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    Enhancing Mo leaching efficiency from spent catalyst via Fenton-like oxidation process: A comprehensive investigation of leaching effects, mechanism and environmental impacts
    (Elsevier B.V., 2024) Yu, Haoran; Liu, Shuo; Hu, Linchao; Zhang, Wenyi; Peng, Mingguo; Arslanoğlu, Hasan
    Spent hydrodesulfurization (HDS) catalyst contains considerable amounts of Mo, Ni and V, is an important secondary resource for these valuable metals. Direct acid solution leaching method exhibits poor separation effect from catalyst carrier for Mo due to greater stability of MoS2. This study explored Mo leaching efficiencies from spent HDS catalyst by Fenton-like oxidation systems (H2O2 and K2S2O8), which were frequently employed in the wastewater treatment. To further improve Mo leaching efficiency, nano zero-valent iron (nZVFe) was used to activate H2O2/K2S2O8 and produce more free radicals (·OH and ·SO4-). Approximate 96.0 % and 93.3 % of Mo were leached from spent HDS catalyst in nZVFe + H2O2 + H2SO4 and nZVFe + K2S2O8 + H2SO4 systems under optimal experimental conditions, increased by 16.2 % and 8.2 % than normal H2O2 (79.8 %) and K2S2O8 (85.1 %) system without nZVFe. The leaching process of Mo in both nZVFe + H2O2 + H2SO4 and nZVFe + K2S2O8 + H2SO4 systems conformed to the shrinkage core model. Kinetic analysis and molecular calculation demonstrated the leaching process of Mo in nZVFe + H2O2 + H2SO4 system was driven by chemical reaction and solid film diffusion, and the leaching and oxidation reactions of MoS2 occurred simultaneously. However, the leaching process of Mo in nZVFe + K2S2O8 + H2SO4 system was driven only by chemical reaction, solid MoS2 was firstly dissolved into Mo4+ by H+, and then oxidized into Mo6+ by ·SO4-. The economic and environmental impacts evaluation indicated that the separation of Mo from spent HDS catalysts by nZVFe + H2O2 + H2SO4 was assigned as a better choice than normal H2O2 and K2S2O8 system without nZVFe due to higher leaching efficiency and lower cost.
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    Recovery of valuable metals from spent hydrodesulfurization (HDS) catalysts: A comprehensive research review and specific industrial cases
    (Academic Press Ltd- Elsevier Science Ltd, 2025) Yu, Haoran; Liu, Shuo; Yaras, Ali; Enkhchimeg, Battsengel; Hu, Linchao; Zhang, Wenyi; Peng, Mingguo; Arslanoğlu, Hasan
    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 separationpurification 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.