Green and selective recovery process of Mo, V, and Ni from spent hydrodesulfurization catalysts via novel ionic liquids and deep eutectic solvents technology

Ionic liquids (ILs) and deep eutectic solvents (DESs) are promising candidates as viable alternatives in the metal recovery process. Conventional methods predominantly concentrated on the extraction of metals employing ionic liquids or deep eutectic solvents from either acidic or alkaline media subjected to leaching by acids or bases. Therefore, in this work, a novel approach integrating ILs and DES was investigated, wherein the entire sequence from the leaching process to the precipitation step exclusively involves the utilization of DES and ILs. Firstly, the spent hydrodesulfurization (HDS) catalyst underwent leaching with an ionic liquid (IL), which selectively leached molybdenum (Mo) and vanadium (V). Subsequently, the residual material remaining after IL leaching underwent a further leaching process utilizing a deep eutectic solvent (DES) to facilitate the recovery of nickel (Ni). The effect of different parameters on the leaching percentage was studied and optimized for both IL and DES. Vanadium was recovered as NH4VO3 from the loaded IL phase, which was selectively precipitated over molybdenum using NH4Cl solution and molybdenum was precipitated as BaMoO4 by introducing an excess of BaCl2 solution to the filtrate. For the nickel recovery, the residue obtained after leaching using ionic liquid was treated with DES-1 and finally nickel was recovered from the mixture through cementation with aluminum. This study establishes a novel green approach based on IL and DES to recover Mo, V, and Ni from the spent catalysts without roasting and harsh acidic or basic conditions.