Effect and mechanism of microemulsion on low-rank coal flotation by mixing AEO-3 and diesel oil

Low-rank bituminous coal has a low degree of metamorphism, a high oxygen content, and poor hydrophobicity. When using a conventional collector, it renders a low yield of clean coal, making it difficult to improve the quality via flotation. In this work, a type of diesel microemulsion (C1) was prepared using primary alcohol ethoxylate (AEO-3), which was adopted to conduct flotation. The results demonstrated that compared with a conventional diesel collector, the yield of clean coal was increased by 44.37%; the content of tailing ash was increased by 37.60%; the combustible recovery rate was improved by 55.65%, respectively; and the flotation kinetic constant was increased by 0.505. The addition of AEO-3 could significantly reduce the surface tension and generate smaller emulsion droplets, which could also adhere to coal particles, easily enhancing their hydrophobicity. An X-ray photoelectron spectroscopy analysis and its contact angle verify a significant enhancement in the hydrophobicity of the coal surface. More importantly, a molecular dynamic simulation revealed that adding AEO-3 could augment the electrostatic interaction between the collector (diesel) molecules and coal particles, as well as reduce the mean square displacement, i.e., the adsorption strength between the collector molecules and coal particles. On the other hand, the microemulsion could improve the hydrophobicity and floatability of coal particles and enhance the wrap angle of particle-bubble. And accelerating the generation of stable mineral flocculation, which was the main reason for the faster flotation process.