Influence of sulfuric acid baking on leaching of spent Ni-Mo/Al_2O_3 hydro-processing catalyst

摘要

A low temperature sulfuric acid baking and mild acid leaching process was explored for maximum dissolution of metal values from a spent Ni-Mo/Al_2O_3 hydro-processing catalyst obtained from a Korean refinery. The spent catalyst was found to be a matrix of gamma-Al_2O_3. containing 27.1 percent Al, 11.6 percent Mo, 2.5 percent Ni, 9.7 percent S, 4.8 percent C, 1.9 percent P, 0.4 percent Si and trace amounts of Co and Fe. Various baking parameters such as baking temperature, sulfuric acid concentration and baking duration were optimized according to 23 full factorial method for maximum dissolutions of Mo, Al and Ni during leaching. Under optimum baking conditions (400 deg C; 1.28 stoichiometric H_2SO_4; 1 h), >96 percent Mo, 99 percent Al and 95 percent Ni were readily dissolved from the spent catalyst by 2 percent v/v H_2SO_4 at 80 °C. Carbon and sulfur analyses of the baked samples and leaching residues indicated only 10-15 percent of residual hydrocarbons reacted during acid baking, while most of the sulfur (assumed to be metal sulfides) was converted into soluble sulfates/oxy-sulfates. By comparison, direct sulfuric acid leaching of the catalyst resulted in poor dissolution of Mo and Al, even with large excess of acid, thus demonstrating the beneficial effect of sulfuric acid baking.