Experimental investigation on physicochemical and wetting characteristics of modified gas coal: Effects of multicomponent acids and surfactant

In this study, the effects of the different concentrations of hydrochloric acid, hydrofluoric acid, and acetic acid and a surfactant on the physicochemical characteristics of coal, such as pore diameter distribution, pore fractal dimension, and chemical structures were studied. The wettability performance of the reagent-modified coal was proposed. The results demonstrated that the mineral dissolution rate of HF in coal sample was much higher than those by HCl and HAC treatment, which increases the surface roughness of coal. With the increase of the concentration of multicomponent acid solution, the number of micropores decreased and the number of macropores increased. Moreover, both fractal dimensions D1 and D2 of the coal sample treated with the multicomponent acid comprising 6% HCl, 6% HF, and 6% HAC (#3) were the smallest. This shows that compound reagent #3 is available to enhance the pore size distribution with a better effect than the other five ones. Compared with the raw coal (#7), treatment with high concentrations of HCl (#4) significantly decreased the contact angle on coal (#4), whereas treatment with high concentrations of HF or HAC (#6 or #5), significantly increased it.