Enhancing low-rank coal flotation using mixed collector of dodecane and oleic acid: Effect of droplet dispersion and its interaction with coal particle

Low-rank coal is difficult to float using oily collectors due to the rich oxygen-containing functional groups on the surface. In recent years, a variety of mixed collectors have been used to enhance the low-rank coal flotation. In this study, the effects of droplets dispersion and interaction with particles on the low-rank coal flotation using mixed collector (MC) of dodecane (D) and oleic acid (OA) were discussed. Interfacial tension experiment and Focused Beam Reflectance Measurement (FBRM) was used to analyze the oil droplets dispersion. The interaction energy estimation using EDLVO theory and the induction time measurement was performed to investigate the interaction between oil droplets and coal particles. The results showed that the addition of OA can significantly reduce the oil-water interfacial tension and shorten the time of interfacial tension equilibrium, which decreased droplets size and increased droplets counts. There was always attraction interaction between oil droplets and coal particles, and the absolute value of interaction energy and attraction force decreased in the order of D > MC > OA. The results of induction time measurement confirmed the interaction energy estimation using EDLVO theory. The flotation performance of the single reagent was greatly improved by mixed use, and OA and D showed synergistic effect. It was indicated that the effect of OA in mixed collector was to promote dispersion, that is, to reduce droplets size and increase droplets counts, rather than to improve interaction energy between oil droplets and coal particles.