The present invention comprises: a separation silo, a discharge silo, a upper sidewall of the separation silo communicated with the discharge silo through a communication port, wherein an air curtain is disposed in the communication port to isolate the silos from each other, a discharge port is disposed at the bottom of the discharge silo, a suction outlet is mounted on the top of the separation silo, a feeding port is disposed at the lower part of a sidewall of the separation silo, which is precisely facing towards the underside of the end of the belt conveyer, a vibration trough is arranged at the lower part of the separation silo, a damper plate is disposed underside thereof, an air inlet is located underbelly thereof at the bottom of the separation silo, a rejection outlet is installed at the underside end of the vibrating trough.