(76d) Toner Particle - Bubble Interactions in Deinking Flotation

The demand for recycled fiber, coupled with the availability of new printing technologies and the prevalence of new contaminant varieties, has brought about an increased need to better understand flotation processes. Deinking flotation is a separation process that uses bubbles to remove contaminant particles from the repulped fiber slurry stream. Successful flotation depends upon a complicated combination of surface chemistry and fluid mechanics, with the central phenomenon being the interactions of solid particles with rising bubble interfaces.

This talk will present results from high-speed imaging techniques used to study the behavior of toner particles at bubble surfaces. Methods for the examination of the interactions between particles and stationary and flowing bubbles will be discussed. Imaging results have been used to quantify the effect of system parameters on the mass of ink adsorbed to each bubble. Results of these techniques are used to examine the role of particle size, surfactant type, and Calcium ion concentration in the deinking flotation of toner ink particles. Our techniques have shown oleate fatty acid surfactant to be superior to lauryl sulfate for promotion of toner particle adhesion at bubble surfaces. For the particles size ranges studied, the mass of ink attached to each bubble doubled with oleate compared to lauryl sulfate. Calcium ions are also seen to be helpful in promoting adhesion in the systems studied, compared to sodium ions. The implications of these findings to deinking plant operations will be discussed.