Innovative separation strategies for low-rank coal flotation: Filling self-generated pores with gutter oil collectors to enhance hydrophobic sites

Low-rank coal (LRC) has strong hydrophobicity, which leads to low efficiency in conventional flotation that coal particles need to be mixed with water first, making it difficult for collector molecules to replace water molecules. An innovative technology for microwave heating to remove moisture and dry adsorption of gutter oil collectors was proposed to make the collectors efficient in adsorbing on coal surface. Firstly, the particle morphology and phase composition of LRC were analysed through SEM and XRD to clarify the impact of particle morphology and mineral composition on floatability. Furthermore, the functional group composition and hydrophobic group content of the modified LRC were analysed by FTIR and XPS, respectively. Contact angle analysis and wrap angle analysis were used to investigate the stability of particle-bubble adhesion. Finally, flotation experiments and flotation kinetics analysis were conducted to verify the flotation characteristics of modified LRC. The SEM analysis results indicate that the high porosity of LRC can intercept more water and form a thick water film. The XPS analysis results indicate that the content of hydrophobic groups in LRC is only 61.69 %, which is the core reason why it is difficult for LRC to float. The content of hydrophobic groups C–C/C–H in modified LRC increases to 86.05 % after collector adsorption. In addition, the contact angle increases from 13.71° to 74.63°, further improving the adhesion stability between LRC particles and bubbles, while the wrap angle increases from 18° to 131° for 0.5–0.25 mm. Compared to raw coal, the combustible recovery of modified LRC increases from 23.13 % to 66.89 % with a collector dosage of 9000 g/t. The flotation kinetics results demonstrate that the flotation characteristics of various particle sizes of modified LRC have been significantly improved. Research provides an innovative and sustainable way to improve the flotation efficiency of LRC.