Removal of resin from mechanical pulps by selective flotation: Mechanisms of resin flotation and yield loss of fibers

The amount of wood resin in mechanical pulp suspensions could be decreased using a selective flotation process. In selective flotation air-bubbles are dispersed into low consistency pulp suspensions mechanically by an impeller or by injectors. Resin particles attach to the air-bubbles and are lifted to the top of the pulp suspension from where they are removed, along with the flotation froth. The very small size of the resin particles (average diameter < 1.0 micron) suggests that they are driven toward the air-bubbles mainly by Brownian diffusion and that attachment of the resin particles to the air-bubbles takes place through colloidal interactions. The resin flotation followed approximate first-order kinetics. The mechanism of yield loss of fibers was entrainment, whereby they were hydraulically transported into the froth along with the water.