Investigation on mechanism of the oleic acid/methyl oleate/diesel ternary compound collector in low-rank coal flotation

Polar and compound collectors are current research hotspots in the field of low-rank coal (LRC) flotation. However, most studies only focus on the collecting ability of collectors while ignoring its selectivity. This study presents the design for a novel high-efficiency ternary compound collector (oleic acid (OA), methyl oleate (MO) and diesel) with great selectivity, strong collecting and spreading ability for Sujiagou LRC. In comparison to diesel, the clean coal yield is increased by 41.40%, and its ash content is reduced by 0.91% at optimal dosage of 2000 g/t. And we propose some new insights on the mechanism of ternary compound collector through density functional theory (DFT) calculations, focused beam reflectance measurement (FBRM), and molecular dynamics (MD) simulations. OA has the strongest collecting ability with the shortest adsorption distance and smallest frontier orbital gap, which ensures the flotation efficiency and collecting ability of ternary compound collector. The great selectivity of ternary compound collector owing to these two reasons: MO adsorbs more strongly on the LRC surface through the flat-lying adsorption at the junction of hydrophilic and hydrophobic parts; the "wasteful adsorption" on the gangue surface is prevented as the nonpolar parts of ternary compound collector attract polar collectors. Finally, a firm oil film with strong spreading ability is formed on the LRC surface, which can achieve a spread across the hydrophilic area even without the adsorption of polar collectors. The synergistic adsorption not only improves the collecting ability of the ternary compound collector but also ensures its selectivity.