Enhancing Mo leaching efficiency from spent catalyst via Fenton-like oxidation process: A comprehensive investigation of leaching effects, mechanism and environmental impacts
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 MoS 2 . This study explored Mo leaching efficiencies from spent HDS catalyst by Fenton-like oxidation systems (H 2 O 2 and K 2 S 2 O 8 ), which were frequently employed in the wastewater treatment. To further improve Mo leaching efficiency, nano zero-valent iron (nZVFe) was used to activate H 2 O 2 /K 2 S 2 O 8 and produce more free radicals (·OH and ·SO 4 - ). Approximate 96.0 % and 93.3 % of Mo were leached from spent HDS catalyst in nZVFe + H 2 O 2 + H 2 SO 4 and nZVFe + K 2 S 2 O 8 + H 2 SO 4 systems under optimal experimental conditions, increased by 16.2 % and 8.2 % than normal H 2 O 2 (79.8 %) and K 2 S 2 O 8 (85.1 %) system without nZVFe. The leaching process of Mo in both nZVFe + H 2 O 2 + H 2 SO 4 and nZVFe + K 2 S 2 O 8 + H 2 SO 4 systems conformed to the shrinkage core model. Kinetic analysis and molecular calculation demonstrated the leaching process of Mo in nZVFe + H 2 O 2 + H 2 SO 4 system was driven by chemical reaction and solid film diffusion, and the leaching and oxidation reactions of MoS 2 occurred simultaneously. However, the leaching process of Mo in nZVFe + K 2 S 2 O 8 + H 2 SO 4 system was driven only by chemical reaction, solid MoS 2 was firstly dissolved into Mo 4+ by H + , and then oxidized into Mo 6+ by ·SO 4 - . The economic and environmental impacts evaluation indicated that the separation of Mo from spent HDS catalysts by nZVFe + H 2 O 2 + H 2 SO 4 was assigned as a better choice than normal H 2 O 2 and K 2 S 2 O 8 system without nZVFe due to higher leaching efficiency and lower cost.
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