A method and means for maximizing the use of the kiln capacity in a rotary kiln, directly reducing metal oxides using solid carbonaceous materials as the source of fuel and reducant, is disclosed involving the creation of an annular dam arrangement within the kiln at a selected position between the feed end and the discharge end dams, which arrangement is located and dimensioned with respect to the end dams, such that the materials in the charge bed suitably fill the kiln volume and have sufficient residence time in the feed end portion of the kiln, to permit adequate heat transfer thereto, thus minimizing the portion of the kiln needed for preheating and maximizing the remaining portion of the kiln available for reduction. In a kiln of a given size, the spacing and dimensions of the end dams and one or more intermediate dams are designed in combination with the degree of kiln inclination, the kiln rotational speed and the required heat transfer rate to the surface of the charge bed to obtain a volume filling in the charge bed in the preheat zone, and hence a solids residence time therein, which is optimum so that the mass flow rate and the degree of metallization of the metal oxides may be maximized for the available kiln volume.