Abstract: An apparatus for separating metal particles from a material stream of a bulk material, comprising a detection device for detecting metal particles in the material stream and a separating device configured to separate a portion of the material stream in which the metal particles are contained, the separating device comprising a housing having a material inlet, a good-material outlet and a bad-material outlet; a rotary piston rotatably mounted in the housing and configured to guide the material stream from the material inlet to the good-material outlet or to the bad-material outlet depending on the detection result of the detection device; a drive unit configured to position the rotary piston at least in a first and a second rotary position; wherein the drive unit is configured to rotate the rotary piston between the first rotary position and the second rotary position by an angle of rotation greater than 90°.