Characterization of Cobalt Oxalate Dihydrate Obtained from Spent Co-Mo/Al2O3 Hydrodesulfurization Catalyst

Abstract

In this study, roasted spent Co-Mo/Al2O3 hydrodesulfurization (HDS) catalyst was dissolved in oxalic acid (H2C2O4) solution and optimum conditions were determined for obtaining cobalt oxalate dihydrate (CoC2O4∙2H2O). The thermal decomposition behavior of the obtained CoC2O4∙2H2O was investigated by TG/DTG-DTA analysis. The characterization of CoC2O4∙2H2O was carried out by XRD, FT-IR and SEM-EDS analytical techniques. Optimum conditions for the production of CoC2O4∙2H2O were determined as 25 oC temperature, 0.25 M H2C2O4 concentration, 1/20 g mL-1 solid/liquid ratio and 300 rpm stirring speed. CoC2O4∙2H2O was obtained with a reaction yield of 90.9 %. TG/DTG-DTA analysis carried out in dry air atmosphere showed that CoC2O4∙2H2O decomposed in two steps. In the first step that occurs between 118-196 oC temperatures, CoC2O4∙2H2O is dehydrated. In the second step, which occurs between 248-279 oC temperatures, it was determined that metallic cobalt was formed first, and then metallic cobalt was oxidized and converted into Co3O4 compound because it was performed in the air atmosphere.