Study on recovery of residual carbon from coal gasification fine slag and the influence of oxidation on its characteristics

Coal gasification fine slag (CGFS) is a kind of solid waste that is difficult to separate and utilize. In this work, ultrasonic-assisted flotation was used to recover residual carbon (RC) from CGFS. The ultrasonic treatment not only promotes the separation of RC and ash, but also improves the surface hydrophobicity of CGFS. Compared with conventional flotation, the loss on ignition (LOI) of concentrates and flotation perfect index obtained by ultrasonic-assisted flotation were increased by 12.21% and 4.57%, respectively. In addition, the RC was modified by air and steam. The characterization results of the samples show that air oxidation can significantly improve the oxygen-containing groups on the RC surface, especially the CO groups, and steam treatment is more conducive to increase the disorder of carbon microstructure. Furthermore, the textural properties of the RC were developed by air-steam treatment, and the highest specific surface area and pore volume of the oxidized RC were increased by 27.25 times and 6 times than the raw RC, respectively. RC-A2S2 obtained by air-steam alternating treatment had a high CO2 storage capacity of 2.00 mmol/g at 25 °C. The above research results have important reference value for strengthening of CGFS flotation and utilization of RC.