Stepwise separation and recovery of molybdenum, vanadium, and nickel from spent hydrogenation catalyst

Recovering metal values in hazardous spent hydrogenation catalysts is of vital economic and environmental importance. Herein, the selective recovery of valuable molybdenum (Mo), vanadium (V), and nickel (Ni) from spent hydroprocessing catalysts are achieved by using a sulfuric acid leaching-stepwise extraction process. After roasting in the air at 400 °C, the valuable metals are effectively leached within 20 min by 1 mol/L sulfuric acid at 75 °C. The leaching efficiency of Al, Ni, Mo, and V is 22.16%, 99.44%, 98.59%, and 100%, respectively. Based on the species analysis of the leachate, a stepwise extraction separation route was established for selective recovery of Mo, Ni, and V from the acidic leachate. Mo and V are preferentially co-extracted by the mixed TOA/Cyanex272 with a molar ratio of 7:3, which exhibits an excellent extraction selectivity over Ni and Al. Increasing the concentration of Cyanex272 in the mixed system can effectively improve the selective stripping of vanadium but slightly inhibit its extraction. Residual Ni in the raffinate can be selectively separated by 50%(V/V) commercial HBL110 with an extraction efficiency of 98.5%. Especially, the reductive sodium sulfite can greatly enhance the selective stripping of vanadium from the loaded organic phase. Residual Mo in the organic phase can be well stripped with an alkaline solution. The selective stripping mechanism of vanadium is revealed by the FT-IR and Raman spectra. This work proposes a sustainable stepwise separation route for recovering valuable metals in the spent hydroprocessing catalyst.