The invention relates to a system and method for separating pieces having a second density (9c) from granular material. The system includes a separation tank (2) comprising a first side wall (12) provided with a tank outlet (6), a bottom (7), a pipe (4) defining a channel (3a) for allowing a slurry to enter the tank (2). A pipe outlet (4b) is spaced apart from the tank outlet and arranged vertically below the outlet (6). The separation tank (2) comprises a trap (5) for collecting said pieces. A separation chamber (8a) is arranged in liquid communication with the pipe outlet to allow slurry to enter the separation chamber. The pipe outlet is in a lower third of the separation tank facing the bottom of the tank so that slurry flows vertically through the pipe outlet towards the bottom causing a turbulent flow of the slurry in the tank.