Effect of mixed cationic/anionic surfactants on the low-rank coal wettability by an experimental and molecular dynamics simulation

Abstract

Mixed surfactants consisting of the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and the anionic surfactant sodium dodecyl sulfate (SDS) demonstrated high floatability of low-rank coal, and the optimal molar ratio of CTAB and SDS was 1:9. The surface and thermodynamic parameters (CMC, γCMC, Γmax, Amin, ΔGm0) obtained from surface measurements indicated higher surface activity and denser molecular arrangement in the mixed CTAB/SDS surfactants than in single CTAB or SDS. The contact angle of the coal sample increased from 38.9° to 73.7°, and the wetting heat of the coal became less negative, which showed a better positive effect on enhancing the contact angle and restricting the hydrophilicity of the coal surface. Molecular dynamics (MD) simulations were carried out to investigate the influence on the wettability of low-rank coal. The results indicated a significant increase in hydrophobicity of the low-rank coal. Furthermore, the combustible recovery was enhanced significantly by up to 47.67%, and the concentrated ash value was increased by up to 3.63%.