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

This study discusses an effective and environmentally friendly process for recovering vanadium, nickel, and molybdenum from spent hydrodesulfurization catalysts using an (NH4)(2)SO4-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 degrees C, liquid to solid mass ratio 15/1, and time 180 min). The presence of MoV9O285- changed the solubility of NH4VO3 in the (NH4)(2)SO4 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)(2)SO4 solution. After oxidation, MoV9O285- was converted to MoO3(O-2)(2-) and V10O286-, and precipitated from the leachate as H2MoO5 center dot H2O and (NH4)(2)V6O16 center dot 1.5 H2O. Finally, NH4VO3 and (NH4)(6)Mo7O24 center dot 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)center dot 12 H2O using cooling crystallization, with a purity of 99.88 %. Thus, the leaching solution could be effectively recycled.

Automated summary

This study presents an effective and environmentally friendly method for recovering vanadium, nickel, and molybdenum from spent hydrodesulfurization catalysts. The leaching efficiencies of the three metals were determined, and it was found that MoV9O285- influenced the solubility of NH4VO3. The separation process involved pre-oxidizing MoV9O285- and precipitating it as MoO3(O-2)(2-) and V10O286-, while nickel was recovered through cooling crystallization.