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.