Renewable collectors derived from plant extracts for sustainable flotation of lignite: experimental studies and theoretical insights

COB was synthesized with a predominant composition of ester compounds, constituting approximately 97% of its main components. Flotation experiments revealed that the combustible material recovery rate of CO was about 17% lower than that of COB, while its ash content was approximately 4% lower than that of diesel and 5.5% lower than that of COB. Although the selectivity of the CO collector was superior, the combustible material recovery rate achieved with COB was higher. The co-flotation performance of COB and CO was investigated. It was found that the distance between the active functional groups in the collector molecules and the oxygen-containing functional groups on the lignite surface was shorter compared to when COB was used alone, leading to stronger interactions. This enhanced the surface coating properties of the coal particles, effectively hindering the interaction between water molecules and the coal surface, thereby improving the hydrophobicity of the lignite. When the mass ratio of CO to COB was 1:1, the composite collector exhibited the best flotation performance. The combustible material recovery rate was approximately 10% higher than that achieved with diesel, while the ash content of the product remained around 14%. This demonstrates that the composite collector significantly improves both flotation performance and selectivity.