Removal Mechanism
Separation physics governs the industrial extraction of non-cellulosic impurities from a pulp suspension through the selective attachment of hydrophobic contaminants to rising air bubbles. Flotation deinking relies on the density differential between ink particles and the water medium to facilitate removal at the surface of a flotation cell. Small air bubbles are injected into the tank to capture ink pigments, fillers, and binders that have been chemically detached from cellulose fibres.
These hydrophobic clusters form a stable foam layer that overflows the weir, effectively cleaning the stock for further processing. Secondary cleaners operate downstream to catch residual contaminants that bypass the initial air bubble capture.
Process Performance
Mill operators tune the chemical environment to manage the efficiency of ink recovery while preserving the mechanical integrity of the recovered fibre. Flotation deinking efficiency depends on the dosage of surfactants that lower surface tension and promote air bubble collision with ink particles. The sizing of these bubbles remains tight to ensure they collide with hydrophobic contaminants rather than the paper fibres themselves.
Calcium ions are frequently added to stabilize the process by reacting with fatty acids to form soap precipitates that improve particle capture. Excessive chemical dosage reduces the quality of the output by trapping air in the pulp, whereas insufficient chemistry results in grey or speckled final sheets. The slurry temperature must remain consistent throughout the run to prevent variations in bubble size or particle attachment rate.
Accurate control of the aeration rate ensures that the volume of foam produced matches the rate of ink removal, preventing the loss of usable long fibres in the sludge.
Grade Constraint
Final pulp cleanliness determines the brightness and opacity levels achievable when the recycled fibres are converted into new paper rolls. Flotation deinking produces a stock with significantly lower residual ink content than washing techniques alone, which makes it suitable for high-grade graphic paper and tissue manufacturing. Packaging mills rely on this procedure to remove dark adhesives and plastic particles that affect the structural strength of a box.
High-purity recycled stock requires an optimal feed consistency to prevent particle redeposition onto clean fibres during the flotation phase. Consistent removal of impurities stabilizes the wet end of the paper machine.
