The fundamentals of flotation deinking

Flotation deinking is a separation process in which swarms of air bubbles are injected into a relatively low consistency pulp slurry so that hydrophobic contaminant particles attach to the hydrophobic bubble surface. As the bubbles rise, they carry the contaminants to the surface where they are removed from the system. Understanding the fundamentals of this complex process will help in developing flotation models that can be used in the mill to determine if a given process change will help or hinder flotation performance before an expensive mill trial is attempted. In addition, knowledge of these fundamentals can also be used to improve equipment performance. The purpose of this paper is to review the fundamentals of flotation separation. Since flotation use in paper recycling was adopted from the mineral processing industry, flotation deinking will be compared to mineral flotation. The fundamentals of mineral flotation, when applied to flotation deinking, are assumed to be similar, and the fundamental microprocesses related to flotation will be reviewed. These microprocesses, including capture (or interception), attachment by sliding, three-phase contact, and stability, are typically utilized to model flotation separation, and selected models will be summarized. Finally, the bridge between the fundamentals of flotation deinking and the current technology used in the pulp and paper industry will be briefly reviewed.