Abstract: An apparatus and operation is disclosed in which light solid material such as shredded paper passes from an upper end of a column and heavier material such as glass and metal particles drop from a lower end of the column. The column includes an air locked feed chute having a downwardly inclined material feeding surface, that opens intermediate the column ends into a stream of air moving upwardly in the column, for admitting mixed light and heavy solid particles of refuse material to the air stream. The column beneath the discharge end of the chute has vertical walls defining a rectangular air intake zone. The vertical wall opposite to and facing the chute is pivotally hung from an inclined member which is in turn pivotally supported by the column so this pivotally hung wall can move toward and away from the chute while remaining vertical.