Enhanced flotation separation of coal gasification fine slag by composite collectors containing polar fatty acids

Coal gasification fine slag (CGFS) is a large solid waste in the field of coal chemical industry, and the separation of its carbon and ash is a prerequisite for the large-scale utilization of CGFS. At present, the flotation separation process of CGFS faces the prominent bottleneck of high consumption of traditional non-polar hydrocarbon oil collectors and poor flotation effect. To address this challenge, three fatty acids, oleic acid (OA), n-decanoic acid (DA), and naphthenic acid (NA), were used in this study to compound with the nonpolar hydrocarbon oil dodecane, respectively, as novel collectors for CGFS flotation. The effect and action mechanism of the composite collectors on CGFS flotation were investigated through flotation experiments as well as surface/interfacial tension, laser particle size, heat of wetting, FTIR, XPS, and induction time tests. The results show that the composite collectors can enhance the flotation effect of CGFS while reducing the chemical consumption. The addition of polar fatty acids can effectively reduce the interfacial tension of the collector-water system and thus increase the dispersion of the collector in water. Meanwhile, the addition of fatty acids makes the composite collector contain both polar and nonpolar groups. The polar groups form hydrogen bonds with the oxygen-containing groups on the residual carbon surface to mask the hydrophilic region, and the nonpolar groups are exposed to the slurry to enhance the hydrophobicity of the residual carbon surface, which makes the residual carbon adhere to the air bubbles more easily and thus facilitates its flotation recovery from CGFS. This study has important theoretical guidance for the efficient separation and resource recovery of CGFS.