For treating petrochemical catalysts for the selective extraction of molybdenum therefrom, a plant and a process are proposed for extracting the molybdenum by charging a batch of catalysts to a rotary kiln of which the refractory is heated or preheated to a high temperature, and setting the kiln in rotation so that the catalyst charge undergoes constant renewal of the surface in contact with the superheated refractory. The catalyst charge is brought to temperatures of the order of 1300 C. (1250 to 1350 C.), which allow around 95% of the molybdenum present to sublime.