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: The invention relates to a method and apparatus for sorting out recycled paper pulp obtained from scrap material containing contaminants in the form of large pieces of foreign material such as plastics, adhesives, pieces of rope and the like.The invention avoids the need to disintegrate such large pieces of foreign material prior to their removal.The device of the invention comprises a drum (1) with an horizontal axis (2), an end wall (3) of the drum being fitted with a perforated plate (4) and an helical stirrer (5) having profiled blades rotating in a plane parallel to this plate at a short distance thereof, these blades having a transverse cross-section with a hydrodynamic profile adapted for generating a depression in front of the perforated plate, and a leading edge (6) forming a Bernouilli spiral with a constant angle of approximately 30.degree.