Abstract: A rotary air classifier for separating light material from a mixture of heavy and light material, or for separating large particles from small particles in a single material or a mixture of materials, such as in the sorting of municipal garbage, in which a tapered, e.g. frusto-conical, vessel is mounted about an axis, so that the lower surface of the vessel slopes downwardly towards the open lower end. Air is caused to spiral from the open lower end to the open upper end and takes with it the ligher fraction of material to be classified. The heavy articles slide or roll downwardly out of the open lower end.