| 摘要 |
PCT No. PCT/DE79/00090 Sec. 371 Date Apr. 21, 1980 Sec. 102(e) Date Apr. 21, 1980 PCT Filed Aug. 18, 1979 PCT Pub. No. WO80/00423 PCT Pub. Date Mar. 20, 1980. 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. As a result, an intensive air-pulp contact is created.
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