(703a) Advanced Froth Flotation Using Oil-Coated Bubbles and Its Application in De-Inking

Froth flotation is a highly efficient solid-liquid separation technique with a history of more than one century. It has been applied in many industrial processes, such as wastewater treatment, mining operations and paper recycling. The separation mechanism is that hydrophobic particles can attach to rising gas bubbles and are lifted to the top, creating a layer of froth which can be skimmed off, whereas more hydrophilic particles cannot attach to gas bubbles and will remain in the mixture. In many cases, however, the particles that we want to separate are less hydrophobic and cannot attach to gas bubbles. To overcome this limitation, our strategy is to coat the gas bubbles with a thin layer of oil, making the bubble surface more polar compared to uncoated bubbles; as a result, less hydrophobic or even mildly hydrophilic particles can attach as well. In the present work, we show that oil-coated bubble flotation has thermodynamic, kinetic and hydrodynamic advantages over the traditional method. With regard to flotation de-inking as a practical application, we find that oil-coated bubbles are far more efficient than uncoated bubbles at removing hydrophilic ink pigment particles from aqueous solutions.