Investigation of dissolution conditions and kinetics in the presence of complexing agents of spent Co-Mo-Ni/Al2O3 catalyst

In this thesis; the process conditions for the recovery of molybdenum (Mo), nickel (Ni) cobalt (Co) and aluminum (Al) metals from the spent hydrodesulfurization (HDS) catalyst in the presence of complexing agent were investigated. Ethylenediamine tetra acetic acid (EDTA) was used as a complexing reagent in the leaching process due to high ability to bind with metal ions. In the experiments, the roasting pre-treatment was firstly applied to the spent catalyst to convert metals in catalyst structure into more soluble forms. Then, the selective leaching was carried out by precipitating Mo, Ni and Co metals in the forms of ammonium molybdate, nickel dimethylglycoxime and cobalt hydroxide at pH: 2, pH: 6 and pH: 10 respectively. Highest metal extraction yields (90.22% Mo, 96.71% Co, 95.31% Ni and 19.98% Al) were achieved under optimum experiment conditions. According to the thermodynamic data of the process; activation energy values (Ea) of Co, Mo and Ni were calculated as 14.36 kJ/mol, 16.85 kJ/mol and 15.93 kJ/mol, respectively. It was determined that leaching kinetics fit to pseudo-first homogeneous kinetic model and the process was controlled by diffusion. Kinetic equation of the process as a function of the process parameters was obtained as follows. The results provide a new approach in terms of reducing the solid waste load of the petrochemical industry and efficient recovery of metals from the spent HDS catalyst using EDTA.