In present study, the leaching kinetics of the spent Mo-Co-Ni/Al2O3
catalyst was investigated in the presence of formic acid as an organic
leaching agent. Firstly, the spent catalyst was roasted in different
roasting temperature (200-700 degrees C) and time (15-240 min), the
maximum metal extraction was achieved that at 500 degrees C with 90 min.
Then, the leaching experiments were carried out to determine the
influences of process parameters following; particle size, liquid/solid
ratio, formic acid concentration, leaching temperature, leaching time
and stirring speed. According to the experimental results, the highest
dissolution rates of molybdenum (Mo, 75.82\%), cobalt (Co, 96.81\%),
nickel (Ni, 93.44\%) and aluminum (Al, 19.46\%) were reached under
optimum experimental conditions; particle size thorn75 degrees 30 mm;
liquid/ solid ratio 10 ml/g; formic acid concentration 0.6M; leaching
temperature 80 degrees C; leaching time 90 min and stirring speed 300
r/min. Moreover, the leaching kinetics clearly reveal that the leaching
reaction is controlled by liquid film diffusion and that the activation
energy values (Ea) of Co, Ni, Mo and Al were to be 24.49, 25.98, 32.36
and 33.47 kJ/mol, respectively. In conclusion, the leaching process can
be conducted in the presence of formic acid for the various industrial
wastes in similar structure and composition to Mo-Co-Ni/Al2O3 spent
catalyst