Oily collector pre-dispersion for enhanced surface adsorption during fine low-rank coal flotation

[Display omitted] •A novel low-rank coal flotation flowsheet (collector pre-dispersion) was proposed.•Collector pre-dispersion enhanced the low-rank coal flotation recovery by 5–10%.•The oil–water–coal contact angle was significantly larger than that of oil–coal.•Oil molecules self-aggregated into spheres when water molecules were adsorbed first.•Water molecule adsorption was inhibited when oil molecules were adsorbed first. The prior adsorption of water molecules on low-rank coal surface suppresses the adsorption of collectors and decreases the surface hydrophobicity during flotation. To improve the adsorption of oil molecules, this study proposed an innovative flotation flowsheet, i.e., oily collector pre-dispersion. Oily collector pre-dispersion enhances the flotation recovery by 5–10% compared with the traditional flowsheet. The underlying oil/water‒coal interaction mechanisms were investigated by combining experiment and simulation. The results indicated that oil droplets adsorbed quickly on the low-rank coal surface in an air environment and, notably, the contact angle was smaller than that of a water droplet. However, in a water environment, the contact angle of the oil droplet on the low-rank coal surface was large and stable. Molecular dynamics simulations of coal/oil/water adsorption configurations revealed that oil molecules self-aggregated into spheres when water molecules surrounded the low-rank coal surface. In contrast, water molecules were largely repelled when the oil molecules were preadsorbed on the low-rank coal surface. Adsorption capacity measurements directly confirmed that the adsorption capacities of oily collectors improved with collector pre-dispersion. Thus, water/coal adsorption can be controlled by realizing full contact between oil and low-rank coal. This finding suggests a technical modification that can be adopted to enhance low-rank coal flotation.