Wettability Modification of Lignite by Adsorption of Dodecyl Based Surfactants for Inhibition of Moisture Re‐adsorption

Abstract

AbstractIn order to restrain moisture re‐adsorption of dried lignite, a series of dodecyl based surfactants with various hydrophilic heads including dodecyltrimethylammonium bromide (DTAB), sodium dodecyl sulfonate (SDS), dodecyl nonaethoxyl ether (C12EO9) and a gemini surfactant (G12‐2‐12) were used to adsorb on lignite surface for wettability modification. The adsorption isotherms and zeta potential were determined to study the adsorption process. Lagergren‐first‐order and pseudo‐second‐order kinetics models were used to simulate the adsorption kinetics. The modified lignite was characterized by FTIR spectroscopy, and the wettability of it was evaluated by the wetting heat and moisture re‐adsorption ratio. The results indicate that hydrophilic heads of surfactants play an important role in adsorption mechanisms and structures of their adsorption layers on lignite surface, which are responsible for wettability alteration. Four surfactants produce different effects on restraining moisture re‐adsorption of lignite: the effect of cationic surfactants is better and worse for anionic surfactant SDS, while the non‐ionic surfactant C12EO9 shows intermediate behavior. But with the formation of double‐layer adsorption, hydrophilic headgroups of surfactant face outward, which causes hydrophilicity of lignite to rise again. Combining adsorption situations and wettability modification effects, the relationship between molecular orientation of four surfactants on a lignite surface and wettability reversal of lignite are discussed.