In a device for oxidizing, reducing, calcining, sintering or melting dusts such as, e.g., furnace or steel dusts, marl and lime dust mixtures, shredder light fractions, mineral dusts such as, e.g., glass dusts, cement kiln bypass dusts, dry sewage sludge, paper slurries or oil-containing grinding dust suspensions, using a dosing cyclone into which the dusts are charged and to which a tangential connector for feeding carrier gases is connected, and a combustion chamber following the dosing cyclone in the axial direction, wherein fuel and optionally additional carrier gas are injected into the combustion chamber coaxially with the discharge opening of the cyclone, a lance is arranged in the interior of the dosing cyclone, coaxially with the discharge opening of the dosing cyclone, for the introduction of liquid substances, substances dissolved in liquids or suspended in gases, or gaseous oxidizable substances and, in particular, fuels. According to the proposed method, the dosing cyclone is operated at a pressure reduced relative to the pressure prevailing in the fuel lance.