Selective dissolution of critical metals from diesel and naptha spent hydrodesulphurization catalysts

The petroleum refining industry makes extensive use of catalysts, containing critical metals, such as, Mo, Co and Ni, for the desulphurization of various oil fractions. The selective recovery of these metals from two uncrushed and at low temperature calcined industrial hydrodesulphurization (Mo---Co/Al₂O₃ and Mo---Ni/Al₂O₃---SiO₂) catalysts was studied, applying a two-step alkali-acid procedure. Fundamental kinetic aspects of the process, such as, reaction time, leaching reagents concentration and reaction temperature, were studied. Recoveries up to 97% for Mo and up to 92% for Co or Ni in separate solutions were achieved, using low cost and easily available reagents, such as sodium hydroxide and sulphuric acid.