Dissolution kinetics of nickel from spent catalyst in nitric acid medium

In this study, the kinetics of nitric acid leaching of a spent NiO-Al2O3 catalyst was investigated. Influence of leaching parameters such as temperature (60-90 degrees C), acid concentration (1.5-5 M) and average particle size (75-601 mu m) was studied. For average particle size <= 75 mu m, dissolution data followed surface reaction controlled shrinking core model at all temperatures and acid concentration. However, for higher particle sizes product layer diffusion controlled the overall kinetics. The estimated activation energy for the surface reaction controlled mechanism was 83.44 kJ/mol and the empirical order of reaction with respect to [HNO3] was nearly 2. In general, the reaction mechanism shifted from surface reaction controlled to diffusion controlled when the extraction reached similar to 90%. The shift in reaction mechanism was explained by calculating the theoretical reaction rates. (C) 2012 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.