Recovery of Metal Values from Spent Hydrodesulfurization Catalyst by Solvent Extraction with PIA-8

Abstract

The total dissolution in sulfuric acid of spent hydrodesulfurization catalyst yields an acidic solution containing molybdenum, vanadium, cobalt, nickel, aluminum and iron. For the purpose of recovering the rare metals from the solution, the fundamental extraction characteristics of these metals involved with a novel type of commercial extractant PIA-8, and the synergistic extraction behaviors of cobalt, nickel and aluminum with a mixture consisting of PIA-8 and LIX 63 were investigated in the present work. Based on the results obtained, an elemental process for recovery of molybdenum, vanadium, cobalt and nickel from the actual solution of the total dissolution mentioned above was proposed. This process includes mainly the following steps: 1). The selective extraction of molybdenum, vanadium and iron from the solution in the presence of cobalt, nickel and aluminum at pH around 1.5 with PIA-8 in EXXSOL D80. 2). The scrub of vanadium from the loaded organic phase with H2SO4 solution and the second extraction of vanadium from the scrub solution at pH 1.5 with PIA-8 in EXXSOL D80. 3). The strip of molybdenum and vanadium from the loaded organic phase by aqueous ammonia. 4). The recovery of cobalt and nickel from the raffinate containing an appreciable amount of aluminum. This can be achieved by two special approaches. One is to separate aluminum first from cobalt and nickel by precipitating aluminum as hydroxides with aqueous ammonia at pH 6.2, then to extract cobalt selectively from the filtrate at equilibrium pH ca. 5.2 with PIA-8 and to recover nickel from the raffinate. Another is to extract cobalt and nickel directly in the presence of aluminum by contacting with a maixture of PIA-8 in combination with LIX 63 at pH approx. 2.4 and then to further separate cobalt from nickel by stripping the two metals from the loaded organic phase selectively with solutions of different H2SO4 concentrations. © 1995, The Chemical Society of Japan. All rights reserved.