Solvent washing strategy for optimal vanadium and molybdenum recovery from spent hydrodesulfurization catalysts without thermal pre-treatment

The recovery of critical raw materials from spent hydrodesulfurization catalysts is essential to avoid dispersing metal flows with high strategic value, which is dangerous for the environment and human health. These spent catalysts have high concentrations of vanadium and molybdenum and can represent a secondary supply source. Different processes allow the selective recovery of vanadium and molybdenum from solid matrices, such as the catalysts. This work presents a hydrometallurgical process patented by the ORIM-CAT2 process. In the first step of the process, the catalyst was washed with acetone; the latter, thanks to its high volatility, can be quickly recovered by distillation and used for subsequent steps. It has been shown that acetone removes more than 30 % of C, about 51 % of H, and about 7 % of S and can be recirculated with recovery yields and purities higher than 95 %. The effect of the pretreatment on the leaching phase using a solution of NaOH and H2O2 and on the precipitation phase using NH4Cl was analyzed. The significance of the effects of important leaching parameters such as temperature, particle size, and reagent concentration was evaluated using ANOVA. Finally, the optimal values of the leaching phase were obtained by applying the response surface methodology. Recovery yields of about 90 % were obtained without thermal pre-treatment with optimal concentrations of 1.8 M and 1.6 M of H2O2 and NaOH, respectively.