Extraction and Recovery of Metals from Spent HDS Catalysts: Lab- and Pilot-Scale Results of the Overall Process

The present study proposes an overall recycling process for spent hydrodesulfurization (HDS) catalysts. The process put together stages already known in the technical literature, tested again with samples coming from the roasting stage in a pilot kiln, which is the most limiting stage of metal recovery from spent catalysts. These catalysts contain valuable metals such as cobalt (Co), molybdenum (Mo), nickel (Ni), and vanadium (V). In particular, a dry Co-Mo catalyst was used and treated in order to optimize the roasting step (time, soda ash, and temperature) at a pilot scale and thus maximize the extraction yield of molybdenum (Mo) and vanadium (V). After roasting at 700 ◦C for 2.5 h, the best conditions, the catalysts underwent water leaching, separating Mo and V from Co and the alumina carrier, which remained in the solid residue. The pregnant solution was treated to remove arsenic (As) and phosphorus (P), representing the main impurities for producing steel alloys. V was precipitated with NH4Cl, and further calcined to obtain commercial-grade V2O5.