RECOVERY OF MOLYBDENUM AND VANADIUM FROM SPENT HYDRODESULFURIZATION CATALYSTS BY MEANS OF LIQUID-LIQUID-EXTRACTION

The total dissolution in sulfuric acid of spent hydrodesulfurization c atalysts results in an acidic solution containing a certain amount of rare metals like molybdenum, vanadium, cobalt and nickel as well as a large excess amount of aluminum. In the present work, the fundamental extraction characteristics of these metals from the sulfuric acid medi a with some typical commercial acidic organophosphorus compounds such as TR-83, PC-88A and CYANEX 272 have been investigated to develop an e xtraction process for the recovery of molybdenum and vanadium from the solution of the total dissolution. The experimental results demonstra ted that CYANEX 272 was suitable for selectively separating and recove ring molybdenum and vanadium over the other metals involved in the sul fate solutions at comparatively low pH. An elemental recovery processi ng route was proposed. Molybdenum was recovered by extracting with 40% CYANEX 272 in EXXSOL D80 from the sulfuric solution at pH 1.5, and by stripping with 6% NH4OH solution after the co-extracted iron and vana dium were scrubbed from the loaded solvent with a moderate concentrati on of H2SO4 solution. Vanadium in the scrub solution was further recov ered by again extracting with the same extractant after the pH was adj usted to 1.5 with Ca (OH)(2) powder and by stripping with 6% NH4OH sol ution.