Spent catalyst: secondary source for molybdenum recovery

Molybdenum-containing catalysts are mostly used in petroleum-refining industries for mild hydrogenation processes. These catalytic processes generate huge quantity of spent catalyst. With the increasing demand of metal values and environmental awareness, catalysts can serve as a secondary source for metal recovery. hydro-refining catalyst mainly consists of 10–20% MoO3, 6–8% CaO, 0–12% V2O5, 0.5–6% NiO, 10% S, 10–12% carbon and the balance is Al2O3. The spent catalyst was roasted with soda ash to convert molybdenum into a water-soluble compound. Various parameters like temperature, time and soda ash addition have been studied thoroughly and conditions for the maximum recovery of molybdenum have been established. It has been found that at 600 °C with 30 min of retention time and using 12 wt.% soda ash, it is possible to extract 92% of molybdenum from the spent catalyst. The molybdenum is extracted as sodium molybdate. This sodium molybdate is further purified using carbon adsorption method to obtain a pure grade of molybdenum trioxide.