Experimental study on coal dust wettability strengthened by surface active ionic liquids

The water wettability of coal dust was very important for dust control when using water-based dust suppressant materials. The coal dust wettability strengthened by surface active ionic liquid was studied in this paper. The surface activity of ten ionic liquids with different anions Cl^-, Br^-, [BF₄]^-, [NTf₂]^- and cations [HOEtMIm]⁺, [C_nmim]⁺ (n = 4, 12, 14, 16) was studied by surface tension test. The water wettability of raw coal dust can be improved individually by adding ionic liquid to water or pre-treating coal dust by ionic liquids. The wettability of lignite was improved little, but that of bituminous coal and anthracite were improved much. The dual strengthened effects of ionic liquids on coal dust wettability were studied by the wetting results between ionic liquids solutions and ionic liquid-treated coal samples. The wettability of lignite can be strengthened under the combined action of [HOEtMIm][NTf₂] and [C₁₂MIm]Br, while other dual effects were not satisfactory. All ionic liquids combination had strengthened effects on the wettability of bituminous coal and anthracite, especially the [C₁₂MIm]Br treatment and [C₁₂MIm]Br solutions together had the best dual effects. The functional groups results indicated that the hydrophilic oxygen-containing functional groups in treated coal samples increased, the hydrophobic aliphatic hydrocarbon functional groups decreased and part of ionic liquids were adsorbed on the coal surface. These changes together enhanced the wettability of coal with high coalification degrees.