Flotation Chemistry
Anionic surface-active agents derived from vegetable or tall oil fractions condition hydrophobic ink particles for selective separation in paper deinking cells. Formulating fatty acid collectors enables the preferential attachment of detached offset and flexographic ink residues to rising air bubbles during pulp flotation. These chemicals adsorb onto dispersed pigment particulates, converting weakly hydrophilic pigment surfaces into hydrophobic agglomerates ready for froth skim removal.
Standard industrial practice employs saponified oleic, linoleic, or stearic acid blends. The scope remains restricted to flotation deinking, leaving mechanical screening, hydrocyclone cleaning and bleaching chemistry unaffected.
Agglomeration Dynamics
Froth stability depends directly on collector carbon chain distribution and calcium hardness in the repulped slurry. Introducing fatty acid collectors into the deinking loop requires dissolved calcium ions, which form insoluble calcium soap bridges between fatty carboxylate groups and ink resins. This bridge builds larger ink agglomerates measuring between 10 and 150 microns.
Particles falling below this size escape air bubbles, while oversized ink flocs drop back into the pulp suspension under excessive turbulent shear. Operating flotation cells at elevated alkaline pH maximizes collector ionization. Temperature swings alter solubility and cause surface-tension drops across flotation tanks.
Furnish Cleanliness
Ink elimination efficiency determines recycled paper whiteness, cleanliness and suitability for direct food-contact boxboard. Regulating the addition of fatty acid collectors reduces residual ink concentrations, lowering effective residual ink concentration values before subsequent pulp brightening stages. Low collector dosages result in poor ink detachment, leaving specks visible on finished linerboard sheets.
High dosages generate excessive foam volume, entrapping valuable short cellulose fibers and increasing fibre yield loss in the flotation reject stream. Effluent treatment plants monitor collector wash water to prevent grease-trap blockages and chemical oxygen demand surges. Precise flotation chemistry balances optical brightness targets against fibre retention economics.
