Exploration of innovative pathways for the preparation of ultra-clean coal from low-rank coal: a study on multi-stage flotation processes and mechanisms based on reagent synergy

Ultra-clean coal (UCC), valued for its low impurity content and high added value, is widely used in the production of coal-based carbon materials and as an industrial reductant. However, the production of UCC from low-rank coals presents significant challenges, primarily due to the weak interaction between the coal and flotation reagents. This study aims to improve the flotation performance of low-rank coal by exploring the synergistic effects of dodecane and Span80, as well as the impact of pH control on the flotation process. A series of flotation experiments were conducted using a combination of dodecane and Span80 (SD3 reagent) in a mass ratio of 7:3. The flotation process was optimized by adjusting the pH to 5 and employing a three-stage flotation approach. The results demonstrated that the SD3 reagent significantly improved the hydrophobicity of low-rank coal, promoted the formation of hydrophobic flocs, and enhanced foam stability. At an optimal pH of 5, UCC was obtained with a yield of 41.12% and an ash content of 1.95%. In conclusion, this study provides valuable insights into the synergistic mechanisms of reagent action and pH regulation in the flotation of low-rank coal, offering a viable pathway for the efficient production of UCC.