MMIJ Annual Meeting

Recovery of critical metals such as cobalt and molybdenum from spent hydrodesulfurization (HDS) catalysts has gained attention due to the fast depletion of natural sources, the criticality in supplying these metals and the transition toward a circular economy. The conventional metal recovery methods from the spent catalyst by pyrometallurgical and conventional hydrometallurgical approaches could lead to secondary pollution. In this study, amino acids were tested as the main lixiviant to recover Mo and Co from the spent catalyst (consisting of MoS2 and Co3O4 supported on Al2O3). Alanine (Ala) was screened as the most effective amino acid to be used for sequential leaching of Mo and Co. Therefore, Ala was used to selectively recover Mo and Co through sequential 3-step leaching; Step-1: Alkaline Ala leaching at 45℃ for Mo, Step-2: Hot water leaching at 70℃ for Co, Step-3: Second alkaline Ala leaching at 45℃ for more Mo. It was found that Mo dissolved in alkaline pH while Al remained in solid, and Ala could selectively co-precipitate with Co by forming Co-Ala complex, which was then readily re-dissolved in hot water. The selective dissolution and precipitation enabled the recovery of Mo-rich leachate (96% Ni, 19% Co and 2.1% Al dissolved) and Co-rich leachates (<1% Mo, 79% Co, Al not detected), emphasizing the potential of using amino acids as environmentally benign alternative metal dissolvent and precipitant for the recycling of waste materials.