RECOVERY OF METAL VALUES FROM SPENT HYDRO DESULFURIZATION CATALYST BYSOLVENT-EXTRACTION WITH PIA-8

The total dissolution in sulfuric acid of spent hydrodesulfurization c atalyst yields an acidic solution containing molybdenum, vanadium, cob alt, 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 PI A-8, and the synergistic extraction behaviors of cobalt, nickel and al uminum with a mixture consisting of PIA-8 and LIX 63 were investigated in the present work. Based on the results obtained, an elemental proc ess for recovery of molybdenum, vanadium, cobalt and nickel from the a ctual solution of the total dissolution mentioned above was proposed. This process includes mainly the following steps: 1). The selective ex traction of molybdenum, vanadium and iron from the solution in the pre sence of cobalt, nickel and aluminum at pH around 1.5 with PIA-8 in EX XSOL D80. 2). The scrub of vanadium from the loaded organic phase with H2SO4 solution and the second extraction of vanadium from the scrub s olution at pH 1.5 with PIA-8 in EXXSOL D80. 3). The strip of molybdenu m and vanadium from the loaded organic phase by aqueous ammonia. 4). T he recovery of cobalt and nickel from the raffinate containing an appr eciable amount of aluminum. This can be achieved by two special approa ches. One is to separate aluminum first from cobalt and nickel by prec ipitating 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 con tacting with a maixture of PIA-8 in combination with LIX 63 at pH appr ox. 2.4 and then to further separate cobalt from nickel by stripping t he two metals from the loaded organic phase selectively with solutions of different H2SO4 concentrations.