Efficient recovery of all valuable metals from spent HDS catalysts: Based on roasting mechanisms for enhanced selective leaching and separation

Recovery of all valuable metals such as Ni, Mo, V and Al from spent hydrodesulfurization (HDS) catalysts is beneficial to environmental protection and resource recycling. The current recycling process mostly considers the recovery of Mo and V than recovery of Ni and Al, and generates a large amount of difficult-to-decompose Ni-Al residue and wastewater. Aiming at the insufficiency of the current recycling process, in this study, a novel pyrohydrometallurgical process for efficient and complete recovery of metals from spent HDS catalysts was proposed. The mechanisms of phase transformation during roasting and leaching are investigated by XRD, XPS and SEM in depth. The modulation of the phase transformation of the spent HDS catalyst in the oxidative roasting process is the key to the influence on the leaching of Ni and Al. Inhibition of theta-Al2O3 phase and Ni-Al spinel generation by controlled roasting can achieve efficient leaching of Mo, V, Ni and Al. Subsequently, Mo and V were selectively leached with 2 mol/L Na2CO3, and the alkaline leach residue obtained was treated with 6 mol/L HCl. The results showed that alkaline leaching efficiencies of Mo and V reached 99.73 % and 91.86 % while acid leaching efficiencies of Ni and Al reached 99.71 % and 90.27 %, respectively. The metals of acid leach solution were recovered by using N235, HBL110 and NaAlO2 stepwise. This new process has the advantages of high efficiency and comprehensive metal recovery, high product purity, and low amount of slag and wastewater, and has good prospects for industrial application.