Recovery of valuable metals from spent hydrodesulfurization (HDS) catalysts: A comprehensive research review and specific industrial cases

Spent hydrodesulfurization (HDS) catalysts, produced in the petroleum refining process, are usually classified in hazardous solid waste. Recovery of valuable metals from spent HDS catalyst not only reduce substantially environmental risk but is an important way to alleviate global resource shortages for high-valuable metals. This study reviews numerous references regarding to recovery valuable metals from spent HDS catalyst in last decades, and divided current methods into three processes: pretreatment, oxidation-leaching, and separation-purification processes. Roasting and solvent washing usually emerge as primary methods in the pretreatment process, and effectively eliminate the surface oily substances and sulfur. Sodium salt roasting-leaching are considered as higher efficient among all leaching methods. The application of organic acid in the leaching can separate valuable metals selectively and simplify subsequent purification steps. In separation-purification processes, solvent extraction is still a standout method to isolate challenging metals such as Mo, W and V. However, the burgeoning field of ion imprinting technology exhibits the promising potential. Additionally, Random Forest and XGBoost model are used to analyze reported methods to recovery Mo and Ni and predict the key factor to regulate recovery efficiency. The results show that Mo recovery process is depended on the spent HDS characteristics and solid-liquid ratio in leaching process, while Ni recovery processes is depended on the roasting time and roasting temperature. Finally, serval specific industrial cases on recycling valuable metals from spent HDS were given, and found that sodium salt roasting-water leaching process was still frequent used in practical application due to its characteristics of high efficiency and low cost.