The effect of the structure of the solid binder on material viscosity during drum granulation was investigated it was found that nucleation was the most important step in the wet granulation process, but the rate of nucleation was determined by the viscosity of the fertilizer material, through the study of the surface structure of calcium carbonate, coarse whiting, attapulgite, desulfurization gypsum powders, and different binder content versus viscosity plots. The results showed that the adsorption ability of calcium carbonate, the formation of the water film of attapulgite, and the production of whiskers of desulfurization gypsum influenced the fertilizer material's viscosity and granulation. Meanwhile the work provided a theoretical basis for the study of the mechanism of nucleation. (C) 2013 Elsevier B.V. All rights reserved.