Metals recovery from spent hydrotreatment catalysts in a fluoride-bearing medium

This work examines the dissolution of spent commercial NiMo/Al2O3 and CoMo/Al2O3-SiO2 catalysts in aqueous solutions containing fluoride ions under mild experimental conditions. Solubilization of samples in the presence of fluoride salts alone was insignificant, but solubilization in pure HF was quantitative after 14-16 h. The addition of a strong inorganic acid led to full solubilization after 30 min (NiMo) or 4 h (CoMo) at 50-60 °C and a stirring speed of 400 rpm. This time was reduced by at least 75% when hydrogen peroxide was added. HF was the best source of fluoride ions for dissolving SiO2 and phosphate-containing species. The recovery of metals from the leach solution could be accomplished very efficiently and with low residue generation.