Desulfurization and decarburization processes are key issues in the recovery of valuable metals from spent industrial catalysts because the carbon and sulfide on the surface of the spent catalyst are not conducive to metal leaching. This manuscript addresses the development of a process of roasting spent catalyst with microwave heating. In the present investigation, desulfurization and decarburization of the spent catalyst were studied by treating with microwave heating for the recovery of molybdenum. We also studied the effect of various reaction conditions (temperature, holding time, microwave power, and granularity of the spent catalyst) on desulfurization and decarburization, and the leaching of molybdenum. The maximum desulfurization (96.7%) and decarburization (99.7%) were achieved when the spent catalyst (200 mesh) was treated using microwave power (960 W) at a temperature of 650 degrees C for 45 min. The results show that no complex metal oxides such as CoMoO4 were found in the XPS and XRD spectra of the samples after desulfurization and decarburization and that <96% of molybdenum is leached with a sodium carbonate solution. This method not only promotes rapid desulfurization and decarburization but also does not produce any complex metal oxides, thereby promoting the recovery of valuable metals in spent catalysts. (C) 2018 Elsevier B.V. All rights reserved.