Abstract: A re-entrant circulating stream mill vents a part of the circulating stream adjacent the annular peripheral wall of the mill directly to the junction in each of a plurality of sets of pressure nozzles and cooperating acceleration tubes which are used to form the circulating stream. Each pressure nozzle provides a high velocity gaseous jet stream that entrains material as it enters the acceleration tube where the material is accelerated to its maximum velocity before it is discharged into the vortex chamber of the mill and impacts upon the circulating stream adjacent the annular peripheral wall of the vortex chamber. The apparatus also takes advantage of the comminution of the material which takes place in the acceleration tube.