In a known method for treating pourable, inorganic grain, a heated rotary tube is used that rotates about an axis of rotation and surrounds a treatment chamber that is divided into a plurality of treatment zones by means of separating elements. The grain is supplied to the treatment chamber at a grain inlet side and is transported, in a grain transport direction, to a grain outlet side and is exposed to a treatment gas in the process. In order, proceeding herefrom, to allow for reliable and reproducible thermal treatment of pourable inorganic grain, in particular SiO.sub.2 grain in the rotary kiln, in a manner having low and effective consumption of treatment gas, it is proposed for spent treatment gas to be suctioned out of a reaction zone of the treatment chamber, by a gas manifold that rotates about the longitudinal axis thereof.

In a known method for treating pourable, inorganic grain, a heated rotary tube is used that rotates about an axis of rotation and surrounds a treatment chamber that is divided into a plurality of treatment zones by means of separating elements. The grain is supplied to the treatment chamber at a grain inlet side and is transported, in a grain transport direction, to a grain outlet side and is exposed to a treatment gas in the process. In order, proceeding herefrom, to allow for reliable and reproducible thermal treatment of pourable inorganic grain, in particular SiO.sub.2 grain in the rotary kiln, in a manner having low and effective consumption of treatment gas, it is proposed for spent treatment gas to be suctioned out of a reaction zone of the treatment chamber, by a gas manifold that rotates about the longitudinal axis thereof.