Effect of frother addition mode on coal flotation in down flow flotation column

Using a downflow flotation column, we comparatively investigated the effects of two frother addition modes on clean coal production and bubble characteristics. These modes are traditional frother mode, which involves the direct addition of liquid Sec-Octyl alcohol (2-octanol) to slurry, and a novel addition mode, which injects 2-octanol vapor into the bubbles. Compared with the traditional mode, the vapor addition mode produced a higher concentrate yield, lower ash content, and higher combustible matter recovery. This result suggests that the vapor addition mode facilitates the larger product yield, producing a cleaner coal product. The consumption of 2-octanol under the liquid addition mode was reduced by 53.57% compared with that under the vapor mode to achieve 83% recovery of combustible matter. In the first 0.5 min and last 1.0 min of the 3 min flotation time, the vapor addition mode showed a slower flotation rate, whereas in the middle 1.5 min, the rate was faster. In addition, the vapor addition mode led to a smaller bubble size, critical coalescence concentration (CCC), and 23.21% reduction in 2-octanol consumption to achieve a constant bubble size. The higher capture probability of hydrophobic coal particles presented by the vapor addition mode is considered the fundamental cause for the enhanced clean coal yield and combustible matter recovery. With the increase in frother dosage, the particle-bubble collision probability was identified as the main factor determining the increase in the ash content of the concentrate at a concentration below the CCC. At a concentration above the CCC, the viscosity of bubble surfaces became the main factor. (C) 2020 Elsevier Ltd. All rights reserved.