LAUSR

Abstract To study the effects of ethylene oxide (EO) number in surfactants on low rank coal (LRC) flotation, dodecyl ethoxyl ethers (C12EOn) with three different EO numbers were selected and their adsorption and flotation behaviors were experimentally investigated. The results show that all C12EOn can obtain the same maximum flotation recovery. Increasing the number of EO in C12EOn lowers the necessary amount of reagent. Greater selectivity can be achieved with increasing EO number in C12EOn. Furthermore, the surface model of LRC (organic matter) and kaolinite (representative of mineral matter) was constructed, and the adsorption behavior of C12EOn on the LRC surface was analyzed based on the adsorption configuration, interaction energy, hydrogen bond interaction and surface areas. The calculated results show that increasing the EO number in C12EOn could accelerate the interaction between LRC and C12EOn at low surfactant concentrations. Since the same chemical structure of C12EOn, increasing the EO number does not make any significant difference in their interaction when the surfactant concentration is high. A combined theoretical approach [density functional theory (DFT) calculations and molecular dynamics simulations (MD)] was adopted to investigate the microscopic mechanism of the increase in LRC hydrophobicity by C12EOn adsorption. Finally, the competitive adsorption of C12EOn between organic matter and kaolinite was studied. The research results indicate that the selectivity is higher with increasing EO number in C12EOn, which is consistent with the experimental results. The microscopic mechanism of EO groups in surfactants on LRC flotation discussed in this study may have potential use in surfactant design and selection.