Synergistic improvement of the fine size coal dewatering performance by using binary surfactant mixtures

In this study, gemini surfactants and binary surfactant mixtures were used in order to enhance the dewatering performance of fine size coal particles. Compared to three single gemini surfactants, binary surfactant mixtures presented a better dewatering performance of fine size coal particles, especially the binary surfactant mixture composed of Gemini - 1 surfactant and sodium dodecyl benzene sulfonate (SDBS). Meanwhile, the binary surfactant mixture composed of Gemini - 1 surfactant and sodium dodecyl sulfonate (SDS) was further used in the experimental test as a comparison and showed better dewatering performance than that of the binary surfactant mixture composed of Gemini - 1 surfactant and SDBS. The lowest cake moisture content (20.72 %) was gained when the dosage of Gemini - 1 surfactant and SDS was 400 g/t at the molar ratio of 6 to 7. Surface functional groups of the prepared coal samples were characterized by a Fourier transform infrared spectroscopy (FTIR). Wetting heat values of coal samples before and after adsorbing surfactants were measured by a microcalorimeter. The adsorption capacity of surfactant on coal surface was investigated for studying the difference between three single surfactants and the binary surfactant mixture. Intermolecular interaction calculation and thermodynamics of micellization for the judgment of synergistic effect indicated that the synergistic interaction was formed in the binary surfactant mixture and the binary surfactant mixture of Gemini - 1 surfactant and SDS showed a stronger synergistic interaction. A possible hydrophobic mechanism was supposed that the water molecules were displaced by the binary surfactant mixture for the improvement of hydrophobicity of coal particle surface.