Enhancement of the wettability of a coal seam during water injection: effect and mechanism of surfactant concentrations above the CMC.

This paper determines the optimal surfactant concentration for enhancing coal's wettability and explores the wetting mechanism at surfactant concentrations above the critical micelle concentration (CMC) during coal seam water injection. In this study, laboratory experiments and field tests were used to investigate the influence of monomeric surfactants and compound surfactants at various concentrations on coal's wettability. The results showed that when the surfactant solution concentration was greater than the CMC, the coal's wettability was significantly enhanced as the surfactant concentration increased. However, the coal's wettability did not monotonically increase with the concentration, and the maximum value was reached in the range of 0.5-3 wt.%. Increasing the surfactant adsorption density and changing the adsorption state on the coal surface were the essential reasons surfactants continued improving the coal's wettability at concentrations above the CMC. The Marangoni flow effect and changes in the viscosity of the surfactant solution with concentration were also important factors that affected the coal's wettability.

Suppression Characteristics and Mechanism of Molasses Solution on Coal Dust: A Low-Cost and Environment-Friendly Suppression Method in Coal Mines.

Coal dust pollution poses a serious public health threat. This study aimed to investigate the feasibility of creating a coal dust suppressant using molasses, a byproduct of the sugar industry. We studied the effects of a molasses solution of varying concentrations (i.e., ranging from 0% (pure water) to 40%) on the moisture, bonding, and wind erosion properties of coal dust. Overall, the effectiveness of the molasses increased with their concentration, and it manifested itself in the following way: (1) the molasses improved the anti-evaporation ability of wet coal dust. For example, the evaporation mass of the coal dust wetted using a molasses solution decreased by 82.8%; (2) molasses effectively agglutinated coal dust; (3) molasses can effectively decrease the surface tension and increase the viscosity of the wetting solution. The surface tension of the molasses solution reached 41.37 mN/m and the viscosity increased to 6.79 mPa·s; (4) molasses can significantly suppress the wind erosion of deposited coal dust, with its wind erosion mass decreasing 99.1%; finally, (5) the effectiveness of molasses at suppressing coal dust was discussed at a molecular level. This study highlights the feasibility of a low-cost and environment-friendly dust suppressant in coal mines.