Performance study of nonionic surfactant-enhanced Fischer-Tropsch synthesis intermediate products in low-rank coal flotation

Low rank coal has the characteristics of low coalification degree, high volatile matter, and dense pores, therefore it has problems such as high reagent consumption and high flotation difficulty. This study investigates the effects and mechanisms of surfactant-enhanced Fischer-Tropsch synthesis intermediates (FTI) on the flotation of low-rank coal using a combination of experimental analysis and molecular simulations. When FTI was mixed with 5% surfactant, the collector exhibited improved flotation performance. Three flotation collectors were prepared by blending Span80 and Tween80 with FTI: SFTI-EM (emulsification treatment with Span80 and FTI), SFTI-CO (compound treatment with Span80 and FTI) and TFTI-EM (emulsification treatment with Tween80 and FTI). Flotation test results showed that SFTI-EM and SFTI-CO demonstrated outstanding flotation performance, increasing clean coal yield by 50% compared with diesel collectors. Under identical dosage conditions, SFTI-CO achieved approximately 5% higher clean coal yield than SFTI-EM, while SFTI-EM reduced FTI consumption by about 40%, indicating higher economic value. Molecular dynamics simulations revealed that Span80 molecules adsorbed more firmly on low-rank coal surfaces than Tween80, forming a "bridging" effect between hydrocarbon oil and coal surfaces, thereby enhancing hydrocarbon adsorption on coal. Additionally, the SFTI-EM emulsion exhibited an "oil-water-oil" multiphase droplet structure, facilitating reagent-coal contact. Contact angle measurements further suggested that surfactants contribute to forming more stable mineralized froth, further improving flotation efficiency. This study has not only developed a high-efficiency and economical flotation collector alternative to diesel, but also demonstrated the enhancing effect of non-ionic surfactants combined with FTI on low-rank coal flotation.