Oil-Coated Bubble Flotation for Separating Hydrophilic Particles from Water

Froth flotation is a widely used method for the selective separation of particulates from aqueous dispersions or slurries. This technology is based on the attachment of sufficiently hydrophobic particles to the air–water interface of gas bubbles. However, when the target particles are strongly hydrophilic, the requirement of hydrophobicity limits the effectiveness of conventional froth flotation. A prominent example is the deinking step in paper recycling, where modern hydrophilic inkjet inks are difficult to remove by flotation. In this study, we evaluated oil-coated bubble flotation as an alternative to conventional air flotation for removing inkjet ink from pulped newsprint. We examined the effects of oil type, salt type and concentration, and pH on deinking efficiency. Compared with traditional air flotation, oil-coated bubble flotation produced substantial improvements in standard performance metrics, including ISO brightness, effective residual ink concentration (ERIC), and the fiber retention of recycled paper pads.