Abstract: Separating a mixture comprising at least two solid materials comprises transporting the mixture into a plenum, introducing air into the plenum, removing a heavier fraction of the solid materials from the plenum, removing air having a lighter fraction of the solid materials entrained therein from the plenum, removing the lighter fraction of the solid materials from the air that is removed from the plenum, filtering the remaining air, and re-circulating the air back to the plenum. Valves at the locations where material is introduced to and removed from the system can prevent air flow therethrough while allowing the materials to pass. The air can be introduced into the plenum at an angle with respect to the pathway in which the heavier fraction of the materials falls through the plenum, thereby avoiding damage to a screen that diffuses the air being introduced into the plenum.

Abstract: Separating a mixture comprising at least two solid materials comprises transporting the mixture into a plenum, introducing air into the plenum, removing a heavier fraction of the solid materials from the plenum, removing air having a lighter fraction of the solid materials entrained therein from the plenum, removing the lighter fraction of the solid materials from the air that is removed from the plenum, filtering the remaining air, and re-circulating the air back to the plenum. Valves at the locations where material is introduced to and removed from the system can prevent air flow therethrough while allowing the materials to pass. The air can be introduced into the plenum at an angle with respect to the pathway in which the heavier fraction of the materials falls through the plenum, thereby avoiding damage to a screen that diffuses the air being introduced into the plenum.

Abstract: Separating a mixture comprising at least two solid materials comprises transporting the mixture into a plenum, introducing air into the plenum, removing a heavier fraction of the solid materials from the plenum, removing air having a lighter fraction of the solid materials entrained therein from the plenum, removing the lighter fraction of the solid materials from the air that is removed from the plenum, filtering the remaining air, and re-circulating the air back to the plenum. Valves at the locations where material is introduced to and removed from the system can prevent air flow therethrough while allowing the materials to pass. The air can be introduced into the plenum at an angle with respect to the pathway in which the heavier fraction of the materials falls through the plenum, thereby avoiding damage to a screen that diffuses the air being introduced into the plenum.