Abstract: Efficient flotation separation of rhodochrosite and quartz fines is very important for extracting manganese and reducing impurity from manganese carbonate ores, and influence of the inevitable ion Mn2+ on flotation behavior of quartz cannot be ignored. In this study, fine quartz was selected as the object. We investigated the mechanism of effect of Mn2+ on the agglomeration and flotation behavior of fine quartz using aggregate properties characterization, micro flotation, adsorption amount measurement, surface properties analysis, and DLVO theory calculation. The results indicates that oleic acid has no agglomeration and flotation effect on quartz fines. However, after the addition of Mn2+ and oleic acid, the apparent particle size and recovery ratio of quartz increases significantly, as well as the surface hydrophobicity. As Mn2+ and oleic acid concentration increase, the particle size and recovery ratio of quartz first increase and then decrease. In a weakly alkaline environment, Mn2? has a significant activating effect on both the agglomeration and flotation of quartz, with the optimal activation pH being 10. When the concentrations of Mn2+ and oleic acid are both 1×10-2 mol?L-1 and the pH is 10, the Dmean of quartz agglomerates is greater than 50 μm, along with the 30-100 μm volume content of greater than 50% and recovery ratio of greater than 87%. In addition, the monolayer adsorption density of oleic acid on the quartz surface is larger, resulting in the higher hydrophobic. Mn2+ can be adsorbed on the quartz surface through electrostatic attraction, providing active sites (-Si-O-Mn+) for adsorption of oleic acid and inducing hydrophobic modification of quartz. Furthermore, Under weakly alkaline conditions, Mn(OH)? and Mn?(OH)?? interact with RCOO? and (RCOO)?2?, forming strong hydrophobic interactions on the quartz surface through both physical and chemical adsorption. These hydrophobic interactions can overcome the electrostatic repulsion, thereby promoting agglomeration and flotation of quartz. However, in the strong alkaline environment, Mn(OH)2 colloid dominates the Mn species, which inhibits the adsorption of oleic acid on quartz surface. Therefore, regulating the pulp environment to be weakly acidic can avoid the activation of quartz by Mn2+ with oleic acid, which is conducive to the selective agglomeration and flotation separation of rhodochrosite and quartz.