Efficient Phase Transformation of γ-Al2O3 to α-Al2O3 in Spent Hydrodesulphurization Catalyst by Microwave Roasting Method

In the preparation of hydrodesulphurization (HDS) catalyst, highly reactive γ-Al2O3 is used as a carrier, resulting in an undesirable high leaching of aluminum during the recycling of spent catalyst. In this research, microwave roasting was employed to transform γ-Al2O3 into more stable α-Al2O3 for decreasing Al leaching. The phase transformation was investigated by XRD, XPS, and FTIR, and the results show that the transformation to α-Al2O3 can be achieved at a lower temperature of 1000 °C and a much shorter time of 1 h, compared to the conventional roasting method. The effect of transformation temperature on the leaching of metals was then investigated. The leaching of Al significantly decreased in both alkaline and acid leaching, and moreover the leaching of Co and Ni was reinforced after the transformation of Al2O3. It is helpful to simplify the subsequent process of Al separation and increase the overall recovery rate of valuable metals.