Selective leaching and stepwise separation of V, Mo, and Ni from spent HDS catalysts using a green deep eutectic solvent

The recovery of high value metals from spent hydrodesulfurization catalysts serves as a crucial strategy not only for mitigating environmental pollution but also for alleviating resource shortages. Herein, a hydrated deep eutectic solvent (P-DES) composed of betaine hydrochloride and p-toluenesulfonic acid was developed to selectively leach valuable metals from spent catalysts and enable their stepwise recovery. Under optimal conditions (BeCl:PTSA = 1:2, 45 wt% H 2 O, 90 ℃, 10 g L −1 , 180 min), leaching efficiencies of 90.03% for Ni, 98.60% for Mo, and 94.98% for V were achieved, while Al dissolution was suppressed to 9.82%. Density functional theory (DFT) and leaching kinetics both indicate an apparent metal release order of Mo > V > Ni, which is also consistent with the observed order of leaching efficiency (Mo > V > Ni). Independent Gradient Model based on Hirshfeld partitioning (IGMH) results show that P-DES features a Cl - -centered hydrogen-bond network, which provides a proton-active and chloride-containing microenvironment. During leaching, H + breaks M-O bonds, V(V) is reduced predominantly to V(IV) with minor Mo(VI) reduction, and the dissolved metals are stabilized as chloro or oxychloro species. In the subsequent recovery process, V(IV) was selectively precipitated at pH 5.2 within 3 min and calcined at 450 ℃ to produce V 2 O 5 . Mo was then extracted using an N235/2-ethylhexanol system and recovered as MoO 3 after calcination at 550 ℃. Finally, Ni was precipitated from the raffinate at pH 12.2 as Ni(OH) 2 . The recovery rates of V, Mo and Ni were obtained at 93.36, 97.36, and 89.52%. This work presents an integrated, green hydrometallurgical route for the comprehensive recycling of spent HDS catalysts.