Series of modified with vanadium, cobalt, nickel, manganese and copper montmorillonite were compared as additives for desulfurization during combustion of hard coal. Samples of coal with added montmorillonite were subject to a 211 a flow reactor in the air atmosphere, at 1173 K. The weight ratio of montmorillonite: coal was 1:500. Changes in sulfur dioxide contents in flue gasses caused by the additive were investigated by means of an exhaust gas analyzer. During the co-combustion of coal with montmorillonite modified with vanadium was removed 58-84% of SO2 from flue gasses. Application of Co and Ni led to a reduction in SO2 emissions by 35-53% and 83-90%, respectively. For additions of Ni, Cu and Mn was observed to reduce emissions of SO2 by 60-73%. As a result of using diversified preparatory procedures on montmorillonite additives DESOX obtained were materials with different physicochemical properties. Sulfate forms obtained after the combustion process with addition of montmorillonite additives are amorphous and very well dispersed. (C) 2011 Elsevier B.V. All rights reserved.