Recovering valuable metals from spent hydrodesulfurization catalyst via blank roasting and alkaline leaching.

Spent hydrodesulfurization (HDS) catalysts, containing considerable amount of pollutants and metals including vanadium (V), molybdenum (Mo), aluminum (Al), and nickel (Ni), are considered as hazardous wastes which will result in not only ecosystem damage but also squandering resource. Herein, a process featuring blank roasting-alkaline leaching is proposed to recover spent HDS catalyst. During roasting, low-valence compounds convert to high-valence oxides which can be leached out by NaOH solution. Afterwards, leaching solution is subjected to crystallization to separate metals. The results show that for samples roasted at 650 °C, 97% V, 96% Mo, and 88% Al are leached out at optimal condition; for samples roasted at 1000 °C, selective leaching of 91% V and 96% Mo respectively, are realized, with negligible Al being dissolved. NiO is insoluble in strong alkali leaving in residue. The advantages of this process are that first, the leaching of V, Mo, and Al can be manipulated by controlling roasting conditions, providing flexible process design. Second, leaching solution can be fully recycled. Finally, mild leaching condition and clean separation of V, Mo, and Al is achieved, proving fundamental information for peer researches to facilitate their future research on the development of more efficient and cleaner technologies.