An apparatus for conveying, comminuting and mixing materials comprising/not comprising solid matter having a stator (8) featuring teeth extended inwardly comprises a plurality of racks (13) arranged alongside each other. These racks (13) are held at the ends of the stator (8) in fixing rings (15). The racks (13) may be arranged with a spacing (17) from each other which is defined by blades (16) formed on the fixing rings. The toothed sections of the rotor or impeller (7) and of the racks (13) may be arranged replaceable. Between the inner wall (22) of the casing (2) and the outer wall (21) of the stator cylinder a discharge passage (20) is provided which in a special embodiment is flared scroll-shaped in the direction of the discharge opening (6).