Molybdenum-containing catalysts are mostly used in petroleum-refining industries for mild hydrogenation processes. These catalytic processes generate huge quantity of spent catalysts. With the increasing demand of metal values and environmental awareness, these catalysts can serve as a secondary source for metal recovery. They are roasted with soda ash to convert molybdenum into a water-soluble compound. The molybdenum is extracted as sodium molybdate, and further purified using carbon adsorption method to obtain a pure grade of molybdenum trioxide. This hydrometallurgical processing is also applicable to wulfenite, off-grade molybdenum concentrates, lead-molybdenum ores etc.