Metal extraction from spent sulfuric acid catalyst through alkaline and acid leaching

Spent catalyst from manufacture of sulfuric acid production (main elemental composition: 3.5% V, 0.63% Ni, 7.9% Fe and 9.64% Si) can be used as a secondary source of vanadium and nickel. Extraction of these metals was studied using two different leaching systems (alkaline and acidic). Statistical design of the experiments and ANOVA (analysis of variance) were performed in order to determine the main effects and interactions of the factors under research, which were roasting, leaching temperature, concentration of the leaching reagent (H2SO4 and NaOH), liquid/solid (L/S) ratio (at 100mL of liquid reagent), and presence of hydrogen peroxide. The results obtained after acidic treatment show that nickel extraction yield of 96% is achieved after roasting at 600 °C, followed by leaching with 5mL/g 1 M sulfuric acid at 80 °C for a 30 min reaction time. The highest vanadium extraction yield was 59% after roasting at 400 °C and leaching at 80 °C by 0.3 M sulfuric acid for 6 h and 10mL/g L/S ratio. A full factorial experiment was also performed by application of sodium hydroxide for vanadium extraction in the second leaching system. The highest vanadium extraction yield after alkaline treatment was 78%, obtained through roasting at 400 °C, leaching at 80 °C by 4 M NaOH for 2 h and 10mL/g L/S ratio. Because nickel is not dissolved by sodium hydroxide, a sequential acidic leaching was conducted using the alkaline leaching residue, obtaining a nickel extraction yield of 88%.