Efficient flotation recovery mechanism of residual carbon from coal gasification fine slag by liquid paraffin pretreatment

Coal Gasification Fine Slag (CGFS) is a type of solid waste that is rich in residual carbon. However, the complex pore structure and severe surface oxidation of CGFS have limited the efficient recovery and utilization of residual carbon. In this study, the liquid paraffin (LP) was used as the pretreatment reagent to improve the flotation recovery of residual carbon from CGFS. The mechanisms were investigated by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), zeta potential, fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible spectrophotometry (UV–VIS), microcalorimeter, and contact angle measurements. Compared with the conventional flotation without the presence of LP, the concentrate yield, loss on ignition, residual carbon recovery and separation efficiency by LP was increased by 21.59%, 11.24%, 44.09%, 29.91%, respectively. SEM-EDS results indicated that the raw CGFS surface was covered with numerous fine inorganic mineral particles. For CGFS with LP-kerosene (KE) treatment, the fine inorganic mineral particles on CGFS surface were significantly reduced. LP physically pre-adsorbed on residual carbon surfaces to enhance the adsorption amount of KE on residual carbon. The surface of CGFS adsorbed by LP and KE was covered by the hydrophobic oil film, significantly masking the hydrophilic groups and enhancing the hydrophobicity of residual carbon. As a result, the flotation performance of residual carbon from CGFS was obviously improved by LP. This study will provide important theoretical value and technical reference for the efficient flotation recovery of residual carbon from CGFS and carbon solid waste resource utilization.