RECOVERY OF COBALT AND NICKEL FROM SPENT HYDRODESULFURIZATION CATALYSTS BY MEANS OF LIQUID-LIQUID-EXTRACTION

The recovery of molybdenum and vanadium from sulfuric acid solution generated from the total dissolution of spent hydrodesulfurization catalysts by means of liquid-liquid extraction with CYANEX 272 resulted in an aqueous raffinate solution with the composition of approximately (ppm) Co 1000, Ni 210, Al 12370 and pH 1.5. For the purpose of recovering nickel and cobalt from the solution, a systematic investigation was conducted on the synergistic extraction behaviors of the mixed extractants of LIX 63, an aliphatic alpha-hydroxyoxime extractant, in combination with a series of acidic organophosphorus reagents such as CYANEX 272, PC-88A, TR -83, D2EHPA and OPEHPA for cobalt, nickel and aluminum. It was elucidated that all of these mixtures exhibit an excellent synergistic effect for extraction of cobalt and nickel and that the lower the pKa of the acidic extractants, the greater the synergism. On the contrary, the extraction of aluminum is greatly suppressed by LIX 63. By using the mixtures, nickel and cobalt are effectively and selectively extracted from the sulfate solution at low pH leaving aluminum in the solution. In particular the mixture of LIX 63 and CYANEX 272 appears to be the most feasible and economic from a process standpoint because of the substantial separation efficiency for cobalt and nickel over aluminum, the comparatively mild acidities necessary for stripping cobalt and nickel, and the negligible degradation of LIX 63.