Physicochemical properties of fine slag of Ningdong coal gasification and its carbon⁃ash separation products

Coal gasification is a key technology for the clean and efficient utilization of coal. A large amount of fine slag is produced during the coal gasification process. The utilization of gasification fine slag is limited by its complex car⁃ bon⁃ash fusion structure and high moisture content. The carbon ash separation is a necessary process for the utilization of gasification fine slag. In this study，the froth flotation method was used for the carbon⁃ash separation of gasification fine slags from three different gasification processes (SNB1 fine slag，XTY fine slag，and JC fine slag)，then the basic properties and moisture holding capacity of gasification fine slag and its carbon⁃ash separation products were analyzed. Moreover，the Fourier transform infrared spectrometer，scanning electron microscope and physical adsorption instrument were adopted to comparatively study the physical and chemical structure of different gasification fine slag and its carbon⁃ash separation products，which is expected to provide reference for the low⁃cost disposal and resource utilization of gasification fine slag. The results show that the carbon and ash could be separated to varying degrees by the forth flotation process. The froth flotation process can effectively separate the spherical mineral particles that ex⁃ ist alone from the residual carbon particles. However，the spherical mineral particles melted or attached to the surface of the residual carbon particles and in the pores were difficult to be separated. Among them，the SNB1 fine slag has the best carbon⁃ash separation effect. The ash content in the SNB1 residual carbon was reduced to 38. 65%. At the same time，the ash content of tail ash could be achieved to 99. 16%. After froth flotation，the moisture holding capacity of the residual carbon and tail ash are reduced to varying degrees compared with the corresponding raw gasification fine slag， among which the decreasing amplitude of the moisture holding capacity of three kinds of tail ash is significant (79. 34%-96. 61%). There are a large number of cylindrical pores in the gasification fine slag and its flo⁃ tation separation products. The carbon⁃ash separation process makes the fine spherical mineral particles， which blocked the pores of the residual carbon particles partially detached，resulted in the increase of micropores and meso⁃ pores in the residual carbon，thereby the specific surface area of residual carbon also increased. The pores in tail ash were mainly composed of the gaps formed by the mutual melting of spherical mineral particles. The carbon⁃ash separa⁃ tion process partially removed the hydrophilic fine spherical mineral particles entrained in the residual carbon pores. Thus，the silica hydrophilic sites in residual carbon were relatively reduced，which made the moisture holding capacity of the residual carbon reduced，compared with the raw fine slag. Due to the lowest specific surface area (29. 383- 46. 875 m2 /g)，the tail ash had the lowest moisture holding capacity.