppression technologies is heavily limited by the poor wettability of coal dust. To explore the effect reasons of the surface pore parameters of coal dust on its wettability, in this study, 18 original coal dust (OCD) samples produced in underground mining sites were collected from various underground coal mines in north China. The surface micropore (pore size < 2 nm) and mesopore (2 nm < pore size < 50 nm) characteristics of the OCD samples were measured with the nitrogen (N-2) adsorption/desorption method. Subsequently, the correlations between the pore characteristics of the OCD samples and their moisture contents and initial contact angle (ICA) were established and discussed. The results demonstrate that the pore structures of the OCD samples are significantly developed, and the impermeable pores with one open end are the dominant pore types in the OCD. The micropore structure of the OCD samples considerably affects its moisture content, thus influencing its wettability. As the increase of micropore size, micropore volume, and specific surface area (SSA), the moisture content of the OCD samples linearly decreased (R-2 = 0.55), linearly increased (R-2 = 0.66), and linearly increased (R-2 = 0.65), respectively. The large capillary force caused by the developed SSA accounts for the significant moisture conservation property of the micropore structures, which improves the wettability of the OCD. The variation of the ICA with the pore parameters well verifies this conclusion.