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Wettability modification of lignite by adsorption of alkyltrimethylammonium bromides with different alkyl chain length

ABSTRACT To overcome the problem of moisture re-adsorption of dried lignite with common evaporation drying methods, a set of linear alkyl quaternary ammonium surfactants (C10TAB, C12TAB, and C16TAB) were used to modify lignite surface, and the effects of alkyl chain length on the adsorption characteristics of surfactants and wettability of lignite surface were evaluated. Pseudo-first and pseudo-second-order kinetic models and Langmuir model were, respectively, used to simulate adsorption kinetics and adsorption isotherms. The results showed that three surfactants gradually formed double-layer adsorption on lignite surface and the loading of surfactant increased with the length of alkyl chain. X-ray photoelectron spectroscopy analysis showed that C3H9N+ moiety of the surfactants would preferentially interact with O˭C‒O groups of lignite. Results of wetting heating and moisture re-adsorption showed that three surfactants obviously decreased hydrophilicity and restrained moisture re-adsorption of lignite, but with the formation of double-layer adsorption, hydrophilic headgroups of surfactant faced outward, which caused increase in hydrophilicity of lignite. As a result of two opposite effects of surfactant chain length on lignite wettability, the effect of C12TAB on decreasing hydrophilicity was the best among the three chosen surfactants.