A method for the thermal treatment of bulk materials in a rotary tube with at least one infrared light unit. Bulk material is introduced into the rotary tube, which is provided on its inner wall with at least one mixing element and in the interior space of which the pressure of the ambient atmosphere prevails. A heat treatment of the bulk material is performed by at least one electrical infrared light unit, which is arranged at the center of the rotary tube and the light cone of which is directed onto the bed of bulk material that lies on the inner wall of the rotary tube. The bulk material is discharged from the rotary tube. Water vapor is directed onto the surface of the bulk material. The vapor is introduced into the interior space of the rotary tube through a nozzle tube.