Abstract: In deinking, the flotation of fiber suspensions is performed in a cylindrical tank 2 to which the fiber suspension is fed through a coupling means 36 as primary stream. The fiber suspension is already aerated and is withdrawn through a suction connection 33 below the coupling means 36 and fed after another aeration through a secondary connection 35 above the coupling means. The volume of the circulated secondary stream is greater than the volume of the primary stream. It is thereby assured that the fiber suspension is aerated at least twice and thus better cleaned.

Abstract: The aeration of dispersions, especially the aeration of fiber suspensions in a flotation apparatus 1, is performed with a ring injector 2 to which air is delivered through air feed ducts 11 in the mixing section 4. The annular gap forming in the ring injector 2 is thus aerated inside and out. The center core 7, which tapers in the direction of the greatest free cross section Q4 of the ring injector 2, is provided with a fin 56 which prevents the rotation of the dispersion.

Abstract: Flotation apparatus for de-inking of pulp suspension in a flotation cell with injectors for feeding the pulp suspension into the cell and for aerating the pulp suspension. The injectors are equipped with wide slot nozzles through which the suspension flows having a ratio of cross-sectional area to periphery of between 1.5 mm and 4.0 mm. A mixing chamber receiving pulp suspension flow from the wide slot nozzles is provided having a cross-sectional area which is between 1.3 to 1.7 times the cross-sectional area of the wide slot nozzles.

Abstract: A pulp suspension of waste paper which is laden with air bubbles is introduced into a flotation cell. Fine air bubbles rise through the pulp suspension toward the top. Printing ink and other impurities are deposited on the bubbles which form a foam layer on the surface of the pulp suspension. The foam which is laden with impurities is drawn off from the surface. The fibers which have been subjected to preliminary purification in this manner sink downwardly. For reducing the number of cells connected in series to fewer than a third, while obtaining the same degree of whiteness, the fibers which were subjected to preliminary purification are drawn off and are once again supplied to the flotation cell in the form of an air-laden pulp suspension. Alternatively, instead of the air-laden pulp suspension, a water-air suspension can be injected. The air bubbles which are thus introduced once again rise toward the top and traverse the sinking fibers in a counterflow.