Aerosol-enhanced deinking of recycled paper by column flotation

Flotation deinking has become the process of choice for removing ink from re-pulped paper. Hydrophobic ink particles are removed from the pulp after collection and transport by rising air bubbles. Previous work demonstrated that coating air bubbles with an insoluble liquid (silicone oil) enhanced their ability to remove carbon black particles from a dispersion in water. Bubbles were coated with the oil by dispersing air containing small oil droplets (aerosol). This work describes tests designed to establish the effectiveness of aerosol-enhanced flotation in the deinking of industrial pulps. The experiments were run at Bowater's Gatineau mill (Quebec) in a laboratory flotation column provided with an aerosol generator and an Venturi aerator. The column was fed continuously with pulp diverted from the line feeding the plant flotation circuit. The results showed that, for otherwise equivalent conditions, higher gas holdups were obtained when silicone oil was used, and the use of silicone oil substantially reduced the amount of air required to match plant brightness gains.