One-step high-efficiency recovery of high-purity MoO₃ from spent hydrodesulfurization catalyst by water-vapor...

Spent hydrodesulfurization (HDS) catalysts were considered as a vital secondary resource for precious metals like Mo. The current pyrometallurgy and hydrometallurgy usually exhibits the characteristic of remarkable high energy consumption and high secondary pollutions. This study proposes an innovative technique to recycling MoO₃ from spent HDS catalyst by sublimation process at high temperature, which has notable advantages of zero wastewater-generation and zero chemical reagent consumption. Notably, MoO₃ recovery efficiency was improved remarkably with the introduction of water-vapor. About 99.33 % of MoO₃ was recovered by heating spent HDS catalyst at 1100℃ for 2.5 h in water-vapor atmosphere with partial pressure of 101.33 kPa. The yielded MoO₃ was tested with the purity of 99.94 % and exhibited the appearance of thin strips. Furthermore, the sublimation kinetic of MoO₃ in air was adhered to a desorption model, while agreed with a non-desorption model in water-vapor atmosphere. Density Functional Theory (DFT) calculations revealed that -OH obtained by the dissociation of H₂O molecules preferably combined with MoO₃ and formed the volatile MoO₃-OH, which was responsible for enhancing MoO₃ sublimation efficiency significantly in water-vapor atmosphere. Economic analysis suggested that the direct cost of this method was 345 $/t, accounting for around 50 % compared to current roasting-leaching-purification methods. Overall, MoO₃ sublimation enhanced by water-vapor atmosphere can be considered as a high-efficient and environmental-friendly approach for Mo recovery from spent catalysts.