Aerosol-Enhanced Deinking of Recycled Paper by Column Flotation

McGill University McMaster University Cesar O. Gomez, Claudio Acuña* , James A. Finch, and Department of Mining and Metallurgical Engineering McGill University Robert Pelton McMaster Centre for Pulp and Paper Research McMaster University * Current address:Departamento de Ingeniería Química, Universidad Católica del Norte, Antofagasta, Chile

Abstract Flotation de-inking has become the process of choice for removing ink from re-pulped paper. Hydrophobic ink particles are collected and carried by rising air bubbles which remove them from the paper pulp. Coating air bubbles with an insoluble hydrophobic material (like silicone oil) increased the ability of the bubbles to remove carbon black particles from a dispersion in water. Forming a layer of hydrophobic material on the surface of bubbles was done by injecting small oil droplets into the air to form an aerosol. This work describes tests designed to establish the effectiveness of aerosol-enhanced flotation in the de-inking of industrial pulps.

Stages involved in flotation Transport: bubble-particle aggregate moves to the top Attachment: solid/water/air interface forms Collision: particle reaches the bubble surface

Flotation with oil-coated bubbles Oil-coated bubbles: attachment requires a solid/water/oil or a solid/oil/air contact line Air bubbles: attachment requires a solid/liquid/air contact line

Schematics of testing equipment Flotation column REJECTS P F FEED P F P ACCEPTS Aerosol generator F AIR Venturi aerator F OIL RECYCLE Syringe pump

Schematics of the system for generating and injecting aerosol into the column To flotation column Atomizing chamber AIR Ultra-sonic nozzle OIL FEED and RECYCLE

Plant results: effect of oil injection on brightness gain

Conclusions Dispersing an aerosol (silicone oil) in wastepaper pulp is an effective method to generate oil-coated bubbles. Gas holdup increases obtained when oil was injected indicated that bubbles were smaller or rose slower. Oil-coated bubbles showed an enhanced deinking ability (larger brightness gains). Use of silicone oil substantially reduced air requirements to match plant brightness gains.

Deinking flotation cells (Bowater) Ottawa