Recent advances and conceptualizations in process intensification of coal gasification fine slag flotation

Coal gasification technology is an effective means to achieve clean and efficient utilization of coal. Coal gasification slag is generated in the process of coal gasification owing to the existence of minerals in the coal, particularly the incomplete reaction of the organic carbon elements in the coal. This results in different contents of residual carbon in the coal gasification slag. The mixture of residual carbon and inorganic minerals (ash materials; a solid waste with a low resource utilization rate) restricts their utilization. The efficient separation of residual carbon and ash materials in coal gasification slag is essential for the resource utilization of coal gasification slag. The particle size of coal gasification fine slag (CGFS) is relatively fine, and the separation effect of the physical sorting method is low. In addition, flotation is still one of the most feasible means for the efficient separation of residual carbon and ash materials. Owing to the physical and chemical properties of CGFS, the large amount of reagents and low sorting effect severely restrict its industrial implementation. This review summarizes and analyzes the main reasons for the flotation process of coal gasification slag from three aspects (the flotation basis of minerals, difficult flotation, and difficulty of selection). The analysis is based on the development of an efficient collector for CGFS flotation, pretreatment of raw materials before flotation, addition of adjustment, and flotation optimization methods. Furthermore, it puts forward four directions for enhancing the flotation process of CGFS: the principle of the comprehensive analysis of the flotation separation of CGFS based on a variety of technologies, the selection and combination of high–efficiency collectors, precise adjustments based on the surface properties of CGFS, the design of synergistic regulation devices based on energy input and particles–bubbles action, and the comprehensive utilization of solid waste resources based on gravity separation–magnetic separation–flotation. The solutions for the above critical scientific and technical problems would provide technical and theoretical support for a feasible method to realize the resource, reduction, and high–value utilization of coal gasification slag all around the world.