Structural properties of residual carbon in coal gasification fine slag and their influence on flotation separation and resource utilization: A review

Coal gasification fine slag (FS) is a typical solid waste generated in coal gasification. Its current disposal methods of stockpiling and landfilling have caused serious soil and ecological hazards. Separation recovery and the high-value utilization of residual carbon (RC) in FS are the keys to realizing the win-win situation of the coal chemical industry in terms of economic and environmental benefits. The structural properties, such as pore, surface functional group, and microcrystalline structures, of RC in FS (FS-RC) not only affect the flotation recovery efficiency of FS-RC but also form the basis for the high-value utilization of FS-RC. In this paper, the characteristics of FS-RC in terms of pore structure, surface functional groups, and microcrystalline structure are sorted out in accordance with gasification type and FS particle size. The reasons for the formation of the special structural properties of FS-RC are analyzed, and their influence on the flotation separation and high-value utilization of FS-RC is summarized. Separation methods based on the pore structural characteristics of FS-RC, such as ultrasonic pretreatment–pore-blocking flotation and pore breaking–flocculation flotation, are proposed to be the key development technologies for improving FS-RC recovery in the future. The design of low-cost, low-dose collectors containing polar bonds based on the surface and microcrystalline structures of FS-RC is proposed to be an important breakthrough point for strengthening the flotation efficiency of FS-RC in the future. The high-value utilization of FS should be based on the physicochemical structural properties of FS-RC and should focus on the environmental impact of hazardous elements and the recyclability of chemical waste liquid to establish an environmentally friendly utilization method. This review is of great theoretical importance for the comprehensive understanding of the unique structural properties of FS-RC, the breakthrough of the technological bottleneck in the efficient flotation separation of FS, and the expansion of the field of the high value-added utilization of FS-RC.