RECOVERY OF METAL VALUES FROM SPENT HYDRODESULFURIZATION CATALYSTS BYLIQUID-LIQUID-EXTRACTION

The total dissolution of spent hydrodesulfurization catalysts in sulfu ric acid yields an acidic solution containing a certain amount of rare metals like molybdenum, vanadium, cobalt, nickel, and a small amount of iron as well as an appreciable amount of aluminum. For the purpose of recovering the metallic values present in the solution, in the curr ent work, the fundamental extraction characteristics of these metals w ith some typical commercial acidic organophosphorus compounds such as TR-83, PC-88A, PIA-8, and CYANEX 272 from the sulfuric acid media were investigated, and CYANEX 272 and PIA-8 were found to be suitable for selectively separating and recovering molybdenum and vanadium over the other metals from the specific solution at comparatively low pH. In a ddition, in order to further recover cobalt and nickel from the raffin ate in the presence of a large excess of aluminum, a systematic invest igation was conducted on the synergistic extraction behaviors of the m ixed solvents consisting of LIX 63, an aliphatic alpha-hydroxyoxime ex tractant, and a series of acidic extractants such as CYANEX 272, PIA-8 , PC-88A, D(2)EHPA, TR-83, and OPEHPA for cobalt, nickel, and aluminum . It was elucidated that all of these mixtures could exhibit a good sy nergistic effect for extraction of cobalt and nickel and that the lowe r the pK(a) of the acidic extractants, the greater the synergism. Cont rarily, the extraction of aluminum, was considerably depressed by LIX 63. Using the difference in synergistic extraction performance between these metals, the effective extraction of cobalt and nickel away from aluminum was achieved from the sulfate solution at relatively low pH with the mixtures. In particular, the mixtures of LM 63 in combination with CYANEX 272 or PIA-8 appeared to be the most feasible and economi c from a practical point of view yielding acceptable separation effici ency for cobalt and nickel over aluminum and a low acidity requirement for stripping cobalt and nickel as well as negligible degradation of LIX 63. A full recovery processing route is proposed based on the expe rimental results.