Kinetics and statistical analysis of nickel leaching from spent catalyst in nitric acid solution

• We report a leaching kinetics study of nickel from the spent catalyst.
• Statistical analysis was used to determine the effect of leaching parameter on nickel extraction.
• The leaching data were well fitted by stochastic model.
• A linear relationship between the activation energy and average particle diameter was observed.
• We report that the dissolution rate controlling step is depending of the reaction time and particle size.

In this study, the kinetics of nitric acid leaching of a spent NiO–Al2O3 catalyst was investigated. The effect of leaching parameters such as reaction time (30–120 min), temperature (25–65 °C), stirring speed (500–1300 min− 1) and average particle size (63–300 μm) on Ni extraction were determined by statistical analysis. The results obtained show that extraction of about 85% was achieved under the following conditions: average particle size 75 μm, temperature 65 °C, reaction time 120 min, stirring speed 600 min− 1, nitric acid concentration 50% and solid/liquid ratio 1:3. The kinetics study indicates that diffusion through the product layer is the rate-controlling process during the reaction. The activation energy for the different particle size using a stochastic model was determined. Activation energy values from 13.07–25 kJ/mol are consistent with that reported for mixed or intermediate-controlled processes. The linear relationship observed between the activation energy Ea and the inverse of the initial particle diameter suggest that the dissolution rate controlling step may shift from product layer diffusion to intermediate-controlled process by decreasing particle size.