Emulsified Collectors in Coal Slime Flotation: Linking Collector Dispersion, Flotation Performance, and Microbial Survival

Emulsified collectors (ECs) have attracted increasing attention in coal slime flotation because of their superior dispersion characteristics and collecting performance compared with conventional hydrocarbon collectors. However, the relationship between flotation performance and the effects of ECs on microorganisms in circulating water remains poorly understood. In this study, four ECs were prepared using cationic (dodecyltrimethylammonium bromide (DTAB)), anionic (sodium dodecyl sulfate (SDS)), nonionic (Tween-80), and solid particle-based (β-cyclodextrin (CD)) emulsifiers. The droplet size distribution, flotation performance, adsorption behavior, and microbial response were systematically evaluated. The results showed that ECs significantly improved coal slime flotation compared with conventional kerosene. Among the surfactant-based ECs, smaller oil droplet sizes resulted in higher clean coal recovery, demonstrating the critical role of collector dispersion in flotation performance. Fourier transform infrared spectroscopy provided qualitative evidence of stronger relative adsorption of ECs on coal surfaces than that of conventional kerosene. Yeast survival tests revealed that all ECs exhibited less adverse impact on microorganisms than kerosene. However, for surfactant-based ECs, microbial survival decreased as flotation performance increased. A preliminary negative correlation (R2 = 0.9323, n = 4, where “n” denotes the number of collector formulations tested) was observed between the yeast survival rate and the number of oil droplets, suggesting that fine oil droplets remaining in the aqueous phase may have contributed to reduced microbial viability. In contrast, the β-CD-stabilized Pickering emulsion achieved both the highest flotation efficiency index (56.22) and the highest yeast survival rate (66.49%), outperforming Tween-80-EC (54.90 and 58.65%), SDS-EC (50.95 and 61.45%), DTAB-EC (50.08 and 63.31%), and conventional kerosene (40.32 and 53.35%). These findings demonstrate the importance of balancing flotation performance and environmental compatibility in the design of sustainable flotation collectors for coal processing.