Kinetic data concerning nickel oxide acid leaching from spent steam reforming catalysts are presented. Based on this data, a sigmoid model that describes nickel dissolution is presented. The model reveals that two steps are involved in Ni leaching: a first one with a time increasing reaction rate, corresponding to free NiO dissolution, and a second one with a time decreasing reaction rate, attributed to the dissolution of the nickel oxide entrapped in the alumina crystalline structure.
