Metal Extraction from Spent HDS Catalyst by alkaline and acidic leaching

During desulphurization of petroleum product, there is generation of a huge quantity of hydro-refining spent catalyst. These catalysts contain environmentally critical and economically valuable metals such as Mo, V, Co and Ni. In the current study the investigated spent catalyst is with main elemental composition: 19.4% Mo, 2.5% Co and 44.4% Al. Hydrometallurgical processing of spent hydrodesulphurization (HDS) catalyst for the recovery of cobalt and molybdenum was investigated using two different leaching systems (acidic and alkaline). Statistical design of experiments and analysis of variance (ANOVA) were performed in order to determine the main effects and interactions of the investigated factors, which were temperature of roasting, concentration of the leaching reagent (H2SO4 and NaOH) and presence of hydrogen peroxide as an oxidizing agent. Full factorial designs were performed in both experiments. According to acidic leaching system, roasting process and presence of hydrogen peroxide in the reaction medium have positive effect on the Co and Mo extraction, but there is no interaction between them. According to alkaline leaching system, the selective dissolution of Mo was largely dependent on the roasting process. In that conditions Co was not dissolved. After alkaline leaching, precipitation test was performed and Al was precipitated at pH about 8.