An apparatus is described which serves for a pyrometallurgical processing of fine-grained solids suspended in high-oxygen gases, comprising a generally horizontally extending cylindrical vessel and a combustion shaft, which communicates with and vertically opens into the vessel which is provided with a gas outlet opening and with an opening for discharging molten material. An almost complete separation of the molten particles is effected in that the mouth of the combustion shaft tangentially opens into the vessel at the entrance of a spiral-shaped entrance passage, which opens into a discharge slot, which is formed in the shell of the vessel and which in the lower portion of the shell of the substantially cylindrical vessel extends substantially parallel to the longitudinal axis of the vessel.