Promotion of hydrophobic-hydrophilic separation of coal gasification fine slag through ultrasonic pre-treatment

Coal gasification fine slag (CGFS) is a solid waste byproduct generated during the coal gasification process. However, the high content of residual carbon hinders its potential for resource utilization. The urgent need for an efficient carbon extraction and ash reduction technology is evident. Hydrophobic–hydrophilic separation (HHS) is a technology that enriches hydrophobic particles in the oil phase while hydrophilic particles are in the water phase by stirring, and the different hydrophobic particles are separated by the separation of the oil and water phases. The molecular dynamics simulations revealed that the adsorption of n-heptane onto the residual carbon surface occurred spontaneously and was primarily driven by van der Waals forces. Ultrasonic pre-treatment pulp could enhance the effect of HHS. The fluctuation in tailings ash did not exceed 2% while the concentrate ash was reduced from 31.81% to 18.93% with a continual increase in ultrasonic power. The application of ultrasonic treatment on CGFS facilitated the separation of Carbon-ash molten state, as well as the elimination of ash materials particles residing within the pores of the residual carbon matrix and on its surface. Notably, many residual carbon particles are concentrated in the particle size range of 0.045–0 mm. The heightened hydrophobicity exhibited by particles within this size range enhanced the capture of oil droplets, thereby promoting the efficiency of HHS. This research aims to provide technical support and theoretical foundation for utilizing ultrasonic pretreatment as a means to enhance the HHS efficiency of CGFS.