A novel method to leach vanadium, molybdenum and nickel from spent hydrodesulfurization catalysts using hydroxyl radicals (HO') in Fe2O3-assisted oxygen microbubble process

As one of hazardous wastes, the ever-increasing number of spent hydrodesulfurization (HDS) catalysts which consists of a considerable amount of heavy metals, such as vanadium (V), molybdenum (Mo) along with nickel (Ni) and other organic contaminant has presented a serious waste-management challenge. In this study, we propose the Fe2O3-assisted oxygen microbubble Fenton-like process for spent HDS catalysts recovery. The leaching efficiencies of vanadium, molybdenum, and nickel are close to 89%, 90%, and 97%, respectively, under the optimum operating conditions (Fe2O3/raw materials mass ratio 4%, pH 3.2, temperature 80 degrees C, liquid solid mass ratio 15/1 and leaching time of 90 min). The advantages of this strategy are two fold: (i) using commercial oxygen and Fe2O3 as oxidants, avoid high costs and consumption of oxidants, (ii) oxygen micro bubbles are introduced into the system and the free radicals (HO') generated by microbubbles collapsing during aeration enhance the mass transfer and oxidizing rates. However, the presence of strong reductive free radicals (H') makes microbubbles incompatible for use. Moreover, Fe2O3 is proven to promote the generation of HO' from collapsing oxygen microbubbles under acidic conditions. These findings significantly increase the potential use of microbubble technique in resource recovery and provide fundamental information for peer researches facilitate their future research on the development of more efficient and cleaner technologies.