New Approach to the Selective Removal of Ink Particles by Flotation, 1996 Pulping Conference Proceedings

Hiromichi Takahashi, Yuichi lrinatsu, Takanobu Shiroishi, Takeshi Edo

Kao Corporation

Usually, deinking of newspaper is carried out under alkaline conditions with nonionic surfactants and/or fatty acids. Under alkaline conditions, the surface charge of both the ink particles and the pulp fibers are negative, c.-35mV and c.-10mV, respectively. i.e. all particles are strongly electronegative. If the pH of the pulp slurry is changed to neutral, it was found that although the surface charge of ink particles remains negative(c -25mV) , the charge on the fiber approaches zero. Therefore, in the neutral pH condition, a cationic promoter will preferentially associate with ink particles and make them into an aggregate, which is a more suitable size for flotation. Consequently, re-adsorption of ink on the fiber will be minimized, yielding higher brightness pulp. Laboratory flotation studies, under neutral conditions with specially prepared cationic promoters. were carried out to examine the above. Deinked pulp with higher brightness was obtained with lower fiber loss This trend confirmed under pilot plant conditions and selective removal of ink particles in the flotation process was achieved. The mechanism proposed, is one of electrostatic adsorption of the cationic promoter on the ink particles and subsequent aggregation of these ink particles. These aggregates being larger than I0 um are more effectively removed by the flotation process.