Abstract: The removal of sticky contaminants during the production of recycled paper is accomplished utilizing a hydrocyclone froth flotation process. Paper having sticky contaminants from labels, tapes, hot melts, and other tacky substances, is reduced to a finely comminuted liquid solids suspension of about 1-4% consistency. The suspension is introduced into a first end of a vortex in a hydrocyclone, and the air is sparged radially inwardly into the suspension vortex by passing it through a porous inner wall of the hydrocyclone. Ligher weight sticky contaminants move to the center of the hydrocyclone, facilitated by the radially inward movement of the sparging air, and hydrophobic sticky contaminants attach to the air bubbles and form a foam. The foam and lightweight sticky contaminants are removed from the first end of the vortex, while the pulp which has had sticky contaminants removed therefrom is discharged from the second end of the vortex, opposite the first end.

Abstract: Deinking of paper having print during the production of recycled paper is accomplished by a froth flotation process using a hydrocyclone. A finely comminuted liquid solids used paper suspension having a consistency of about 1 to 4% is introduced into a generally vertical axis vortex provided in a hydrocyclone. Air is sparged into the suspension in the vortex, by passing through a porous inner wall of the hydrocyclone, to cause ink particles to attach to the air bubbles and to rise in a foam while cellulosic pulp moves downwardly in the vortex. The foam--containing the ink particles--and the pulp are removed from the vortex in separate streams. The pulp is deaerated and the air component of the foam is removed in the cyclone. About 5-15% of the total flow of the suspension is removed with the foam in each stage, and about 95-85% with the pulp.