Increase in wettability difference between organic and mineral matter to promote low-rank coal flotation by using ultrasonic treatment

Due to Van der Waals or electrostatic interactions of surfactants active to all kinds of minerals, in low-rank coal (LRC) flotation, surfactants could both adsorb on the organic and mineral matter of LRC, thus increasing the hydrophobicity of them and resulting in the increase of clean coal yield as well as the ash content. In this work, density functional theory (DFT) calculations were clarified the adsorption mechanism of surfactant (C₁₂EO, lauryl polyoxyethylene ether) on the LRC model molecules and kaolinite surfaces (the representative of organic and mineral matter in LRC). The DFT results demonstrate that the interaction strength between C₁₂EO and LRC model molecules is stronger than that of kaolinite. Based on the calculation results, ultrasonic treatment was selected to expand the wettability difference between organic and mineral matter that adsorbed C₁₂EO. The microcalorimetry results show that the wetting heat of organic matter that is adsorbed C₁₂EO is unchanged basically after 30 s ultrasonic treatment. However, there is an obvious increase trend for the wetting heat of kaolinite. Flotation experiments of artificial mixed samples proved that ultrasonic treatment is useful in decreasing the extent of ash content in LRC flotation, thus improving the quality of clean coal in LRC flotation.