Recovering valuable metals from spent hydrodesulfurization catalysts by co-leaching, dissociation, and stepwise precipitation

Abstract

This study discusses an effective and environmentally friendly process for recovering vanadium, nickel, and molybdenum from spent hydrodesulfurization catalysts using an (NH4)2SO4-H2O2 solution. The leaching efficiencies of vanadium, nickel, and molybdenum were close to 92 %, 97 %, and 84 % under optimum operating conditions (H2O2 concentration 1.5 mol/L, pH 3.5, temperature 55 °C, liquid to solid mass ratio 15/1, and time 180 min). The presence of MoV9O285- changed the solubility of NH4VO3 in the (NH4)2SO4 solution. Therefore, it is difficult to separate NH4VO3 using the traditional cooling crystallization method. MoV9O285- was pre-oxidized by adding H2O2 to the leachate to separate vanadium and molybdenum from the (NH4)2SO4 solution. After oxidation, MoV9O285- was converted to MoO3(O2)2- and V10O286-, and precipitated from the leachate as H2MoO5·H2O and (NH4)2V6O16·1.5 H2O. Finally, NH4VO3 and (NH4)6Mo7O24·4 H2O with purities of 99.59 % and 99.04 %, respectively, were obtained via sequential precipitation. In addition, after separating vanadium and molybdenum, nickel was recovered from the leachate in the form of Ni(NH4)2(SO4)2·12 H2O using cooling crystallization, with a purity of 99.88 %. Thus, the leaching solution could be effectively recycled.